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GNU Emacs Manual

Emacs is the extensible, customizable, self-documenting real-time display editor. This Info file describes how to edit with Emacs and some of how to customize it; it corresponds to GNU Emacs version 21.2. For information on extending Emacs, see section `Top' in The Emacs Lisp Reference Manual.

Distribution  How to get the latest Emacs distribution.
GNU GENERAL PUBLIC LICENSE  The GNU General Public License gives you permission to redistribute GNU Emacs on certain terms; it also explains that there is no warranty.
A. GNU Free Documentation License  The license for this documentation.
Introduction  An introduction to Emacs concepts.
Glossary  The glossary.
AF. Emacs 20 Antinews  Information about Emacs version 20.
AG. Emacs and the Mac OS  Using Emacs in the Mac.
AH. Emacs and MS-DOS  Using Emacs on MS-DOS (otherwise known as "MS-DOG").
The GNU Manifesto  What's GNU? Gnu's Not Unix!
AI. Acknowledgments  Major contributors to GNU Emacs.

Indexes (nodes containing large menus)
Key (Character) Index  An item for each standard Emacs key sequence.
Command and Function Index  An item for each command name.
Variable Index  An item for each documented variable.
Concept Index  An item for each concept.
Command-Line Options Index  An item for every command-line option.

Important General Concepts
B. The Organization of the Screen  How to interpret what you see on the screen.
B.5 Kinds of User Input  Kinds of input events (characters, buttons, function keys).
B.6 Keys  Key sequences: what you type to request one editing action.
B.7 Keys and Commands  Named functions run by key sequences to do editing.
B.8 Character Set for Text  Character set for text (the contents of buffers and strings).
C. Entering and Exiting Emacs  Starting Emacs from the shell.
C.1 Exiting Emacs  Stopping or killing Emacs.
AE. Command Line Arguments  Hairy startup options.

Fundamental Editing Commands
D. Basic Editing Commands  The most basic editing commands.
E. The Minibuffer  Entering arguments that are prompted for.
F. Running Commands by Name  Invoking commands by their names.
G. Help  Commands for asking Emacs about its commands.

Important Text-Changing Commands
H. The Mark and the Region  The mark: how to delimit a "region" of text.
H.7 Deletion and Killing  Killing text.
H.8 Yanking  Recovering killed text. Moving text.
H.9 Accumulating Text  Other ways of copying text.
H.10 Rectangles  Operating on the text inside a rectangle on the screen.
I. Registers  Saving a text string or a location in the buffer.
J. Controlling the Display  Controlling what text is displayed.
K. Searching and Replacement  Finding or replacing occurrences of a string.
L. Commands for Fixing Typos  Commands especially useful for fixing typos.

Major Structures of Emacs
M. File Handling  All about handling files.
N. Using Multiple Buffers  Multiple buffers; editing several files at once.
O. Multiple Windows  Viewing two pieces of text at once.
P. Frames and X Windows  Running the same Emacs session in multiple X windows.
Q. International Character Set Support  Using non-ASCII character sets (the MULE features).

Advanced Features
R. Major Modes  Text mode vs. Lisp mode vs. C mode ...
S. Indentation  Editing the white space at the beginnings of lines.
T. Commands for Human Languages  Commands and modes for editing English.
U. Editing Programs  Commands and modes for editing programs.
V. Compiling and Testing Programs  Compiling, running and debugging programs.
W. Maintaining Programs  Features for maintaining large programs.
X. Abbrevs  How to define text abbreviations to reduce the number of characters you must type.
Y. Editing Pictures  Editing pictures made up of characters using the quarter-plane screen model.
Z. Sending Mail  Sending mail in Emacs.
AA. Reading Mail with Rmail  Reading mail in Emacs.
AB. Dired, the Directory Editor  You can "edit" a directory to manage files in it.
AC. The Calendar and the Diary  The calendar and diary facilities.
AC.14 Gnus  How to read netnews with Emacs.
AC.15 Running Shell Commands from Emacs  Executing shell commands from Emacs.
AC.16 Using Emacs as a Server  Using Emacs as an editing server for mail, etc.
AC.18 Hardcopy Output  Printing buffers or regions.
AC.19 PostScript Hardcopy  Printing buffers or regions as PostScript.
AC.20 Variables for PostScript Hardcopy  Customizing the PostScript printing commands.
AC.21 Sorting Text  Sorting lines, paragraphs or pages within Emacs.
AC.22 Narrowing  Restricting display and editing to a portion of the buffer.
AC.23 Two-Column Editing  Splitting apart columns to edit them in side-by-side windows.
AC.24 Editing Binary Files  Using Hexl mode to edit binary files.
AC.25 Saving Emacs Sessions  Saving Emacs state from one session to the next.
AC.26 Recursive Editing Levels  A command can allow you to do editing
  "within the command".  This is called a
  "recursive editing level".
AC.27 Emulation  Emulating some other editors with Emacs.
AC.28 Hyperlinking and Navigation Features  Following links in buffers.
AC.29 Dissociated Press  Dissociating text for fun.
AC.30 Other Amusements  Various games and hacks.
AD. Customization  Modifying the behavior of Emacs.

Recovery from Problems
AD.8 Quitting and Aborting  Quitting and aborting.
AD.9 Dealing with Emacs Trouble  What to do if Emacs is hung or malfunctioning.
AD.10 Reporting Bugs  How and when to report a bug.
AD.11 Contributing to Emacs Development  How to contribute improvements to Emacs.
AD.12 How To Get Help with GNU Emacs  How to get help for your own Emacs needs.

Here are some other nodes which are really inferiors of the ones
already listed, mentioned here so you can get to them in one step:

 -- The Detailed Node Listing ---

The Organization of the Screen

B.1 Point  The place in the text where editing commands operate.
B.2 The Echo Area  Short messages appear at the bottom of the screen.
B.3 The Mode Line  Interpreting the mode line.
B.4 The Menu Bar  How to use the menu bar.

Basic Editing Commands

D.1 Inserting Text  Inserting text by simply typing it.
D.2 Changing the Location of Point  How to move the cursor to the place where you want to change something.
D.3 Erasing Text  Deleting and killing text.
D.4 Undoing Changes  Undoing recent changes in the text.
D.5 Files  Visiting, creating, and saving files.
D.6 Help  Asking what a character does.
D.7 Blank Lines  Commands to make or delete blank lines.
D.8 Continuation Lines  Lines too wide for the screen.
D.9 Cursor Position Information  What page, line, row, or column is point on?
D.10 Numeric Arguments  Numeric arguments for repeating a command.

The Minibuffer

E.1 Minibuffers for File Names  Entering file names with the minibuffer.
E.2 Editing in the Minibuffer  How to edit in the minibuffer.
E.3 Completion  An abbreviation facility for minibuffer input.
E.4 Minibuffer History  Reusing recent minibuffer arguments.
E.5 Repeating Minibuffer Commands  Re-executing commands that used the minibuffer.

Help

G.1 Help Summary  Brief list of all Help commands.
G.2 Documentation for a Key  Asking what a key does in Emacs.
G.3 Help by Command or Variable Name  Asking about a command, variable or function name.
G.4 Apropos  Asking what pertains to a given topic.
G.5 Keyword Search for Lisp Libraries  Finding Lisp libraries by keywords (topics).
G.6 Help for International Language Support  Help relating to international language support.
G.8 Other Help Commands  Other help commands.

The Mark and the Region

H.1 Setting the Mark  Commands to set the mark.
H.2 Transient Mark Mode  How to make Emacs highlight the region-- when there is one.
H.3 Operating on the Region  Summary of ways to operate on contents of the region.
H.4 Commands to Mark Textual Objects  Commands to put region around textual units.
H.5 The Mark Ring  Previous mark positions saved so you can go back there.
H.6 The Global Mark Ring  Previous mark positions in various buffers.

Deletion and Killing

H.7.1 Deletion  Commands for deleting small amounts of text and blank areas.
H.7.2 Killing by Lines  How to kill entire lines of text at one time.
H.7.3 Other Kill Commands  Commands to kill large regions of text and syntactic units such as words and sentences.

Yanking

H.8.1 The Kill Ring  Where killed text is stored. Basic yanking.
H.8.2 Appending Kills  Several kills in a row all yank together.
H.8.3 Yanking Earlier Kills  Yanking something killed some time ago.

Registers

I.1 Saving Positions in Registers  Saving positions in registers.
I.2 Saving Text in Registers  Saving text in registers.
I.3 Saving Rectangles in Registers  Saving rectangles in registers.
I.4 Saving Window Configurations in Registers  Saving window configurations in registers.
I.6 Keeping File Names in Registers  File names in registers.
I.7 Bookmarks  Bookmarks are like registers, but persistent.

Controlling the Display

J.6 Scrolling  Moving text up and down in a window.
J.7 Horizontal Scrolling  Moving text left and right in a window.
J.8 Follow Mode  Follow mode lets two windows scroll as one.
J.9 Selective Display  Hiding lines with lots of indentation.
J.10 Optional Mode Line Features  Optional mode line display features.
J.11 How Text Is Displayed  How text is normally displayed.
J.12 Customization of Display  Information on variables for customizing display.

Searching and Replacement

K.1 Incremental Search  Search happens as you type the string.
K.2 Nonincremental Search  Specify entire string and then search.
K.3 Word Search  Search for sequence of words.
K.4 Regular Expression Search  Search for match for a regexp.
K.5 Syntax of Regular Expressions  Syntax of regular expressions.
K.6 Searching and Case  To ignore case while searching, or not.
K.7 Replacement Commands  Search, and replace some or all matches.
K.8 Other Search-and-Loop Commands  Operating on all matches for some regexp.

Replacement Commands

K.7.1 Unconditional Replacement  Replacing all matches for a string.
K.7.2 Regexp Replacement  Replacing all matches for a regexp.
K.7.3 Replace Commands and Case  How replacements preserve case of letters.
K.7.4 Query Replace  How to use querying.

Commands for Fixing Typos

L.1 Killing Your Mistakes  Commands to kill a batch of recently entered text.
L.2 Transposing Text  Exchanging two characters, words, lines, lists...
L.3 Case Conversion  Correcting case of last word entered.
L.4 Checking and Correcting Spelling  Apply spelling checker to a word or a whole buffer.

File Handling

M.1 File Names  How to type and edit file-name arguments.
M.2 Visiting Files  Visiting a file prepares Emacs to edit the file.
M.3 Saving Files  Saving makes your changes permanent.
M.4 Reverting a Buffer  Reverting cancels all the changes not saved.
M.5 Auto-Saving: Protection Against Disasters  Auto Save periodically protects against loss of data.
M.6 File Name Aliases  Handling multiple names for one file.
M.7 Version Control  Version control systems (RCS, CVS and SCCS).
M.8 File Directories  Creating, deleting, and listing file directories.
M.9 Comparing Files  Finding where two files differ.
M.10 Miscellaneous File Operations  Other things you can do on files.
M.11 Accessing Compressed Files  Accessing compressed files.
M.13 Remote Files  Accessing files on other sites.
M.14 Quoted File Names  Quoting special characters in file names.

Saving Files

M.3.1 Backup Files  How Emacs saves the old version of your file.
M.3.2 Protection against Simultaneous Editing  How Emacs protects against simultaneous editing of one file by two users.

Version Control

M.7.1 Introduction to Version Control  How version control works in general.
M.7.2 Version Control and the Mode Line  How the mode line shows version control status.
M.7.3 Basic Editing under Version Control  How to edit a file under version control.
M.7.4 Examining And Comparing Old Versions  Examining and comparing old versions.
M.7.5 The Secondary Commands of VC  The commands used a little less frequently.
M.7.6 Multiple Branches of a File  Multiple lines of development.
M.7.8 Snapshots  Sets of file versions treated as a unit.
M.7.9 Miscellaneous Commands and Features of VC  Various other commands and features of VC.
M.7.10 Customizing VC  Variables that change VC's behavior.

Using Multiple Buffers

N.1 Creating and Selecting Buffers  Creating a new buffer or reselecting an old one.
N.2 Listing Existing Buffers  Getting a list of buffers that exist.
N.3 Miscellaneous Buffer Operations  Renaming; changing read-onliness; copying text.
N.4 Killing Buffers  Killing buffers you no longer need.
N.5 Operating on Several Buffers  How to go through the list of all buffers and operate variously on several of them.
N.6 Indirect Buffers  An indirect buffer shares the text of another buffer.

Multiple Windows

O.1 Concepts of Emacs Windows  Introduction to Emacs windows.
O.2 Splitting Windows  New windows are made by splitting existing windows.
O.3 Using Other Windows  Moving to another window or doing something to it.
O.4 Displaying in Another Window  Finding a file or buffer in another window.
O.5 Forcing Display in the Same Window  Forcing certain buffers to appear in the selected window rather than in another window.
O.6 Deleting and Rearranging Windows  Deleting windows and changing their sizes.

Frames and X Windows

P.1 Mouse Commands for Editing  Moving, cutting, and pasting, with the mouse.
P.2 Secondary Selection  Cutting without altering point and mark.
P.3 Using the Clipboard  Using the clipboard for selections.
P.4 Following References with the Mouse  Using the mouse to select an item from a list.
P.5 Mouse Clicks for Menus  Mouse clicks that bring up menus.
P.6 Mode Line Mouse Commands  Mouse clicks on the mode line.
P.7 Creating Frames  Creating additional Emacs frames with various contents.
P.8 Frame Commands  Iconifying, deleting, and switching frames.
P.9 Making and Using a Speedbar Frame  How to make and use a speedbar frame.
P.10 Multiple Displays  How one Emacs job can talk to several displays.
P.11 Special Buffer Frames  You can make certain buffers have their own frames.
P.12 Setting Frame Parameters  Changing the colors and other modes of frames.
P.13 Scroll Bars  How to enable and disable scroll bars; how to use them.
P.14 Scrolling With "Wheeled" Mice  Using mouse wheels for scrolling.
P.15 Menu Bars  Enabling and disabling the menu bar.
P.16 Tool Bars  Enabling and disabling the tool bar.
P.17 Using Dialog Boxes  Controlling use of dialog boxes.
J.1 Using Multiple Typefaces  How to change the display style using faces.
J.2 Font Lock mode  Minor mode for syntactic highlighting using faces.
J.3 Highlight Changes Mode  Using colors to show where you changed the buffer.
J.4 Interactive Highlighting by Matching  Tell Emacs what text to highlight.
J.5 Trailing Whitespace  Showing possibly-spurious trailing whitespace.
P.18 Tooltips (or "Balloon Help")  Showing "tooltips", AKA "ballon help" for active text.
P.19 Mouse Avoidance  Moving the mouse pointer out of the way.
P.20 Non-Window Terminals  Multiple frames on terminals that show only one.
P.21 Using a Mouse in Terminal Emulators  Using the mouse in an XTerm terminal emulator.

International Character Set Support

Q.1 Introduction to International Character Sets  Basic concepts of multibyte characters.
Q.2 Enabling Multibyte Characters  Controlling whether to use multibyte characters.
Q.3 Language Environments  Setting things up for the language you use.
Q.4 Input Methods  Entering text characters not on your keyboard.
Q.5 Selecting an Input Method  Specifying your choice of input methods.
Q.7 Coding Systems  Character set conversion when you read and write files, and so on.
Q.8 Recognizing Coding Systems  How Emacs figures out which conversion to use.
Q.9 Specifying a Coding System  Various ways to choose which conversion to use.
Q.10 Fontsets  Fontsets are collections of fonts that cover the whole spectrum of characters.
Q.11 Defining fontsets  Defining a new fontset.
Q.13 Single-byte Character Set Support  You can pick one European character set to use without multibyte characters.

Major Modes

R.1 How Major Modes are Chosen  How major modes are specified or chosen.

Indentation

S.1 Indentation Commands and Techniques  Various commands and techniques for indentation.
S.2 Tab Stops  You can set arbitrary "tab stops" and then indent to the next tab stop when you want to.
S.3 Tabs vs. Spaces  You can request indentation using just spaces.

Commands for Human Languages

T.1 Words  Moving over and killing words.
T.2 Sentences  Moving over and killing sentences.
T.3 Paragraphs  Moving over paragraphs.
T.4 Pages  Moving over pages.
T.5 Filling Text  Filling or justifying text.
T.6 Case Conversion Commands  Changing the case of text.
T.7 Text Mode  The major modes for editing text files.
T.8 Outline Mode  Editing outlines.
T.9 TeX Mode  Editing input to the formatter TeX.
T.10 Nroff Mode  Editing input to the formatter nroff.
T.11 Editing Formatted Text  Editing formatted text directly in WYSIWYG fashion.

Filling Text

T.5.1 Auto Fill Mode  Auto Fill mode breaks long lines automatically.
T.5.3 Explicit Fill Commands  Commands to refill paragraphs and center lines.
T.5.4 The Fill Prefix  Filling paragraphs that are indented or in a comment, etc.
T.5.5 Adaptive Filling  How Emacs can determine the fill prefix automatically.

Editing Programs

U.1 Major Modes for Programming Languages  Major modes for editing programs.
U.2 Top-Level Definitions, or Defuns  Commands to operate on major top-level parts of a program.
U.3 Indentation for Programs  Adjusting indentation to show the nesting.
U.5 Manipulating Comments  Inserting, killing, and aligning comments.
U.4 Commands for Editing with Parentheses  Commands that operate on parentheses.
U.6 Documentation Lookup  Getting documentation of functions you plan to call.
U.7 Hideshow minor mode  Displaying blocks selectively.
U.8 Completion for Symbol Names  Completion on symbol names of your program or language.
U.9 Glasses minor mode  Making identifiersLikeThis more readable.
U.10 Other Features Useful for Editing Programs  Other Emacs features useful for editing programs.
U.11 C and Related Modes  Special commands of C, C++, Objective-C, Java, and Pike modes.
U.12 Fortran Mode  Fortran mode and its special features.
U.13 Asm Mode  Asm mode and its special features.

Top-Level Definitions, or Defuns

U.2.1 Left Margin Convention  An open-paren or similar opening delimiter starts a defun if it is at the left margin.
U.2.2 Moving by Defuns  Commands to move over or mark a major definition.
U.2.3 Imenu  Making buffer indexes as menus.
U.2.4 Which Function Mode  Which Function mode shows which function you are in.

Indentation for Programs

U.3.1 Basic Program Indentation Commands  Indenting a single line.
U.3.2 Indenting Several Lines  Commands to reindent many lines at once.
U.3.3 Customizing Lisp Indentation  Specifying how each Lisp function should be indented.
U.3.4 Commands for C Indentation  Extra features for indenting C and related modes.
U.3.5 Customizing C Indentation  Controlling indentation style for C and related modes.

Commands for Editing with Parentheses

U.4.1 Expressions with Balanced Parentheses  Expressions with balanced parentheses.
U.4.2 Moving in the Parenthesis Structure  Commands for moving up, down and across in the structure of parentheses.
U.4.3 Automatic Display Of Matching Parentheses  Insertion of a close-delimiter flashes matching open.

Manipulating Comments

U.5.1 Comment Commands  Inserting, killing, and indenting comments.
U.5.2 Multiple Lines of Comments  Commands for adding and editing multi-line comments.
U.5.3 Options Controlling Comments  Customizing the comment features.

Documentation Lookup

U.6.1 Info Documentation Lookup  Looking up library functions and commands in Info files.
U.6.2 Man Page Lookup  Looking up man pages of library functions and commands.
U.6.3 Emacs Lisp Documentation Lookup  Looking up Emacs Lisp functions, etc.

C and Related Modes

U.11.1 C Mode Motion Commands  Commands to move by C statements, etc.
U.11.2 Electric C Characters  Colon and other chars can automatically reindent.
U.11.3 Hungry Delete Feature in C  A more powerful DEL command.
U.11.4 Other Commands for C Mode  Filling comments, viewing expansion of macros, and other neat features.
U.11.5 Comments in C Modes  Options for customizing comment style.

Fortran Mode

U.12.1 Motion Commands  Moving point by statements or subprograms.
U.12.2 Fortran Indentation  Indentation commands for Fortran.
U.12.3 Fortran Comments  Inserting and aligning comments.
U.12.4 Fortran Auto Fill Mode  Auto fill minor mode for Fortran.
U.12.5 Checking Columns in Fortran  Measuring columns for valid Fortran.
U.12.6 Fortran Keyword Abbrevs  Built-in abbrevs for Fortran keywords.

Compiling and Testing Programs

V.1 Running Compilations under Emacs  Compiling programs in languages other than Lisp (C, Pascal, etc.).
V.3 Compilation Mode  The mode for visiting compiler errors.
V.4 Subshells for Compilation  Customizing your shell properly for use in the compilation buffer.
V.5 Running Debuggers Under Emacs  Running symbolic debuggers for non-Lisp programs.
V.6 Executing Lisp Expressions  Various modes for editing Lisp programs, with different facilities for running the Lisp programs.
V.7 Libraries of Lisp Code for Emacs  Creating Lisp programs to run in Emacs.
V.9 Lisp Interaction Buffers  Executing Lisp in an Emacs buffer.
V.8 Evaluating Emacs-Lisp Expressions  Executing a single Lisp expression in Emacs.
V.10 Running an External Lisp  Communicating through Emacs with a separate Lisp.

Running Debuggers Under Emacs

V.5.1 Starting GUD  How to start a debugger subprocess.
V.5.2 Debugger Operation  Connection between the debugger and source buffers.
V.5.3 Commands of GUD  Key bindings for common commands.
V.5.4 GUD Customization  Defining your own commands for GUD.

Maintaining Programs

W.1 Change Logs  Maintaining a change history for your program.
W.2 Tags Tables  Go direct to any function in your program in one command. Tags remembers which file it is in.
W.3 Merging Files with Emerge  A convenient way of merging two versions of a program.

Tags Tables

W.2.1 Source File Tag Syntax  Tag syntax for various types of code and text files.
W.2.2 Creating Tags Tables  Creating a tags table with etags.
W.2.4 Selecting a Tags Table  How to visit a tags table.
W.2.5 Finding a Tag  Commands to find the definition of a specific tag.
W.2.6 Searching and Replacing with Tags Tables  Using a tags table for searching and replacing.
W.2.7 Tags Table Inquiries  Listing and finding tags defined in a file.

Merging Files with Emerge

W.3.1 Overview of Emerge  How to start Emerge. Basic concepts.
W.3.2 Submodes of Emerge  Fast mode vs. Edit mode. Skip Prefers mode and Auto Advance mode.
W.3.3 State of a Difference  You do the merge by specifying state A or B for each difference.
W.3.4 Merge Commands  Commands for selecting a difference, changing states of differences, etc.
W.3.5 Exiting Emerge  What to do when you've finished the merge.
W.3.6 Combining the Two Versions  How to keep both alternatives for a difference.
W.3.7 Fine Points of Emerge  Misc.

Abbrevs

X.1 Abbrev Concepts  Fundamentals of defined abbrevs.
X.2 Defining Abbrevs  Defining an abbrev, so it will expand when typed.
X.3 Controlling Abbrev Expansion  Controlling expansion: prefixes, canceling expansion.
X.4 Examining and Editing Abbrevs  Viewing or editing the entire list of defined abbrevs.
X.5 Saving Abbrevs  Saving the entire list of abbrevs for another session.
X.6 Dynamic Abbrev Expansion  Abbreviations for words already in the buffer.

Editing Pictures

Y.1 Basic Editing in Picture Mode  Basic concepts and simple commands of Picture Mode.
Y.2 Controlling Motion after Insert  Controlling direction of cursor motion after "self-inserting" characters.
Y.3 Picture Mode Tabs  Various features for tab stops and indentation.
Y.4 Picture Mode Rectangle Commands  Clearing and superimposing rectangles.

Sending Mail

Z.1 The Format of the Mail Buffer  Format of the mail being composed.
Z.2 Mail Header Fields  Details of permitted mail header fields.
Z.3 Mail Aliases  Abbreviating and grouping mail addresses.
Z.4 Mail Mode  Special commands for editing mail being composed.
Z.5 Mail Amusements  Distract the NSA's attention; add a fortune to a msg.
Z.6 Mail-Composition Methods  Using alternative mail-composition methods.

Reading Mail with Rmail

AA.1 Basic Concepts of Rmail  Basic concepts of Rmail, and simple use.
AA.2 Scrolling Within a Message  Scrolling through a message.
AA.3 Moving Among Messages  Moving to another message.
AA.4 Deleting Messages  Deleting and expunging messages.
AA.5 Rmail Files and Inboxes  How mail gets into the Rmail file.
AA.6 Multiple Rmail Files  Using multiple Rmail files.
AA.7 Copying Messages Out to Files  Copying message out to files.
AA.8 Labels  Classifying messages by labeling them.
AA.9 Rmail Attributes  Certain standard labels, called attributes.
AA.10 Sending Replies  Sending replies to messages you are viewing.
AA.11 Summaries  Summaries show brief info on many messages.
AA.12 Sorting the Rmail File  Sorting messages in Rmail.
AA.13 Display of Messages  How Rmail displays a message; customization.
AA.15 Editing Within a Message  Editing message text and headers in Rmail.
AA.16 Digest Messages  Extracting the messages from a digest message.
AA.17 Converting an Rmail File to Inbox Format  Converting an Rmail file to mailbox format.
AA.18 Reading Rot13 Messages  Reading messages encoded in the rot13 code.
AA.19 movemail and POP  More details of fetching new mail.

Dired, the Directory Editor

AB.1 Entering Dired  How to invoke Dired.
AB.2 Navigation in the Dired Buffer  How to move in the Dired buffer.
AB.3 Deleting Files with Dired  Deleting files with Dired.
AB.4 Flagging Many Files at Once  Flagging files based on their names.
AB.5 Visiting Files in Dired  Other file operations through Dired.
AB.6 Dired Marks vs. Flags  Flagging for deletion vs marking.
AB.7 Operating on Files  How to copy, rename, print, compress, etc. either one file or several files.
AB.8 Shell Commands in Dired  Running a shell command on the marked files.
AB.9 Transforming File Names in Dired  Using patterns to rename multiple files.
AB.10 File Comparison with Dired  Running `diff' by way of Dired.
AB.11 Subdirectories in Dired  Adding subdirectories to the Dired buffer.
AB.12 Moving Over Subdirectories  Moving across subdirectories, and up and down.
AB.13 Hiding Subdirectories  Making subdirectories visible or invisible.
AB.14 Updating the Dired Buffer  Discarding lines for files of no interest.
AB.15 Dired and find  Using `find' to choose the files for Dired.

The Calendar and the Diary

AC.1 Movement in the Calendar  Moving through the calendar; selecting a date.
AC.2 Scrolling in the Calendar  Bringing earlier or later months onto the screen.
AC.3 Counting Days  How many days are there between two dates?
AC.4 Miscellaneous Calendar Commands  Exiting or recomputing the calendar.
AC.5 LaTeX Calendar  Print a calendar using LaTeX.
AC.6 Holidays  Displaying dates of holidays.
AC.7 Times of Sunrise and Sunset  Displaying local times of sunrise and sunset.
AC.8 Phases of the Moon  Displaying phases of the moon.
AC.9 Conversion To and From Other Calendars  Converting dates to other calendar systems.
AC.10 The Diary  Displaying events from your diary.
AC.11 Appointments  Reminders when it's time to do something.
AC.12 Daylight Savings Time  How to specify when daylight savings time is active.

Movement in the Calendar

AC.1.1 Motion by Standard Lengths of Time  Moving by days, weeks, months, and years.
AC.1.2 Beginning or End of Week, Month or Year  Moving to start/end of weeks, months, and years.
AC.1.3 Specified Dates  Moving to the current date or another specific date.

Conversion To and From Other Calendars

AC.9.1 Supported Calendar Systems  The calendars Emacs understands
     (aside from Gregorian).
AC.9.2 Converting To Other Calendars  Converting the selected date to various calendars.
AC.9.3 Converting From Other Calendars  Moving to a date specified in another calendar.
AC.9.4 Converting from the Mayan Calendar  Moving to a date specified in a Mayan calendar.

The Diary

AC.10.1 Commands Displaying Diary Entries  Viewing diary entries and associated calendar dates.
AC.10.2 The Diary File  Entering events in your diary.
AC.10.3 Date Formats  Various ways you can specify dates.
AC.10.4 Commands to Add to the Diary  Commands to create diary entries.
AC.10.5 Special Diary Entries  Anniversaries, blocks of dates, cyclic entries, etc.

GNUS

AC.14.1 Gnus Buffers  The group, summary, and article buffers.
AC.14.2 When Gnus Starts Up  What you should know about starting Gnus.
AC.14.3 Summary of Gnus Commands  A short description of the basic Gnus commands.

Running Shell Commands from Emacs

AC.15.1 Single Shell Commands  How to run one shell command and return.
AC.15.2 Interactive Inferior Shell  Permanent shell taking input via Emacs.
AC.15.3 Shell Mode  Special Emacs commands used with permanent shell.
AC.15.4 Shell Command History  Repeating previous commands in a shell buffer.
AC.15.6 Shell Mode Options  Options for customizing Shell mode.
AC.15.10 Remote Host Shell  Connecting to another computer.

Customization

AD.1 Minor Modes  Each minor mode is one feature you can turn on independently of any others.
AD.2 Variables  Many Emacs commands examine Emacs variables to decide what to do; by setting variables, you can control their functioning.
AD.3 Keyboard Macros  A keyboard macro records a sequence of keystrokes to be replayed with a single command.
AD.4 Customizing Key Bindings  The keymaps say what command each key runs. By changing them, you can "redefine keys".
AD.5 Keyboard Translations  If your keyboard passes an undesired code for a key, you can tell Emacs to substitute another code.
AD.6 The Syntax Table  The syntax table controls how words and expressions are parsed.
AD.7 The Init File, `~/.emacs'  How to write common customizations in the
  `.emacs' file. 

Variables

AD.2.1 Examining and Setting Variables  Examining or setting one variable's value.
AD.2.2 Easy Customization Interface  Convenient and easy customization of variables.
AD.2.3 Hooks  Hook variables let you specify programs for parts of Emacs to run on particular occasions.
AD.2.4 Local Variables  Per-buffer values of variables.
AD.2.5 Local Variables in Files  How files can specify variable values.

Keyboard Macros

AD.3.1 Basic Use  Defining and running keyboard macros.
AD.3.2 Naming and Saving Keyboard Macros  Giving keyboard macros names; saving them in files.
AD.3.3 Executing Macros with Variations  Making keyboard macros do different things each time.

Customizing Key Bindings

AD.4.1 Keymaps  Generalities. The global keymap.
AD.4.2 Prefix Keymaps  Keymaps for prefix keys.
AD.4.3 Local Keymaps  Major and minor modes have their own keymaps.
AD.4.4 Minibuffer Keymaps  The minibuffer uses its own local keymaps.
AD.4.5 Changing Key Bindings Interactively  How to redefine one key's meaning conveniently.
AD.4.6 Rebinding Keys in Your Init File  Rebinding keys with your init file, `.emacs'.
AD.4.7 Rebinding Function Keys  Rebinding terminal function keys.
AD.4.8 Named ASCII Control Characters  Distinguishing TAB from C-i, and so on.
AD.4.10 Rebinding Mouse Buttons  Rebinding mouse buttons in Emacs.
AD.4.11 Disabling Commands  Disabling a command means confirmation is required before it can be executed. This is done to protect beginners from surprises.

The Init File, `~/.emacs'

AD.7.1 Init File Syntax  Syntax of constants in Emacs Lisp.
AD.7.2 Init File Examples  How to do some things with an init file.
AD.7.3 Terminal-specific Initialization  Each terminal type can have an init file.
AD.7.4 How Emacs Finds Your Init File  How Emacs finds the init file.

Dealing with Emacs Trouble

AD.9.1 If DEL Fails to Delete  What to do if DEL doesn't delete.
AD.9.2 Recursive Editing Levels  `[...]' in mode line around the parentheses.
AD.9.3 Garbage on the Screen  Garbage on the screen.
AD.9.4 Garbage in the Text  Garbage in the text.
AD.9.5 Spontaneous Entry to Incremental Search  Spontaneous entry to incremental search.
AD.9.6 Running out of Memory  How to cope when you run out of memory.
AD.9.8 Emergency Escape  Emergency escape--- What to do if Emacs stops responding.
AD.9.9 Help for Total Frustration  When you are at your wits' end.

Reporting Bugs

AD.10.1 When Is There a Bug  Have you really found a bug?
AD.10.2 Understanding Bug Reporting  How to report a bug effectively.
AD.10.3 Checklist for Bug Reports  Steps to follow for a good bug report.
AD.10.4 Sending Patches for GNU Emacs  How to send a patch for GNU Emacs.

Command Line Options and Arguments

AE.1 Action Arguments  Arguments to visit files, load libraries, and call functions.
AE.2 Initial Options  Arguments that take effect while starting Emacs.
AE.3 Command Argument Example  Examples of using command line arguments.
AE.4 Resuming Emacs with Arguments  Specifying arguments when you resume a running Emacs.
AE.5 Environment Variables  Environment variables that Emacs uses.

AE.6 Specifying the Display Name  Changing the default display and using remote login.
AE.7 Font Specification Options  Choosing a font for text, under X.
AE.8 Window Color Options  Choosing colors, under X.
AE.9 Options for Window Geometry  Start-up window size, under X.
AE.10 Internal and External Borders  Internal and external borders, under X.
AE.11 Frame Titles  Specifying the initial frame's title.
AE.12 Icons  Choosing what sort of icon to use, under X.
AE.13 X Resources  Advanced use of classes and resources, under X.
AE.14 Lucid Menu X Resources  X resources for Lucid menus.
AE.15 LessTif Menu X Resources  X resources for LessTif and Motif menus.

Environment Variables

AE.5.1 General Variables  Environment variables that all versions of Emacs use.
AE.5.2 Miscellaneous Variables  Certain system specific variables.

MS-DOS and Windows 95/98/NT

AH.1 Keyboard and Mouse on MS-DOS  Keyboard and mouse usage on MS-DOS.
AH.2 Display on MS-DOS  Fonts, frames and display size on MS-DOS.
AH.3 File Names on MS-DOS  File-name conventions on MS-DOS.
AH.4 Text Files and Binary Files  Text files on MS-DOS use CRLF to separate lines.
AH.5 Printing and MS-DOS  How to specify the printer on MS-DOS.
AH.7 Subprocesses on MS-DOS  Running subprocesses on MS-DOS.
AH.8 Subprocesses on Windows 9X/ME and Windows NT/2K  Running subprocesses on Windows.
AH.9 Using the System Menu on Windows  Controlling what the ALT key does.


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Distribution

GNU Emacs is free software; this means that everyone is free to use it and free to redistribute it on certain conditions. GNU Emacs is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of GNU Emacs that they might get from you. The precise conditions are found in the GNU General Public License that comes with Emacs and also appears following this section.

One way to get a copy of GNU Emacs is from someone else who has it. You need not ask for our permission to do so, or tell any one else; just copy it. If you have access to the Internet, you can get the latest distribution version of GNU Emacs by anonymous FTP; see the file `etc/FTP' in the Emacs distribution for more information.

You may also receive GNU Emacs when you buy a computer. Computer manufacturers are free to distribute copies on the same terms that apply to everyone else. These terms require them to give you the full sources, including whatever changes they may have made, and to permit you to redistribute the GNU Emacs received from them under the usual terms of the General Public License. In other words, the program must be free for you when you get it, not just free for the manufacturer.

You can also order copies of GNU Emacs from the Free Software Foundation on CD-ROM. This is a convenient and reliable way to get a copy; it is also a good way to help fund our work. (The Foundation has always received most of its funds in this way.) An order form is included in the file `etc/ORDERS' in the Emacs distribution, and on our web site in http://www.gnu.org/order/order.html. For further information, write to

 
Free Software Foundation
59 Temple Place, Suite 330
Boston, MA  02111-1307 USA
USA

The income from distribution fees goes to support the foundation's purpose: the development of new free software, and improvements to our existing programs including GNU Emacs.

If you find GNU Emacs useful, please send a donation to the Free Software Foundation to support our work. Donations to the Free Software Foundation are tax deductible in the US. If you use GNU Emacs at your workplace, please suggest that the company make a donation. If company policy is unsympathetic to the idea of donating to charity, you might instead suggest ordering a CD-ROM from the Foundation occasionally, or subscribing to periodic updates.


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GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

 
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.


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Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  1. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program," below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification.") Each licensee is addressed as "you."

    Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

  2. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

    You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

  3. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

    1. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

    2. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

    3. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

    These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

    Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

    In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

  4. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

    1. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

    2. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

    3. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

    The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

    If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

  5. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

  6. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

  7. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

  8. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

    If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

    It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

    This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

  9. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

  10. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

    Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version," you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

  11. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

    NO WARRANTY

  12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

  13. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS


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How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.

 
one line to give the program's name and an idea of what it does.
Copyright (C) 19yy  name of author

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

 
Gnomovision version 69, Copyright (C) 20yy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c' 
for details.

The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:

 
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written 
by James Hacker.

signature of Ty Coon, 1 April 1989
Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.


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A. GNU Free Documentation License

Version 1.1, March 2000

 
Copyright (C) 2000  Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other written document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you."

    A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.

    The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.

    A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not "Transparent" is called "Opaque."

    Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.

    The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

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ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

 
Copyright (C)  year  your name.
Permission is granted to copy, distribute and/or modify this document
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or any later version published by the Free Software Foundation;
with the Invariant Sections being list their titles, with the
Front-Cover Texts being list, and with the Back-Cover Texts being list.
A copy of the license is included in the section entitled "GNU
Free Documentation License."

If you have no Invariant Sections, write "with no Invariant Sections" instead of saying which ones are invariant. If you have no Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being list"; likewise for Back-Cover Texts.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


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Introduction

You are reading about GNU Emacs, the GNU incarnation of the advanced, self-documenting, customizable, extensible real-time display editor Emacs. (The `G' in `GNU' is not silent.)

We say that Emacs is a display editor because normally the text being edited is visible on the screen and is updated automatically as you type your commands. See section Display.

We call it a real-time editor because the display is updated very frequently, usually after each character or pair of characters you type. This minimizes the amount of information you must keep in your head as you edit. See section Basic Editing.

We call Emacs advanced because it provides facilities that go beyond simple insertion and deletion: controlling subprocesses; automatic indentation of programs; viewing two or more files at once; editing formatted text; and dealing in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in several different programming languages.

Self-documenting means that at any time you can type a special character, Control-h, to find out what your options are. You can also use it to find out what any command does, or to find all the commands that pertain to a topic. See section G. Help.

Customizable means that you can change the definitions of Emacs commands in little ways. For example, if you use a programming language in which comments start with `<**' and end with `**>', you can tell the Emacs comment manipulation commands to use those strings (see section U.5 Manipulating Comments). Another sort of customization is rearrangement of the command set. For example, if you prefer the four basic cursor motion commands (up, down, left and right) on keys in a diamond pattern on the keyboard, you can rebind the keys that way. See section AD. Customization.

Extensible means that you can go beyond simple customization and write entirely new commands, programs in the Lisp language to be run by Emacs's own Lisp interpreter. Emacs is an "on-line extensible" system, which means that it is divided into many functions that call each other, any of which can be redefined in the middle of an editing session. Almost any part of Emacs can be replaced without making a separate copy of all of Emacs. Most of the editing commands of Emacs are written in Lisp; the few exceptions could have been written in Lisp but are written in C for efficiency. Although only a programmer can write an extension, anybody can use it afterward. If you want to learn Emacs Lisp programming, we recommend the Introduction to Emacs Lisp by Robert J. Chassell, also published by the Free Software Foundation.

When run under the X Window System, Emacs provides its own menus and convenient bindings to mouse buttons. But Emacs can provide many of the benefits of a window system on a text-only terminal. For instance, you can look at or edit several files at once, move text between files, and edit files while running shell commands.


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B. The Organization of the Screen

On a text-only terminal, the Emacs display occupies the whole screen. On the X Window System, Emacs creates its own X windows to use. We use the term frame to mean an entire text-only screen or an entire X window used by Emacs. Emacs uses both kinds of frames in the same way to display your editing. Emacs normally starts out with just one frame, but you can create additional frames if you wish. See section P. Frames and X Windows.

When you start Emacs, the entire frame except for the top and bottom is devoted to the text you are editing. This area is called the window. At the top there is normally a menu bar where you can access a series of menus; then there may be a tool bar, a row of icons that perform editing commands if you click on them. Below this, the window begins. The last line is a special echo area or minibuffer window, where prompts appear and where you can enter information when Emacs asks for it. See below for more information about these special lines.

You can subdivide the large text window horizontally or vertically into multiple text windows, each of which can be used for a different file (see section O. Multiple Windows). In this manual, the word "window" always refers to the subdivisions of a frame within Emacs.

The window that the cursor is in is the selected window, in which editing takes place. Most Emacs commands implicitly apply to the text in the selected window (though mouse commands generally operate on whatever window you click them in, whether selected or not). The other windows display text for reference only, unless/until you select them. If you use multiple frames under the X Window System, then giving the input focus to a particular frame selects a window in that frame.

Each window's last line is a mode line, which describes what is going on in that window. It appears in inverse video, if the terminal supports that; its contents normally begin with `--:-- *scratch*' when Emacs starts. The mode line displays status information such as what buffer is being displayed above it in the window, what major and minor modes are in use, and whether the buffer contains unsaved changes.

B.1 Point  The place in the text where editing commands operate.
B.2 The Echo Area  Short messages appear at the bottom of the screen.
B.3 The Mode Line  Interpreting the mode line.
B.4 The Menu Bar  How to use the menu bar.


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B.1 Point

Within Emacs, the terminal's cursor shows the location at which editing commands will take effect. This location is called point. Many Emacs commands move point through the text, so that you can edit at different places in it. You can also place point by clicking mouse button 1.

While the cursor appears to point at a character, you should think of point as between two characters; it points before the character that appears under the cursor. For example, if your text looks like `frob' with the cursor over the `b', then point is between the `o' and the `b'. If you insert the character `!' at that position, the result is `fro!b', with point between the `!' and the `b'. Thus, the cursor remains over the `b', as before.

Sometimes people speak of "the cursor" when they mean "point," or speak of commands that move point as "cursor motion" commands.

Text-only terminals have only one cursor, and when output is in progress it must appear where the output is being displayed. This does not mean that point is moving. It is only that Emacs has no way to show you the location of point except when the terminal is idle.

If you are editing several files in Emacs, each in its own buffer, each buffer has its own point location. A buffer that is not currently displayed remembers where point is in case you display it again later.

When Emacs displays multiple windows, each window has its own point location. On text-only terminals, the cursor shows the location of point in the selected window. On graphical terminals, Emacs shows a cursor in each window; the selected window's cursor is solid, and the other cursors are hollow. Either way, the cursor or cursors tell you which window is selected. If the same buffer appears in more than one window, each window has its own position for point in that buffer, and (when possible) its own cursor.

See section J.13 Displaying the Cursor, for customization options that control display of the cursor or cursors.

The term "point" comes from the character `.', which was the command in TECO (the language in which the original Emacs was written) for accessing the value now called "point."


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B.2 The Echo Area

The line at the bottom of the frame (below the mode line) is the echo area. It is used to display small amounts of text for several purposes.

Echoing means displaying the characters that you type. Outside Emacs, the operating system normally echoes all your input. Emacs handles echoing differently.

Single-character commands do not echo in Emacs, and multi-character commands echo only if you pause while typing them. As soon as you pause for more than a second in the middle of a command, Emacs echoes all the characters of the command so far. This is to prompt you for the rest of the command. Once echoing has started, the rest of the command echoes immediately as you type it. This behavior is designed to give confident users fast response, while giving hesitant users maximum feedback. You can change this behavior by setting a variable (see section J.12 Customization of Display).

If a command cannot be executed, it may display an error message in the echo area. Error messages are accompanied by beeping or by flashing the screen. The error also discards any input you have typed ahead.

Some commands display informative messages in the echo area. These messages look much like error messages, but they are not announced with a beep and do not throw away input. Sometimes the message tells you what the command has done, when this is not obvious from looking at the text being edited. Sometimes the sole purpose of a command is to show you a message giving you specific information--for example, C-x = displays a message describing the character position of point in the text and its current column in the window. Commands that take a long time often display messages ending in `...' while they are working, and add `done' at the end when they are finished.

Echo-area informative messages are saved in an editor buffer named `*Messages*'. (We have not explained buffers yet; see N. Using Multiple Buffers, for more information about them.) If you miss a message that appears briefly on the screen, you can switch to the `*Messages*' buffer to see it again. (Successive progress messages are often collapsed into one in that buffer.)

The size of `*Messages*' is limited to a certain number of lines. The variable message-log-max specifies how many lines. Once the buffer has that many lines, each line added at the end deletes one line from the beginning. See section AD.2 Variables, for how to set variables such as message-log-max.

The echo area is also used to display the minibuffer, a window that is used for reading arguments to commands, such as the name of a file to be edited. When the minibuffer is in use, the echo area begins with a prompt string that usually ends with a colon; also, the cursor appears in that line because it is the selected window. You can always get out of the minibuffer by typing C-g. See section E. The Minibuffer.


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B.3 The Mode Line

Each text window's last line is a mode line, which describes what is going on in that window. When there is only one text window, the mode line appears right above the echo area; it is the next-to-last line in the frame. The mode line starts and ends with dashes. On a text-mode display, the mode line is in inverse video if the terminal supports that; on a graphics display, the mode line has a 3D box appearance to help it stand out.

Normally, the mode line looks like this:

 
-cs:ch  buf      (major minor)--line--pos------

This gives information about the buffer being displayed in the window: the buffer's name, what major and minor modes are in use, whether the buffer's text has been changed, and how far down the buffer you are currently looking.

ch contains two stars `**' if the text in the buffer has been edited (the buffer is "modified"), or `--' if the buffer has not been edited. For a read-only buffer, it is `%*' if the buffer is modified, and `%%' otherwise.

buf is the name of the window's buffer. In most cases this is the same as the name of a file you are editing. See section N. Using Multiple Buffers.

The buffer displayed in the selected window (the window that the cursor is in) is also Emacs's current buffer, the one that editing takes place in. When we speak of what some command does to "the buffer," we are talking about the current buffer.

line is `L' followed by the current line number of point. This is present when Line Number mode is enabled (which it normally is). You can optionally display the current column number too, by turning on Column Number mode (which is not enabled by default because it is somewhat slower). See section J.10 Optional Mode Line Features.

pos tells you whether there is additional text above the top of the window, or below the bottom. If your buffer is small and it is all visible in the window, pos is `All'. Otherwise, it is `Top' if you are looking at the beginning of the buffer, `Bot' if you are looking at the end of the buffer, or `nn%', where nn is the percentage of the buffer above the top of the window.

major is the name of the major mode in effect in the buffer. At any time, each buffer is in one and only one of the possible major modes. The major modes available include Fundamental mode (the least specialized), Text mode, Lisp mode, C mode, Texinfo mode, and many others. See section R. Major Modes, for details of how the modes differ and how to select one.

Some major modes display additional information after the major mode name. For example, Rmail buffers display the current message number and the total number of messages. Compilation buffers and Shell buffers display the status of the subprocess.

minor is a list of some of the minor modes that are turned on at the moment in the window's chosen buffer. For example, `Fill' means that Auto Fill mode is on. `Abbrev' means that Word Abbrev mode is on. `Ovwrt' means that Overwrite mode is on. See section AD.1 Minor Modes, for more information. `Narrow' means that the buffer being displayed has editing restricted to only a portion of its text. This is not really a minor mode, but is like one. See section AC.22 Narrowing. `Def' means that a keyboard macro is being defined. See section AD.3 Keyboard Macros.

In addition, if Emacs is currently inside a recursive editing level, square brackets (`[...]') appear around the parentheses that surround the modes. If Emacs is in one recursive editing level within another, double square brackets appear, and so on. Since recursive editing levels affect Emacs globally, not just one buffer, the square brackets appear in every window's mode line or not in any of them. See section AC.26 Recursive Editing Levels.

Non-windowing terminals can only show a single Emacs frame at a time (see section P. Frames and X Windows). On such terminals, the mode line displays the name of the selected frame, after ch. The initial frame's name is `F1'.

cs states the coding system used for the file you are editing. A dash indicates the default state of affairs: no code conversion, except for end-of-line translation if the file contents call for that. `=' means no conversion whatsoever. Nontrivial code conversions are represented by various letters--for example, `1' refers to ISO Latin-1. See section Q.7 Coding Systems, for more information. If you are using an input method, a string of the form `i>' is added to the beginning of cs; i identifies the input method. (Some input methods show `+' or `@' instead of `>'.) See section Q.4 Input Methods.

When you are using a character-only terminal (not a window system), cs uses three characters to describe, respectively, the coding system for keyboard input, the coding system for terminal output, and the coding system used for the file you are editing.

When multibyte characters are not enabled, cs does not appear at all. See section Q.2 Enabling Multibyte Characters.

The colon after cs can change to another string in certain circumstances. Emacs uses newline characters to separate lines in the buffer. Some files use different conventions for separating lines: either carriage-return linefeed (the MS-DOS convention) or just carriage-return (the Macintosh convention). If the buffer's file uses carriage-return linefeed, the colon changes to either a backslash (`\') or `(DOS)', depending on the operating system. If the file uses just carriage-return, the colon indicator changes to either a forward slash (`/') or `(Mac)'. On some systems, Emacs displays `(Unix)' instead of the colon even for files that use newline to separate lines.

You can customize the mode line display for each of the end-of-line formats by setting each of the variables eol-mnemonic-unix, eol-mnemonic-dos, eol-mnemonic-mac, and eol-mnemonic-undecided to any string you find appropriate. See section AD.2 Variables, for an explanation of how to set variables.

See section J.10 Optional Mode Line Features, for features that add other handy information to the mode line, such as the current column number of point, the current time, and whether new mail for you has arrived.

The mode line is mouse-sensitive; when you move the mouse across various parts of it, Emacs displays help text to say what a click in that place will do. See section P.6 Mode Line Mouse Commands.


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B.4 The Menu Bar

Each Emacs frame normally has a menu bar at the top which you can use to perform certain common operations. There's no need to list them here, as you can more easily see for yourself.

When you are using a window system, you can use the mouse to choose a command from the menu bar. An arrow pointing right, after the menu item, indicates that the item leads to a subsidiary menu; `...' at the end means that the command will read arguments from the keyboard before it actually does anything.

To view the full command name and documentation for a menu item, type C-h k, and then select the menu bar with the mouse in the usual way (see section G.2 Documentation for a Key).

On text-only terminals with no mouse, you can use the menu bar by typing M-` or F10 (these run the command tmm-menubar). This command enters a mode in which you can select a menu item from the keyboard. A provisional choice appears in the echo area. You can use the left and right arrow keys to move through the menu to different choices. When you have found the choice you want, type RET to select it.

Each menu item also has an assigned letter or digit which designates that item; it is usually the initial of some word in the item's name. This letter or digit is separated from the item name by `=>'. You can type the item's letter or digit to select the item.

Some of the commands in the menu bar have ordinary key bindings as well; if so, the menu lists one equivalent key binding in parentheses after the item itself.


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B.5 Kinds of User Input

GNU Emacs uses an extension of the ASCII character set for keyboard input; it also accepts non-character input events including function keys and mouse button actions.

ASCII consists of 128 character codes. Some of these codes are assigned graphic symbols such as `a' and `='; the rest are control characters, such as Control-a (usually written C-a for short). C-a gets its name from the fact that you type it by holding down the CTRL key while pressing a.

Some ASCII control characters have special names, and most terminals have special keys you can type them with: for example, RET, TAB, DEL and ESC. The space character is usually referred to below as SPC, even though strictly speaking it is a graphic character whose graphic happens to be blank. Some keyboards have a key labeled "linefeed" which is an alias for C-j.

Emacs extends the ASCII character set with thousands more printing characters (see section Q. International Character Set Support), additional control characters, and a few more modifiers that can be combined with any character.

On ASCII terminals, there are only 32 possible control characters. These are the control variants of letters and `@[]\^_'. In addition, the shift key is meaningless with control characters: C-a and C-A are the same character, and Emacs cannot distinguish them.

But the Emacs character set has room for control variants of all printing characters, and for distinguishing between C-a and C-A. The X Window System makes it possible to enter all these characters. For example, C-- (that's Control-Minus) and C-5 are meaningful Emacs commands under X.

Another Emacs character-set extension is additional modifier bits. Only one modifier bit is commonly used; it is called Meta. Every character has a Meta variant; examples include Meta-a (normally written M-a, for short), M-A (not the same character as M-a, but those two characters normally have the same meaning in Emacs), M-RET, and M-C-a. For reasons of tradition, we usually write C-M-a rather than M-C-a; logically speaking, the order in which the modifier keys CTRL and META are mentioned does not matter.

Some terminals have a META key, and allow you to type Meta characters by holding this key down. Thus, Meta-a is typed by holding down META and pressing a. The META key works much like the SHIFT key. Such a key is not always labeled META, however, as this function is often a special option for a key with some other primary purpose. Sometimes it is labeled ALT or EDIT; on a Sun keyboard, it may have a diamond on it.

If there is no META key, you can still type Meta characters using two-character sequences starting with ESC. Thus, you can enter M-a by typing ESC a. You can enter C-M-a by typing ESC C-a. ESC is allowed on terminals with META keys, too, in case you have formed a habit of using it. The X Window System provides several other modifier keys that can be applied to any input character. These are called SUPER, HYPER and ALT. We write `s-', `H-' and `A-' to say that a character uses these modifiers. Thus, s-H-C-x is short for Super-Hyper-Control-x. Not all X terminals actually provide keys for these modifier flags--in fact, many terminals have a key labeled ALT which is really a META key. The standard key bindings of Emacs do not include any characters with these modifiers. But you can assign them meanings of your own by customizing Emacs.

Keyboard input includes keyboard keys that are not characters at all: for example function keys and arrow keys. Mouse buttons are also outside the gamut of characters. You can modify these events with the modifier keys CTRL, META, SUPER, HYPER and ALT, just like keyboard characters.

Input characters and non-character inputs are collectively called input events. See section `Input Events' in The Emacs Lisp Reference Manual, for more information. If you are not doing Lisp programming, but simply want to redefine the meaning of some characters or non-character events, see AD. Customization.

ASCII terminals cannot really send anything to the computer except ASCII characters. These terminals use a sequence of characters to represent each function key. But that is invisible to the Emacs user, because the keyboard input routines recognize these special sequences and convert them to function key events before any other part of Emacs gets to see them.


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B.6 Keys

A key sequence (key, for short) is a sequence of input events that are meaningful as a unit--as "a single command." Some Emacs command sequences are just one character or one event; for example, just C-f is enough to move forward one character in the buffer. But Emacs also has commands that take two or more events to invoke.

If a sequence of events is enough to invoke a command, it is a complete key. Examples of complete keys include C-a, X, RET, NEXT (a function key), DOWN (an arrow key), C-x C-f, and C-x 4 C-f. If it isn't long enough to be complete, we call it a prefix key. The above examples show that C-x and C-x 4 are prefix keys. Every key sequence is either a complete key or a prefix key.

Most single characters constitute complete keys in the standard Emacs command bindings. A few of them are prefix keys. A prefix key combines with the following input event to make a longer key sequence, which may itself be complete or a prefix. For example, C-x is a prefix key, so C-x and the next input event combine to make a two-event key sequence. Most of these key sequences are complete keys, including C-x C-f and C-x b. A few, such as C-x 4 and C-x r, are themselves prefix keys that lead to three-event key sequences. There's no limit to the length of a key sequence, but in practice people rarely use sequences longer than four events.

By contrast, you can't add more events onto a complete key. For example, the two-event sequence C-f C-k is not a key, because the C-f is a complete key in itself. It's impossible to give C-f C-k an independent meaning as a command. C-f C-k is two key sequences, not one.

All told, the prefix keys in Emacs are C-c, C-h, C-x, C-x RET, C-x @, C-x a, C-x n, C-x r, C-x v, C-x 4, C-x 5, C-x 6, ESC, and M-g. But this list is not cast in concrete; it is just a matter of Emacs's standard key bindings. If you customize Emacs, you can make new prefix keys, or eliminate these. See section AD.4 Customizing Key Bindings.

If you do make or eliminate prefix keys, that changes the set of possible key sequences. For example, if you redefine C-f as a prefix, C-f C-k automatically becomes a key (complete, unless you define that too as a prefix). Conversely, if you remove the prefix definition of C-x 4, then C-x 4 f (or C-x 4 anything) is no longer a key.

Typing the help character (C-h or F1) after a prefix key displays a list of the commands starting with that prefix. There are a few prefix keys for which C-h does not work--for historical reasons, they have other meanings for C-h which are not easy to change. But F1 should work for all prefix keys.


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B.7 Keys and Commands

This manual is full of passages that tell you what particular keys do. But Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named commands, and then gives keys their meanings by binding them to commands.

Every command has a name chosen by a programmer. The name is usually made of a few English words separated by dashes; for example, next-line or forward-word. A command also has a function definition which is a Lisp program; this is what makes the command do what it does. In Emacs Lisp, a command is actually a special kind of Lisp function; one which specifies how to read arguments for it and call it interactively. For more information on commands and functions, see section `What Is a Function' in The Emacs Lisp Reference Manual. (The definition we use in this manual is simplified slightly.)

The bindings between keys and commands are recorded in various tables called keymaps. See section AD.4.1 Keymaps.

When we say that "C-n moves down vertically one line" we are glossing over a distinction that is irrelevant in ordinary use but is vital in understanding how to customize Emacs. It is the command next-line that is programmed to move down vertically. C-n has this effect because it is bound to that command. If you rebind C-n to the command forward-word then C-n will move forward by words instead. Rebinding keys is a common method of customization.

In the rest of this manual, we usually ignore this subtlety to keep things simple. To give the information needed for customization, we state the name of the command which really does the work in parentheses after mentioning the key that runs it. For example, we will say that "The command C-n (next-line) moves point vertically down," meaning that next-line is a command that moves vertically down, and C-n is a key that is normally bound to it.

While we are on the subject of information for customization only, it's a good time to tell you about variables. Often the description of a command will say, "To change this, set the variable mumble-foo." A variable is a name used to remember a value. Most of the variables documented in this manual exist just to facilitate customization: some command or other part of Emacs examines the variable and behaves differently according to the value that you set. Until you are interested in customizing, you can ignore the information about variables. When you are ready to be interested, read the basic information on variables, and then the information on individual variables will make sense. See section AD.2 Variables.


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B.8 Character Set for Text

Text in Emacs buffers is a sequence of 8-bit bytes. Each byte can hold a single ASCII character. Both ASCII control characters (octal codes 000 through 037, and 0177) and ASCII printing characters (codes 040 through 0176) are allowed; however, non-ASCII control characters cannot appear in a buffer. The other modifier flags used in keyboard input, such as Meta, are not allowed in buffers either.

Some ASCII control characters serve special purposes in text, and have special names. For example, the newline character (octal code 012) is used in the buffer to end a line, and the tab character (octal code 011) is used for indenting to the next tab stop column (normally every 8 columns). See section J.11 How Text Is Displayed.

Non-ASCII printing characters can also appear in buffers. When multibyte characters are enabled, you can use any of the non-ASCII printing characters that Emacs supports. They have character codes starting at 256, octal 0400, and each one is represented as a sequence of two or more bytes. See section Q. International Character Set Support. Single-byte characters with codes 128 through 255 can also appear in multibyte buffers.

If you disable multibyte characters, then you can use only one alphabet of non-ASCII characters, but they all fit in one byte. They use codes 0200 through 0377. See section Q.13 Single-byte Character Set Support.


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C. Entering and Exiting Emacs

The usual way to invoke Emacs is with the shell command emacs. Emacs clears the screen and then displays an initial help message and copyright notice. Some operating systems discard all type-ahead when Emacs starts up; they give Emacs no way to prevent this. Therefore, it is advisable to wait until Emacs clears the screen before typing your first editing command.

If you run Emacs from a shell window under the X Window System, run it in the background with emacs&. This way, Emacs does not tie up the shell window, so you can use that to run other shell commands while Emacs operates its own X windows. You can begin typing Emacs commands as soon as you direct your keyboard input to the Emacs frame.

When Emacs starts up, it creates a buffer named `*scratch*'. That's the buffer you start out in. The `*scratch*' buffer uses Lisp Interaction mode; you can use it to type Lisp expressions and evaluate them, or you can ignore that capability and simply doodle. (You can specify a different major mode for this buffer by setting the variable initial-major-mode in your init file. See section AD.7 The Init File, `~/.emacs'.)

It is possible to specify files to be visited, Lisp files to be loaded, and functions to be called, by giving Emacs arguments in the shell command line. See section AE. Command Line Arguments. But we don't recommend doing this. The feature exists mainly for compatibility with other editors.

Many other editors are designed to be started afresh each time you want to edit. You edit one file and then exit the editor. The next time you want to edit either another file or the same one, you must run the editor again. With these editors, it makes sense to use a command-line argument to say which file to edit.

But starting a new Emacs each time you want to edit a different file does not make sense. For one thing, this would be annoyingly slow. For another, this would fail to take advantage of Emacs's ability to visit more than one file in a single editing session. And it would lose the other accumulated context, such as the kill ring, registers, undo history, and mark ring.

The recommended way to use GNU Emacs is to start it only once, just after you log in, and do all your editing in the same Emacs session. Each time you want to edit a different file, you visit it with the existing Emacs, which eventually comes to have many files in it ready for editing. Usually you do not kill the Emacs until you are about to log out. See section M. File Handling, for more information on visiting more than one file.


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C.1 Exiting Emacs

There are two commands for exiting Emacs because there are two kinds of exiting: suspending Emacs and killing Emacs.

Suspending means stopping Emacs temporarily and returning control to its parent process (usually a shell), allowing you to resume editing later in the same Emacs job, with the same buffers, same kill ring, same undo history, and so on. This is the usual way to exit.

Killing Emacs means destroying the Emacs job. You can run Emacs again later, but you will get a fresh Emacs; there is no way to resume the same editing session after it has been killed.

C-z
Suspend Emacs (suspend-emacs) or iconify a frame (iconify-or-deiconify-frame).
C-x C-c
Kill Emacs (save-buffers-kill-emacs).

To suspend Emacs, type C-z (suspend-emacs). This takes you back to the shell from which you invoked Emacs. You can resume Emacs with the shell command %emacs in most common shells.

On systems that do not support suspending programs, C-z starts an inferior shell that communicates directly with the terminal. Emacs waits until you exit the subshell. (The way to do that is probably with C-d or exit, but it depends on which shell you use.) The only way on these systems to get back to the shell from which Emacs was run (to log out, for example) is to kill Emacs.

Suspending also fails if you run Emacs under a shell that doesn't support suspending programs, even if the system itself does support it. In such a case, you can set the variable cannot-suspend to a non-nil value to force C-z to start an inferior shell. (One might also describe Emacs's parent shell as "inferior" for failing to support job control properly, but that is a matter of taste.)

When Emacs communicates directly with an X server and creates its own dedicated X windows, C-z has a different meaning. Suspending an application that uses its own X windows is not meaningful or useful. Instead, C-z runs the command iconify-or-deiconify-frame, which temporarily iconifies (or "minimizes") the selected Emacs frame (see section P. Frames and X Windows). Then you can use the window manager to get back to a shell window.

To exit and kill Emacs, type C-x C-c (save-buffers-kill-emacs). A two-character key is used for this to make it harder to type by accident. This command first offers to save any modified file-visiting buffers. If you do not save them all, it asks for reconfirmation with yes before killing Emacs, since any changes not saved will be lost forever. Also, if any subprocesses are still running, C-x C-c asks for confirmation about them, since killing Emacs will also kill the subprocesses.

If the value of the variable confirm-kill-emacs is non-nil, C-x C-c assumes that its value is a predicate function, and calls that function. If the result is non-nil, the session is killed, otherwise Emacs continues to run. One convenient function to use as the value of confirm-kill-emacs is the function yes-or-no-p. The default value of confirm-kill-emacs is nil.

There is no way to resume an Emacs session once you have killed it. You can, however, arrange for Emacs to record certain session information when you kill it, such as which files are visited, so that the next time you start Emacs it will try to visit the same files and so on. See section AC.25 Saving Emacs Sessions.

The operating system usually listens for certain special characters whose meaning is to kill or suspend the program you are running. This operating system feature is turned off while you are in Emacs. The meanings of C-z and C-x C-c as keys in Emacs were inspired by the use of C-z and C-c on several operating systems as the characters for stopping or killing a program, but that is their only relationship with the operating system. You can customize these keys to run any commands of your choice (see section AD.4.1 Keymaps).


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D. Basic Editing Commands

We now give the basics of how to enter text, make corrections, and save the text in a file. If this material is new to you, you might learn it more easily by running the Emacs learn-by-doing tutorial. To use the tutorial, run Emacs and type Control-h t (help-with-tutorial).

To clear the screen and redisplay, type C-l (recenter).


D.1 Inserting Text  Inserting text by simply typing it.
D.2 Changing the Location of Point  How to move the cursor to the place where you want to change something.
D.3 Erasing Text  Deleting and killing text.
D.4 Undoing Changes  Undoing recent changes in the text.
D.5 Files  Visiting, creating, and saving files.
D.6 Help  Asking what a character does.
D.7 Blank Lines  Commands to make or delete blank lines.
D.8 Continuation Lines  Lines too wide for the screen.
D.9 Cursor Position Information  What page, line, row, or column is point on?
D.10 Numeric Arguments  Numeric arguments for repeating a command.
D.11 Repeating a Command  A short-cut for repeating the previous command.


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D.1 Inserting Text

To insert printing characters into the text you are editing, just type them. This inserts the characters you type into the buffer at the cursor (that is, at point; see section B.1 Point). The cursor moves forward, and any text after the cursor moves forward too. If the text in the buffer is `FOOBAR', with the cursor before the `B', then if you type XX, you get `FOOXXBAR', with the cursor still before the `B'.

To delete text you have just inserted, use the large key labeled DEL, BACKSPACE or DELETE which is a short distance above the RET or ENTER key. This is the key you normally use, outside Emacs, for erasing the last character that you typed. Regardless of the label on that key, Emacs thinks of it as DEL, and that's what we call it in this manual.

The DEL key deletes the character before the cursor. As a consequence, the cursor and all the characters after it move backwards. If you type a printing character and then type DEL, they cancel out.

On most computers, Emacs recognizes automatically which key ought to be DEL, and sets it up that way. But in some cases, especially with text-only terminals, you will need to tell Emacs which key to use for that purpose. If the large key not far above the RET or ENTER key doesn't delete backwards, you need to do this. See section AD.9.1 If DEL Fails to Delete, for an explanation of how.

Most PC keyboards have both a BACKSPACE key a short ways above RET or ENTER, and a DELETE key elsewhere. On these keyboards, Emacs supports when possible the usual convention that the BACKSPACE key deletes backwards (it is DEL), while the DELETE key deletes "forwards," deleting the character after point, the one underneath the cursor, like C-d (see below).

To end a line and start typing a new one, type RET. This inserts a newline character in the buffer. If point is in the middle of a line, RET splits the line. Typing DEL when the cursor is at the beginning of a line deletes the preceding newline, thus joining the line with the preceding line.

Emacs can split lines automatically when they become too long, if you turn on a special minor mode called Auto Fill mode. See section T.5 Filling Text, for how to use Auto Fill mode.

If you prefer to have text characters replace (overwrite) existing text rather than shove it to the right, you can enable Overwrite mode, a minor mode. See section AD.1 Minor Modes.

Direct insertion works for printing characters and SPC, but other characters act as editing commands and do not insert themselves. If you need to insert a control character or a character whose code is above 200 octal, you must quote it by typing the character Control-q (quoted-insert) first. (This character's name is normally written C-q for short.) There are two ways to use C-q:

When multibyte characters are enabled, if you specify a code in the range 0200 through 0377 octal, C-q assumes that you intend to use some ISO 8859-n character set, and converts the specified code to the corresponding Emacs character code. See section Q.2 Enabling Multibyte Characters. You select which of the ISO 8859 character sets to use through your choice of language environment (see section Q.3 Language Environments).

To use decimal or hexadecimal instead of octal, set the variable read-quoted-char-radix to 10 or 16. If the radix is greater than 10, some letters starting with a serve as part of a character code, just like digits.

A numeric argument to C-q specifies how many copies of the quoted character should be inserted (see section D.10 Numeric Arguments).

Customization information: DEL in most modes runs the command delete-backward-char; RET runs the command newline, and self-inserting printing characters run the command self-insert, which inserts whatever character was typed to invoke it. Some major modes rebind DEL to other commands.


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D.2 Changing the Location of Point

To do more than insert characters, you have to know how to move point (see section B.1 Point). The simplest way to do this is with arrow keys, or by clicking the left mouse button where you want to move to.

There are also control and meta characters for cursor motion. Some are equivalent to the arrow keys (these date back to the days before terminals had arrow keys, and are usable on terminals which don't have them). Others do more sophisticated things.

C-a
Move to the beginning of the line (beginning-of-line).
C-e
Move to the end of the line (end-of-line).
C-f
Move forward one character (forward-char). The right-arrow key does the same thing.
C-b
Move backward one character (backward-char). The left-arrow key has the same effect.
M-f
Move forward one word (forward-word).
M-b
Move backward one word (backward-word).
C-n
Move down one line, vertically (next-line). This command attempts to keep the horizontal position unchanged, so if you start in the middle of one line, you end in the middle of the next. The down-arrow key does the same thing.
C-p
Move up one line, vertically (previous-line). The up-arrow key has the same effect.
M-r
Move point to left margin, vertically centered in the window (move-to-window-line). Text does not move on the screen.

A numeric argument says which screen line to place point on. It counts screen lines down from the top of the window (zero for the top line). A negative argument counts lines from the bottom (-1 for the bottom line).

M-<
Move to the top of the buffer (beginning-of-buffer). With numeric argument n, move to n/10 of the way from the top. See section D.10 Numeric Arguments, for more information on numeric arguments.
M->
Move to the end of the buffer (end-of-buffer).
C-v
Scroll the display one screen forward, and move point if necessary to put it on the screen (scroll-up). This doesn't always move point, but it is commonly used to do so. If your keyboard has a PAGEDOWN key, it does the same thing.

Scrolling commands are further described in J.6 Scrolling.

M-v
Scroll one screen backward, and move point if necessary to put it on the screen (scroll-down). This doesn't always move point, but it is commonly used to do so. The PAGEUP key has the same effect.
M-x goto-char
Read a number n and move point to buffer position n. Position 1 is the beginning of the buffer.
M-x goto-line
Read a number n and move point to line number n. Line 1 is the beginning of the buffer.
C-x C-n
Use the current column of point as the semipermanent goal column for C-n and C-p (set-goal-column). Henceforth, those commands always move to this column in each line moved into, or as close as possible given the contents of the line. This goal column remains in effect until canceled.
C-u C-x C-n
Cancel the goal column. Henceforth, C-n and C-p once again try to stick to a fixed horizontal position, as usual.

If you set the variable track-eol to a non-nil value, then C-n and C-p, when starting at the end of the line, move to the end of another line. Normally, track-eol is nil. See section AD.2 Variables, for how to set variables such as track-eol.

C-n normally gets an error when you use it on the last line of the buffer (just as C-p gets an error on the first line). But if you set the variable next-line-add-newlines to a non-nil value, C-n on the last line of a buffer creates an additional line at the end and moves down onto it.


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D.3 Erasing Text

DEL
Delete the character before point (delete-backward-char).
C-d
Delete the character after point (delete-char).
DELETE
BACKSPACE
One of these keys, whichever is the large key above the RET or ENTER key, deletes the character before point, like DEL. If that is BACKSPACE, and your keyboard also has DELETE, then DELETE deletes forwards, like C-d.
C-k
Kill to the end of the line (kill-line).
M-d
Kill forward to the end of the next word (kill-word).
M-DEL
Kill back to the beginning of the previous word (backward-kill-word).

You already know about the DEL key which deletes the character before point (that is, before the cursor). Another key, Control-d (C-d for short), deletes the character after point (that is, the character that the cursor is on). This shifts the rest of the text on the line to the left. If you type C-d at the end of a line, it joins together that line and the next line.

To erase a larger amount of text, use the C-k key, which kills a line at a time. If you type C-k at the beginning or middle of a line, it kills all the text up to the end of the line. If you type C-k at the end of a line, it joins that line and the next line.

See section H.7 Deletion and Killing, for more flexible ways of killing text.


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D.4 Undoing Changes

You can undo all the recent changes in the buffer text, up to a certain point. Each buffer records changes individually, and the undo command always applies to the current buffer. Usually each editing command makes a separate entry in the undo records, but some commands such as query-replace make many entries, and very simple commands such as self-inserting characters are often grouped to make undoing less tedious.

C-x u
Undo one batch of changes--usually, one command worth (undo).
C-_
The same.
C-u C-x u
Undo one batch of changes in the region.

The command C-x u or C-_ is how you undo. The first time you give this command, it undoes the last change. Point moves back to where it was before the command that made the change.

Consecutive repetitions of C-_ or C-x u undo earlier and earlier changes, back to the limit of the undo information available. If all recorded changes have already been undone, the undo command displays an error message and does nothing.

Any command other than an undo command breaks the sequence of undo commands. Starting from that moment, the previous undo commands become ordinary changes that you can undo. Thus, to redo changes you have undone, type C-f or any other command that will harmlessly break the sequence of undoing, then type more undo commands.

Ordinary undo applies to all changes made in the current buffer. You can also perform selective undo, limited to the current region. To do this, specify the region you want, then run the undo command with a prefix argument (the value does not matter): C-u C-x u or C-u C-_. This undoes the most recent change in the region. To undo further changes in the same region, repeat the undo command (no prefix argument is needed). In Transient Mark mode, any use of undo when there is an active region performs selective undo; you do not need a prefix argument.

If you notice that a buffer has been modified accidentally, the easiest way to recover is to type C-_ repeatedly until the stars disappear from the front of the mode line. At this time, all the modifications you made have been canceled. Whenever an undo command makes the stars disappear from the mode line, it means that the buffer contents are the same as they were when the file was last read in or saved.

If you do not remember whether you changed the buffer deliberately, type C-_ once. When you see the last change you made undone, you will see whether it was an intentional change. If it was an accident, leave it undone. If it was deliberate, redo the change as described above.

Not all buffers record undo information. Buffers whose names start with spaces don't; these buffers are used internally by Emacs and its extensions to hold text that users don't normally look at or edit.

You cannot undo mere cursor motion; only changes in the buffer contents save undo information. However, some cursor motion commands set the mark, so if you use these commands from time to time, you can move back to the neighborhoods you have moved through by popping the mark ring (see section H.5 The Mark Ring).

When the undo information for a buffer becomes too large, Emacs discards the oldest undo information from time to time (during garbage collection). You can specify how much undo information to keep by setting two variables: undo-limit and undo-strong-limit. Their values are expressed in units of bytes of space.

The variable undo-limit sets a soft limit: Emacs keeps undo data for enough commands to reach this size, and perhaps exceed it, but does not keep data for any earlier commands beyond that. Its default value is 20000. The variable undo-strong-limit sets a stricter limit: the command which pushes the size past this amount is itself forgotten. Its default value is 30000.

Regardless of the values of those variables, the most recent change is never discarded, so there is no danger that garbage collection occurring right after an unintentional large change might prevent you from undoing it.

The reason the undo command has two keys, C-x u and C-_, set up to run it is that it is worthy of a single-character key, but on some keyboards it is not obvious how to type C-_. C-x u is an alternative you can type straightforwardly on any terminal.


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D.5 Files

The commands described above are sufficient for creating and altering text in an Emacs buffer; the more advanced Emacs commands just make things easier. But to keep any text permanently you must put it in a file. Files are named units of text which are stored by the operating system for you to retrieve later by name. To look at or use the contents of a file in any way, including editing the file with Emacs, you must specify the file name.

Consider a file named `/usr/rms/foo.c'. In Emacs, to begin editing this file, type

 
C-x C-f /usr/rms/foo.c RET

Here the file name is given as an argument to the command C-x C-f (find-file). That command uses the minibuffer to read the argument, and you type RET to terminate the argument (see section E. The Minibuffer).

Emacs obeys the command by visiting the file: creating a buffer, copying the contents of the file into the buffer, and then displaying the buffer for you to edit. If you alter the text, you can save the new text in the file by typing C-x C-s (save-buffer). This makes the changes permanent by copying the altered buffer contents back into the file `/usr/rms/foo.c'. Until you save, the changes exist only inside Emacs, and the file `foo.c' is unaltered.

To create a file, just visit the file with C-x C-f as if it already existed. This creates an empty buffer in which you can insert the text you want to put in the file. The file is actually created when you save this buffer with C-x C-s.

Of course, there is a lot more to learn about using files. See section M. File Handling.


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D.6 Help

If you forget what a key does, you can find out with the Help character, which is C-h (or F1, which is an alias for C-h). Type C-h k followed by the key you want to know about; for example, C-h k C-n tells you all about what C-n does. C-h is a prefix key; C-h k is just one of its subcommands (the command describe-key). The other subcommands of C-h provide different kinds of help. Type C-h twice to get a description of all the help facilities. See section G. Help.


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D.7 Blank Lines

Here are special commands and techniques for putting in and taking out blank lines.

C-o
Insert one or more blank lines after the cursor (open-line).
C-x C-o
Delete all but one of many consecutive blank lines (delete-blank-lines).

When you want to insert a new line of text before an existing line, you can do it by typing the new line of text, followed by RET. However, it may be easier to see what you are doing if you first make a blank line and then insert the desired text into it. This is easy to do using the key C-o (open-line), which inserts a newline after point but leaves point in front of the newline. After C-o, type the text for the new line. C-o F O O has the same effect as F O O RET, except for the final location of point.

You can make several blank lines by typing C-o several times, or by giving it a numeric argument to tell it how many blank lines to make. See section D.10 Numeric Arguments, for how. If you have a fill prefix, then C-o command inserts the fill prefix on the new line, when you use it at the beginning of a line. See section T.5.4 The Fill Prefix.

The easy way to get rid of extra blank lines is with the command C-x C-o (delete-blank-lines). C-x C-o in a run of several blank lines deletes all but one of them. C-x C-o on a solitary blank line deletes that blank line. When point is on a nonblank line, C-x C-o deletes any blank lines following that nonblank line.


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D.8 Continuation Lines

If you add too many characters to one line without breaking it with RET, the line grows to occupy two (or more) lines on the screen. On graphical displays, Emacs indicates line wrapping with small bent arrows in the fringes to the left and right of the window. On text-only terminals, Emacs displays a `\' character at the right margin of a screen line if it is not the last in its text line. This `\' character says that the following screen line is not really a distinct line in the text, just a continuation of a line too long to fit the screen. Continuation is also called line wrapping.

When line wrapping occurs before a character that is wider than one column, some columns at the end of the previous screen line may be "empty." In this case, Emacs displays additional `\' characters in the "empty" columns, just before the `\' character that indicates continuation.

Sometimes it is nice to have Emacs insert newlines automatically when a line gets too long. Continuation on the screen does not do that. Use Auto Fill mode (see section T.5 Filling Text) if that's what you want.

As an alternative to continuation, Emacs can display long lines by truncation. This means that all the characters that do not fit in the width of the screen or window do not appear at all. They remain in the buffer, temporarily invisible. On terminals, `$' in the last column informs you that the line has been truncated on the display. On window systems, a small straight arrow in the fringe to the right of the window indicates a truncated line.

Truncation instead of continuation happens whenever horizontal scrolling is in use, and optionally in all side-by-side windows (see section O. Multiple Windows). You can enable or disable truncation for a particular buffer with the command M-x toggle-truncate-lines.

See section J.12 Customization of Display, for additional variables that affect how text is displayed.


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D.9 Cursor Position Information

Here are commands to get information about the size and position of parts of the buffer, and to count lines.

M-x what-page
Display the page number of point, and the line number within the page.
M-x what-line
Display the line number of point in the buffer.
M-x line-number-mode
M-x column-number-mode
Toggle automatic display of current line number or column number. See section J.10 Optional Mode Line Features.
M-=
Display the number of lines in the current region (count-lines-region). See section H. The Mark and the Region, for information about the region.
C-x =
Display the character code of character after point, character position of point, and column of point (what-cursor-position).
M-x hl-line-mode
Enable or disable highlighting of the current line. See section J.13 Displaying the Cursor.

There are two commands for working with line numbers. M-x what-line computes the current line number and displays it in the echo area. To go to a given line by number, use M-x goto-line; it prompts you for the number. These line numbers count from one at the beginning of the buffer.

You can also see the current line number in the mode line; see B.3 The Mode Line. If you narrow the buffer, then the line number in the mode line is relative to the accessible portion (see section AC.22 Narrowing). By contrast, what-line shows both the line number relative to the narrowed region and the line number relative to the whole buffer.

M-x what-page counts pages from the beginning of the file, and counts lines within the page, showing both numbers in the echo area. See section T.4 Pages.

While on this subject, we might as well mention M-= (count-lines-region), which displays the number of lines in the region (see section H. The Mark and the Region). See section T.4 Pages, for the command C-x l which counts the lines in the current page.

The command C-x = (what-cursor-position) can be used to find out the column that the cursor is in, and other miscellaneous information about point. It displays a line in the echo area that looks like this:

 
Char: c (0143, 99, 0x63)  point=21044 of 26883(78%)  column 53 

(In fact, this is the output produced when point is before the `column' in the example.)

The four values after `Char:' describe the character that follows point, first by showing it and then by giving its character code in octal, decimal and hex. For a non-ASCII multibyte character, these are followed by `ext' and the character's representation, in hex, in the buffer's coding system, if that coding system encodes the character safely and with a single byte (see section Q.7 Coding Systems). If the character's encoding is longer than one byte, Emacs shows `ext ...'.

`point=' is followed by the position of point expressed as a character count. The front of the buffer counts as position 1, one character later as 2, and so on. The next, larger, number is the total number of characters in the buffer. Afterward in parentheses comes the position expressed as a percentage of the total size.

`column' is followed by the horizontal position of point, in columns from the left edge of the window.

If the buffer has been narrowed, making some of the text at the beginning and the end temporarily inaccessible, C-x = displays additional text describing the currently accessible range. For example, it might display this:

 
Char: C (0103, 67, 0x43)  point=252 of 889(28%) <231 - 599>  column 0 

where the two extra numbers give the smallest and largest character position that point is allowed to assume. The characters between those two positions are the accessible ones. See section AC.22 Narrowing.

If point is at the end of the buffer (or the end of the accessible part), the C-x = output does not describe a character after point. The output might look like this:

 
point=26957 of 26956(100%)  column 0 

C-u C-x = displays additional information about a character, in place of the buffer coordinates and column: the character set name and the codes that identify the character within that character set; ASCII characters are identified as belonging to the ASCII character set. In addition, the full character encoding, even if it takes more than a single byte, is shown after `ext'. Here's an example for a Latin-1 character A with a grave accent in a buffer whose coding system is iso-2022-7bit(1):

 
Char: À (04300, 2240, 0x8c0, ext ESC , A @) (latin-iso8859-1 64)


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D.10 Numeric Arguments

In mathematics and computer usage, the word argument means "data provided to a function or operation." You can give any Emacs command a numeric argument (also called a prefix argument). Some commands interpret the argument as a repetition count. For example, C-f with an argument of ten moves forward ten characters instead of one. With these commands, no argument is equivalent to an argument of one. Negative arguments tell most such commands to move or act in the opposite direction.

If your terminal keyboard has a META key, the easiest way to specify a numeric argument is to type digits and/or a minus sign while holding down the META key. For example,

 
M-5 C-n

would move down five lines. The characters Meta-1, Meta-2, and so on, as well as Meta--, do this because they are keys bound to commands (digit-argument and negative-argument) that are defined to contribute to an argument for the next command. Meta-- without digits normally means -1. Digits and - modified with Control, or Control and Meta, also specify numeric arguments.

Another way of specifying an argument is to use the C-u (universal-argument) command followed by the digits of the argument. With C-u, you can type the argument digits without holding down modifier keys; C-u works on all terminals. To type a negative argument, type a minus sign after C-u. Just a minus sign without digits normally means -1.

C-u followed by a character which is neither a digit nor a minus sign has the special meaning of "multiply by four." It multiplies the argument for the next command by four. C-u twice multiplies it by sixteen. Thus, C-u C-u C-f moves forward sixteen characters. This is a good way to move forward "fast," since it moves about 1/5 of a line in the usual size screen. Other useful combinations are C-u C-n, C-u C-u C-n (move down a good fraction of a screen), C-u C-u C-o (make "a lot" of blank lines), and C-u C-k (kill four lines).

Some commands care only about whether there is an argument, and not about its value. For example, the command M-q (fill-paragraph) with no argument fills text; with an argument, it justifies the text as well. (See section T.5 Filling Text, for more information on M-q.) Plain C-u is a handy way of providing an argument for such commands.

Some commands use the value of the argument as a repeat count, but do something peculiar when there is no argument. For example, the command C-k (kill-line) with argument n kills n lines, including their terminating newlines. But C-k with no argument is special: it kills the text up to the next newline, or, if point is right at the end of the line, it kills the newline itself. Thus, two C-k commands with no arguments can kill a nonblank line, just like C-k with an argument of one. (See section H.7 Deletion and Killing, for more information on C-k.)

A few commands treat a plain C-u differently from an ordinary argument. A few others may treat an argument of just a minus sign differently from an argument of -1. These unusual cases are described when they come up; they are always for reasons of convenience of use of the individual command.

You can use a numeric argument to insert multiple copies of a character. This is straightforward unless the character is a digit; for example, C-u 6 4 a inserts 64 copies of the character `a'. But this does not work for inserting digits; C-u 6 4 1 specifies an argument of 641, rather than inserting anything. To separate the digit to insert from the argument, type another C-u; for example, C-u 6 4 C-u 1 does insert 64 copies of the character `1'.

We use the term "prefix argument" as well as "numeric argument" to emphasize that you type the argument before the command, and to distinguish these arguments from minibuffer arguments that come after the command.


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D.11 Repeating a Command

Many simple commands, such as those invoked with a single key or with M-x command-name RET, can be repeated by invoking them with a numeric argument that serves as a repeat count (see section D.10 Numeric Arguments). However, if the command you want to repeat prompts for some input, or uses a numeric argument in another way, repetition using a numeric argument might be problematical.

The command C-x z (repeat) provides another way to repeat an Emacs command many times. This command repeats the previous Emacs command, whatever that was. Repeating a command uses the same arguments that were used before; it does not read new arguments each time.

To repeat the command more than once, type additional z's: each z repeats the command one more time. Repetition ends when you type a character other than z, or press a mouse button.

For example, suppose you type C-u 2 0 C-d to delete 20 characters. You can repeat that command (including its argument) three additional times, to delete a total of 80 characters, by typing C-x z z z. The first C-x z repeats the command once, and each subsequent z repeats it once again.


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E. The Minibuffer

The minibuffer is the facility used by Emacs commands to read arguments more complicated than a single number. Minibuffer arguments can be file names, buffer names, Lisp function names, Emacs command names, Lisp expressions, and many other things, depending on the command reading the argument. You can use the usual Emacs editing commands in the minibuffer to edit the argument text.

When the minibuffer is in use, it appears in the echo area, and the terminal's cursor moves there. The beginning of the minibuffer line displays a prompt which says what kind of input you should supply and how it will be used. Often this prompt is derived from the name of the command that the argument is for. The prompt normally ends with a colon.

Sometimes a default argument appears in parentheses after the colon; it too is part of the prompt. The default will be used as the argument value if you enter an empty argument (that is, just type RET). For example, commands that read buffer names always show a default, which is the name of the buffer that will be used if you type just RET.

The simplest way to enter a minibuffer argument is to type the text you want, terminated by RET which exits the minibuffer. You can cancel the command that wants the argument, and get out of the minibuffer, by typing C-g.

Since the minibuffer uses the screen space of the echo area, it can conflict with other ways Emacs customarily uses the echo area. Here is how Emacs handles such conflicts:

E.1 Minibuffers for File Names  Entering file names with the minibuffer.
E.2 Editing in the Minibuffer  How to edit in the minibuffer.
E.3 Completion  An abbreviation facility for minibuffer input.
E.4 Minibuffer History  Reusing recent minibuffer arguments.
E.5 Repeating Minibuffer Commands  Re-executing commands that used the minibuffer.


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E.1 Minibuffers for File Names

Sometimes the minibuffer starts out with text in it. For example, when you are supposed to give a file name, the minibuffer starts out containing the default directory, which ends with a slash. This is to inform you which directory the file will be found in if you do not specify a directory.

For example, the minibuffer might start out with these contents:

 
Find File: /u2/emacs/src/

where `Find File: ' is the prompt. Typing buffer.c specifies the file `/u2/emacs/src/buffer.c'. To find files in nearby directories, use ..; thus, if you type ../lisp/simple.el, you will get the file named `/u2/emacs/lisp/simple.el'. Alternatively, you can kill with M-DEL the directory names you don't want (see section T.1 Words).

If you don't want any of the default, you can kill it with C-a C-k. But you don't need to kill the default; you can simply ignore it. Insert an absolute file name, one starting with a slash or a tilde, after the default directory. For example, to specify the file `/etc/termcap', just insert that name, giving these minibuffer contents:

 
Find File: /u2/emacs/src//etc/termcap

GNU Emacs gives a special meaning to a double slash (which is not normally a useful thing to write): it means, "ignore everything before the second slash in the pair." Thus, `/u2/emacs/src/' is ignored in the example above, and you get the file `/etc/termcap'.

If you set insert-default-directory to nil, the default directory is not inserted in the minibuffer. This way, the minibuffer starts out empty. But the name you type, if relative, is still interpreted with respect to the same default directory.


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E.2 Editing in the Minibuffer

The minibuffer is an Emacs buffer (albeit a peculiar one), and the usual Emacs commands are available for editing the text of an argument you are entering.

Since RET in the minibuffer is defined to exit the minibuffer, you can't use it to insert a newline in the minibuffer. To do that, type C-o or C-q C-j. (Recall that a newline is really the character control-J.)

The minibuffer has its own window which always has space on the screen but acts as if it were not there when the minibuffer is not in use. When the minibuffer is in use, its window is just like the others; you can switch to another window with C-x o, edit text in other windows and perhaps even visit more files, before returning to the minibuffer to submit the argument. You can kill text in another window, return to the minibuffer window, and then yank the text to use it in the argument. See section O. Multiple Windows.

There are some restrictions on the use of the minibuffer window, however. You cannot switch buffers in it--the minibuffer and its window are permanently attached. Also, you cannot split or kill the minibuffer window. But you can make it taller in the normal fashion with C-x ^.

The minibuffer window expands vertically as necessary to hold the text that you put in the minibuffer, if resize-mini-windows is non-nil. If resize-mini-windows is t, the window is always resized to fit the size of the text it displays. If resize-mini-windows is the symbol grow-only, the window grows when the size of displayed text increases, but shrinks (back to the normal size) only when the minibuffer becomes inactive.

The variable max-mini-window-height controls the maximum height for resizing the minibuffer window: a floating-point number specifies a fraction of the frame's height; an integer specifies the maximum number of lines; nil means do not resize the minibuffer window automatically. The default value is 0.25.

If while in the minibuffer you issue a command that displays help text of any sort in another window, you can use the C-M-v command while in the minibuffer to scroll the help text. This lasts until you exit the minibuffer. This feature is especially useful when you display a buffer listing possible completions. See section O.3 Using Other Windows.

Emacs normally disallows most commands that use the minibuffer while the minibuffer is active. This rule is to prevent recursive minibuffers from confusing novice users. If you want to be able to use such commands in the minibuffer, set the variable enable-recursive-minibuffers to a non-nil value.


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E.3 Completion

For certain kinds of arguments, you can use completion to enter the argument value. Completion means that you type part of the argument, then Emacs visibly fills in the rest, or as much as can be determined from the part you have typed.

When completion is available, certain keys---TAB, RET, and SPC---are rebound to complete the text present in the minibuffer into a longer string that it stands for, by matching it against a set of completion alternatives provided by the command reading the argument. ? is defined to display a list of possible completions of what you have inserted.

For example, when M-x uses the minibuffer to read the name of a command, it provides a list of all available Emacs command names to complete against. The completion keys match the text in the minibuffer against all the command names, find any additional name characters implied by the ones already present in the minibuffer, and add those characters to the ones you have given. This is what makes it possible to type M-x ins SPC b RET instead of M-x insert-buffer RET (for example).

Case is normally significant in completion, because it is significant in most of the names that you can complete (buffer names, file names and command names). Thus, `fo' does not complete to `Foo'. Completion does ignore case distinctions for certain arguments in which case does not matter.

E.3.1 Completion Example  
E.3.2 Completion Commands  
E.3.3 Strict Completion  
E.3.4 Completion Options  


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E.3.1 Completion Example

A concrete example may help here. If you type M-x au TAB, the TAB looks for alternatives (in this case, command names) that start with `au'. There are several, including auto-fill-mode and auto-save-mode---but they are all the same as far as auto-, so the `au' in the minibuffer changes to `auto-'.

If you type TAB again immediately, there are multiple possibilities for the very next character--it could be any of `cfilrs'---so no more characters are added; instead, TAB displays a list of all possible completions in another window.

If you go on to type f TAB, this TAB sees `auto-f'. The only command name starting this way is auto-fill-mode, so completion fills in the rest of that. You now have `auto-fill-mode' in the minibuffer after typing just au TAB f TAB. Note that TAB has this effect because in the minibuffer it is bound to the command minibuffer-complete when completion is available.


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E.3.2 Completion Commands

Here is a list of the completion commands defined in the minibuffer when completion is available.

TAB
Complete the text in the minibuffer as much as possible (minibuffer-complete).
SPC
Complete the minibuffer text, but don't go beyond one word (minibuffer-complete-word).
RET
Submit the text in the minibuffer as the argument, possibly completing first as described below (minibuffer-complete-and-exit).
?
Display a list of all possible completions of the text in the minibuffer (minibuffer-list-completions).

SPC completes much like TAB, but never goes beyond the next hyphen or space. If you have `auto-f' in the minibuffer and type SPC, it finds that the completion is `auto-fill-mode', but it stops completing after `fill-'. This gives `auto-fill-'. Another SPC at this point completes all the way to `auto-fill-mode'. The command that implements this behavior is called minibuffer-complete-word.

Here are some commands you can use to choose a completion from a window that displays a list of completions:

Mouse-2
Clicking mouse button 2 on a completion in the list of possible completions chooses that completion (mouse-choose-completion). You normally use this command while point is in the minibuffer, but you must click in the list of completions, not in the minibuffer itself.

PRIOR
M-v
Typing PRIOR or PAGE-UP, or M-v, while in the minibuffer, selects the window showing the completion list buffer (switch-to-completions). This paves the way for using the commands below. (Selecting that window in the usual ways has the same effect, but this way is more convenient.)

RET
Typing RET in the completion list buffer chooses the completion that point is in or next to (choose-completion). To use this command, you must first switch windows to the window that shows the list of completions.

RIGHT
Typing the right-arrow key RIGHT in the completion list buffer moves point to the following completion (next-completion).

LEFT
Typing the left-arrow key LEFT in the completion list buffer moves point toward the beginning of the buffer, to the previous completion (previous-completion).


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E.3.3 Strict Completion

There are three different ways that RET can work in completing minibuffers, depending on how the argument will be used.

The completion commands display a list of all possible completions in a window whenever there is more than one possibility for the very next character. Also, typing ? explicitly requests such a list. If the list of completions is long, you can scroll it with C-M-v (see section O.3 Using Other Windows).


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E.3.4 Completion Options

When completion is done on file names, certain file names are usually ignored. The variable completion-ignored-extensions contains a list of strings; a file whose name ends in any of those strings is ignored as a possible completion. The standard value of this variable has several elements including ".o", ".elc", ".dvi" and "~". The effect is that, for example, `foo' can complete to `foo.c' even though `foo.o' exists as well. However, if all the possible completions end in "ignored" strings, then they are not ignored. Ignored extensions do not apply to lists of completions--those always mention all possible completions.

Normally, a completion command that cannot determine even one additional character automatically displays a list of all possible completions. If the variable completion-auto-help is set to nil, this automatic display is disabled, so you must type ? to display the list of completions.

Partial Completion mode implements a more powerful kind of completion that can complete multiple words in parallel. For example, it can complete the command name abbreviation p-b into print-buffer, because no other command starts with two words whose initials are `p' and `b'.

Partial completion of directories in file names uses `*' to indicate the places for completion; thus, `/u*/b*/f*' might complete to `/usr/bin/foo'.

To enable this mode, use the command M-x partial-completion-mode, or customize the option partial-completion-mode. This binds the partial completion commands to TAB, SPC, RET, and ?. The usual completion commands are available on M-TAB, M-SPC, M-RET and M-?.

Another feature of Partial Completion mode is to extend find-file so that the `<include>' stands for the file named include in some directory in the path PC-include-file-path. If you set PC-disable-includes to non-nil, this feature is disabled.

Icomplete mode presents a constantly-updated display that tells you what completions are available for the text you've entered so far. The command to enable or disable this minor mode is M-x icomplete-mode.


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E.4 Minibuffer History

Every argument that you enter with the minibuffer is saved on a minibuffer history list so that you can use it again later in another argument. Special commands load the text of an earlier argument in the minibuffer. They discard the old minibuffer contents, so you can think of them as moving through the history of previous arguments.

UP
M-p
Move to the next earlier argument string saved in the minibuffer history (previous-history-element).
DOWN
M-n
Move to the next later argument string saved in the minibuffer history (next-history-element).
M-r regexp RET
Move to an earlier saved argument in the minibuffer history that has a match for regexp (previous-matching-history-element).
M-s regexp RET
Move to a later saved argument in the minibuffer history that has a match for regexp (next-matching-history-element).

The simplest way to reuse the saved arguments in the history list is to move through the history list one element at a time. While in the minibuffer, use M-p or up-arrow (previous-history-element) to "move to" the next earlier minibuffer input, and use M-n or down-arrow (next-history-element) to "move to" the next later input.

The previous input that you fetch from the history entirely replaces the contents of the minibuffer. To use it as the argument, exit the minibuffer as usual with RET. You can also edit the text before you reuse it; this does not change the history element that you "moved" to, but your new argument does go at the end of the history list in its own right.

For many minibuffer arguments there is a "default" value. In some cases, the minibuffer history commands know the default value. Then you can insert the default value into the minibuffer as text by using M-n to move "into the future" in the history. Eventually we hope to make this feature available whenever the minibuffer has a default value.

There are also commands to search forward or backward through the history; they search for history elements that match a regular expression that you specify with the minibuffer. M-r (previous-matching-history-element) searches older elements in the history, while M-s (next-matching-history-element) searches newer elements. By special dispensation, these commands can use the minibuffer to read their arguments even though you are already in the minibuffer when you issue them. As with incremental searching, an upper-case letter in the regular expression makes the search case-sensitive (see section K.6 Searching and Case).

All uses of the minibuffer record your input on a history list, but there are separate history lists for different kinds of arguments. For example, there is a list for file names, used by all the commands that read file names. (As a special feature, this history list records the absolute file name, no more and no less, even if that is not how you entered the file name.)

There are several other very specific history lists, including one for command names read by M-x, one for buffer names, one for arguments of commands like query-replace, and one for compilation commands read by compile. Finally, there is one "miscellaneous" history list that most minibuffer arguments use.

The variable history-length specifies the maximum length of a minibuffer history list; once a list gets that long, the oldest element is deleted each time an element is added. If the value of history-length is t, though, there is no maximum length and elements are never deleted.


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E.5 Repeating Minibuffer Commands

Every command that uses the minibuffer at least once is recorded on a special history list, together with the values of its arguments, so that you can repeat the entire command. In particular, every use of M-x is recorded there, since M-x uses the minibuffer to read the command name.

C-x ESC ESC
Re-execute a recent minibuffer command (repeat-complex-command).
M-x list-command-history
Display the entire command history, showing all the commands C-x ESC ESC can repeat, most recent first.

C-x ESC ESC is used to re-execute a recent minibuffer-using command. With no argument, it repeats the last such command. A numeric argument specifies which command to repeat; one means the last one, and larger numbers specify earlier ones.

C-x ESC ESC works by turning the previous command into a Lisp expression and then entering a minibuffer initialized with the text for that expression. If you type just RET, the command is repeated as before. You can also change the command by editing the Lisp expression. Whatever expression you finally submit is what will be executed. The repeated command is added to the front of the command history unless it is identical to the most recently executed command already there.

Even if you don't understand Lisp syntax, it will probably be obvious which command is displayed for repetition. If you do not change the text, it will repeat exactly as before.

Once inside the minibuffer for C-x ESC ESC, you can use the minibuffer history commands (M-p, M-n, M-r, M-s; see section E.4 Minibuffer History) to move through the history list of saved entire commands. After finding the desired previous command, you can edit its expression as usual and then resubmit it by typing RET as usual.

The list of previous minibuffer-using commands is stored as a Lisp list in the variable command-history. Each element is a Lisp expression which describes one command and its arguments. Lisp programs can re-execute a command by calling eval with the command-history element.


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F. Running Commands by Name

Every Emacs command has a name that you can use to run it. Commands that are used often, or that must be quick to type, are also bound to keys--short sequences of characters--for convenient use. You can run them by name if you don't remember the keys. Other Emacs commands that do not need to be quick are not bound to keys; the only way to run them is by name. See section AD.4 Customizing Key Bindings, for the description of how to bind commands to keys.

By convention, a command name consists of one or more words, separated by hyphens; for example, auto-fill-mode or manual-entry. The use of English words makes the command name easier to remember than a key made up of obscure characters, even though it is more characters to type.

The way to run a command by name is to start with M-x, type the command name, and finish it with RET. M-x uses the minibuffer to read the command name. RET exits the minibuffer and runs the command. The string `M-x' appears at the beginning of the minibuffer as a prompt to remind you to enter the name of a command to be run. See section E. The Minibuffer, for full information on the features of the minibuffer.

You can use completion to enter the command name. For example, you can invoke the command forward-char by name by typing either

 
M-x forward-char RET

or

 
M-x forw TAB c RET

Note that forward-char is the same command that you invoke with the key C-f. You can run any Emacs command by name using M-x, whether or not any keys are bound to it.

If you type C-g while the command name is being read, you cancel the M-x command and get out of the minibuffer, ending up at top level.

To pass a numeric argument to the command you are invoking with M-x, specify the numeric argument before the M-x. M-x passes the argument along to the command it runs. The argument value appears in the prompt while the command name is being read.

If the command you type has a key binding of its own, Emacs mentions this in the echo area, two seconds after the command finishes (if you don't type anything else first). For example, if you type M-x forward-word, the message says that you can run the same command more easily by typing M-f. You can turn off these messages by setting suggest-key-bindings to nil.

Normally, when describing in this manual a command that is run by name, we omit the RET that is needed to terminate the name. Thus we might speak of M-x auto-fill-mode rather than M-x auto-fill-mode RET. We mention the RET only when there is a need to emphasize its presence, such as when we show the command together with following arguments.

M-x works by running the command execute-extended-command, which is responsible for reading the name of another command and invoking it.


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G. Help

Emacs provides extensive help features accessible through a single character, C-h. C-h is a prefix key that is used for commands that display documentation. The characters that you can type after C-h are called help options. One help option is C-h; that is how you ask for help about using C-h. To cancel, type C-g. The function key F1 is equivalent to C-h.

C-h C-h (help-for-help) displays a list of the possible help options, each with a brief description. Before you type a help option, you can use SPC or DEL to scroll through the list.

C-h or F1 means "help" in various other contexts as well. For example, in the middle of query-replace, it describes the options available for how to operate on the current match. After a prefix key, it displays a list of the alternatives that can follow the prefix key. (A few prefix keys don't support C-h, because they define other meanings for it, but they all support F1.)

Most help buffers use a special major mode, Help mode, which lets you scroll conveniently with SPC and DEL. It also offers hyperlinks to further help regarding cross-referenced names, Info nodes, customization buffers and the like. See section G.7 Help Mode Commands.

If you are looking for a certain feature, but don't know where exactly it is documented, and aren't sure of the name of a related command or option, we recommend trying these methods. Usually it is best to start with an apropos command, then try searching the manual index, then finally look in the FAQ and the package keywords.

C-h a topic RET
This searches for commands whose names match topic, which should be a regular expression (see section K.5 Syntax of Regular Expressions). Browse the buffer that this command displays to find what you are looking for. See section G.4 Apropos.

M-x apropos RET topic RET
This works like C-h a, but it also searches for user options and other variables, in case the feature you are looking for is controlled by an option, not a command. See section G.4 Apropos.

M-x apropos-documentation RET topic RET
This searches the documentation strings (the built-in short descriptions) of all variables and functions (not their names) for a match for topic, a regular expression. See section G.4 Apropos.

C-h i d m emacs RET i topic RET
This looks up topic in the indices of the Emacs on-line manual. If there are several matches, Emacs displays the first one. You can then press , to move to other matches, until you find what you are looking for.

C-h i d m emacs RET s topic RET
Similar, but searches for topic (which can be a regular expression) in the text of the manual rather than in its indices.

C-h F
This brings up the Emacs FAQ, where you can use the usual search commands (see section K. Searching and Replacement) to find the information.

C-h p
Finally, you can try looking up a suitable package using keywords pertinent to the feature you need. See section G.5 Keyword Search for Lisp Libraries.

To find the documentation of a key sequence or a menu item, type C-h C-k and then type that key sequence or select the menu item. This looks up the description of the command invoked by the key or the menu in the appropriate manual (not necessarily the Emacs manual). Likewise, use C-h C-f for reading documentation of a command.

G.1 Help Summary  Brief list of all Help commands.
G.2 Documentation for a Key  Asking what a key does in Emacs.
G.3 Help by Command or Variable Name  Asking about a command, variable or function name.
G.4 Apropos  Asking what pertains to a given topic.
G.5 Keyword Search for Lisp Libraries  Finding Lisp libraries by keywords (topics).
G.6 Help for International Language Support  Help relating to international language support.
G.7 Help Mode Commands  Special features of Help mode and Help buffers.
G.8 Other Help Commands  Other help commands.
G.9 Help on Active Text and Tooltips  Help on active text and tooltips (`balloon help')


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G.1 Help Summary

Here is a summary of the defined help commands.

C-h a regexp RET
Display a list of commands whose names match regexp (apropos-command).
C-h b
Display a table of all key bindings in effect now, in this order: minor mode bindings, major mode bindings, and global bindings (describe-bindings).
C-h c key
Show the name of the command that key runs (describe-key-briefly). Here c stands for "character." For more extensive information on key, use C-h k.
C-h f function RET
Display documentation on the Lisp function named function (describe-function). Since commands are Lisp functions, a command name may be used.
C-h h
Display the `HELLO' file, which shows examples of various character sets.
C-h i
Run Info, the program for browsing documentation files (info). The complete Emacs manual is available on-line in Info.
C-h k key
Display the name and documentation of the command that key runs (describe-key).
C-h l
Display a description of the last 100 characters you typed (view-lossage).
C-h m
Display documentation of the current major mode (describe-mode).
C-h n
Display documentation of Emacs changes, most recent first (view-emacs-news).
C-h P
Display info on known problems with Emacs and possible workarounds (view-emacs-problems).
C-h p
Find packages by topic keyword (finder-by-keyword).
C-h s
Display the current contents of the syntax table, plus an explanation of what they mean (describe-syntax). See section AD.6 The Syntax Table.
C-h t
Enter the Emacs interactive tutorial (help-with-tutorial).
C-h v var RET
Display the documentation of the Lisp variable var (describe-variable).
C-h w command RET
Show which keys run the command named command (where-is).
C-h C coding RET
Describe coding system coding (describe-coding-system).
C-h C RET
Describe the coding systems currently in use.
C-h I method RET
Describe an input method (describe-input-method).
C-h L language-env RET
Display information on the character sets, coding systems, and input methods used for language environment language-env (describe-language-environment).
C-h C-c
Display the copying conditions for GNU Emacs.
C-h C-d
Display information about getting new versions of GNU Emacs.
C-h C-f function RET
Enter Info and go to the node documenting the Emacs function function (Info-goto-emacs-command-node).
C-h C-k key
Enter Info and go to the node where the key sequence key is documented (Info-goto-emacs-key-command-node).
C-h C-p
Display information about the GNU Project.
C-h TAB symbol RET
Display the Info documentation on symbol symbol according to the programming language you are editing (info-lookup-symbol).


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G.2 Documentation for a Key

The most basic C-h options are C-h c (describe-key-briefly) and C-h k (describe-key). C-h c key displays in the echo area the name of the command that key is bound to. For example, C-h c C-f displays `forward-char'. Since command names are chosen to describe what the commands do, this is a good way to get a very brief description of what key does.

C-h k key is similar but gives more information: it displays the documentation string of the command as well as its name. This is too big for the echo area, so a window is used for the display.

C-h c and C-h k work for any sort of key sequences, including function keys and mouse events.


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G.3 Help by Command or Variable Name

C-h f (describe-function) reads the name of a Lisp function using the minibuffer, then displays that function's documentation string in a window. Since commands are Lisp functions, you can use this to get the documentation of a command that you know by name. For example,

 
C-h f auto-fill-mode RET

displays the documentation of auto-fill-mode. This is the only way to get the documentation of a command that is not bound to any key (one which you would normally run using M-x).

C-h f is also useful for Lisp functions that you are planning to use in a Lisp program. For example, if you have just written the expression (make-vector len) and want to check that you are using make-vector properly, type C-h f make-vector RET. Because C-h f allows all function names, not just command names, you may find that some of your favorite abbreviations that work in M-x don't work in C-h f. An abbreviation may be unique among command names yet fail to be unique when other function names are allowed.

The default function name for C-h f to describe, if you type just RET, is the name of the function called by the innermost Lisp expression in the buffer around point, provided that is a valid, defined Lisp function name. For example, if point is located following the text `(make-vector (car x)', the innermost list containing point is the one that starts with `(make-vector', so the default is to describe the function make-vector.

C-h f is often useful just to verify that you have the right spelling for the function name. If C-h f mentions a name from the buffer as the default, that name must be defined as a Lisp function. If that is all you want to know, just type C-g to cancel the C-h f command, then go on editing.

C-h w command RET tells you what keys are bound to command. It displays a list of the keys in the echo area. If it says the command is not on any key, you must use M-x to run it. C-h w runs the command where-is.

C-h v (describe-variable) is like C-h f but describes Lisp variables instead of Lisp functions. Its default is the Lisp symbol around or before point, but only if that is the name of a known Lisp variable. See section AD.2 Variables.

Help buffers describing variables or functions defined in Lisp normally have hyperlinks to the Lisp definition, if you have the Lisp source files installed. If you know Lisp, this provides the ultimate documentation. If you don't know Lisp, you should learn it. If you are treating Emacs as an object file, then you are just using Emacs. For real intimacy with Emacs, you must read the source code.


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G.4 Apropos

A more sophisticated sort of question to ask is, "What are the commands for working with files?" To ask this question, type C-h a file RET, which displays a list of all command names that contain `file', including copy-file, find-file, and so on. With each command name appears a brief description of how to use the command, and what keys you can currently invoke it with. For example, it would say that you can invoke find-file by typing C-x C-f. The a in C-h a stands for "Apropos"; C-h a runs the command apropos-command. This command normally checks only commands (interactive functions); if you specify a prefix argument, it checks noninteractive functions as well.

Because C-h a looks only for functions whose names contain the string you specify, you must use ingenuity in choosing the string. If you are looking for commands for killing backwards and C-h a kill-backwards RET doesn't reveal any, don't give up. Try just kill, or just backwards, or just back. Be persistent. Also note that you can use a regular expression as the argument, for more flexibility (see section K.5 Syntax of Regular Expressions).

Here is a set of arguments to give to C-h a that covers many classes of Emacs commands, since there are strong conventions for naming the standard Emacs commands. By giving you a feel for the naming conventions, this set should also serve to aid you in developing a technique for picking apropos strings.

char, line, word, sentence, paragraph, region, page, sexp, list, defun, rect, buffer, frame, window, face, file, dir, register, mode, beginning, end, forward, backward, next, previous, up, down, search, goto, kill, delete, mark, insert, yank, fill, indent, case, change, set, what, list, find, view, describe, default.

To list all user variables that match a regexp, use the command M-x apropos-variable. This command shows only user variables and customization options by default; if you specify a prefix argument, it checks all variables.

To list all Lisp symbols that contain a match for a regexp, not just the ones that are defined as commands, use the command M-x apropos instead of C-h a. This command does not check key bindings by default; specify a numeric argument if you want it to check them.

The apropos-documentation command is like apropos except that it searches documentation strings as well as symbol names for matches for the specified regular expression.

The apropos-value command is like apropos except that it searches symbols' values for matches for the specified regular expression. This command does not check function definitions or property lists by default; specify a numeric argument if you want it to check them.

If the variable apropos-do-all is non-nil, the commands above all behave as if they had been given a prefix argument.

If you want more information about a function definition, variable or symbol property listed in the Apropos buffer, you can click on it with Mouse-2 or move there and type RET.


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G.5 Keyword Search for Lisp Libraries

The C-h p command lets you search the standard Emacs Lisp libraries by topic keywords. Here is a partial list of keywords you can use:

 
abbrev --- abbreviation handling, typing shortcuts, macros.
bib --- support for the bibliography processor bib.
c --- C and C++ language support.
calendar --- calendar and time management support.
comm --- communications, networking, remote access to files.
data --- support for editing files of data.
docs --- support for Emacs documentation.
emulations --- emulations of other editors.
extensions --- Emacs Lisp language extensions.
faces --- support for using faces (fonts and colors; see section J.1 Using Multiple Typefaces).
frames --- support for Emacs frames and window systems.
games --- games, jokes and amusements.
hardware --- support for interfacing with exotic hardware.
help --- support for on-line help systems.
hypermedia --- support for links within text, or other media types.
i18n --- internationalization and alternate character-set support.
internal --- code for Emacs internals, build process, defaults.
languages --- specialized modes for editing programming languages.
lisp --- support for using Lisp (including Emacs Lisp).
local --- libraries local to your site.
maint --- maintenance aids for the Emacs development group.
mail --- modes for electronic-mail handling.
matching --- searching and matching.
news --- support for netnews reading and posting.
non-text --- support for editing files that are not ordinary text.
oop --- support for object-oriented programming.
outlines --- hierarchical outlining.
processes --- process, subshell, compilation, and job control support.
terminals --- support for terminal types.
tex --- support for the TeX formatter.
tools --- programming tools.
unix --- front-ends/assistants for, or emulators of, system features.
vms --- support code for VMS.
wp --- word processing.


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G.6 Help for International Language Support

You can use the command C-h L (describe-language-environment) to find out information about the support for a specific language environment. See section Q.3 Language Environments. This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts.

The command C-h h (view-hello-file) displays the file `etc/HELLO', which shows how to say "hello" in many languages.

The command C-h I (describe-input-method) describes information about input methods--either a specified input method, or by default the input method in use. See section Q.4 Input Methods.

The command C-h C (describe-coding-system) describes information about coding systems--either a specified coding system, or the ones currently in use. See section Q.7 Coding Systems.


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G.7 Help Mode Commands

Help buffers provide the same commands as View mode (see section M.10 Miscellaneous File Operations), plus a few special commands of their own.

SPC
Scroll forward.
DEL
BS
Scroll backward. On some keyboards, this key is known as BS or backspace.
RET
Follow a cross reference at point.
TAB
Move point forward to the next cross reference.
S-TAB
Move point back to the previous cross reference.
Mouse-2
Follow a cross reference that you click on.

When a command name (see section Running Commands by Name) or variable name (see section AD.2 Variables) appears in the documentation, it normally appears inside paired single-quotes. You can click on the name with Mouse-2, or move point there and type RET, to view the documentation of that command or variable. Use C-c C-b to retrace your steps.

There are convenient commands for moving point to cross references in the help text. TAB (help-next-ref) moves point down to the next cross reference. Use S-TAB to move point up to the previous cross reference (help-previous-ref).


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G.8 Other Help Commands

C-h i (info) runs the Info program, which is used for browsing through structured documentation files. The entire Emacs manual is available within Info. Eventually all the documentation of the GNU system will be available. Type h after entering Info to run a tutorial on using Info.

If you specify a numeric argument, C-h i prompts for the name of a documentation file. This way, you can browse a file which doesn't have an entry in the top-level Info menu. It is also handy when you need to get to the documentation quickly, and you know the exact name of the file.

There are two special help commands for accessing Emacs documentation through Info. C-h C-f function RET enters Info and goes straight to the documentation of the Emacs function function. C-h C-k key enters Info and goes straight to the documentation of the key key. These two keys run the commands Info-goto-emacs-command-node and Info-goto-emacs-key-command-node. You can use C-h C-k to find the documentation of a menu item: just select that menu item when C-h C-k prompts for a key.

C-h C-f and C-h C-k know about commands and keys described in manuals other than the Emacs manual. Thus, they make it easier to find the documentation of commands and keys when you are not sure which manual describes them, like when using some specialized mode.

When editing a program, if you have an Info version of the manual for the programming language, you can use the command C-h C-i to refer to the manual documentation for a symbol (keyword, function or variable). The details of how this command works depend on the major mode.

If something surprising happens, and you are not sure what commands you typed, use C-h l (view-lossage). C-h l displays the last 100 command characters you typed in. If you see commands that you don't know, you can use C-h c to find out what they do.

Emacs has numerous major modes, each of which redefines a few keys and makes a few other changes in how editing works. C-h m (describe-mode) displays documentation on the current major mode, which normally describes all the commands that are changed in this mode.

C-h b (describe-bindings) and C-h s (describe-syntax) present other information about the current Emacs mode. C-h b displays a list of all the key bindings now in effect, showing the local bindings defined by the current minor modes first, then the local bindings defined by the current major mode, and finally the global bindings (see section AD.4 Customizing Key Bindings). C-h s displays the contents of the syntax table, with explanations of each character's syntax (see section AD.6 The Syntax Table).

You can get a similar list for a particular prefix key by typing C-h after the prefix key. (There are a few prefix keys for which this does not work--those that provide their own bindings for C-h. One of these is ESC, because ESC C-h is actually C-M-h, which marks a defun.)

The other C-h options display various files containing useful information. C-h C-w displays the full details on the complete absence of warranty for GNU Emacs. C-h n (view-emacs-news) displays the file `emacs/etc/NEWS', which contains documentation on Emacs changes arranged chronologically. C-h F (view-emacs-FAQ) displays the Emacs frequently-answered-questions list. C-h t (help-with-tutorial) displays the learn-by-doing Emacs tutorial. C-h C-c (describe-copying) displays the file `emacs/etc/COPYING', which tells you the conditions you must obey in distributing copies of Emacs. C-h C-d (describe-distribution) displays the file `emacs/etc/DISTRIB', which tells you how you can order a copy of the latest version of Emacs. C-h C-p (describe-project) displays general information about the GNU Project. C-h P (view-emacs-problems) displays the file `emacs/etc/PROBLEMS', which lists known problems with Emacs in various situations with solutions or workarounds in many cases.


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G.9 Help on Active Text and Tooltips

When a region of text is "active," so that you can select it with the mouse or a key like RET, it often has associated help text. Areas of the mode line are examples. This help will normally be shown in the echo area when you move point into the active text. In a window system you can display the help text as a "tooltip" (sometimes known as "balloon help"). See section P.18 Tooltips (or "Balloon Help").


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H. The Mark and the Region

Many Emacs commands operate on an arbitrary contiguous part of the current buffer. To specify the text for such a command to operate on, you set the mark at one end of it, and move point to the other end. The text between point and the mark is called the region. Emacs highlights the region whenever there is one, if you enable Transient Mark mode (see section H.2 Transient Mark Mode).

Certain Emacs commands set the mark; other editing commands do not affect it, so the mark remains where you set it last. Each Emacs buffer has its own mark, and setting the mark in one buffer has no effect on other buffers' marks. When you return to a buffer that was current earlier, its mark is at the same place as before.

The ends of the region are always point and the mark. It doesn't matter which of them was put in its current place first, or which one comes earlier in the text--the region starts from point or the mark (whichever comes first), and ends at point or the mark (whichever comes last). Every time you move point, or set the mark in a new place, the region changes.

Many commands that insert text, such as C-y (yank) and M-x insert-buffer, position point and the mark at opposite ends of the inserted text, so that the region consists of the text just inserted.

Aside from delimiting the region, the mark is also useful for remembering a spot that you may want to go back to. To make this feature more useful, each buffer remembers 16 previous locations of the mark in the mark ring.

H.1 Setting the Mark  Commands to set the mark.
H.2 Transient Mark Mode  How to make Emacs highlight the region-- when there is one.
H.3 Operating on the Region  Summary of ways to operate on contents of the region.
H.4 Commands to Mark Textual Objects  Commands to put region around textual units.
H.5 The Mark Ring  Previous mark positions saved so you can go back there.
H.6 The Global Mark Ring  Previous mark positions in various buffers.


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H.1 Setting the Mark

Here are some commands for setting the mark:

C-SPC
Set the mark where point is (set-mark-command).
C-@
The same.
C-x C-x
Interchange mark and point (exchange-point-and-mark).
Drag-Mouse-1
Set point and the mark around the text you drag across.
Mouse-3
Set the mark where point is, then move point to where you click (mouse-save-then-kill).

For example, suppose you wish to convert part of the buffer to upper case, using the C-x C-u (upcase-region) command, which operates on the text in the region. You can first go to the beginning of the text to be capitalized, type C-SPC to put the mark there, move to the end, and then type C-x C-u. Or, you can set the mark at the end of the text, move to the beginning, and then type C-x C-u.

The most common way to set the mark is with the C-SPC command (set-mark-command). This sets the mark where point is. Then you can move point away, leaving the mark behind.

There are two ways to set the mark with the mouse. You can drag mouse button one across a range of text; that puts point where you release the mouse button, and sets the mark at the other end of that range. Or you can click mouse button three, which sets the mark at point (like C-SPC) and then moves point (like Mouse-1). Both of these methods copy the region into the kill ring in addition to setting the mark; that gives behavior consistent with other window-driven applications, but if you don't want to modify the kill ring, you must use keyboard commands to set the mark. See section P.1 Mouse Commands for Editing.

Ordinary terminals have only one cursor, so there is no way for Emacs to show you where the mark is located. You have to remember. The usual solution to this problem is to set the mark and then use it soon, before you forget where it is. Alternatively, you can see where the mark is with the command C-x C-x (exchange-point-and-mark) which puts the mark where point was and point where the mark was. The extent of the region is unchanged, but the cursor and point are now at the previous position of the mark. In Transient Mark mode, this command reactivates the mark.

C-x C-x is also useful when you are satisfied with the position of point but want to move the other end of the region (where the mark is); do C-x C-x to put point at that end of the region, and then move it. Using C-x C-x a second time, if necessary, puts the mark at the new position with point back at its original position.

For more facilities that allow you to go to previously set marks, see H.5 The Mark Ring.

There is no such character as C-SPC in ASCII; when you type SPC while holding down CTRL, what you get on most ordinary terminals is the character C-@. This key is actually bound to set-mark-command. But unless you are unlucky enough to have a terminal where typing C-SPC does not produce C-@, you might as well think of this character as C-SPC. Under X, C-SPC is actually a distinct character, but its binding is still set-mark-command.


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H.2 Transient Mark Mode

On a terminal that supports colors, Emacs can highlight the current region. But normally it does not. Why not?

Highlighting the region whenever it exists would not be desirable in Emacs, because once you have set a mark, there is always a region (in that buffer). And highlighting the region all the time would be a nuisance. So normally Emacs highlights the region only immediately after you have selected one with the mouse.

You can turn on region highlighting by enabling Transient Mark mode. This is a more rigid mode of operation in which the region "lasts" only temporarily, so you must set up a region for each command that uses one. In Transient Mark mode, most of the time there is no region; therefore, highlighting the region when it exists is useful and not annoying.

To enable Transient Mark mode, type M-x transient-mark-mode. This command toggles the mode, so you can repeat the command to turn off the mode.

Here are the details of Transient Mark mode:

The highlighting of the region uses the region face; you can customize the appearance of the highlighted region by changing this face. See section AD.2.2.3 Customizing Faces.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point (though they all share one common mark position). Ordinarily, only the selected window highlights its region (see section O. Multiple Windows). However, if the variable highlight-nonselected-windows is non-nil, then each window highlights its own region (provided that Transient Mark mode is enabled and the mark in the window's buffer is active).

When Transient Mark mode is not enabled, every command that sets the mark also activates it, and nothing ever deactivates it.

If the variable mark-even-if-inactive is non-nil in Transient Mark mode, then commands can use the mark and the region even when it is inactive. Region highlighting appears and disappears just as it normally does in Transient Mark mode, but the mark doesn't really go away when the highlighting disappears.

Transient Mark mode is also sometimes known as "Zmacs mode" because the Zmacs editor on the MIT Lisp Machine handled the mark in a similar way.


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H.3 Operating on the Region

Once you have a region and the mark is active, here are some of the ways you can operate on the region:

Most commands that operate on the text in the region have the word region in their names.


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H.4 Commands to Mark Textual Objects

Here are the commands for placing point and the mark around a textual object such as a word, list, paragraph or page.

M-@
Set mark after end of next word (mark-word). This command and the following one do not move point.
C-M-@
Set mark after end of following balanced expression (mark-sexp).
M-h
Put region around current paragraph (mark-paragraph).
C-M-h
Put region around current defun (mark-defun).
C-x h
Put region around the entire buffer (mark-whole-buffer).
C-x C-p
Put region around current page (mark-page).

M-@ (mark-word) puts the mark at the end of the next word, while C-M-@ (mark-sexp) puts it at the end of the next balanced expression (see section U.4.1 Expressions with Balanced Parentheses). These commands handle arguments just like M-f and C-M-f.

Other commands set both point and mark, to delimit an object in the buffer. For example, M-h (mark-paragraph) moves point to the beginning of the paragraph that surrounds or follows point, and puts the mark at the end of that paragraph (see section T.3 Paragraphs). It prepares the region so you can indent, case-convert, or kill a whole paragraph.

C-M-h (mark-defun) similarly puts point before, and the mark after, the current (or following) major top-level definition, or defun (see section U.2.2 Moving by Defuns). C-x C-p (mark-page) puts point before the current page, and mark at the end (see section T.4 Pages). The mark goes after the terminating page delimiter (to include it in the region), while point goes after the preceding page delimiter (to exclude it). A numeric argument specifies a later page (if positive) or an earlier page (if negative) instead of the current page.

Finally, C-x h (mark-whole-buffer) sets up the entire buffer as the region, by putting point at the beginning and the mark at the end.

In Transient Mark mode, all of these commands activate the mark.


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H.5 The Mark Ring

Aside from delimiting the region, the mark is also useful for remembering a spot that you may want to go back to. To make this feature more useful, each buffer remembers 16 previous locations of the mark, in the mark ring. Commands that set the mark also push the old mark onto this ring. To return to a marked location, use C-u C-SPC (or C-u C-@); this is the command set-mark-command given a numeric argument. It moves point to where the mark was, and restores the mark from the ring of former marks. Thus, repeated use of this command moves point to all of the old marks on the ring, one by one. The mark positions you move through in this way are not lost; they go to the end of the ring.

Each buffer has its own mark ring. All editing commands use the current buffer's mark ring. In particular, C-u C-SPC always stays in the same buffer.

Many commands that can move long distances, such as M-< (beginning-of-buffer), start by setting the mark and saving the old mark on the mark ring. This is to make it easier for you to move back later. Searches set the mark if they move point. You can tell when a command sets the mark because it displays `Mark set' in the echo area.

If you want to move back to the same place over and over, the mark ring may not be convenient enough. If so, you can record the position in a register for later retrieval (see section Saving Positions in Registers).

The variable mark-ring-max specifies the maximum number of entries to keep in the mark ring. If that many entries exist and another one is pushed, the earliest one in the list is discarded. Repeating C-u C-SPC cycles through the positions currently in the ring.

The variable mark-ring holds the mark ring itself, as a list of marker objects, with the most recent first. This variable is local in every buffer.


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H.6 The Global Mark Ring

In addition to the ordinary mark ring that belongs to each buffer, Emacs has a single global mark ring. It records a sequence of buffers in which you have recently set the mark, so you can go back to those buffers.

Setting the mark always makes an entry on the current buffer's mark ring. If you have switched buffers since the previous mark setting, the new mark position makes an entry on the global mark ring also. The result is that the global mark ring records a sequence of buffers that you have been in, and, for each buffer, a place where you set the mark.

The command C-x C-SPC (pop-global-mark) jumps to the buffer and position of the latest entry in the global ring. It also rotates the ring, so that successive uses of C-x C-SPC take you to earlier and earlier buffers.


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H.7 Deletion and Killing

Most commands which erase text from the buffer save it in the kill ring so that you can move or copy it to other parts of the buffer. These commands are known as kill commands. The rest of the commands that erase text do not save it in the kill ring; they are known as delete commands. (This distinction is made only for erasure of text in the buffer.) If you do a kill or delete command by mistake, you can use the C-x u (undo) command to undo it (see section D.4 Undoing Changes).

You cannot kill read-only text, since such text does not allow any kind of modification. But some users like to use the kill commands to copy read-only text into the kill ring, without actually changing it. If you set the variable kill-read-only-ok to a non-nil value, the kill commands work specially in a read-only buffer: they move over text, and copy it to the kill ring, without actually deleting it from the buffer. When this happens, a message in the echo area tells you what is happening.

The delete commands include C-d (delete-char) and DEL (delete-backward-char), which delete only one character at a time, and those commands that delete only spaces or newlines. Commands that can destroy significant amounts of nontrivial data generally do a kill operation instead. The commands' names and individual descriptions use the words `kill' and `delete' to say which kind of operation they perform.

Many window systems follow the convention that insertion while text is selected deletes the selected text. You can make Emacs behave this way by enabling Delete Selection mode, with M-x delete-selection-mode, or using Custom. Another effect of this mode is that DEL, C-d and some other keys, when a selection exists, will kill the whole selection. It also enables Transient Mark mode (see section H.2 Transient Mark Mode).

H.7.1 Deletion  Commands for deleting small amounts of text and blank areas.
H.7.2 Killing by Lines  How to kill entire lines of text at one time.
H.7.3 Other Kill Commands  Commands to kill large regions of text and syntactic units such as words and sentences.


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H.7.1 Deletion

Deletion means erasing text and not saving it in the kill ring. For the most part, the Emacs commands that delete text are those that erase just one character or only whitespace.

C-d
Delete
Delete next character (delete-char). If your keyboard has a Delete function key (usually located in the edit keypad), Emacs binds it to delete-char as well.
DEL
BS
Delete previous character (delete-backward-char). Some keyboards refer to this key as a "backspace key" and label it with a left arrow.
M-\
Delete spaces and tabs around point (delete-horizontal-space).
M-SPC
Delete spaces and tabs around point, leaving one space (just-one-space).
C-x C-o
Delete blank lines around the current line (delete-blank-lines).
M-^
Join two lines by deleting the intervening newline, along with any indentation following it (delete-indentation).

The most basic delete commands are C-d (delete-char) and DEL (delete-backward-char). C-d deletes the character after point, the one the cursor is "on top of." This doesn't move point. DEL deletes the character before the cursor, and moves point back. You can delete newlines like any other characters in the buffer; deleting a newline joins two lines. Actually, C-d and DEL aren't always delete commands; when given arguments, they kill instead, since they can erase more than one character this way.

Every keyboard has a large key, labeled DEL, BACKSPACE, BS or DELETE, which is a short distance above the RET or ENTER key and is normally used for erasing what you have typed. Regardless of the actual name on the key, in Emacs it is equivalent to DEL---or it should be.

Many keyboards (including standard PC keyboards) have a BACKSPACE key a short ways above RET or ENTER, and a DELETE key elsewhere. In that case, the BACKSPACE key is DEL, and the DELETE key is equivalent to C-d---or it should be.

Why do we say "or it should be"? When Emacs starts up using a window system, it determines automatically which key or keys should be equivalent to DEL. As a result, BACKSPACE and/or DELETE keys normally do the right things. But in some unusual cases Emacs gets the wrong information from the system. If these keys don't do what they ought to do, you need to tell Emacs which key to use for DEL. See section AD.9.1 If DEL Fails to Delete, for how to do this.

On most text-only terminals, Emacs cannot tell which keys the keyboard really has, so it follows a uniform plan which may or may not fit your keyboard. The uniform plan is that the ASCII DEL character deletes, and the ASCII BS (backspace) character asks for help (it is the same as C-h). If this is not right for your keyboard, such as if you find that the key which ought to delete backwards enters Help instead, see AD.9.1 If DEL Fails to Delete.

The other delete commands are those which delete only whitespace characters: spaces, tabs and newlines. M-\ (delete-horizontal-space) deletes all the spaces and tab characters before and after point. M-SPC (just-one-space) does likewise but leaves a single space after point, regardless of the number of spaces that existed previously (even if there were none before).

C-x C-o (delete-blank-lines) deletes all blank lines after the current line. If the current line is blank, it deletes all blank lines preceding the current line as well (leaving one blank line, the current line).

M-^ (delete-indentation) joins the current line and the previous line, by deleting a newline and all surrounding spaces, usually leaving a single space. See section M-^.


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H.7.2 Killing by Lines

C-k
Kill rest of line or one or more lines (kill-line).

The simplest kill command is C-k. If given at the beginning of a line, it kills all the text on the line, leaving it blank. When used on a blank line, it kills the whole line including its newline. To kill an entire non-blank line, go to the beginning and type C-k twice.

More generally, C-k kills from point up to the end of the line, unless it is at the end of a line. In that case it kills the newline following point, thus merging the next line into the current one. Spaces and tabs that you can't see at the end of the line are ignored when deciding which case applies, so if point appears to be at the end of the line, you can be sure C-k will kill the newline.

When C-k is given a positive argument, it kills that many lines and the newlines that follow them (however, text on the current line before point is not killed). With a negative argument -n, it kills n lines preceding the current line (together with the text on the current line before point). Thus, C-u - 2 C-k at the front of a line kills the two previous lines.

C-k with an argument of zero kills the text before point on the current line.

If the variable kill-whole-line is non-nil, C-k at the very beginning of a line kills the entire line including the following newline. This variable is normally nil.


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H.7.3 Other Kill Commands

C-w
Kill region (from point to the mark) (kill-region).
M-d
Kill word (kill-word). See section T.1 Words.
M-DEL
Kill word backwards (backward-kill-word).
C-x DEL
Kill back to beginning of sentence (backward-kill-sentence). See section T.2 Sentences.
M-k
Kill to end of sentence (kill-sentence).
C-M-k
Kill the following balanced expression (kill-sexp). See section U.4.1 Expressions with Balanced Parentheses.
M-z char
Kill through the next occurrence of char (zap-to-char).

A kill command which is very general is C-w (kill-region), which kills everything between point and the mark. With this command, you can kill any contiguous sequence of characters, if you first set the region around them.

A convenient way of killing is combined with searching: M-z (zap-to-char) reads a character and kills from point up to (and including) the next occurrence of that character in the buffer. A numeric argument acts as a repeat count. A negative argument means to search backward and kill text before point.

Other syntactic units can be killed: words, with M-DEL and M-d (see section T.1 Words); balanced expressions, with C-M-k (see section U.4.1 Expressions with Balanced Parentheses); and sentences, with C-x DEL and M-k (see section T.2 Sentences).

You can use kill commands in read-only buffers. They don't actually change the buffer, and they beep to warn you of that, but they do copy the text you tried to kill into the kill ring, so you can yank it into other buffers. Most of the kill commands move point across the text they copy in this way, so that successive kill commands build up a single kill ring entry as usual.


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H.8 Yanking

Yanking means reinserting text previously killed. This is what some systems call "pasting." The usual way to move or copy text is to kill it and then yank it elsewhere one or more times.

C-y
Yank last killed text (yank).
M-y
Replace text just yanked with an earlier batch of killed text (yank-pop).
M-w
Save region as last killed text without actually killing it (kill-ring-save).
C-M-w
Append next kill to last batch of killed text (append-next-kill).

H.8.1 The Kill Ring  Where killed text is stored. Basic yanking.
H.8.2 Appending Kills  Several kills in a row all yank together.
H.8.3 Yanking Earlier Kills  Yanking something killed some time ago.


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H.8.1 The Kill Ring

All killed text is recorded in the kill ring, a list of blocks of text that have been killed. There is only one kill ring, shared by all buffers, so you can kill text in one buffer and yank it in another buffer. This is the usual way to move text from one file to another. (See section H.9 Accumulating Text, for some other ways.)

The command C-y (yank) reinserts the text of the most recent kill. It leaves the cursor at the end of the text. It sets the mark at the beginning of the text. See section H. The Mark and the Region.

C-u C-y leaves the cursor in front of the text, and sets the mark after it. This happens only if the argument is specified with just a C-u, precisely. Any other sort of argument, including C-u and digits, specifies an earlier kill to yank (see section H.8.3 Yanking Earlier Kills).

To copy a block of text, you can use M-w (kill-ring-save), which copies the region into the kill ring without removing it from the buffer. This is approximately equivalent to C-w followed by C-x u, except that M-w does not alter the undo history and does not temporarily change the screen.


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H.8.2 Appending Kills

Normally, each kill command pushes a new entry onto the kill ring. However, two or more kill commands in a row combine their text into a single entry, so that a single C-y yanks all the text as a unit, just as it was before it was killed.

Thus, if you want to yank text as a unit, you need not kill all of it with one command; you can keep killing line after line, or word after word, until you have killed it all, and you can still get it all back at once.

Commands that kill forward from point add onto the end of the previous killed text. Commands that kill backward from point add text onto the beginning. This way, any sequence of mixed forward and backward kill commands puts all the killed text into one entry without rearrangement. Numeric arguments do not break the sequence of appending kills. For example, suppose the buffer contains this text:

 
This is a line -!-of sample text.

with point shown by -!-. If you type M-d M-DEL M-d M-DEL, killing alternately forward and backward, you end up with `a line of sample' as one entry in the kill ring, and `This is text.' in the buffer. (Note the double space between `is' and `text', which you can clean up with M-SPC or M-q.)

Another way to kill the same text is to move back two words with M-b M-b, then kill all four words forward with C-u M-d. This produces exactly the same results in the buffer and in the kill ring. M-f M-f C-u M-DEL kills the same text, all going backward; once again, the result is the same. The text in the kill ring entry always has the same order that it had in the buffer before you killed it.

If a kill command is separated from the last kill command by other commands (not just numeric arguments), it starts a new entry on the kill ring. But you can force it to append by first typing the command C-M-w (append-next-kill) right before it. The C-M-w tells the following command, if it is a kill command, to append the text it kills to the last killed text, instead of starting a new entry. With C-M-w, you can kill several separated pieces of text and accumulate them to be yanked back in one place.

A kill command following M-w does not append to the text that M-w copied into the kill ring.


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H.8.3 Yanking Earlier Kills

To recover killed text that is no longer the most recent kill, use the M-y command (yank-pop). It takes the text previously yanked and replaces it with the text from an earlier kill. So, to recover the text of the next-to-the-last kill, first use C-y to yank the last kill, and then use M-y to replace it with the previous kill. M-y is allowed only after a C-y or another M-y.

You can understand M-y in terms of a "last yank" pointer which points at an entry in the kill ring. Each time you kill, the "last yank" pointer moves to the newly made entry at the front of the ring. C-y yanks the entry which the "last yank" pointer points to. M-y moves the "last yank" pointer to a different entry, and the text in the buffer changes to match. Enough M-y commands can move the pointer to any entry in the ring, so you can get any entry into the buffer. Eventually the pointer reaches the end of the ring; the next M-y loops back around to the first entry again.

M-y moves the "last yank" pointer around the ring, but it does not change the order of the entries in the ring, which always runs from the most recent kill at the front to the oldest one still remembered.

M-y can take a numeric argument, which tells it how many entries to advance the "last yank" pointer by. A negative argument moves the pointer toward the front of the ring; from the front of the ring, it moves "around" to the last entry and continues forward from there.

Once the text you are looking for is brought into the buffer, you can stop doing M-y commands and it will stay there. It's just a copy of the kill ring entry, so editing it in the buffer does not change what's in the ring. As long as no new killing is done, the "last yank" pointer remains at the same place in the kill ring, so repeating C-y will yank another copy of the same previous kill.

If you know how many M-y commands it would take to find the text you want, you can yank that text in one step using C-y with a numeric argument. C-y with an argument restores the text from the specified kill ring entry, counting back from the most recent as 1. Thus, C-u 2 C-y gets the next-to-the-last block of killed text--it is equivalent to C-y M-y. C-y with a numeric argument starts counting from the "last yank" pointer, and sets the "last yank" pointer to the entry that it yanks.

The length of the kill ring is controlled by the variable kill-ring-max; no more than that many blocks of killed text are saved.

The actual contents of the kill ring are stored in a variable named kill-ring; you can view the entire contents of the kill ring with the command C-h v kill-ring.


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H.9 Accumulating Text

Usually we copy or move text by killing it and yanking it, but there are other methods convenient for copying one block of text in many places, or for copying many scattered blocks of text into one place. To copy one block to many places, store it in a register (see section I. Registers). Here we describe the commands to accumulate scattered pieces of text into a buffer or into a file.

M-x append-to-buffer
Append region to the contents of a specified buffer.
M-x prepend-to-buffer
Prepend region to the contents of a specified buffer.
M-x copy-to-buffer
Copy region into a specified buffer, deleting that buffer's old contents.
M-x insert-buffer
Insert the contents of a specified buffer into current buffer at point.
M-x append-to-file
Append region to the contents of a specified file, at the end.

To accumulate text into a buffer, use M-x append-to-buffer. This reads a buffer name, then inserts a copy of the region into the buffer specified. If you specify a nonexistent buffer, append-to-buffer creates the buffer. The text is inserted wherever point is in that buffer. If you have been using the buffer for editing, the copied text goes into the middle of the text of the buffer, starting from wherever point happens to be at that moment.

Point in that buffer is left at the end of the copied text, so successive uses of append-to-buffer accumulate the text in the specified buffer in the same order as they were copied. Strictly speaking, append-to-buffer does not always append to the text already in the buffer--it appends only if point in that buffer is at the end. However, if append-to-buffer is the only command you use to alter a buffer, then point is always at the end.

M-x prepend-to-buffer is just like append-to-buffer except that point in the other buffer is left before the copied text, so successive prependings add text in reverse order. M-x copy-to-buffer is similar, except that any existing text in the other buffer is deleted, so the buffer is left containing just the text newly copied into it.

To retrieve the accumulated text from another buffer, use the command M-x insert-buffer; this too takes buffername as an argument. It inserts a copy of the whole text in buffer buffername into the current buffer at point, and sets the mark after the inserted text. Alternatively, you can select the other buffer for editing, then copy text from it by killing. See section N. Using Multiple Buffers, for background information on buffers.

Instead of accumulating text within Emacs, in a buffer, you can append text directly into a file with M-x append-to-file, which takes filename as an argument. It adds the text of the region to the end of the specified file. The file is changed immediately on disk.

You should use append-to-file only with files that are not being visited in Emacs. Using it on a file that you are editing in Emacs would change the file behind Emacs's back, which can lead to losing some of your editing.


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H.10 Rectangles

The rectangle commands operate on rectangular areas of the text: all the characters between a certain pair of columns, in a certain range of lines. Commands are provided to kill rectangles, yank killed rectangles, clear them out, fill them with blanks or text, or delete them. Rectangle commands are useful with text in multicolumn formats, and for changing text into or out of such formats.

When you must specify a rectangle for a command to work on, you do it by putting the mark at one corner and point at the opposite corner. The rectangle thus specified is called the region-rectangle because you control it in much the same way as the region is controlled. But remember that a given combination of point and mark values can be interpreted either as a region or as a rectangle, depending on the command that uses them.

If point and the mark are in the same column, the rectangle they delimit is empty. If they are in the same line, the rectangle is one line high. This asymmetry between lines and columns comes about because point (and likewise the mark) is between two columns, but within a line.

C-x r k
Kill the text of the region-rectangle, saving its contents as the "last killed rectangle" (kill-rectangle).
C-x r d
Delete the text of the region-rectangle (delete-rectangle).
C-x r y
Yank the last killed rectangle with its upper left corner at point (yank-rectangle).
C-x r o
Insert blank space to fill the space of the region-rectangle (open-rectangle). This pushes the previous contents of the region-rectangle rightward.
M-x clear-rectangle
Clear the region-rectangle by replacing its contents with spaces.
M-x delete-whitespace-rectangle
Delete whitespace in each of the lines on the specified rectangle, starting from the left edge column of the rectangle.
C-x r t string RET
Replace rectangle contents with string on each line. (string-rectangle).
M-x string-insert-rectangle RET string RET
Insert string on each line of the rectangle.

The rectangle operations fall into two classes: commands for deleting and inserting rectangles, and commands for blank rectangles.

There are two ways to get rid of the text in a rectangle: you can discard the text (delete it) or save it as the "last killed" rectangle. The commands for these two ways are C-x r d (delete-rectangle) and C-x r k (kill-rectangle). In either case, the portion of each line that falls inside the rectangle's boundaries is deleted, causing any following text on the line to move left into the gap.

Note that "killing" a rectangle is not killing in the usual sense; the rectangle is not stored in the kill ring, but in a special place that can only record the most recent rectangle killed. This is because yanking a rectangle is so different from yanking linear text that different yank commands have to be used and yank-popping is hard to make sense of.

To yank the last killed rectangle, type C-x r y (yank-rectangle). Yanking a rectangle is the opposite of killing one. Point specifies where to put the rectangle's upper left corner. The rectangle's first line is inserted there, the rectangle's second line is inserted at the same horizontal position, but one line vertically down, and so on. The number of lines affected is determined by the height of the saved rectangle.

You can convert single-column lists into double-column lists using rectangle killing and yanking; kill the second half of the list as a rectangle and then yank it beside the first line of the list. See section AC.23 Two-Column Editing, for another way to edit multi-column text.

You can also copy rectangles into and out of registers with C-x r r r and C-x r i r. See section Rectangle Registers.

There are two commands you can use for making blank rectangles: M-x clear-rectangle which blanks out existing text, and C-x r o (open-rectangle) which inserts a blank rectangle. Clearing a rectangle is equivalent to deleting it and then inserting a blank rectangle of the same size.

The command M-x delete-whitespace-rectangle deletes horizontal whitespace starting from a particular column. This applies to each of the lines in the rectangle, and the column is specified by the left edge of the rectangle. The right edge of the rectangle does not make any difference to this command.

The command C-x r t (string-rectangle) replaces the contents of a region-rectangle with a string on each line. The string's width need not be the same as the width of the rectangle. If the string's width is less, the text after the rectangle shifts left; if the string is wider than the rectangle, the text after the rectangle shifts right.

The command M-x string-insert-rectangle is similar to string-rectangle, but inserts the string on each line, shifting the original text to the right.


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I. Registers

Emacs registers are compartments where you can save text, rectangles, positions, and other things for later use. Once you save text or a rectangle in a register, you can copy it into the buffer once, or many times; you can move point to a position saved in a register once, or many times.

Each register has a name, which consists of a single character. A register can store a piece of text, a rectangle, a position, a window configuration, or a file name, but only one thing at any given time. Whatever you store in a register remains there until you store something else in that register. To see what a register r contains, use M-x view-register.

M-x view-register RET r
Display a description of what register r contains.

I.1 Saving Positions in Registers  Saving positions in registers.
I.2 Saving Text in Registers  Saving text in registers.
I.3 Saving Rectangles in Registers  Saving rectangles in registers.
I.4 Saving Window Configurations in Registers  Saving window configurations in registers.
I.6 Keeping File Names in Registers  File names in registers.
I.5 Keeping Numbers in Registers  Numbers in registers.
I.7 Bookmarks  Bookmarks are like registers, but persistent.


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I.1 Saving Positions in Registers

Saving a position records a place in a buffer so that you can move back there later. Moving to a saved position switches to that buffer and moves point to that place in it.

C-x r SPC r
Save position of point in register r (point-to-register).
C-x r j r
Jump to the position saved in register r (jump-to-register).

To save the current position of point in a register, choose a name r and type C-x r SPC r. The register r retains the position thus saved until you store something else in that register.

The command C-x r j r moves point to the position recorded in register r. The register is not affected; it continues to hold the same position. You can jump to the saved position any number of times.

If you use C-x r j to go to a saved position, but the buffer it was saved from has been killed, C-x r j tries to create the buffer again by visiting the same file. Of course, this works only for buffers that were visiting files.


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I.2 Saving Text in Registers

When you want to insert a copy of the same piece of text several times, it may be inconvenient to yank it from the kill ring, since each subsequent kill moves that entry further down the ring. An alternative is to store the text in a register and later retrieve it.

C-x r s r
Copy region into register r (copy-to-register).
C-x r i r
Insert text from register r (insert-register).
M-x append-to-register RET r
Append region to text in register r.
M-x prepend-to-register RET r
Prepend region to text in register r.

C-x r s r stores a copy of the text of the region into the register named r. C-u C-x r s r, the same command with a numeric argument, deletes the text from the buffer as well; you can think of this as "moving" the region text into the register.

M-x append-to-register RET r appends the copy of the text in the region to the text already stored in the register named r. If invoked with a numeric argument, it deletes the region after appending it to the register. A similar command prepend-to-register works the same, except that it prepends the region text to the text in the register, rather than appending it.

C-x r i r inserts in the buffer the text from register r. Normally it leaves point before the text and places the mark after, but with a numeric argument (C-u) it puts point after the text and the mark before.


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I.3 Saving Rectangles in Registers

A register can contain a rectangle instead of linear text. The rectangle is represented as a list of strings. See section H.10 Rectangles, for basic information on how to specify a rectangle in the buffer.

C-x r r r
Copy the region-rectangle into register r (copy-rectangle-to-register). With numeric argument, delete it as well.
C-x r i r
Insert the rectangle stored in register r (if it contains a rectangle) (insert-register).

The C-x r i r command inserts a text string if the register contains one, and inserts a rectangle if the register contains one.

See also the command sort-columns, which you can think of as sorting a rectangle. See section AC.21 Sorting Text.


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I.4 Saving Window Configurations in Registers

You can save the window configuration of the selected frame in a register, or even the configuration of all windows in all frames, and restore the configuration later.

C-x r w r
Save the state of the selected frame's windows in register r (window-configuration-to-register).
C-x r f r
Save the state of all frames, including all their windows, in register r (frame-configuration-to-register).

Use C-x r j r to restore a window or frame configuration. This is the same command used to restore a cursor position. When you restore a frame configuration, any existing frames not included in the configuration become invisible. If you wish to delete these frames instead, use C-u C-x r j r.


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I.5 Keeping Numbers in Registers

There are commands to store a number in a register, to insert the number in the buffer in decimal, and to increment it. These commands can be useful in keyboard macros (see section AD.3 Keyboard Macros).

C-u number C-x r n r
Store number into register r (number-to-register).
C-u number C-x r + r
Increment the number in register r by number (increment-register).
C-x r g r
Insert the number from register r into the buffer.

C-x r g is the same command used to insert any other sort of register contents into the buffer. C-x r + with no numeric argument increments the register value by 1; C-x r n with no numeric argument stores zero in the register.


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I.6 Keeping File Names in Registers

If you visit certain file names frequently, you can visit them more conveniently if you put their names in registers. Here's the Lisp code used to put a file name in a register:

 
(set-register ?r '(file . name))

For example,

 
(set-register ?z '(file . "/gd/gnu/emacs/19.0/src/ChangeLog"))

puts the file name shown in register `z'.

To visit the file whose name is in register r, type C-x r j r. (This is the same command used to jump to a position or restore a frame configuration.)


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I.7 Bookmarks

Bookmarks are somewhat like registers in that they record positions you can jump to. Unlike registers, they have long names, and they persist automatically from one Emacs session to the next. The prototypical use of bookmarks is to record "where you were reading" in various files.

C-x r m RET
Set the bookmark for the visited file, at point.

C-x r m bookmark RET
Set the bookmark named bookmark at point (bookmark-set).

C-x r b bookmark RET
Jump to the bookmark named bookmark (bookmark-jump).

C-x r l
List all bookmarks (list-bookmarks).

M-x bookmark-save
Save all the current bookmark values in the default bookmark file.

The prototypical use for bookmarks is to record one current position in each of several files. So the command C-x r m, which sets a bookmark, uses the visited file name as the default for the bookmark name. If you name each bookmark after the file it points to, then you can conveniently revisit any of those files with C-x r b, and move to the position of the bookmark at the same time.

To display a list of all your bookmarks in a separate buffer, type C-x r l (list-bookmarks). If you switch to that buffer, you can use it to edit your bookmark definitions or annotate the bookmarks. Type C-h m in the bookmark buffer for more information about its special editing commands.

When you kill Emacs, Emacs offers to save your bookmark values in your default bookmark file, `~/.emacs.bmk', if you have changed any bookmark values. You can also save the bookmarks at any time with the M-x bookmark-save command. The bookmark commands load your default bookmark file automatically. This saving and loading is how bookmarks persist from one Emacs session to the next.

If you set the variable bookmark-save-flag to 1, then each command that sets a bookmark will also save your bookmarks; this way, you don't lose any bookmark values even if Emacs crashes. (The value, if a number, says how many bookmark modifications should go by between saving.)

Bookmark position values are saved with surrounding context, so that bookmark-jump can find the proper position even if the file is modified slightly. The variable bookmark-search-size says how many characters of context to record on each side of the bookmark's position.

Here are some additional commands for working with bookmarks:

M-x bookmark-load RET filename RET
Load a file named filename that contains a list of bookmark values. You can use this command, as well as bookmark-write, to work with other files of bookmark values in addition to your default bookmark file.

M-x bookmark-write RET filename RET
Save all the current bookmark values in the file filename.

M-x bookmark-delete RET bookmark RET
Delete the bookmark named bookmark.

M-x bookmark-insert-location RET bookmark RET
Insert in the buffer the name of the file that bookmark bookmark points to.

M-x bookmark-insert RET bookmark RET
Insert in the buffer the contents of the file that bookmark bookmark points to.

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J. Controlling the Display

Since only part of a large buffer fits in the window, Emacs tries to show a part that is likely to be interesting. Display-control commands allow you to specify which part of the text you want to see, and how to display it.

J.1 Using Multiple Typefaces  How to change the display style using faces.
J.2 Font Lock mode  Minor mode for syntactic highlighting using faces.
J.3 Highlight Changes Mode  Using colors to show where you changed the buffer.
J.4 Interactive Highlighting by Matching  Tell Emacs what text to highlight.
J.5 Trailing Whitespace  Showing possibly-spurious trailing whitespace.
J.6 Scrolling  Moving text up and down in a window.
J.7 Horizontal Scrolling  Moving text left and right in a window.
J.8 Follow Mode  Follow mode lets two windows scroll as one.
J.9 Selective Display  Hiding lines with lots of indentation.
J.10 Optional Mode Line Features  Optional mode line display features.
J.11 How Text Is Displayed  How text characters are normally displayed.
J.12 Customization of Display  Information on variables for customizing display.
J.13 Displaying the Cursor  Features for displaying the cursor.


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J.1 Using Multiple Typefaces

When using Emacs with a window system, you can set up multiple styles of displaying characters. Each style is called a face. Each face can specify various attributes, such as the height, weight and slant of the characters, the foreground and background color, and underlining. But it does not have to specify all of them.

Emacs on a character terminal supports only part of face attributes. Which attributes are supported depends on your display type, but many displays support inverse video, bold, and underline attributes, and some support colors.

Features which rely on text in multiple faces (such as Font Lock mode) will also work on non-windowed terminals that can display more than one face, whether by colors or underlining and emboldening. This includes the console on GNU/Linux, an xterm which supports colors, the MS-DOS display (see section AH. Emacs and MS-DOS), and the MS-Windows version invoked with the `-nw' option. Emacs determines automatically whether the terminal has this capability.

You control the appearance of a part of the text in the buffer by specifying the face or faces to use for it. The style of display used for any given character is determined by combining the attributes of all the applicable faces specified for that character. Any attribute that isn't specified by these faces is taken from the default face, whose attributes reflect the default settings of the frame itself.

Enriched mode, the mode for editing formatted text, includes several commands and menus for specifying faces for text in the buffer. See section T.11.4 Faces in Formatted Text, for how to specify the font for text in the buffer. See section T.11.5 Colors in Formatted Text, for how to specify the foreground and background color.

To alter the appearance of a face, use the customization buffer. See section AD.2.2.3 Customizing Faces. You can also use X resources to specify attributes of particular faces (see section AE.13 X Resources). Alternatively, you can change the foreground and background colors of a specific face with M-x set-face-foreground and M-x set-face-background. These commands prompt in the minibuffer for a face name and a color name, with completion, and then set that face to use the specified color. Changing the colors of the default face also changes the foreground and background colors on all frames, both existing and those to be created in the future. (You can also set foreground and background colors for the current frame only; see P.12 Setting Frame Parameters.)

Emacs 21 can correctly display variable-width fonts, but Emacs commands that calculate width and indentation do not know how to calculate variable widths. This can sometimes lead to incorrect results when you use variable-width fonts. In particular, indentation commands can give inconsistent results, so we recommend you avoid variable-width fonts for editing program source code. Filling will sometimes make lines too long or too short. We plan to address these issues in future Emacs versions.

To see what faces are currently defined, and what they look like, type M-x list-faces-display. It's possible for a given face to look different in different frames; this command shows the appearance in the frame in which you type it. Here's a list of the standard defined faces:

default
This face is used for ordinary text that doesn't specify any other face.
mode-line
This face is used for mode lines. By default, it's drawn with shadows for a "raised" effect on window systems, and drawn as the inverse of the default face on non-windowed terminals. See section J.12 Customization of Display.
header-line
Similar to mode-line for a window's header line. Most modes don't use the header line, but the Info mode does.
highlight
This face is used for highlighting portions of text, in various modes. For example, mouse-sensitive text is highlighted using this face.
isearch
This face is used for highlighting Isearch matches.
isearch-lazy-highlight-face
This face is used for lazy highlighting of Isearch matches other than the current one.
region
This face is used for displaying a selected region (when Transient Mark mode is enabled--see below).
secondary-selection
This face is used for displaying a secondary X selection (see section P.2 Secondary Selection).
bold
This face uses a bold variant of the default font, if it has one.
italic
This face uses an italic variant of the default font, if it has one.
bold-italic
This face uses a bold italic variant of the default font, if it has one.
underline
This face underlines text.
fixed-pitch
The basic fixed-pitch face.
fringe
The face for the fringes to the left and right of windows on graphic displays. (The fringes are the narrow portions of the Emacs frame between the text area and the window's right and left borders.)
scroll-bar
This face determines the visual appearance of the scroll bar.
border
This face determines the color of the frame border.
cursor
This face determines the color of the cursor.
mouse
This face determines the color of the mouse pointer.
tool-bar
This is the basic tool-bar face. No text appears in the tool bar, but the colors of this face affect the appearance of tool bar icons.
tooltip
This face is used for tooltips.
menu
This face determines the colors and font of Emacs's menus. Setting the font of LessTif/Motif menus is currently not supported; attempts to set the font are ignored in this case.
trailing-whitespace
The face for highlighting trailing whitespace when show-trailing-whitespace is non-nil; see J.5 Trailing Whitespace.
variable-pitch
The basic variable-pitch face.

When Transient Mark mode is enabled, the text of the region is highlighted when the mark is active. This uses the face named region; you can control the style of highlighting by changing the style of this face (see section AD.2.2.3 Customizing Faces). See section H.2 Transient Mark Mode, for more information about Transient Mark mode and activation and deactivation of the mark.

One easy way to use faces is to turn on Font Lock mode. This minor mode, which is always local to a particular buffer, arranges to choose faces according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs. See section J.2 Font Lock mode, for more information about Font Lock mode and syntactic highlighting.

You can print out the buffer with the highlighting that appears on your screen using the command ps-print-buffer-with-faces. See section AC.19 PostScript Hardcopy.


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J.2 Font Lock mode

Font Lock mode is a minor mode, always local to a particular buffer, which highlights (or "fontifies") using various faces according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs--for example, names of functions being defined or reserved keywords.

The command M-x font-lock-mode turns Font Lock mode on or off according to the argument, and toggles the mode when it has no argument. The function turn-on-font-lock unconditionally enables Font Lock mode. This is useful in mode-hook functions. For example, to enable Font Lock mode whenever you edit a C file, you can do this:

 
(add-hook 'c-mode-hook 'turn-on-font-lock)

To turn on Font Lock mode automatically in all modes which support it, customize the user option global-font-lock-mode or use the function global-font-lock-mode in your `.emacs' file, like this:

 
(global-font-lock-mode 1)

Font Lock mode uses several specifically named faces to do its job, including font-lock-string-face, font-lock-comment-face, and others. The easiest way to find them all is to use completion on the face name in set-face-foreground.

To change the colors or the fonts used by Font Lock mode to fontify different parts of text, just change these faces. There are two ways to do it:

To get the full benefit of Font Lock mode, you need to choose a default font which has bold, italic, and bold-italic variants; or else you need to have a color or gray-scale screen.

The variable font-lock-maximum-decoration specifies the preferred level of fontification, for modes that provide multiple levels. Level 1 is the least amount of fontification; some modes support levels as high as 3. The normal default is "as high as possible." You can specify an integer, which applies to all modes, or you can specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use this:

 
(setq font-lock-maximum-decoration
      '((c-mode . 1) (c++-mode . 1)))

Fontification can be too slow for large buffers, so you can suppress it. The variable font-lock-maximum-size specifies a buffer size, beyond which buffer fontification is suppressed.

Comment and string fontification (or "syntactic" fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including C mode and Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment. (See section U.2.1 Left Margin Convention.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment.

The variable font-lock-beginning-of-syntax-function (always buffer-local) specifies how Font Lock mode can find a position guaranteed to be outside any comment or string. In modes which use the leftmost column parenthesis convention, the default value of the variable is beginning-of-defun---that tells Font Lock mode to use the convention. If you set this variable to nil, Font Lock no longer relies on the convention. This avoids incorrect results, but the price is that, in some cases, fontification for a changed text must rescan buffer text from the beginning of the buffer. This can considerably slow down redisplay while scrolling, particularly if you are close to the end of a large buffer.

Font Lock highlighting patterns already exist for many modes, but you may want to fontify additional patterns. You can use the function font-lock-add-keywords, to add your own highlighting patterns for a particular mode. For example, to highlight `FIXME:' words in C comments, use this:

 
(font-lock-add-keywords
 'c-mode
 '(("\\<\\(FIXME\\):" 1 font-lock-warning-face t)))

To remove keywords from the font-lock highlighting patterns, use the function font-lock-remove-keywords.


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J.3 Highlight Changes Mode

Use M-x highlight-changes-mode to enable a minor mode that uses faces (colors, typically) to indicate which parts of the buffer were changed most recently.


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J.4 Interactive Highlighting by Matching

It is sometimes useful to highlight the strings that match a certain regular expression. For example, you might wish to see all the references to a certain variable in a program source file, or highlight certain parts in a voluminous output of some program, or make certain cliches stand out in an article.

Use the M-x hi-lock-mode command to turn on a minor mode that allows you to specify regular expressions of the text to be highlighted. Hi-lock mode works like Font Lock (see section J.2 Font Lock mode), except that it lets you specify explicitly what parts of text to highlight. You control Hi-lock mode with these commands:

C-x w h regexp RET face RET
Highlight text that matches regexp using face face (highlight-regexp). By using this command more than once, you can highlight various parts of the text in different ways.

C-x w r regexp RET
Unhighlight regexp (unhighlight-regexp). You must enter one of the regular expressions currently specified for highlighting. (You can use completion, or choose from a menu, to enter one of them conveniently.)

C-x w l regexp RET face RET
Highlight entire lines containing a match for regexp, using face face (highlight-lines-matching-regexp).

C-x w b
Insert all the current highlighting regexp/face pairs into the buffer at point, with comment delimiters to prevent them from changing your program. This key binding runs the hi-lock-write-interactive-patterns command.

These patterns will be read the next time you visit the file while Hi-lock mode is enabled, or whenever you use the M-x hi-lock-find-patterns command.

C-x w i
Re-read regexp/face pairs in the current buffer (hi-lock-write-interactive-patterns). The list of pairs is found no matter where in the buffer it may be.

This command does nothing if the major mode is a member of the list hi-lock-exclude-modes.


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J.5 Trailing Whitespace

It is easy to leave unnecessary spaces at the end of a line without realizing it. In most cases, this trailing whitespace has no effect, but there are special circumstances where it matters.

You can make trailing whitespace visible on the screen by setting the buffer-local variable show-trailing-whitespace to t. Then Emacs displays trailing whitespace in the face trailing-whitespace.

Trailing whitespace is defined as spaces or tabs at the end of a line. But trailing whitespace is not displayed specially if point is at the end of the line containing the whitespace. (Doing that looks ugly while you are typing in new text, and the location of point is enough in that case to show you that the spaces are present.)

To delete all trailing whitespace within the current buffer's restriction (see section AC.22 Narrowing), type M-x delete-trailing-whitespace RET. (This command does not remove the form-feed characters.)

Emacs can indicate empty lines at the end of the buffer with a special bitmap on the left fringe of the window. To enable this feature, set the buffer-local variable indicate-empty-lines to a non-nil value. The default value of this variable is controlled by the variable default-indicate-empty-lines; by setting that variable, you can enable or disable this feature for all new buffers.


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J.6 Scrolling

If a buffer contains text that is too large to fit entirely within a window that is displaying the buffer, Emacs shows a contiguous portion of the text. The portion shown always contains point.

Scrolling means moving text up or down in the window so that different parts of the text are visible. Scrolling forward means that text moves up, and new text appears at the bottom. Scrolling backward moves text down and new text appears at the top.

Scrolling happens automatically if you move point past the bottom or top of the window. You can also explicitly request scrolling with the commands in this section.

C-l
Clear screen and redisplay, scrolling the selected window to center point vertically within it (recenter).
C-v
Scroll forward (a windowful or a specified number of lines) (scroll-up).
NEXT
PAGEDOWN
Likewise, scroll forward.
M-v
Scroll backward (scroll-down).
PRIOR
PAGEUP
Likewise, scroll backward.
arg C-l
Scroll so point is on line arg (recenter).
C-M-l
Scroll heuristically to bring useful information onto the screen (reposition-window).

The most basic scrolling command is C-l (recenter) with no argument. It clears the entire screen and redisplays all windows. In addition, it scrolls the selected window so that point is halfway down from the top of the window.

To read the buffer a windowful at a time, use C-v (scroll-up) with no argument. This scrolls forward by nearly the whole window height. The effect is to take the two lines at the bottom of the window and put them at the top, followed by nearly a whole windowful of lines that were not previously visible. If point was in the text that scrolled off the top, it ends up at the new top of the window.

M-v (scroll-down) with no argument scrolls backward in a similar way, also with overlap. The number of lines of overlap across a C-v or M-v is controlled by the variable next-screen-context-lines; by default, it is 2. The function keys NEXT and PRIOR, or PAGEDOWN and PAGEUP, are equivalent to C-v and M-v.

The commands C-v and M-v with a numeric argument scroll the text in the selected window up or down a few lines. C-v with an argument moves the text and point up, together, that many lines; it brings the same number of new lines into view at the bottom of the window. M-v with numeric argument scrolls the text downward, bringing that many new lines into view at the top of the window. C-v with a negative argument is like M-v and vice versa.

The names of scroll commands are based on the direction that the text moves in the window. Thus, the command to scroll forward is called scroll-up because it moves the text upward on the screen. The keys PAGEDOWN and PAGEUP derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that PAGEDOWN runs scroll-up.

Some users like the full-screen scroll commands to keep point at the same screen line. To enable this behavior, set the variable scroll-preserve-screen-position to a non-nil value. This mode is convenient for browsing through a file by scrolling by screenfuls; if you come back to the screen where you started, point goes back to the line where it started. However, this mode is inconvenient when you move to the next screen in order to move point to the text there.

Another way to do scrolling is with C-l with a numeric argument. C-l does not clear the screen when given an argument; it only scrolls the selected window. With a positive argument n, it repositions text to put point n lines down from the top. An argument of zero puts point on the very top line. Point does not move with respect to the text; rather, the text and point move rigidly on the screen. C-l with a negative argument puts point that many lines from the bottom of the window. For example, C-u - 1 C-l puts point on the bottom line, and C-u - 5 C-l puts it five lines from the bottom. C-u C-l scrolls to put point at the center (vertically) of the selected window.

The C-M-l command (reposition-window) scrolls the current window heuristically in a way designed to get useful information onto the screen. For example, in a Lisp file, this command tries to get the entire current defun onto the screen if possible.

Scrolling happens automatically when point moves out of the visible portion of the text. Normally, automatic scrolling centers point vertically within the window. However, if you set scroll-conservatively to a small number n, then if you move point just a little off the screen--less than n lines--then Emacs scrolls the text just far enough to bring point back on screen. By default, scroll-conservatively is 0.

When the window does scroll by a longer distance, you can control how aggressively it scrolls, by setting the variables scroll-up-aggressively and scroll-down-aggressively. The value of scroll-up-aggressively should be either nil, or a fraction f between 0 and 1. A fraction specifies where on the screen to put point when scrolling upward. More precisely, when a window scrolls up because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.

nil, which is the default, scrolls to put point at the center. So it is equivalent to .5.

Likewise, scroll-down-aggressively is used for scrolling down. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value is more aggressive.

The variable scroll-margin restricts how close point can come to the top or bottom of a window. Its value is a number of screen lines; if point comes within that many lines of the top or bottom of the window, Emacs recenters the window. By default, scroll-margin is 0.


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J.7 Horizontal Scrolling

Horizontal scrolling means shifting all the lines sideways within a window--so that some of the text near the left margin is not displayed at all. Emacs does this automatically in any window that uses line truncation rather than continuation: whenever point moves off the left or right edge of the screen, Emacs scrolls the buffer horizontally to make point visible.

When a window has been scrolled horizontally, text lines are truncated rather than continued (see section D.8 Continuation Lines), with a `$' appearing in the first column when there is text truncated to the left, and in the last column when there is text truncated to the right.

You can use these commands to do explicit horizontal scrolling.

C-x <
Scroll text in current window to the left (scroll-left).
C-x >
Scroll to the right (scroll-right).

The command C-x < (scroll-left) scrolls the selected window to the left by n columns with argument n. This moves part of the beginning of each line off the left edge of the window. With no argument, it scrolls by almost the full width of the window (two columns less, to be precise).

C-x > (scroll-right) scrolls similarly to the right. The window cannot be scrolled any farther to the right once it is displayed normally (with each line starting at the window's left margin); attempting to do so has no effect. This means that you don't have to calculate the argument precisely for C-x >; any sufficiently large argument will restore the normal display.

If you scroll a window horizontally by hand, that sets a lower bound for automatic horizontal scrolling. Automatic scrolling will continue to scroll the window, but never farther to the right than the amount you previously set by scroll-left.

To disable automatic horizontal scrolling, set the variable automatic-hscrolling to nil.


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J.8 Follow Mode

Follow mode is a minor mode that makes two windows showing the same buffer scroll as one tall "virtual window." To use Follow mode, go to a frame with just one window, split it into two side-by-side windows using C-x 3, and then type M-x follow-mode. From then on, you can edit the buffer in either of the two windows, or scroll either one; the other window follows it.

In Follow mode, if you move point outside the portion visible in one window and into the portion visible in the other window, that selects the other window--again, treating the two as if they were parts of one large window.

To turn off Follow mode, type M-x follow-mode a second time.


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J.9 Selective Display

Emacs has the ability to hide lines indented more than a certain number of columns (you specify how many columns). You can use this to get an overview of a part of a program.

To hide lines, type C-x $ (set-selective-display) with a numeric argument n. Then lines with at least n columns of indentation disappear from the screen. The only indication of their presence is that three dots (`...') appear at the end of each visible line that is followed by one or more hidden ones.

The commands C-n and C-p move across the hidden lines as if they were not there.

The hidden lines are still present in the buffer, and most editing commands see them as usual, so you may find point in the middle of the hidden text. When this happens, the cursor appears at the end of the previous line, after the three dots. If point is at the end of the visible line, before the newline that ends it, the cursor appears before the three dots.

To make all lines visible again, type C-x $ with no argument.

If you set the variable selective-display-ellipses to nil, the three dots do not appear at the end of a line that precedes hidden lines. Then there is no visible indication of the hidden lines. This variable becomes local automatically when set.


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J.10 Optional Mode Line Features

The current line number of point appears in the mode line when Line Number mode is enabled. Use the command M-x line-number-mode to turn this mode on and off; normally it is on. The line number appears before the buffer percentage pos, with the letter `L' to indicate what it is. See section AD.1 Minor Modes, for more information about minor modes and about how to use this command.

If you have narrowed the buffer (see section AC.22 Narrowing), the displayed line number is relative to the accessible portion of the buffer.

If the buffer is very large (larger than the value of line-number-display-limit), then the line number doesn't appear. Emacs doesn't compute the line number when the buffer is large, because that would be too slow. Set it to nil to remove the limit.

Line-number computation can also be slow if the lines in the buffer are too long. For this reason, Emacs normally doesn't display line numbers if the average width, in characters, of lines near point is larger than the value of the variable line-number-display-limit-width. The default value is 200 characters.

You can also display the current column number by turning on Column Number mode. It displays the current column number preceded by the letter `C'. Type M-x column-number-mode to toggle this mode.

Emacs can optionally display the time and system load in all mode lines. To enable this feature, type M-x display-time or customize the option display-time-mode. The information added to the mode line usually appears after the buffer name, before the mode names and their parentheses. It looks like this:

 
hh:mmpm l.ll

Here hh and mm are the hour and minute, followed always by `am' or `pm'. l.ll is the average number of running processes in the whole system recently. (Some fields may be missing if your operating system cannot support them.) If you prefer time display in 24-hour format, set the variable display-time-24hr-format to t.

The word `Mail' appears after the load level if there is mail for you that you have not read yet. On a graphical display you can use an icon instead of `Mail' by customizing display-time-use-mail-icon; this may save some space on the mode line. You can customize display-time-mail-face to make the mail indicator prominent.

By default, the mode line is drawn on graphics displays with 3D-style highlighting, like that of a button when it is not being pressed. If you don't like this effect, you can disable the 3D highlighting of the mode line, by customizing the attributes of the mode-line face in your `.emacs' init file, like this:

 
(set-face-attribute 'mode-line nil :box nil)

Alternatively, you can turn off the box attribute in your `.Xdefaults' file:

 
Emacs.mode-line.AttributeBox: off


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J.11 How Text Is Displayed

ASCII printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics, as are non-ASCII multibyte printing characters (octal codes above 0400).

Some ASCII control characters are displayed in special ways. The newline character (octal code 012) is displayed by starting a new line. The tab character (octal code 011) is displayed by moving to the next tab stop column (normally every 8 columns).

Other ASCII control characters are normally displayed as a caret (`^') followed by the non-control version of the character; thus, control-A is displayed as `^A'.

Non-ASCII characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as `\230'. The display of character codes 0240 through 0377 (octal) may be either as escape sequences or as graphics. They do not normally occur in multibyte buffers, but if they do, they are displayed as Latin-1 graphics. In unibyte mode, if you enable European display they are displayed using their graphics (assuming your terminal supports them), otherwise as escape sequences. See section Q.13 Single-byte Character Set Support.


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J.12 Customization of Display

This section contains information for customization only. Beginning users should skip it.

The variable mode-line-inverse-video is an obsolete way of controlling whether the mode line is displayed in inverse video; the preferred way of doing this is to change the mode-line face. See section B.3 The Mode Line. However, if mode-line-inverse-video has a value of nil, then the mode-line face will be ignored, and mode-lines will be drawn using the default text face. See section J.1 Using Multiple Typefaces.

If the variable inverse-video is non-nil, Emacs attempts to invert all the lines of the display from what they normally are.

If the variable visible-bell is non-nil, Emacs attempts to make the whole screen blink when it would normally make an audible bell sound. This variable has no effect if your terminal does not have a way to make the screen blink.

When you reenter Emacs after suspending, Emacs normally clears the screen and redraws the entire display. On some terminals with more than one page of memory, it is possible to arrange the termcap entry so that the `ti' and `te' strings (output to the terminal when Emacs is entered and exited, respectively) switch between pages of memory so as to use one page for Emacs and another page for other output. Then you might want to set the variable no-redraw-on-reenter non-nil; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there.

The variable echo-keystrokes controls the echoing of multi-character keys; its value is the number of seconds of pause required to cause echoing to start, or zero meaning don't echo at all. See section B.2 The Echo Area.

If the variable ctl-arrow is nil, all control characters in the buffer are displayed with octal escape sequences, except for newline and tab. Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect. The default is initially t. See section `Display Tables' in The Emacs Lisp Reference Manual.

Normally, a tab character in the buffer is displayed as whitespace which extends to the next display tab stop position, and display tab stops come at intervals equal to eight spaces. The number of spaces per tab is controlled by the variable tab-width, which is made local by changing it, just like ctl-arrow. Note that how the tab character in the buffer is displayed has nothing to do with the definition of TAB as a command. The variable tab-width must have an integer value between 1 and 1000, inclusive.

If the variable truncate-lines is non-nil, then each line of text gets just one screen line for display; if the text line is too long, display shows only the part that fits. If truncate-lines is nil, then long text lines display as more than one screen line, enough to show the whole text of the line. See section D.8 Continuation Lines. Altering the value of truncate-lines makes it local to the current buffer; until that time, the default value is in effect. The default is initially nil.

If the variable truncate-partial-width-windows is non-nil, it forces truncation rather than continuation in any window less than the full width of the screen or frame, regardless of the value of truncate-lines. For information about side-by-side windows, see O.2 Splitting Windows. See also section `Display' in The Emacs Lisp Reference Manual.

The variable baud-rate holds the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations. On terminals, it affects padding, and decisions about whether to scroll part of the screen or redraw it instead. It also affects the behavior of incremental search.

On window-systems, baud-rate is only used to determine how frequently to look for pending input during display updating. A higher value of baud-rate means that check for pending input will be done less frequently.

You can customize the way any particular character code is displayed by means of a display table. See section `Display Tables' in The Emacs Lisp Reference Manual.

On a window system, Emacs can optionally display the mouse pointer in a special shape to say that Emacs is busy. To turn this feature on or off, customize the group cursor. You can also control the amount of time Emacs must remain busy before the busy indicator is displayed, by setting the variable hourglass-delay.

On some text-only terminals, bold face and inverse video together result in text that is hard to read. Call the function tty-suppress-bold-inverse-default-colors with a non-nil argument to suppress the effect of bold-face in this case.


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J.13 Displaying the Cursor

There are a number of ways to customize the display of the cursor. M-x hl-line-mode enables or disables a minor mode which highlights the line containing point. On window systems, the command M-x blink-cursor-mode turns on or off the blinking of the cursor. (On terminals, the terminal itself blinks the cursor, and Emacs has no control over it.)

You can customize the cursor's color, and whether it blinks, using the cursor Custom group (see section AD.2.2 Easy Customization Interface).

When displaying on a window system, Emacs can optionally draw the block cursor as wide as the character under the cursor--for example, if the cursor is on a tab character, it would cover the full width occupied by that tab character. To enable this feature, set the variable x-stretch-cursor to a non-nil value.

Normally, the cursor in non-selected windows is shown as a hollow box. To turn off cursor display in non-selected windows, customize the option cursor-in-non-selected-windows to assign it a nil value.


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K. Searching and Replacement

Like other editors, Emacs has commands for searching for occurrences of a string. The principal search command is unusual in that it is incremental; it begins to search before you have finished typing the search string. There are also nonincremental search commands more like those of other editors.

Besides the usual replace-string command that finds all occurrences of one string and replaces them with another, Emacs has a more flexible replacement command called query-replace, which asks interactively which occurrences to replace.

K.1 Incremental Search  Search happens as you type the string.
K.2 Nonincremental Search  Specify entire string and then search.
K.3 Word Search  Search for sequence of words.
K.4 Regular Expression Search  Search for match for a regexp.
K.5 Syntax of Regular Expressions  Syntax of regular expressions.
K.6 Searching and Case  To ignore case while searching, or not.
K.7 Replacement Commands  Search, and replace some or all matches.
K.8 Other Search-and-Loop Commands  Operating on all matches for some regexp.


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K.1 Incremental Search

An incremental search begins searching as soon as you type the first character of the search string. As you type in the search string, Emacs shows you where the string (as you have typed it so far) would be found. When you have typed enough characters to identify the place you want, you can stop. Depending on what you plan to do next, you may or may not need to terminate the search explicitly with RET.

C-s
Incremental search forward (isearch-forward).
C-r
Incremental search backward (isearch-backward).

C-s starts a forward incremental search. It reads characters from the keyboard, and moves point past the next occurrence of those characters. If you type C-s and then F, that puts the cursor after the first `F' (the first following the starting point, since this is a forward search). Then if you type an O, you will see the cursor move just after the first `FO' (the `F' in that `FO' may or may not be the first `F'). After another O, the cursor moves after the first `FOO' after the place where you started the search. At each step, the buffer text that matches the search string is highlighted, if the terminal can do that; the current search string is always displayed in the echo area.

If you make a mistake in typing the search string, you can cancel characters with DEL. Each DEL cancels the last character of search string. This does not happen until Emacs is ready to read another input character; first it must either find, or fail to find, the character you want to erase. If you do not want to wait for this to happen, use C-g as described below.

When you are satisfied with the place you have reached, you can type RET, which stops searching, leaving the cursor where the search brought it. Also, any command not specially meaningful in searches stops the searching and is then executed. Thus, typing C-a would exit the search and then move to the beginning of the line. RET is necessary only if the next command you want to type is a printing character, DEL, RET, or another character that is special within searches (C-q, C-w, C-r, C-s, C-y, M-y, M-r, M-s, and some other meta-characters).

Sometimes you search for `FOO' and find one, but not the one you expected to find. There was a second `FOO' that you forgot about, before the one you were aiming for. In this event, type another C-s to move to the next occurrence of the search string. You can repeat this any number of times. If you overshoot, you can cancel some C-s characters with DEL.

After you exit a search, you can search for the same string again by typing just C-s C-s: the first C-s is the key that invokes incremental search, and the second C-s means "search again."

To reuse earlier search strings, use the search ring. The commands M-p and M-n move through the ring to pick a search string to reuse. These commands leave the selected search ring element in the minibuffer, where you can edit it. Type C-s or C-r to terminate editing the string and search for it.

If your string is not found at all, the echo area says `Failing I-Search'. The cursor is after the place where Emacs found as much of your string as it could. Thus, if you search for `FOOT', and there is no `FOOT', you might see the cursor after the `FOO' in `FOOL'. At this point there are several things you can do. If your string was mistyped, you can rub some of it out and correct it. If you like the place you have found, you can type RET or some other Emacs command to remain there. Or you can type C-g, which removes from the search string the characters that could not be found (the `T' in `FOOT'), leaving those that were found (the `FOO' in `FOOT'). A second C-g at that point cancels the search entirely, returning point to where it was when the search started.

An upper-case letter in the search string makes the search case-sensitive. If you delete the upper-case character from the search string, it ceases to have this effect. See section K.6 Searching and Case.

To search for a newline, type C-j. To search for another control character, such as control-S or carriage return, you must quote it by typing C-q first. This function of C-q is analogous to its use for insertion (see section D.1 Inserting Text): it causes the following character to be treated the way any "ordinary" character is treated in the same context. You can also specify a character by its octal code: enter C-q followed by a sequence of octal digits.

To search for non-ASCII characters, you must use an input method (see section Q.4 Input Methods). If an input method is enabled in the current buffer when you start the search, you can use it while you type the search string also. Emacs indicates that by including the input method mnemonic in its prompt, like this:

 
I-search [im]:

where im is the mnemonic of the active input method. You can toggle (enable or disable) the input method while you type the search string with C-\ (isearch-toggle-input-method). You can turn on a certain (non-default) input method with C-^ (isearch-toggle-specified-input-method), which prompts for the name of the input method. The input method you enable during incremental search remains enabled in the current buffer afterwards.

If a search is failing and you ask to repeat it by typing another C-s, it starts again from the beginning of the buffer. Repeating a failing reverse search with C-r starts again from the end. This is called wrapping around, and `Wrapped' appears in the search prompt once this has happened. If you keep on going past the original starting point of the search, it changes to `Overwrapped', which means that you are revisiting matches that you have already seen.

The C-g "quit" character does special things during searches; just what it does depends on the status of the search. If the search has found what you specified and is waiting for input, C-g cancels the entire search. The cursor moves back to where you started the search. If C-g is typed when there are characters in the search string that have not been found--because Emacs is still searching for them, or because it has failed to find them--then the search string characters which have not been found are discarded from the search string. With them gone, the search is now successful and waiting for more input, so a second C-g will cancel the entire search.

You can change to searching backwards with C-r. If a search fails because the place you started was too late in the file, you should do this. Repeated C-r keeps looking for more occurrences backwards. A C-s starts going forwards again. C-r in a search can be canceled with DEL.

If you know initially that you want to search backwards, you can use C-r instead of C-s to start the search, because C-r as a key runs a command (isearch-backward) to search backward. A backward search finds matches that are entirely before the starting point, just as a forward search finds matches that begin after it.

The characters C-y and C-w can be used in incremental search to grab text from the buffer into the search string. This makes it convenient to search for another occurrence of text at point. C-w copies the word after point as part of the search string, advancing point over that word. Another C-s to repeat the search will then search for a string including that word. C-y is similar to C-w but copies all the rest of the current line into the search string. Both C-y and C-w convert the text they copy to lower case if the search is currently not case-sensitive; this is so the search remains case-insensitive.

The character M-y copies text from the kill ring into the search string. It uses the same text that C-y as a command would yank. Mouse-2 in the echo area does the same. See section H.8 Yanking.

When you exit the incremental search, it sets the mark to where point was, before the search. That is convenient for moving back there. In Transient Mark mode, incremental search sets the mark without activating it, and does so only if the mark is not already active.

When you pause for a little while during incremental search, it highlights all other possible matches for the search string. This makes it easier to anticipate where you can get to by typing C-s or C-r to repeat the search. The short delay before highlighting other matches helps indicate which match is the current one. If you don't like this feature, you can turn it off by setting isearch-lazy-highlight to nil.

You can control how this highlighting looks by customizing the faces isearch (used for the current match) and isearch-lazy-highlight-face (for all the other matches).

To customize the special characters that incremental search understands, alter their bindings in the keymap isearch-mode-map. For a list of bindings, look at the documentation of isearch-mode with C-h f isearch-mode RET.


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K.1.1 Slow Terminal Incremental Search

Incremental search on a slow terminal uses a modified style of display that is designed to take less time. Instead of redisplaying the buffer at each place the search gets to, it creates a new single-line window and uses that to display the line that the search has found. The single-line window comes into play as soon as point moves outside of the text that is already on the screen.

When you terminate the search, the single-line window is removed. Emacs then redisplays the window in which the search was done, to show its new position of point.

The slow terminal style of display is used when the terminal baud rate is less than or equal to the value of the variable search-slow-speed, initially 1200. See baud-rate in J.12 Customization of Display.

The number of lines to use in slow terminal search display is controlled by the variable search-slow-window-lines. Its normal value is 1.


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K.2 Nonincremental Search

Emacs also has conventional nonincremental search commands, which require you to type the entire search string before searching begins.

C-s RET string RET
Search for string.
C-r RET string RET
Search backward for string.

To do a nonincremental search, first type C-s RET. This enters the minibuffer to read the search string; terminate the string with RET, and then the search takes place. If the string is not found, the search command signals an error.

When you type C-s RET, the C-s invokes incremental search as usual. That command is specially programmed to invoke nonincremental search, search-forward, if the string you specify is empty. (Such an empty argument would otherwise be useless.) But it does not call search-forward right away. First it checks the next input character to see if is C-w, which specifies a word search. See section K.3 Word Search. C-r RET does likewise, for a reverse incremental search.

Forward and backward nonincremental searches are implemented by the commands search-forward and search-backward. These commands may be bound to keys in the usual manner. The feature that you can get to them via the incremental search commands exists for historical reasons, and to avoid the need to find key sequences for them.


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K.3 Word Search

Word search searches for a sequence of words without regard to how the words are separated. More precisely, you type a string of many words, using single spaces to separate them, and the string can be found even if there are multiple spaces, newlines, or other punctuation characters between these words.

Word search is useful for editing a printed document made with a text formatter. If you edit while looking at the printed, formatted version, you can't tell where the line breaks are in the source file. With word search, you can search without having to know them.

C-s RET C-w words RET
Search for words, ignoring details of punctuation.
C-r RET C-w words RET
Search backward for words, ignoring details of punctuation.

Word search is a special case of nonincremental search and is invoked with C-s RET C-w. This is followed by the search string, which must always be terminated with RET. Being nonincremental, this search does not start until the argument is terminated. It works by constructing a regular expression and searching for that; see K.4 Regular Expression Search.

Use C-r RET C-w to do backward word search.

Forward and backward word searches are implemented by the commands word-search-forward and word-search-backward. These commands may be bound to keys in the usual manner. They are available via the incremental search commands both for historical reasons and to avoid the need to find suitable key sequences for them.


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K.4 Regular Expression Search

A regular expression (regexp, for short) is a pattern that denotes a class of alternative strings to match, possibly infinitely many. GNU Emacs provides both incremental and nonincremental ways to search for a match for a regexp.

Incremental search for a regexp is done by typing C-M-s (isearch-forward-regexp), or by invoking C-s with a prefix argument (whose value does not matter). This command reads a search string incrementally just like C-s, but it treats the search string as a regexp rather than looking for an exact match against the text in the buffer. Each time you add text to the search string, you make the regexp longer, and the new regexp is searched for. To search backward for a regexp, use C-M-r (isearch-backward-regexp), or C-r with a prefix argument.

All of the control characters that do special things within an ordinary incremental search have the same function in incremental regexp search. Typing C-s or C-r immediately after starting the search retrieves the last incremental search regexp used; that is to say, incremental regexp and non-regexp searches have independent defaults. They also have separate search rings that you can access with M-p and M-n.

If you type SPC in incremental regexp search, it matches any sequence of whitespace characters, including newlines. If you want to match just a space, type C-q SPC.

Note that adding characters to the regexp in an incremental regexp search can make the cursor move back and start again. For example, if you have searched for `foo' and you add `\|bar', the cursor backs up in case the first `bar' precedes the first `foo'.

Nonincremental search for a regexp is done by the functions re-search-forward and re-search-backward. You can invoke these with M-x, or bind them to keys, or invoke them by way of incremental regexp search with C-M-s RET and C-M-r RET.

If you use the incremental regexp search commands with a prefix argument, they perform ordinary string search, like isearch-forward and isearch-backward. See section K.1 Incremental Search.


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K.5 Syntax of Regular Expressions

Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression which matches that same character and nothing else. The special characters are `$', `^', `.', `*', `+', `?', `[', `]' and `\'. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it. (When you use regular expressions in a Lisp program, each `\' must be doubled, see the example near the end of this section.)

For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does not match the string `ff'.) Likewise, `o' is a regular expression that matches only `o'. (When case distinctions are being ignored, these regexps also match `F' and `O', but we consider this a generalization of "the same string," rather than an exception.)

Any two regular expressions a and b can be concatenated. The result is a regular expression which matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.

As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something nontrivial, you need to use one of the special characters. Here is a list of them.

. (Period)
is a special character that matches any single character except a newline. Using concatenation, we can make regular expressions like `a.b', which matches any three-character string that begins with `a' and ends with `b'.

*
is not a construct by itself; it is a postfix operator that means to match the preceding regular expression repetitively as many times as possible. Thus, `o*' matches any number of `o's (including no `o's).

`*' always applies to the smallest possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. It matches `f', `fo', `foo', and so on.

The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in case that makes it possible to match the rest of the pattern. For example, in matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully.

+
is a postfix operator, similar to `*' except that it must match the preceding expression at least once. So, for example, `ca+r' matches the strings `car' and `caaaar' but not the string `cr', whereas `ca*r' matches all three strings.

?
is a postfix operator, similar to `*' except that it can match the preceding expression either once or not at all. For example, `ca?r' matches `car' or `cr'; nothing else.

*?, +?, ??
are non-greedy variants of the operators above. The normal operators `*', `+', `?' are greedy in that they match as much as they can, as long as the overall regexp can still match. With a following `?', they are non-greedy: they will match as little as possible.

Thus, both `ab*' and `ab*?' can match the string `a' and the string `abbbb'; but if you try to match them both against the text `abbb', `ab*' will match it all (the longest valid match), while `ab*?' will match just `a' (the shortest valid match).

\{n\}
is a postfix operator that specifies repetition n times--that is, the preceding regular expression must match exactly n times in a row. For example, `x\{4\}' matches the string `xxxx' and nothing else.

\{n,m\}
is a postfix operator that specifies repetition between n and m times--that is, the preceding regular expression must match at least n times, but no more than m times. If m is omitted, then there is no upper limit, but the preceding regular expression must match at least n times.
`\{0,1\}' is equivalent to `?'.
`\{0,\}' is equivalent to `*'.
`\{1,\}' is equivalent to `+'.

[ ... ]
is a character set, which begins with `[' and is terminated by `]'. In the simplest case, the characters between the two brackets are what this set can match.

Thus, `[ad]' matches either one `a' or one `d', and `[ad]*' matches any string composed of just `a's and `d's (including the empty string), from which it follows that `c[ad]*r' matches `cr', `car', `cdr', `caddaar', etc.

You can also include character ranges in a character set, by writing the starting and ending characters with a `-' between them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower-case ASCII letter or `$', `%' or period.

Note that the usual regexp special characters are not special inside a character set. A completely different set of special characters exists inside character sets: `]', `-' and `^'.

To include a `]' in a character set, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character of the set, or put it after a range. Thus, `[]-]' matches both `]' and `-'.

To include `^' in a set, put it anywhere but at the beginning of the set. (At the beginning, it complements the set--see below.)

When you use a range in case-insensitive search, you should write both ends of the range in upper case, or both in lower case, or both should be non-letters. The behavior of a mixed-case range such as `A-z' is somewhat ill-defined, and it may change in future Emacs versions.

[^ ... ]
`[^' begins a complemented character set, which matches any character except the ones specified. Thus, `[^a-z0-9A-Z]' matches all characters except ASCII letters and digits.

`^' is not special in a character set unless it is the first character. The character following the `^' is treated as if it were first (in other words, `-' and `]' are not special there).

A complemented character set can match a newline, unless newline is mentioned as one of the characters not to match. This is in contrast to the handling of regexps in programs such as grep.

^
is a special character that matches the empty string, but only at the beginning of a line in the text being matched. Otherwise it fails to match anything. Thus, `^foo' matches a `foo' that occurs at the beginning of a line.

$
is similar to `^' but matches only at the end of a line. Thus, `x+$' matches a string of one `x' or more at the end of a line.

\
has two functions: it quotes the special characters (including `\'), and it introduces additional special constructs.

Because `\' quotes special characters, `\$' is a regular expression that matches only `$', and `\[' is a regular expression that matches only `[', and so on.

Note: for historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; it is better to quote the special character anyway, regardless of where it appears.

For the most part, `\' followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with `\' that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of `\' constructs.

\|
specifies an alternative. Two regular expressions a and b with `\|' in between form an expression that matches some text if either a matches it or b matches it. It works by trying to match a, and if that fails, by trying to match b.

Thus, `foo\|bar' matches either `foo' or `bar' but no other string.

`\|' applies to the largest possible surrounding expressions. Only a surrounding `\( ... \)' grouping can limit the grouping power of `\|'.

Full backtracking capability exists to handle multiple uses of `\|'.

\( ... \)
is a grouping construct that serves three purposes:

  1. To enclose a set of `\|' alternatives for other operations. Thus, `\(foo\|bar\)x' matches either `foox' or `barx'.

  2. To enclose a complicated expression for the postfix operators `*', `+' and `?' to operate on. Thus, `ba\(na\)*' matches `bananana', etc., with any (zero or more) number of `na' strings.

  3. To record a matched substring for future reference.

This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same `\( ... \)' construct. In practice there is usually no conflict between the two meanings; when there is a conflict, you can use a "shy" group.

\(?: ... \)
specifies a "shy" group that does not record the matched substring; you can't refer back to it with `\d'. This is useful in mechanically combining regular expressions, so that you can add groups for syntactic purposes without interfering with the numbering of the groups that were written by the user.

\d
matches the same text that matched the dth occurrence of a `\( ... \)' construct.

After the end of a `\( ... \)' construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use `\' followed by the digit d to mean "match the same text matched the dth time by the `\( ... \)' construct."

The strings matching the first nine `\( ... \)' constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open-parentheses appear in the regular expression. So you can use `\1' through `\9' to refer to the text matched by the corresponding `\( ... \)' constructs.

For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text.

If a particular `\( ... \)' construct matches more than once (which can easily happen if it is followed by `*'), only the last match is recorded.

\`
matches the empty string, but only at the beginning of the buffer or string being matched against.

\'
matches the empty string, but only at the end of the buffer or string being matched against.

\=
matches the empty string, but only at point.

\b
matches the empty string, but only at the beginning or end of a word. Thus, `\bfoo\b' matches any occurrence of `foo' as a separate word. `\bballs?\b' matches `ball' or `balls' as a separate word.

`\b' matches at the beginning or end of the buffer regardless of what text appears next to it.

\B
matches the empty string, but not at the beginning or end of a word.

\<
matches the empty string, but only at the beginning of a word. `\<' matches at the beginning of the buffer only if a word-constituent character follows.

\>
matches the empty string, but only at the end of a word. `\>' matches at the end of the buffer only if the contents end with a word-constituent character.

\w
matches any word-constituent character. The syntax table determines which characters these are. See section AD.6 The Syntax Table.

\W
matches any character that is not a word-constituent.

\sc
matches any character whose syntax is c. Here c is a character that designates a particular syntax class: thus, `w' for word constituent, `-' or ` ' for whitespace, `.' for ordinary punctuation, etc. See section AD.6 The Syntax Table.

\Sc
matches any character whose syntax is not c.

\cc
matches any character that belongs to the category c. For example, `\cc' matches Chinese characters, `\cg' matches Greek characters, etc. For the description of the known categories, type M-x describe-categories RET.

\Cc
matches any character that does not belong to category c.

The constructs that pertain to words and syntax are controlled by the setting of the syntax table (see section AD.6 The Syntax Table).

Here is a complicated regexp, stored in sentence-end and used by Emacs to recognize the end of a sentence together with any whitespace that follows. We show its Lisp syntax to distinguish the spaces from the tab characters. In Lisp syntax, the string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the regexp, `\\' for a backslash as part of the regexp, `\t' for a tab, and `\n' for a newline.

 
"[.?!][]\"')]*\\($\\| $\\|\t\\|  \\)[ \t\n]*"

This contains four parts in succession: a character set matching period, `?', or `!'; a character set matching close-brackets, quotes, or parentheses, repeated zero or more times; a set of alternatives within backslash-parentheses that matches either end-of-line, a space at the end of a line, a tab, or two spaces; and a character set matching whitespace characters, repeated any number of times.

To enter the same regexp interactively, you would type TAB to enter a tab, and C-j to enter a newline. (When typed interactively, C-j should be preceded by a C-q, to prevent Emacs from running the command bound to a newline.) You would also type single backslashes as themselves, instead of doubling them for Lisp syntax.


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K.6 Searching and Case

Incremental searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for `foo', then `Foo' and `foo' are also considered a match. Regexps, and in particular character sets, are included: `[ab]' would match `a' or `A' or `b' or `B'.

An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for `Foo' does not find `foo' or `FOO'. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string.

Typing M-c within an incremental search toggles the case sensitivity of that search. The effect does not extend beyond the current incremental search to the next one, but it does override the effect of including an upper-case letter in the current search.

If you set the variable case-fold-search to nil, then all letters must match exactly, including case. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. See section AD.2.4 Local Variables. This variable applies to nonincremental searches also, including those performed by the replace commands (see section K.7 Replacement Commands) and the minibuffer history matching commands (see section E.4 Minibuffer History).


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K.7 Replacement Commands

Global search-and-replace operations are not needed often in Emacs, but they are available. In addition to the simple M-x replace-string command which is like that found in most editors, there is a M-x query-replace command which finds each occurrence of the pattern and asks you whether to replace it.

The replace commands normally operate on the text from point to the end of the buffer; however, in Transient Mark mode, when the mark is active, they operate on the region. The replace commands all replace one string (or regexp) with one replacement string. It is possible to perform several replacements in parallel using the command expand-region-abbrevs (see section X.3 Controlling Abbrev Expansion).

K.7.1 Unconditional Replacement  Replacing all matches for a string.
K.7.2 Regexp Replacement  Replacing all matches for a regexp.
K.7.3 Replace Commands and Case  How replacements preserve case of letters.
K.7.4 Query Replace  How to use querying.


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K.7.1 Unconditional Replacement

M-x replace-string RET string RET newstring RET
Replace every occurrence of string with newstring.
M-x replace-regexp RET regexp RET newstring RET
Replace every match for regexp with newstring.

To replace every instance of `foo' after point with `bar', use the command M-x replace-string with the two arguments `foo' and `bar'. Replacement happens only in the text after point, so if you want to cover the whole buffer you must go to the beginning first. All occurrences up to the end of the buffer are replaced; to limit replacement to part of the buffer, narrow to that part of the buffer before doing the replacement (see section AC.22 Narrowing). In Transient Mark mode, when the region is active, replacement is limited to the region (see section H.2 Transient Mark Mode).

When replace-string exits, it leaves point at the last occurrence replaced. It sets the mark to the prior position of point (where the replace-string command was issued); use C-u C-SPC to move back there.

A numeric argument restricts replacement to matches that are surrounded by word boundaries. The argument's value doesn't matter.


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K.7.2 Regexp Replacement

The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.

In replace-regexp, the newstring need not be constant: it can refer to all or part of what is matched by the regexp. `\&' in newstring stands for the entire match being replaced. `\d' in newstring, where d is a digit, stands for whatever matched the dth parenthesized grouping in regexp. To include a `\' in the text to replace with, you must enter `\\'. For example,

 
M-x replace-regexp RET c[ad]+r RET \&-safe RET

replaces (for example) `cadr' with `cadr-safe' and `cddr' with `cddr-safe'.

 
M-x replace-regexp RET \(c[ad]+r\)-safe RET \1 RET

performs the inverse transformation.


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K.7.3 Replace Commands and Case

If the first argument of a replace command is all lower case, the command ignores case while searching for occurrences to replace--provided case-fold-search is non-nil. If case-fold-search is set to nil, case is always significant in all searches.

In addition, when the newstring argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command

 
M-x replace-string RET foo RET bar RET

replaces a lower case `foo' with a lower case `bar', an all-caps `FOO' with `BAR', and a capitalized `Foo' with `Bar'. (These three alternatives--lower case, all caps, and capitalized, are the only ones that replace-string can distinguish.)

If upper-case letters are used in the replacement string, they remain upper case every time that text is inserted. If upper-case letters are used in the first argument, the second argument is always substituted exactly as given, with no case conversion. Likewise, if either case-replace or case-fold-search is set to nil, replacement is done without case conversion.


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K.7.4 Query Replace

M-% string RET newstring RET
M-x query-replace RET string RET newstring RET
Replace some occurrences of string with newstring.
C-M-% regexp RET newstring RET
M-x query-replace-regexp RET regexp RET newstring RET
Replace some matches for regexp with newstring.

If you want to change only some of the occurrences of `foo' to `bar', not all of them, then you cannot use an ordinary replace-string. Instead, use M-% (query-replace). This command finds occurrences of `foo' one by one, displays each occurrence and asks you whether to replace it. Aside from querying, query-replace works just like replace-string. It preserves case, like replace-string, provided case-replace is non-nil, as it normally is. A numeric argument means consider only occurrences that are bounded by word-delimiter characters.

C-M-% performs regexp search and replace (query-replace-regexp).

The characters you can type when you are shown a match for the string or regexp are:

SPC
to replace the occurrence with newstring.

DEL
to skip to the next occurrence without replacing this one.

, (Comma)
to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, DEL and SPC are equivalent in this situation; both move to the next occurrence.

You can type C-r at this point (see below) to alter the replaced text. You can also type C-x u to undo the replacement; this exits the query-replace, so if you want to do further replacement you must use C-x ESC ESC RET to restart (see section E.5 Repeating Minibuffer Commands).

RET
to exit without doing any more replacements.

. (Period)
to replace this occurrence and then exit without searching for more occurrences.

!
to replace all remaining occurrences without asking again.

^
to go back to the position of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake. This works by popping the mark ring. Only one ^ in a row is meaningful, because only one previous replacement position is kept during query-replace.

C-r
to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with newstring. When you are done, exit the recursive editing level with C-M-c to proceed to the next occurrence. See section AC.26 Recursive Editing Levels.

C-w
to delete the occurrence, and then enter a recursive editing level as in C-r. Use the recursive edit to insert text to replace the deleted occurrence of string. When done, exit the recursive editing level with C-M-c to proceed to the next occurrence.

e
to edit the replacement string in the minibuffer. When you exit the minibuffer by typing RET, the minibuffer contents replace the current occurrence of the pattern. They also become the new replacement string for any further occurrences.

C-l
to redisplay the screen. Then you must type another character to specify what to do with this occurrence.

C-h
to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence.

Some other characters are aliases for the ones listed above: y, n and q are equivalent to SPC, DEL and RET.

Aside from this, any other character exits the query-replace, and is then reread as part of a key sequence. Thus, if you type C-k, it exits the query-replace and then kills to end of line.

To restart a query-replace once it is exited, use C-x ESC ESC, which repeats the query-replace because it used the minibuffer to read its arguments. See section C-x ESC ESC.

See also AB.9 Transforming File Names in Dired, for Dired commands to rename, copy, or link files by replacing regexp matches in file names.


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K.8 Other Search-and-Loop Commands

Here are some other commands that find matches for a regular expression. They all ignore case in matching, if the pattern contains no upper-case letters and case-fold-search is non-nil. Aside from occur, all operate on the text from point to the end of the buffer, or on the active region in Transient Mark mode.

M-x occur RET regexp RET
Display a list showing each line in the buffer that contains a match for regexp. To limit the search to part of the buffer, narrow to that part (see section AC.22 Narrowing). A numeric argument n specifies that n lines of context are to be displayed before and after each matching line.

The buffer `*Occur*' containing the output serves as a menu for finding the occurrences in their original context. Click Mouse-2 on an occurrence listed in `*Occur*', or position point there and type RET; this switches to the buffer that was searched and moves point to the original of the chosen occurrence.

M-x list-matching-lines
Synonym for M-x occur.

M-x how-many RET regexp RET
Print the number of matches for regexp that exist in the buffer after point. In Transient Mark mode, if the region is active, the command operates on the region instead.

M-x flush-lines RET regexp RET
Delete each line that contains a match for regexp, operating on the text after point. In Transient Mark mode, if the region is active, the command operates on the region instead.

M-x keep-lines RET regexp RET
Delete each line that does not contain a match for regexp, operating on the text after point. In Transient Mark mode, if the region is active, the command operates on the region instead.

You can also search multiple files under control of a tags table (see section W.2.6 Searching and Replacing with Tags Tables) or through Dired A command (see section AB.7 Operating on Files), or ask the grep program to do it (see section V.2 Searching with Grep under Emacs).


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L. Commands for Fixing Typos

In this chapter we describe the commands that are especially useful for the times when you catch a mistake in your text just after you have made it, or change your mind while composing text on the fly.

The most fundamental command for correcting erroneous editing is the undo command, C-x u or C-_. This command undoes a single command (usually), a part of a command (in the case of query-replace), or several consecutive self-inserting characters. Consecutive repetitions of C-_ or C-x u undo earlier and earlier changes, back to the limit of the undo information available. See section D.4 Undoing Changes, for more information.

L.1 Killing Your Mistakes  Commands to kill a batch of recently entered text.
L.2 Transposing Text  Exchanging two characters, words, lines, lists...
L.3 Case Conversion  Correcting case of last word entered.
L.4 Checking and Correcting Spelling  Apply spelling checker to a word, or a whole file.


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L.1 Killing Your Mistakes

DEL
Delete last character (delete-backward-char).
M-DEL
Kill last word (backward-kill-word).
C-x DEL
Kill to beginning of sentence (backward-kill-sentence).

The DEL character (delete-backward-char) is the most important correction command. It deletes the character before point. When DEL follows a self-inserting character command, you can think of it as canceling that command. However, avoid the mistake of thinking of DEL as a general way to cancel a command!

When your mistake is longer than a couple of characters, it might be more convenient to use M-DEL or C-x DEL. M-DEL kills back to the start of the last word, and C-x DEL kills back to the start of the last sentence. C-x DEL is particularly useful when you change your mind about the phrasing of the text you are writing. M-DEL and C-x DEL save the killed text for C-y and M-y to retrieve. See section H.8 Yanking.

M-DEL is often useful even when you have typed only a few characters wrong, if you know you are confused in your typing and aren't sure exactly what you typed. At such a time, you cannot correct with DEL except by looking at the screen to see what you did. Often it requires less thought to kill the whole word and start again.


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L.2 Transposing Text

C-t
Transpose two characters (transpose-chars).
M-t
Transpose two words (transpose-words).
C-M-t
Transpose two balanced expressions (transpose-sexps).
C-x C-t
Transpose two lines (transpose-lines).

The common error of transposing two characters can be fixed, when they are adjacent, with the C-t command (transpose-chars). Normally, C-t transposes the two characters on either side of point. When given at the end of a line, rather than transposing the last character of the line with the newline, which would be useless, C-t transposes the last two characters on the line. So, if you catch your transposition error right away, you can fix it with just a C-t. If you don't catch it so fast, you must move the cursor back between the two transposed characters before you type C-t. If you transposed a space with the last character of the word before it, the word motion commands are a good way of getting there. Otherwise, a reverse search (C-r) is often the best way. See section K. Searching and Replacement.

M-t transposes the word before point with the word after point (transpose-words). It moves point forward over a word, dragging the word preceding or containing point forward as well. The punctuation characters between the words do not move. For example, `FOO, BAR' transposes into `BAR, FOO' rather than `BAR FOO,'.

C-M-t (transpose-sexps) is a similar command for transposing two expressions (see section U.4.1 Expressions with Balanced Parentheses), and C-x C-t (transpose-lines) exchanges lines. They work like M-t except as regards what units of text they transpose.

A numeric argument to a transpose command serves as a repeat count: it tells the transpose command to move the character (word, expression, line) before or containing point across several other characters (words, expressions, lines). For example, C-u 3 C-t moves the character before point forward across three other characters. It would change `f-!-oobar' into `oobf-!-ar'. This is equivalent to repeating C-t three times. C-u - 4 M-t moves the word before point backward across four words. C-u - C-M-t would cancel the effect of plain C-M-t.

A numeric argument of zero is assigned a special meaning (because otherwise a command with a repeat count of zero would do nothing): to transpose the character (word, expression, line) ending after point with the one ending after the mark.


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L.3 Case Conversion

M-- M-l
Convert last word to lower case. Note Meta-- is Meta-minus.
M-- M-u
Convert last word to all upper case.
M-- M-c
Convert last word to lower case with capital initial.

A very common error is to type words in the wrong case. Because of this, the word case-conversion commands M-l, M-u and M-c have a special feature when used with a negative argument: they do not move the cursor. As soon as you see you have mistyped the last word, you can simply case-convert it and go on typing. See section T.6 Case Conversion Commands.


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L.4 Checking and Correcting Spelling

This section describes the commands to check the spelling of a single word or of a portion of a buffer. These commands work with the spelling checker program Ispell, which is not part of Emacs. See section `Overview ispell' in The Ispell Manual.

M-x flyspell-mode
Enable Flyspell mode, which highlights all misspelled words.
M-$
Check and correct spelling of the word at point (ispell-word).
M-TAB
Complete the word before point based on the spelling dictionary (ispell-complete-word).
M-x ispell
Spell-check the active region or the current buffer.
M-x ispell-buffer
Check and correct spelling of each word in the buffer.
M-x ispell-region
Check and correct spelling of each word in the region.
M-x ispell-message
Check and correct spelling of each word in a draft mail message, excluding cited material.
M-x ispell-change-dictionary RET dict RET
Restart the Ispell process, using dict as the dictionary.
M-x ispell-kill-ispell
Kill the Ispell subprocess.

Flyspell mode is a fully-automatic way to check spelling as you edit in Emacs. It operates by checking words as you change or insert them. When it finds a word that it does not recognize, it highlights that word. This does not interfere with your editing, but when you see the highlighted word, you can move to it and fix it. Type M-x flyspell-mode to enable or disable this mode in the current buffer.

When Flyspell mode highlights a word as misspelled, you can click on it with Mouse-2 to display a menu of possible corrections and actions. You can also correct the word by editing it manually in any way you like.

The other Emacs spell-checking features check or look up words when you give an explicit command to do so. Checking all or part of the buffer is useful when you have text that was written outside of this Emacs session and might contain any number of misspellings.

To check the spelling of the word around or next to point, and optionally correct it as well, use the command M-$ (ispell-word). If the word is not correct, the command offers you various alternatives for what to do about it.

To check the entire current buffer, use M-x ispell-buffer. Use M-x ispell-region to check just the current region. To check spelling in an email message you are writing, use M-x ispell-message; that command checks the whole buffer, except for material that is indented or appears to be cited from other messages.

The M-x ispell command spell-checks the active region if the Transient Mark mode is on (see section H.2 Transient Mark Mode), otherwise it spell-checks the current buffer.

Each time these commands encounter an incorrect word, they ask you what to do. They display a list of alternatives, usually including several "near-misses"---words that are close to the word being checked. Then you must type a single-character response. Here are the valid responses:

SPC
Skip this word--continue to consider it incorrect, but don't change it here.

r new RET
Replace the word (just this time) with new.

R new RET
Replace the word with new, and do a query-replace so you can replace it elsewhere in the buffer if you wish.

digit
Replace the word (just this time) with one of the displayed near-misses. Each near-miss is listed with a digit; type that digit to select it.

a
Accept the incorrect word--treat it as correct, but only in this editing session.

A
Accept the incorrect word--treat it as correct, but only in this editing session and for this buffer.

i
Insert this word in your private dictionary file so that Ispell will consider it correct from now on, even in future sessions.

u
Insert the lower-case version of this word in your private dictionary file.

m
Like i, but you can also specify dictionary completion information.

l word RET
Look in the dictionary for words that match word. These words become the new list of "near-misses"; you can select one of them as the replacement by typing a digit. You can use `*' in word as a wildcard.

C-g
Quit interactive spell checking. You can restart it again afterward with C-u M-$.

X
Same as C-g.

x
Quit interactive spell checking and move point back to where it was when you started spell checking.

q
Quit interactive spell checking and kill the Ispell subprocess.

C-l
Refresh the screen.

C-z
This key has its normal command meaning (suspend Emacs or iconify this frame).

The command ispell-complete-word, which is bound to the key M-TAB in Text mode and related modes, shows a list of completions based on spelling correction. Insert the beginning of a word, and then type M-TAB; the command displays a completion list window. To choose one of the completions listed, click Mouse-2 on it, or move the cursor there in the completions window and type RET. See section T.7 Text Mode.

Once started, the Ispell subprocess continues to run (waiting for something to do), so that subsequent spell checking commands complete more quickly. If you want to get rid of the Ispell process, use M-x ispell-kill-ispell. This is not usually necessary, since the process uses no time except when you do spelling correction.

Ispell uses two dictionaries: the standard dictionary and your private dictionary. The variable ispell-dictionary specifies the file name of the standard dictionary to use. A value of nil says to use the default dictionary. The command M-x ispell-change-dictionary sets this variable and then restarts the Ispell subprocess, so that it will use a different dictionary.


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M. File Handling

The operating system stores data permanently in named files, so most of the text you edit with Emacs comes from a file and is ultimately stored in a file.

To edit a file, you must tell Emacs to read the file and prepare a buffer containing a copy of the file's text. This is called visiting the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you save the buffer back into the file.

In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, keep multiple versions of them, and operate on file directories.

M.1 File Names  How to type and edit file-name arguments.
M.2 Visiting Files  Visiting a file prepares Emacs to edit the file.
M.3 Saving Files  Saving makes your changes permanent.
M.4 Reverting a Buffer  Reverting cancels all the changes not saved.
M.5 Auto-Saving: Protection Against Disasters  Auto Save periodically protects against loss of data.
M.6 File Name Aliases  Handling multiple names for one file.
M.7 Version Control  Version control systems (RCS, CVS and SCCS).
M.8 File Directories  Creating, deleting, and listing file directories.
M.9 Comparing Files  Finding where two files differ.
M.10 Miscellaneous File Operations  Other things you can do on files.
M.11 Accessing Compressed Files  Accessing compressed files.
M.12 File Archives  Operating on tar, zip, jar etc. archive files.
M.13 Remote Files  Accessing files on other sites.
M.14 Quoted File Names  Quoting special characters in file names.
M.15 File Name Cache  Completion against a list of files you often use.
M.16 Convenience Features for Finding Files  


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M.1 File Names

Most Emacs commands that operate on a file require you to specify the file name. (Saving and reverting are exceptions; the buffer knows which file name to use for them.) You enter the file name using the minibuffer (see section E. The Minibuffer). Completion is available (see section E.3 Completion) to make it easier to specify long file names. When completing file names, Emacs ignores those whose file-name extensions appear in the variable completion-ignored-extensions; see E.3.4 Completion Options.

For most operations, there is a default file name which is used if you type just RET to enter an empty argument. Normally the default file name is the name of the file visited in the current buffer; this makes it easy to operate on that file with any of the Emacs file commands.

Each buffer has a default directory which is normally the same as the directory of the file visited in that buffer. When you enter a file name without a directory, the default directory is used. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory. The default directory is kept in the variable default-directory, which has a separate value in every buffer.

For example, if the default file name is `/u/rms/gnu/gnu.tasks' then the default directory is `/u/rms/gnu/'. If you type just `foo', which does not specify a directory, it is short for `/u/rms/gnu/foo'. `../.login' would stand for `/u/rms/.login'. `new/foo' would stand for the file name `/u/rms/gnu/new/foo'.

The command M-x pwd displays the current buffer's default directory, and the command M-x cd sets it (to a value read using the minibuffer). A buffer's default directory changes only when the cd command is used. A file-visiting buffer's default directory is initialized to the directory of the file that is visited in that buffer. If you create a buffer with C-x b, its default directory is copied from that of the buffer that was current at the time.

The default directory actually appears in the minibuffer when the minibuffer becomes active to read a file name. This serves two purposes: it shows you what the default is, so that you can type a relative file name and know with certainty what it will mean, and it allows you to edit the default to specify a different directory. This insertion of the default directory is inhibited if the variable insert-default-directory is set to nil.

Note that it is legitimate to type an absolute file name after you enter the minibuffer, ignoring the presence of the default directory name as part of the text. The final minibuffer contents may look invalid, but that is not so. For example, if the minibuffer starts out with `/usr/tmp/' and you add `/x1/rms/foo', you get `/usr/tmp//x1/rms/foo'; but Emacs ignores everything through the first slash in the double slash; the result is `/x1/rms/foo'. See section E.1 Minibuffers for File Names.

`$' in a file name is used to substitute environment variables. For example, if you have used the shell command export FOO=rms/hacks to set up an environment variable named FOO, then you can use `/u/$FOO/test.c' or `/u/${FOO}/test.c' as an abbreviation for `/u/rms/hacks/test.c'. The environment variable name consists of all the alphanumeric characters after the `$'; alternatively, it may be enclosed in braces after the `$'. Note that shell commands to set environment variables affect Emacs only if done before Emacs is started.

You can use the `~/' in a file name to mean your home directory, or `~user-id/' to mean the home directory of a user whose login name is user-id. (On DOS and Windows systems, where a user doesn't have a home directory, Emacs substitutes `~/' with the value of the environment variable HOME; see AE.5.1 General Variables.)

To access a file with `$' in its name, type `$$'. This pair is converted to a single `$' at the same time as variable substitution is performed for a single `$'. Alternatively, quote the whole file name with `/:' (see section M.14 Quoted File Names). File names which begin with a literal `~' should also be quoted with `/:'.

The Lisp function that performs the substitution is called substitute-in-file-name. The substitution is performed only on file names read as such using the minibuffer.

You can include non-ASCII characters in file names if you set the variable file-name-coding-system to a non-nil value. See section Q.9 Specifying a Coding System.


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M.2 Visiting Files

C-x C-f
Visit a file (find-file).
C-x C-r
Visit a file for viewing, without allowing changes to it (find-file-read-only).
C-x C-v
Visit a different file instead of the one visited last (find-alternate-file).
C-x 4 f
Visit a file, in another window (find-file-other-window). Don't alter what is displayed in the selected window.
C-x 5 f
Visit a file, in a new frame (find-file-other-frame). Don't alter what is displayed in the selected frame.
M-x find-file-literally
Visit a file with no conversion of the contents.

Visiting a file means copying its contents into an Emacs buffer so you can edit them. Emacs makes a new buffer for each file that you visit. We often say that this buffer "is visiting" that file, or that the buffer's "visited file" is that file. Emacs constructs the buffer name from the file name by throwing away the directory, keeping just the name proper. For example, a file named `/usr/rms/emacs.tex' would get a buffer named `emacs.tex'. If there is already a buffer with that name, Emacs constructs a unique name--the normal method is to append `<2>', `<3>', and so on, but you can select other methods (see section N.7.1 Making Buffer Names Unique).

Each window's mode line shows the name of the buffer that is being displayed in that window, so you can always tell what buffer you are editing.

The changes you make with editing commands are made in the Emacs buffer. They do not take effect in the file that you visited, or any place permanent, until you save the buffer. Saving the buffer means that Emacs writes the current contents of the buffer into its visited file. See section M.3 Saving Files.

If a buffer contains changes that have not been saved, we say the buffer is modified. This is important because it implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin to indicate that the buffer is modified.

To visit a file, use the command C-x C-f (find-file). Follow the command with the name of the file you wish to visit, terminated by a RET.

The file name is read using the minibuffer (see section E. The Minibuffer), with defaulting and completion in the standard manner (see section M.1 File Names). While in the minibuffer, you can abort C-x C-f by typing C-g. File-name completion ignores certain filenames; for more about this, see E.3.4 Completion Options.

When Emacs is built with a suitable GUI toolkit, it pops up the standard File Selection dialog of that toolkit instead of prompting for the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs does that when built with LessTif and Motif toolkits; on MS-Windows, the GUI version does that by default.

Your confirmation that C-x C-f has completed successfully is the appearance of new text on the screen and a new buffer name in the mode line. If the specified file does not exist and could not be created, or cannot be read, then you get an error, with an error message displayed in the echo area.

If you visit a file that is already in Emacs, C-x C-f does not make another copy. It selects the existing buffer containing that file. However, before doing so, it checks that the file itself has not changed since you visited or saved it last. If the file has changed, a warning message is shown. See section Simultaneous Editing.

Since Emacs reads the visited file in its entirety, files whose size is larger than the maximum Emacs buffer size (see section N. Using Multiple Buffers) cannot be visited; if you try, Emacs will display an error message saying that the maximum buffer size has been exceeded.

What if you want to create a new file? Just visit it. Emacs displays `(New file)' in the echo area, but in other respects behaves as if you had visited an existing empty file. If you make any changes and save them, the file is created.

Emacs recognizes from the contents of a file which convention it uses to separate lines--newline (used on GNU/Linux and on Unix), carriage-return linefeed (used on Microsoft systems), or just carriage-return (used on the Macintosh)---and automatically converts the contents to the normal Emacs convention, which is that the newline character separates lines. This is a part of the general feature of coding system conversion (see section Q.7 Coding Systems), and makes it possible to edit files imported from different operating systems with equal convenience. If you change the text and save the file, Emacs performs the inverse conversion, changing newlines back into carriage-return linefeed or just carriage-return if appropriate.

If the file you specify is actually a directory, C-x C-f invokes Dired, the Emacs directory browser, so that you can "edit" the contents of the directory (see section AB. Dired, the Directory Editor). Dired is a convenient way to delete, look at, or operate on the files in the directory. However, if the variable find-file-run-dired is nil, then it is an error to try to visit a directory.

Files which are actually collections of other files, or file archives, are visited in special modes which invoke a Dired-like environment to allow operations on archive members. See section M.12 File Archives, for more about these features.

If the file name you specify contains shell-style wildcard characters, Emacs visits all the files that match it. Wildcards include `?', `*', and `[...]' sequences. See section M.14 Quoted File Names, for information on how to visit a file whose name actually contains wildcard characters. You can disable the wildcard feature by customizing find-file-wildcards.

If you visit a file that the operating system won't let you modify, Emacs makes the buffer read-only, so that you won't go ahead and make changes that you'll have trouble saving afterward. You can make the buffer writable with C-x C-q (vc-toggle-read-only). See section N.3 Miscellaneous Buffer Operations.

Occasionally you might want to visit a file as read-only in order to protect yourself from entering changes accidentally; do so by visiting the file with the command C-x C-r (find-file-read-only).

If you visit a nonexistent file unintentionally (because you typed the wrong file name), use the C-x C-v command (find-alternate-file) to visit the file you really wanted. C-x C-v is similar to C-x C-f, but it kills the current buffer (after first offering to save it if it is modified). When C-x C-v reads the file name to visit, it inserts the entire default file name in the buffer, with point just after the directory part; this is convenient if you made a slight error in typing the name.

If you find a file which exists but cannot be read, C-x C-f signals an error.

C-x 4 f (find-file-other-window) is like C-x C-f except that the buffer containing the specified file is selected in another window. The window that was selected before C-x 4 f continues to show the same buffer it was already showing. If this command is used when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. See section O. Multiple Windows.

C-x 5 f (find-file-other-frame) is similar, but opens a new frame, or makes visible any existing frame showing the file you seek. This feature is available only when you are using a window system. See section P. Frames and X Windows.

If you wish to edit a file as a sequence of ASCII characters with no special encoding or conversion, use the M-x find-file-literally command. It visits a file, like C-x C-f, but does not do format conversion (see section T.11 Editing Formatted Text), character code conversion (see section Q.7 Coding Systems), or automatic uncompression (see section M.11 Accessing Compressed Files), and does not add a final newline because of require-final-newline. If you already have visited the same file in the usual (non-literal) manner, this command asks you whether to visit it literally instead.

Two special hook variables allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in the list find-file-not-found-hooks; this variable holds a list of functions, and the functions are called one by one (with no arguments) until one of them returns non-nil. This is not a normal hook, and the name ends in `-hooks' rather than `-hook' to indicate that fact.

Successful visiting of any file, whether existing or not, calls the functions in the list find-file-hooks, with no arguments. This variable is really a normal hook, but it has an abnormal name for historical compatibility. In the case of a nonexistent file, the find-file-not-found-hooks are run first. See section AD.2.3 Hooks.

There are several ways to specify automatically the major mode for editing the file (see section R.1 How Major Modes are Chosen), and to specify local variables defined for that file (see section AD.2.5 Local Variables in Files).


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M.3 Saving Files

Saving a buffer in Emacs means writing its contents back into the file that was visited in the buffer.

C-x C-s
Save the current buffer in its visited file on disk (save-buffer).
C-x s
Save any or all buffers in their visited files (save-some-buffers).
M-~
Forget that the current buffer has been changed (not-modified). With prefix argument (C-u), mark the current buffer as changed.
C-x C-w
Save the current buffer as a specified file name (write-file).
M-x set-visited-file-name
Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type C-x C-s (save-buffer). After saving is finished, C-x C-s displays a message like this:

 
Wrote /u/rms/gnu/gnu.tasks

If the selected buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, C-x C-s displays a message like this in the echo area:

 
(No changes need to be saved)

The command C-x s (save-some-buffers) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of query-replace:

y
Save this buffer and ask about the rest of the buffers.
n
Don't save this buffer, but ask about the rest of the buffers.
!
Save this buffer and all the rest with no more questions.
RET
Terminate save-some-buffers without any more saving.
.
Save this buffer, then exit save-some-buffers without even asking about other buffers.
C-r
View the buffer that you are currently being asked about. When you exit View mode, you get back to save-some-buffers, which asks the question again.
C-h
Display a help message about these options.

C-x C-c, the key sequence to exit Emacs, invokes save-some-buffers and therefore asks the same questions.

If you have changed a buffer but you do not want to save the changes, you should take some action to prevent it. Otherwise, each time you use C-x s or C-x C-c, you are liable to save this buffer by mistake. One thing you can do is type M-~ (not-modified), which clears out the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. (`~' is often used as a mathematical symbol for `not'; thus M-~ is `not', metafied.) You could also use set-visited-file-name (see below) to mark the buffer as visiting a different file name, one which is not in use for anything important. Alternatively, you can cancel all the changes made since the file was visited or saved, by reading the text from the file again. This is called reverting. See section M.4 Reverting a Buffer. You could also undo all the changes by repeating the undo command C-x u until you have undone all the changes; but reverting is easier.

M-x set-visited-file-name alters the name of the file that the current buffer is visiting. It reads the new file name using the minibuffer. Then it marks the buffer as visiting that file name, and changes the buffer name correspondingly. set-visited-file-name does not save the buffer in the newly visited file; it just alters the records inside Emacs in case you do save later. It also marks the buffer as "modified" so that C-x C-s in that buffer will save.

If you wish to mark the buffer as visiting a different file and save it right away, use C-x C-w (write-file). It is precisely equivalent to set-visited-file-name followed by C-x C-s. C-x C-s used on a buffer that is not visiting a file has the same effect as C-x C-w; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory (see section M.1 File Names).

If the new file name implies a major mode, then C-x C-w switches to that major mode, in most cases. The command set-visited-file-name also does this. See section R.1 How Major Modes are Chosen.

If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention. See section Simultaneous Editing.

If the value of the variable require-final-newline is t, Emacs silently puts a newline at the end of any file that doesn't already end in one, every time a file is saved or written. If the value is nil, Emacs leaves the end of the file unchanged; if it's neither nil nor t, Emacs asks you whether to add a newline. The default is nil.

M.3.1 Backup Files  How Emacs saves the old version of your file.
M.3.2 Protection against Simultaneous Editing  How Emacs protects against simultaneous editing of one file by two users.
M.3.3 Shadowing Files  Copying files to "shadows" automatically.
M.3.4 Updating Time Stamps Automatically  Emacs can update time stamps on saved files.


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M.3.1 Backup Files

On most operating systems, rewriting a file automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file--or it would, except that Emacs carefully copies the old contents to another file, called the backup file, before actually saving.

For most files, the variable make-backup-files determines whether to make backup files. On most operating systems, its default value is t, so that Emacs does write backup files.

For files managed by a version control system (see section M.7 Version Control), the variable vc-make-backup-files determines whether to make backup files. By default it is nil, since backup files are redundant when you store all the previous versions in a version control system. See section M.7.10.1 General Options.

The default value of the backup-enable-predicate variable prevents backup files being written for files in the directories used for temporary files, specified by temporary-file-directory or small-temporary-file-directory.

At your option, Emacs can keep either a single backup file or a series of numbered backup files for each file that you edit.

Emacs makes a backup for a file only the first time the file is saved from one buffer. No matter how many times you save a file, its backup file continues to contain the contents from before the file was visited. Normally this means that the backup file contains the contents from before the current editing session; however, if you kill the buffer and then visit the file again, a new backup file will be made by the next save.

You can also explicitly request making another backup file from a buffer even though it has already been saved at least once. If you save the buffer with C-u C-x C-s, the version thus saved will be made into a backup file if you save the buffer again. C-u C-u C-x C-s saves the buffer, but first makes the previous file contents into a new backup file. C-u C-u C-u C-x C-s does both things: it makes a backup from the previous contents, and arranges to make another from the newly saved contents if you save again.

M.3.1.1 Single or Numbered Backups  How backup files are named; choosing single or numbered backup files.
M.3.1.2 Automatic Deletion of Backups  Emacs deletes excess numbered backups.
M.3.1.3 Copying vs. Renaming  Backups can be made by copying or renaming.


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M.3.1.1 Single or Numbered Backups

If you choose to have a single backup file (this is the default), the backup file's name is normally constructed by appending `~' to the file name being edited; thus, the backup file for `eval.c' would be `eval.c~'.

You can change this behavior by defining the variable make-backup-file-name-function to a suitable function. Alternatively you can customize the variable backup-directory-alist to specify that files matching certain patterns should be backed up in specific directories.

A typical use is to add an element ("." . dir) to make all backups in the directory with absolute name dir; Emacs modifies the backup file names to avoid clashes between files with the same names originating in different directories. Alternatively, adding, say, ("." . ".~") would make backups in the invisible subdirectory `.~' of the original file's directory. Emacs creates the directory, if necessary, to make the backup.

If access control stops Emacs from writing backup files under the usual names, it writes the backup file as `%backup%~' in your home directory. Only one such file can exist, so only the most recently made such backup is available.

If you choose to have a series of numbered backup files, backup file names contain `.~', the number, and another `~' after the original file name. Thus, the backup files of `eval.c' would be called `eval.c.~1~', `eval.c.~2~', and so on, all the way through names like `eval.c.~259~' and beyond. The variable backup-directory-alist applies to numbered backups just as usual.

The choice of single backup or numbered backups is controlled by the variable version-control. Its possible values are

t
Make numbered backups.
nil
Make numbered backups for files that have numbered backups already. Otherwise, make single backups.
never
Never make numbered backups; always make single backups.

You can set version-control locally in an individual buffer to control the making of backups for that buffer's file. For example, Rmail mode locally sets version-control to never to make sure that there is only one backup for an Rmail file. See section AD.2.4 Local Variables.

If you set the environment variable VERSION_CONTROL, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable version-control accordingly at startup. If the environment variable's value is `t' or `numbered', then version-control becomes t; if the value is `nil' or `existing', then version-control becomes nil; if it is `never' or `simple', then version-control becomes never.


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M.3.1.2 Automatic Deletion of Backups

To prevent excessive consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made.

The two variables kept-old-versions and kept-new-versions control this deletion. Their values are, respectively, the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The backups in the middle (excluding those oldest and newest) are the excess middle versions--those backups are deleted. These variables' values are used when it is time to delete excess versions, just after a new backup version is made; the newly made backup is included in the count in kept-new-versions. By default, both variables are 2.

If delete-old-versions is non-nil, Emacs deletes the excess backup files silently. If it is nil, the default, Emacs asks you whether it should delete the excess backup versions.

Dired's . (Period) command can also be used to delete old versions. See section AB.3 Deleting Files with Dired.


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M.3.1.3 Copying vs. Renaming

Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names (hard links). If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents.

The method of making a backup file may also affect the file's owner and group. If copying is used, these do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group).

Having the owner change is usually a good idea, because then the owner always shows who last edited the file. Also, the owners of the backups show who produced those versions. Occasionally there is a file whose owner should not change; it is a good idea for such files to contain local variable lists to set backup-by-copying-when-mismatch locally (see section AD.2.5 Local Variables in Files).

The choice of renaming or copying is controlled by four variables. Renaming is the default choice. If the variable backup-by-copying is non-nil, copying is used. Otherwise, if the variable backup-by-copying-when-linked is non-nil, then copying is used for files that have multiple names, but renaming may still be used when the file being edited has only one name. If the variable backup-by-copying-when-mismatch is non-nil, then copying is used if renaming would cause the file's owner or group to change. backup-by-copying-when-mismatch is t by default if you start Emacs as the superuser. The fourth variable, backup-by-copying-when-privileged-mismatch, gives the highest numeric user-id for which backup-by-copying-when-mismatch will be forced on. This is useful when low-numbered user-ids are assigned to special system users, such as root, bin, daemon, etc., which must maintain ownership of files.

When a file is managed with a version control system (see section M.7 Version Control), Emacs does not normally make backups in the usual way for that file. But check-in and check-out are similar in some ways to making backups. One unfortunate similarity is that these operations typically break hard links, disconnecting the file name you visited from any alternate names for the same file. This has nothing to do with Emacs--the version control system does it.


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M.3.2 Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody were informed that this was happening, whichever user saved first would later find that his changes were lost.

On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. On all systems, Emacs checks when you save the file, and warns if you are about to overwrite another user's changes. You can prevent loss of the other user's work by taking the proper corrective action instead of saving the file.

When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that the file is locked by you. (It does this by creating a symbolic link in the same directory with a different name.) Emacs removes the lock when you save the changes. The idea is that the file is locked whenever an Emacs buffer visiting it has unsaved changes.

If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a collision. When Emacs detects a collision, it asks you what to do, by calling the Lisp function ask-user-about-lock. You can redefine this function for the sake of customization. The standard definition of this function asks you a question and accepts three possible answers:

s
Steal the lock. Whoever was already changing the file loses the lock, and you gain the lock.
p
Proceed. Go ahead and edit the file despite its being locked by someone else.
q
Quit. This causes an error (file-locked), and the buffer contents remain unchanged--the modification you were trying to make does not actually take place.

Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not realize that the two names are the same file and cannot prevent two users from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that will not really exist until they are saved.

Some systems are not configured to allow Emacs to make locks, and there are cases where lock files cannot be written. In these cases, Emacs cannot detect trouble in advance, but it still can detect the collision when you try to save a file and overwrite someone else's changes.

If Emacs or the operating system crashes, this may leave behind lock files which are stale, so you may occasionally get warnings about spurious collisions. When you determine that the collision is spurious, just use p to tell Emacs to go ahead anyway.

Every time Emacs saves a buffer, it first checks the last-modification date of the existing file on disk to verify that it has not changed since the file was last visited or saved. If the date does not match, it implies that changes were made in the file in some other way, and these changes are about to be lost if Emacs actually does save. To prevent this, Emacs displays a warning message and asks for confirmation before saving. Occasionally you will know why the file was changed and know that it does not matter; then you can answer yes and proceed. Otherwise, you should cancel the save with C-g and investigate the situation.

The first thing you should do when notified that simultaneous editing has already taken place is to list the directory with C-u C-x C-d (see section M.8 File Directories). This shows the file's current author. You should attempt to contact him to warn him not to continue editing. Often the next step is to save the contents of your Emacs buffer under a different name, and use diff to compare the two files.


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M.3.3 Shadowing Files

M-x shadow-initialize
Set up file shadowing.
M-x shadow-define-literal-group
Declare a single file to be shared between sites.
M-x shadow-define-regexp-group
Make all files that match each of a group of files be shared between hosts.
M-x shadow-define-cluster RET name RET
Define a shadow file cluster name.
M-x shadow-copy-files
Copy all pending shadow files.
M-x shadow-cancel
Cancel the instruction to shadow some files.

You can arrange to keep identical shadow copies of certain files in more than one place--possibly on different machines. To do this, first you must set up a shadow file group, which is a set of identically-named files shared between a list of sites. The file group is permanent and applies to further Emacs sessions as well as the current one. Once the group is set up, every time you exit Emacs, it will copy the file you edited to the other files in its group. You can also do the copying without exiting Emacs, by typing M-x shadow-copy-files.

To set up a shadow file group, use M-x shadow-define-literal-group or M-x shadow-define-regexp-group. See their documentation strings for further information.

Before copying a file to its shadows, Emacs asks for confirmation. You can answer "no" to bypass copying of this file, this time. If you want to cancel the shadowing permanently for a certain file, use M-x shadow-cancel to eliminate or change the shadow file group.

A shadow cluster is a group of hosts that share directories, so that copying to or from one of them is sufficient to update the file on all of them. Each shadow cluster has a name, and specifies the network address of a primary host (the one we copy files to), and a regular expression that matches the host names of all the other hosts in the cluster. You can define a shadow cluster with M-x shadow-define-cluster.


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M.3.4 Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it will be updated automatically each time you edit and save the file. The time stamp has to be in the first eight lines of the file, and you should insert it like this:

 
Time-stamp: <>

or like this:

 
Time-stamp: ""

Then add the hook function time-stamp to the hook write-file-hooks; that hook function will automatically update the time stamp, inserting the current date and time when you save the file. You can also use the command M-x time-stamp to update the time stamp manually. For other customizations, see the Custom group time-stamp. Note that non-numeric fields in the time stamp are formatted according to your locale setting (see section AE.5 Environment Variables).


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M.4 Reverting a Buffer

If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file. To do this, use M-x revert-buffer, which operates on the current buffer. Since reverting a buffer unintentionally could lose a lot of work, you must confirm this command with yes.

revert-buffer keeps point at the same distance (measured in characters) from the beginning of the file. If the file was edited only slightly, you will be at approximately the same piece of text after reverting as before. If you have made drastic changes, the same value of point in the old file may address a totally different piece of text.

Reverting marks the buffer as "not modified" until another change is made.

Some kinds of buffers whose contents reflect data bases other than files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents from the appropriate data base. Buffers created explicitly with C-x b cannot be reverted; revert-buffer reports an error when asked to do so.

When you edit a file that changes automatically and frequently--for example, a log of output from a process that continues to run--it may be useful for Emacs to revert the file without querying you, whenever you visit the file again with C-x C-f.

To request this behavior, set the variable revert-without-query to a list of regular expressions. When a file name matches one of these regular expressions, find-file and revert-buffer will revert it automatically if it has changed--provided the buffer itself is not modified. (If you have edited the text, it would be wrong to discard your changes.)

You may find it useful to have Emacs revert files automatically when they change. Two minor modes are available to do this. In Global Auto-Revert mode, Emacs periodically checks all file buffers and reverts any when the corresponding file has changed. The local variant, Auto-Revert mode, applies only to buffers in which it was activated. Checking the files is done at intervals determined by the variable auto-revert-interval.


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M.5 Auto-Saving: Protection Against Disasters

Emacs saves all the visited files from time to time (based on counting your keystrokes) without being asked. This is called auto-saving. It prevents you from losing more than a limited amount of work if the system crashes.

When Emacs determines that it is time for auto-saving, each buffer is considered, and is auto-saved if auto-saving is turned on for it and it has been changed since the last time it was auto-saved. The message `Auto-saving...' is displayed in the echo area during auto-saving, if any files are actually auto-saved. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing.

M.5.1 Auto-Save Files  The file where auto-saved changes are actually made until you save the file.
M.5.2 Controlling Auto-Saving  Controlling when and how often to auto-save.
M.5.3 Recovering Data from Auto-Saves  Recovering text from auto-save files.


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M.5.1 Auto-Save Files

Auto-saving does not normally save in the files that you visited, because it can be very undesirable to save a program that is in an inconsistent state when you have made half of a planned change. Instead, auto-saving is done in a different file called the auto-save file, and the visited file is changed only when you request saving explicitly (such as with C-x C-s).

Normally, the auto-save file name is made by appending `#' to the front and rear of the visited file name. Thus, a buffer visiting file `foo.c' is auto-saved in a file `#foo.c#'. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is made by appending `#%' to the front and `#' to the rear of buffer name. For example, the `*mail*' buffer in which you compose messages to be sent is auto-saved in a file named `#%*mail*#'. Auto-save file names are made this way unless you reprogram parts of Emacs to do something different (the functions make-auto-save-file-name and auto-save-file-name-p). The file name to be used for auto-saving in a buffer is calculated when auto-saving is turned on in that buffer.

When you delete a substantial part of the text in a large buffer, auto save turns off temporarily in that buffer. This is because if you deleted the text unintentionally, you might find the auto-save file more useful if it contains the deleted text. To reenable auto-saving after this happens, save the buffer with C-x C-s, or use C-u 1 M-x auto-save.

If you want auto-saving to be done in the visited file rather than in a separate auto-save file, set the variable auto-save-visited-file-name to a non-nil value. In this mode, there is no real difference between auto-saving and explicit saving.

A buffer's auto-save file is deleted when you save the buffer in its visited file. To inhibit this, set the variable delete-auto-save-files to nil. Changing the visited file name with C-x C-w or set-visited-file-name renames any auto-save file to go with the new visited name.


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M.5.2 Controlling Auto-Saving

Each time you visit a file, auto-saving is turned on for that file's buffer if the variable auto-save-default is non-nil (but not in batch mode; see section C. Entering and Exiting Emacs). The default for this variable is t, so auto-saving is the usual practice for file-visiting buffers. Auto-saving can be turned on or off for any existing buffer with the command M-x auto-save-mode. Like other minor mode commands, M-x auto-save-mode turns auto-saving on with a positive argument, off with a zero or negative argument; with no argument, it toggles.

Emacs does auto-saving periodically based on counting how many characters you have typed since the last time auto-saving was done. The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300.

Auto-saving also takes place when you stop typing for a while. The variable auto-save-timeout says how many seconds Emacs should wait before it does an auto save (and perhaps also a garbage collection). (The actual time period is longer if the current buffer is long; this is a heuristic which aims to keep out of your way when you are editing long buffers, in which auto-save takes an appreciable amount of time.) Auto-saving during idle periods accomplishes two things: first, it makes sure all your work is saved if you go away from the terminal for a while; second, it may avoid some auto-saving while you are actually typing.

Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as `kill %emacs', or disconnecting a phone line or network connection.

You can request an auto-save explicitly with the command M-x do-auto-save.


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M.5.3 Recovering Data from Auto-Saves

You can use the contents of an auto-save file to recover from a loss of data with the command M-x recover-file RET file RET. This visits file and then (after your confirmation) restores the contents from its auto-save file `#file#'. You can then save with C-x C-s to put the recovered text into file itself. For example, to recover file `foo.c' from its auto-save file `#foo.c#', do:

 
M-x recover-file RET foo.c RET
yes RET
C-x C-s

Before asking for confirmation, M-x recover-file displays a directory listing describing the specified file and the auto-save file, so you can compare their sizes and dates. If the auto-save file is older, M-x recover-file does not offer to read it.

If Emacs or the computer crashes, you can recover all the files you were editing from their auto save files with the command M-x recover-session. This first shows you a list of recorded interrupted sessions. Move point to the one you choose, and type C-c C-c.

Then recover-session asks about each of the files that were being edited during that session, asking whether to recover that file. If you answer y, it calls recover-file, which works in its normal fashion. It shows the dates of the original file and its auto-save file, and asks once again whether to recover that file.

When recover-session is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this--saving them--updates the files themselves.

Emacs records interrupted sessions for later recovery in files named `~/.emacs.d/auto-save-list/.saves-pid-hostname'. The `~/.emacs.d/auto-save-list/.saves-' portion of these names comes from the value of auto-save-list-file-prefix. You can record sessions in a different place by customizing that variable. If you set auto-save-list-file-prefix to nil in your `.emacs' file, sessions are not recorded for recovery.


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M.6 File Name Aliases

Symbolic links and hard links both make it possible for several file names to refer to the same file. Hard links are alternate names that refer directly to the file; all the names are equally valid, and no one of them is preferred. By contrast, a symbolic link is a kind of defined alias: when `foo' is a symbolic link to `bar', you can use either name to refer to the file, but `bar' is the real name, while `foo' is just an alias. More complex cases occur when symbolic links point to directories.

If you visit two names for the same file, normally Emacs makes two different buffers, but it warns you about the situation.

Normally, if you visit a file which Emacs is already visiting under a different name, Emacs displays a message in the echo area and uses the existing buffer visiting that file. This can happen on systems that support symbolic links, or if you use a long file name on a system that truncates long file names. You can suppress the message by setting the variable find-file-suppress-same-file-warnings to a non-nil value. You can disable this feature entirely by setting the variable find-file-existing-other-name to nil: then if you visit the same file under two different names, you get a separate buffer for each file name.

If the variable find-file-visit-truename is non-nil, then the file name recorded for a buffer is the file's truename (made by replacing all symbolic links with their target names), rather than the name you specify. Setting find-file-visit-truename also implies the effect of find-file-existing-other-name.


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M.7 Version Control

Version control systems are packages that can record multiple versions of a source file, usually storing the unchanged parts of the file just once. Version control systems also record history information such as the creation time of each version, who created it, and a description of what was changed in that version.

The Emacs version control interface is called VC. Its commands work with three version control systems--RCS, CVS, and SCCS. The GNU project recommends RCS and CVS, which are free software and available from the Free Software Foundation. We also have free software to replace SCCS, known as CSSC; if you are using SCCS and don't want to make the incompatible change to RCS or CVS, you can switch to CSSC.

M.7.1 Introduction to Version Control  How version control works in general.
M.7.2 Version Control and the Mode Line  How the mode line shows version control status.
M.7.3 Basic Editing under Version Control  How to edit a file under version control.
M.7.4 Examining And Comparing Old Versions  Examining and comparing old versions.
M.7.5 The Secondary Commands of VC  The commands used a little less frequently.
M.7.6 Multiple Branches of a File  Multiple lines of development.
M.7.7 Remote Repositories  Efficient access to remote CVS servers.
M.7.8 Snapshots  Sets of file versions treated as a unit.
M.7.9 Miscellaneous Commands and Features of VC  Various other commands and features of VC.
M.7.10 Customizing VC  Variables that change VC's behavior.


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M.7.1 Introduction to Version Control

VC allows you to use a version control system from within Emacs, integrating the version control operations smoothly with editing. VC provides a uniform interface to version control, so that regardless of which version control system is in use, you can use it the same way.

This section provides a general overview of version control, and describes the version control systems that VC supports. You can skip this section if you are already familiar with the version control system you want to use.

M.7.1.1 Supported Version Control Systems  Supported version control back-end systems.
M.7.1.2 Concepts of Version Control  Words and concepts related to version control.


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M.7.1.1 Supported Version Control Systems

VC currently works with three different version control systems or "back ends": RCS, CVS, and SCCS.

RCS is a free version control system that is available from the Free Software Foundation. It is perhaps the most mature of the supported back ends, and the VC commands are conceptually closest to RCS. Almost everything you can do with RCS can be done through VC.

CVS is built on top of RCS, and extends the features of RCS, allowing for more sophisticated release management, and concurrent multi-user development. VC supports basic editing operations under CVS, but for some less common tasks you still need to call CVS from the command line. Note also that before using CVS you must set up a repository, which is a subject too complex to treat here.

SCCS is a proprietary but widely used version control system. In terms of capabilities, it is the weakest of the three that VC supports. VC compensates for certain features missing in SCCS (snapshots, for example) by implementing them itself, but some other VC features, such as multiple branches, are not available with SCCS. You should use SCCS only if for some reason you cannot use RCS.


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M.7.1.2 Concepts of Version Control

When a file is under version control, we also say that it is registered in the version control system. Each registered file has a corresponding master file which represents the file's present state plus its change history--enough to reconstruct the current version or any earlier version. Usually the master file also records a log entry for each version, describing in words what was changed in that version.

The file that is maintained under version control is sometimes called the work file corresponding to its master file. You edit the work file and make changes in it, as you would with an ordinary file. (With SCCS and RCS, you must lock the file before you start to edit it.) After you are done with a set of changes, you check the file in, which records the changes in the master file, along with a log entry for them.

With CVS, there are usually multiple work files corresponding to a single master file--often each user has his own copy. It is also possible to use RCS in this way, but this is not the usual way to use RCS.

A version control system typically has some mechanism to coordinate between users who want to change the same file. One method is locking (analogous to the locking that Emacs uses to detect simultaneous editing of a file, but distinct from it). The other method is to merge your changes with other people's changes when you check them in.

With version control locking, work files are normally read-only so that you cannot change them. You ask the version control system to make a work file writable for you by locking it; only one user can do this at any given time. When you check in your changes, that unlocks the file, making the work file read-only again. This allows other users to lock the file to make further changes. SCCS always uses locking, and RCS normally does.

The other alternative for RCS is to let each user modify the work file at any time. In this mode, locking is not required, but it is permitted; check-in is still the way to record a new version.

CVS normally allows each user to modify his own copy of the work file at any time, but requires merging with changes from other users at check-in time. However, CVS can also be set up to require locking. (see section M.7.10.3 Options specific for CVS).


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M.7.2 Version Control and the Mode Line

When you visit a file that is under version control, Emacs indicates this on the mode line. For example, `RCS-1.3' says that RCS is used for that file, and the current version is 1.3.

The character between the back-end name and the version number indicates the version control status of the file. `-' means that the work file is not locked (if locking is in use), or not modified (if locking is not in use). `:' indicates that the file is locked, or that it is modified. If the file is locked by some other user (for instance, `jim'), that is displayed as `RCS:jim:1.3'.


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M.7.3 Basic Editing under Version Control

The principal VC command is an all-purpose command that performs either locking or check-in, depending on the situation.

C-x C-q
C-x v v
Perform the next logical version control operation on this file.

Strictly speaking, the command for this job is vc-next-action, bound to C-x v v. However, the normal meaning of C-x C-q is to make a read-only buffer writable, or vice versa; we have extended it to do the same job properly for files managed by version control, by performing the appropriate version control operations. When you type C-x C-q on a registered file, it acts like C-x v v.

The precise action of this command depends on the state of the file, and whether the version control system uses locking or not. SCCS and RCS normally use locking; CVS normally does not use locking.

M.7.3.1 Basic Version Control with Locking  RCS in its default mode, SCCS, and optionally CVS.
M.7.3.2 Basic Version Control without Locking  Without locking: default mode for CVS.
M.7.3.3 Advanced Control in C-x C-q  Advanced features available with a prefix argument.
M.7.3.4 Features of the Log Entry Buffer  Features available in log entry buffers.

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M.7.3.1 Basic Version Control with Locking

If locking is used for the file (as with SCCS, and RCS in its default mode), C-x C-q can either lock a file or check it in:

These rules also apply when you use CVS in locking mode, except that there is no such thing as stealing a lock.


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M.7.3.2 Basic Version Control without Locking

When there is no locking--the default for CVS--work files are always writable; you do not need to do anything before you begin to edit a file. The status indicator on the mode line is `-' if the file is unmodified; it flips to `:' as soon as you save any changes in the work file.

Here is what C-x C-q does when using CVS:

These rules also apply when you use RCS in the mode that does not require locking, except that automatic merging of changes from the master file is not implemented. Unfortunately, this means that nothing informs you if another user has checked in changes in the same file since you began editing it, and when this happens, his changes will be effectively removed when you check in your version (though they will remain in the master file, so they will not be entirely lost). You must therefore verify the current version is unchanged, before you check in your changes. We hope to eliminate this risk and provide automatic merging with RCS in a future Emacs version.

In addition, locking is possible with RCS even in this mode, although it is not required; C-x C-q with an unmodified file locks the file, just as it does with RCS in its normal (locking) mode.


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M.7.3.3 Advanced Control in C-x C-q

When you give a prefix argument to vc-next-action (C-u C-x C-q), it still performs the next logical version control operation, but accepts additional arguments to specify precisely how to do the operation.


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M.7.3.4 Features of the Log Entry Buffer

When you check in changes, C-x C-q first reads a log entry. It pops up a buffer called `*VC-Log*' for you to enter the log entry. When you are finished, type C-c C-c in the `*VC-Log*' buffer. That is when check-in really happens.

To abort check-in, just don't type C-c C-c in that buffer. You can switch buffers and do other editing. As long as you don't try to check in another file, the entry you were editing remains in the `*VC-Log*' buffer, and you can go back to that buffer at any time to complete the check-in.

If you change several source files for the same reason, it is often convenient to specify the same log entry for many of the files. To do this, use the history of previous log entries. The commands M-n, M-p, M-s and M-r for doing this work just like the minibuffer history commands (except that these versions are used outside the minibuffer).

Each time you check in a file, the log entry buffer is put into VC Log mode, which involves running two hooks: text-mode-hook and vc-log-mode-hook. See section AD.2.3 Hooks.


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M.7.4 Examining And Comparing Old Versions

One of the convenient features of version control is the ability to examine any version of a file, or compare two versions.

C-x v ~ version RET
Examine version version of the visited file, in a buffer of its own.

C-x v =
Compare the current buffer contents with the latest checked-in version of the file.

C-u C-x v = file RET oldvers RET newvers RET
Compare the specified two versions of file.

C-x v g
Display the result of the CVS annotate command using colors.

To examine an old version in its entirety, visit the file and then type C-x v ~ version RET (vc-version-other-window). This puts the text of version version in a file named `filename.~version~', and visits it in its own buffer in a separate window. (In RCS, you can also select an old version and create a branch from it. See section M.7.6 Multiple Branches of a File.)

It is usually more convenient to compare two versions of the file, with the command C-x v = (vc-diff). Plain C-x v = compares the current buffer contents (saving them in the file if necessary) with the last checked-in version of the file. C-u C-x v =, with a numeric argument, reads a file name and two version numbers, then compares those versions of the specified file. Both forms display the output in a special buffer in another window.

You can specify a checked-in version by its number; an empty input specifies the current contents of the work file (which may be different from all the checked-in versions). You can also specify a snapshot name (see section M.7.8 Snapshots) instead of one or both version numbers.

If you supply a directory name instead of the name of a registered file, this command compares the two specified versions of all registered files in that directory and its subdirectories.

C-x v = works by running a variant of the diff utility designed to work with the version control system in use. When you invoke diff this way, in addition to the options specified by diff-switches (see section M.9 Comparing Files), it receives those specified by vc-diff-switches, plus those specified for the specific back end by vc-backend-diff-switches. For instance, when the version control back end is RCS, diff uses the options in vc-rcs-diff-switches. The `vc...diff-switches' variables are nil by default.

Unlike the M-x diff command, C-x v = does not try to locate the changes in the old and new versions. This is because normally one or both versions do not exist as files when you compare them; they exist only in the records of the master file. See section M.9 Comparing Files, for more information about M-x diff.

For CVS-controlled files, you can display the result of the CVS annotate command, using colors to enhance the visual appearance. Use the command M-x vc-annotate to do this. It creates a new buffer to display file's text, colored to show how old each part is. Text colored red is new, blue means old, and intermediate colors indicate intermediate ages. By default, the time scale is 360 days, so that everything more than one year old is shown in blue.

When you give a prefix argument to this command, it uses the minibuffer to read two arguments: which version number to display and annotate (instead of the current file contents), and a stretch factor for the time scale. A stretch factor of 0.1 means that the color range from red to blue spans the past 36 days instead of 360 days. A stretch factor greater than 1 means the color range spans more than a year.


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M.7.5 The Secondary Commands of VC

This section explains the secondary commands of VC; those that you might use once a day.

M.7.5.1 Registering a File for Version Control  Putting a file under version control.
M.7.5.2 VC Status Commands  Viewing the VC status of files.
M.7.5.3 Undoing Version Control Actions  Cancelling changes before or after check-in.
M.7.5.4 Dired under VC  Listing files managed by version control.
M.7.5.5 VC Dired Commands  Commands to use in a VC Dired buffer.


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M.7.5.1 Registering a File for Version Control

You can put any file under version control by simply visiting it, and then typing C-x v i (vc-register).

C-x v i
Register the visited file for version control.

To register the file, Emacs must choose which version control system to use for it. If the file's directory already contains files registered in a version control system, Emacs uses that system. If there is more than one system in use for a directory, Emacs uses the one that appears first in vc-handled-backends (see section M.7.10 Customizing VC). On the other hand, if there are no files already registered, Emacs uses the first system from vc-handled-backends that could register the file--for example, you cannot register a file under CVS if its directory is not already part of a CVS tree.

With the default value of vc-handled-backends, this means that Emacs uses RCS if there are any files under RCS control, CVS if there are any files under CVS, SCCS if any files are under SCCS, or RCS as the ultimate default.

If locking is in use, C-x v i leaves the file unlocked and read-only. Type C-x C-q if you wish to start editing it. After registering a file with CVS, you must subsequently commit the initial version by typing C-x C-q.

The initial version number for a newly registered file is 1.1, by default. You can specify a different default by setting the variable vc-default-init-version, or you can give C-x v i a numeric argument; then it reads the initial version number for this particular file using the minibuffer.

If vc-initial-comment is non-nil, C-x v i reads an initial comment to describe the purpose of this source file. Reading the initial comment works like reading a log entry (see section M.7.3.4 Features of the Log Entry Buffer).


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M.7.5.2 VC Status Commands

C-x v l
Display version control state and change history.

To view the detailed version control status and history of a file, type C-x v l (vc-print-log). It displays the history of changes to the current file, including the text of the log entries. The output appears in a separate window.


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M.7.5.3 Undoing Version Control Actions

C-x v u
Revert the buffer and the file to the last checked-in version.

C-x v c
Remove the last-entered change from the master for the visited file. This undoes your last check-in.

If you want to discard your current set of changes and revert to the last version checked in, use C-x v u (vc-revert-buffer). This leaves the file unlocked; if locking is in use, you must first lock the file again before you change it again. C-x v u requires confirmation, unless it sees that you haven't made any changes since the last checked-in version.

C-x v u is also the command to unlock a file if you lock it and then decide not to change it.

To cancel a change that you already checked in, use C-x v c (vc-cancel-version). This command discards all record of the most recent checked-in version. C-x v c also offers to revert your work file and buffer to the previous version (the one that precedes the version that is deleted).

If you answer no, VC keeps your changes in the buffer, and locks the file. The no-revert option is useful when you have checked in a change and then discover a trivial error in it; you can cancel the erroneous check-in, fix the error, and check the file in again.

When C-x v c does not revert the buffer, it unexpands all version control headers in the buffer instead (see section M.7.9.3 Inserting Version Control Headers). This is because the buffer no longer corresponds to any existing version. If you check it in again, the check-in process will expand the headers properly for the new version number.

However, it is impossible to unexpand the RCS `$Log$' header automatically. If you use that header feature, you have to unexpand it by hand--by deleting the entry for the version that you just canceled.

Be careful when invoking C-x v c, as it is easy to lose a lot of work with it. To help you be careful, this command always requires confirmation with yes. Note also that this command is disabled under CVS, because canceling versions is very dangerous and discouraged with CVS.


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M.7.5.4 Dired under VC

The VC Dired Mode described here works with all the version control systems that VC supports. Another more powerful facility, designed specifically for CVS, is called PCL-CVS. See section `About PCL-CVS' in PCL-CVS -- The Emacs Front-End to CVS.

When you are working on a large program, it is often useful to find out which files have changed within an entire directory tree, or to view the status of all files under version control at once, and to perform version control operations on collections of files. You can use the command C-x v d (vc-directory) to make a directory listing that includes only files relevant for version control.

C-x v d creates a buffer which uses VC Dired Mode. This looks much like an ordinary Dired buffer (see section AB. Dired, the Directory Editor); however, normally it shows only the noteworthy files (those locked or not up-to-date). This is called terse display. If you set the variable vc-dired-terse-display to nil, then VC Dired shows all relevant files--those managed under version control, plus all subdirectories (full display). The command v t in a VC Dired buffer toggles between terse display and full display (see section M.7.5.5 VC Dired Commands).

By default, VC Dired produces a recursive listing of noteworthy or relevant files at or below the given directory. You can change this by setting the variable vc-dired-recurse to nil; then VC Dired shows only the files in the given directory.

The line for an individual file shows the version control state in the place of the hard link count, owner, group, and size of the file. If the file is unmodified, in sync with the master file, the version control state shown is blank. Otherwise it consists of text in parentheses. Under RCS and SCCS, the name of the user locking the file is shown; under CVS, an abbreviated version of the `cvs status' output is used. Here is an example using RCS:

 
  /home/jim/project:

  -rw-r--r-- (jim)      Apr  2 23:39 file1
  -r--r--r--            Apr  5 20:21 file2

The files `file1' and `file2' are under version control, `file1' is locked by user jim, and `file2' is unlocked.

Here is an example using CVS:

 
  /home/joe/develop:

  -rw-r--r-- (modified) Aug  2  1997 file1.c
  -rw-r--r--            Apr  4 20:09 file2.c
  -rw-r--r-- (merge)    Sep 13  1996 file3.c

Here `file1.c' is modified with respect to the repository, and `file2.c' is not. `file3.c' is modified, but other changes have also been checked in to the repository--you need to merge them with the work file before you can check it in.

When VC Dired displays subdirectories (in the "full" display mode), it omits some that should never contain any files under version control. By default, this includes Version Control subdirectories such as `RCS' and `CVS'; you can customize this by setting the variable vc-directory-exclusion-list.

You can fine-tune VC Dired's format by typing C-u C-x v d---as in ordinary Dired, that allows you to specify additional switches for the `ls' command.


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M.7.5.5 VC Dired Commands

All the usual Dired commands work normally in VC Dired mode, except for v, which is redefined as the version control prefix. You can invoke VC commands such as vc-diff and vc-print-log by typing v =, or v l, and so on. Most of these commands apply to the file name on the current line.

The command v v (vc-next-action) operates on all the marked files, so that you can lock or check in several files at once. If it operates on more than one file, it handles each file according to its current state; thus, it might lock one file, but check in another file. This could be confusing; it is up to you to avoid confusing behavior by marking a set of files that are in a similar state.

If any files call for check-in, v v reads a single log entry, then uses it for all the files being checked in. This is convenient for registering or checking in several files at once, as part of the same change.

You can toggle between terse display (only locked files, or files not up-to-date) and full display at any time by typing v t (vc-dired-toggle-terse-mode). There is also a special command * l (vc-dired-mark-locked), which marks all files currently locked (or, with CVS, all files not up-to-date). Thus, typing * l t k is another way to delete from the buffer all files except those currently locked.


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M.7.6 Multiple Branches of a File

One use of version control is to maintain multiple "current" versions of a file. For example, you might have different versions of a program in which you are gradually adding various unfinished new features. Each such independent line of development is called a branch. VC allows you to create branches, switch between different branches, and merge changes from one branch to another. Please note, however, that branches are only supported for RCS at the moment.

A file's main line of development is usually called the trunk. The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At any such version, you can start an independent branch. A branch starting at version 1.2 would have version number 1.2.1.1, and consecutive versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4, and so on. If there is a second branch also starting at version 1.2, it would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc.

If you omit the final component of a version number, that is called a branch number. It refers to the highest existing version on that branch--the head version of that branch. The branches in the example above have branch numbers 1.2.1 and 1.2.2.

M.7.6.1 Switching between Branches  How to get to another existing branch.
M.7.6.2 Creating New Branches  How to start a new branch.
M.7.6.3 Merging Branches  Transferring changes between branches.
M.7.6.4 Multi-User Branching  Multiple users working at multiple branches in parallel.


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M.7.6.1 Switching between Branches

To switch between branches, type C-u C-x C-q and specify the version number you want to select. This version is then visited unlocked (write-protected), so you can examine it before locking it. Switching branches in this way is allowed only when the file is not locked.

You can omit the minor version number, thus giving only the branch number; this takes you to the head version on the chosen branch. If you only type RET, Emacs goes to the highest version on the trunk.

After you have switched to any branch (including the main branch), you stay on it for subsequent VC commands, until you explicitly select some other branch.


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M.7.6.2 Creating New Branches

To create a new branch from a head version (one that is the latest in the branch that contains it), first select that version if necessary, lock it with C-x C-q, and make whatever changes you want. Then, when you check in the changes, use C-u C-x C-q. This lets you specify the version number for the new version. You should specify a suitable branch number for a branch starting at the current version. For example, if the current version is 2.5, the branch number should be 2.5.1, 2.5.2, and so on, depending on the number of existing branches at that point.

To create a new branch at an older version (one that is no longer the head of a branch), first select that version (see section M.7.6.1 Switching between Branches), then lock it with C-x C-q. You'll be asked to confirm, when you lock the old version, that you really mean to create a new branch--if you say no, you'll be offered a chance to lock the latest version instead.

Then make your changes and type C-x C-q again to check in a new version. This automatically creates a new branch starting from the selected version. You need not specially request a new branch, because that's the only way to add a new version at a point that is not the head of a branch.

After the branch is created, you "stay" on it. That means that subsequent check-ins create new versions on that branch. To leave the branch, you must explicitly select a different version with C-u C-x C-q. To transfer changes from one branch to another, use the merge command, described in the next section.


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M.7.6.3 Merging Branches

When you have finished the changes on a certain branch, you will often want to incorporate them into the file's main line of development (the trunk). This is not a trivial operation, because development might also have proceeded on the trunk, so that you must merge the changes into a file that has already been changed otherwise. VC allows you to do this (and other things) with the vc-merge command.

C-x v m (vc-merge)
Merge changes into the work file.

C-x v m (vc-merge) takes a set of changes and merges it into the current version of the work file. It firsts asks you in the minibuffer where the changes should come from. If you just type RET, Emacs merges any changes that were made on the same branch since you checked the file out (we call this merging the news). This is the common way to pick up recent changes from the repository, regardless of whether you have already changed the file yourself.

You can also enter a branch number or a pair of version numbers in the minibuffer. Then C-x v m finds the changes from that branch, or the differences between the two versions you specified, and merges them into the current version of the current file.

As an example, suppose that you have finished a certain feature on branch 1.3.1. In the meantime, development on the trunk has proceeded to version 1.5. To merge the changes from the branch to the trunk, first go to the head version of the trunk, by typing C-u C-x C-q RET. Version 1.5 is now current. If locking is used for the file, type C-x C-q to lock version 1.5 so that you can change it. Next, type C-x v m 1.3.1 RET. This takes the entire set of changes on branch 1.3.1 (relative to version 1.3, where the branch started, up to the last version on the branch) and merges it into the current version of the work file. You can now check in the changed file, thus creating version 1.6 containing the changes from the branch.

It is possible to do further editing after merging the branch, before the next check-in. But it is usually wiser to check in the merged version, then lock it and make the further changes. This will keep a better record of the history of changes.

When you merge changes into a file that has itself been modified, the changes might overlap. We call this situation a conflict, and reconciling the conflicting changes is called resolving a conflict.

Whenever conflicts occur during merging, VC detects them, tells you about them in the echo area, and asks whether you want help in merging. If you say yes, it starts an Ediff session (see section `Ediff' in The Ediff Manual).

If you say no, the conflicting changes are both inserted into the file, surrounded by conflict markers. The example below shows how a conflict region looks; the file is called `name' and the current master file version with user B's changes in it is 1.11.

 
<<<<<<< name
  User A's version
=======
  User B's version
>>>>>>> 1.11

Then you can resolve the conflicts by editing the file manually. Or you can type M-x vc-resolve-conflicts after visiting the file. This starts an Ediff session, as described above. Don't forget to check in the merged version afterwards.


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M.7.6.4 Multi-User Branching

It is often useful for multiple developers to work simultaneously on different branches of a file. CVS allows this by default; for RCS, it is possible if you create multiple source directories. Each source directory should have a link named `RCS' which points to a common directory of RCS master files. Then each source directory can have its own choice of selected versions, but all share the same common RCS records.

This technique works reliably and automatically, provided that the source files contain RCS version headers (see section M.7.9.3 Inserting Version Control Headers). The headers enable Emacs to be sure, at all times, which version number is present in the work file.

If the files do not have version headers, you must instead tell Emacs explicitly in each session which branch you are working on. To do this, first find the file, then type C-u C-x C-q and specify the correct branch number. This ensures that Emacs knows which branch it is using during this particular editing session.


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M.7.7 Remote Repositories

A common way of using CVS is to set up a central CVS repository on some Internet host, then have each developer check out a personal working copy of the files on his local machine. Committing changes to the repository, and picking up changes from other users into one's own working area, then works by direct interactions with the CVS server.

One difficulty is that access to the CVS server is often slow, and that developers might need to work off-line as well. VC is designed to reduce the amount of network interaction necessary.

M.7.7.1 Version Backups  Keeping local copies of repository versions.
M.7.7.2 Local Version Control  Using another version system for local editing.


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M.7.7.1 Version Backups

When VC sees that the CVS repository for a file is on a remote machine, it automatically makes local backups of unmodified versions of the file---automatic version backups. This means that you can compare the file to the repository version (C-x v =), or revert to that version (C-x v u), without any network interactions.

The local copy of the unmodified file is called a version backup to indicate that it corresponds exactly to a version that is stored in the repository. Note that version backups are not the same as ordinary Emacs backup files (see section M.3.1 Backup Files). But they follow a similar naming convention.

For a file that comes from a remote CVS repository, VC makes a version backup whenever you save the first changes to the file, and removes it after you have committed your modified version to the repository. You can disable the making of automatic version backups by setting vc-cvs-stay-local to nil (see section M.7.10.3 Options specific for CVS).

The name of the automatic version backup for version version of file file is file.~version.~. This is almost the same as the name used by C-x v ~ (see section M.7.4 Examining And Comparing Old Versions), the only difference being the additional dot (`.') after the version number. This similarity is intentional, because both kinds of files store the same kind of information. The file made by C-x v ~ acts as a manual version backup.

All the VC commands that operate on old versions of a file can use both kinds of version backups. For instance, C-x v ~ uses either an automatic or a manual version backup, if possible, to get the contents of the version you request. Likewise, C-x v = and C-x v u use either an automatic or a manual version backup, if one of them exists, to get the contents of a version to compare or revert to. If you changed a file outside of Emacs, so that no automatic version backup was created for the previous text, you can create a manual backup of that version using C-x v ~, and thus obtain the benefit of the local copy for Emacs commands.

The only difference in Emacs's handling of manual and automatic version backups, once they exist, is that Emacs deletes automatic version backups when you commit to the repository. By contrast, manual version backups remain until you delete them.


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M.7.7.2 Local Version Control

When you make many changes to a file that comes from a remote repository, it can be convenient to have version control on your local machine as well. You can then record intermediate versions, revert to a previous state, etc., before you actually commit your changes to the remote server.

VC lets you do this by putting a file under a second, local version control system, so that the file is effectively registered in two systems at the same time. For the description here, we will assume that the remote system is CVS, and you use RCS locally, although the mechanism works with any combination of version control systems (back ends).

To make it work with other back ends, you must make sure that the "more local" back end comes before the "more remote" back end in the setting of vc-handled-backends (see section M.7.10 Customizing VC). By default, this variable is set up so that you can use remote CVS and local RCS as described here.

To start using local RCS for a file that comes from a remote CVS server, you must register the file in RCS, by typing C-u C-x v v rcs RET. (In other words, use vc-next-action with a prefix argument, and specify RCS as the back end.)

You can do this at any time; it does not matter whether you have already modified the file with respect to the version in the CVS repository. If possible, VC tries to make the RCS master start with the unmodified repository version, then checks in any local changes as a new version. This works if you have not made any changes yet, or if the unmodified repository version exists locally as a version backup (see section M.7.7.1 Version Backups). If the unmodified version is not available locally, the RCS master starts with the modified version; the only drawback to this is that you cannot compare your changes locally to what is stored in the repository.

The version number of the RCS master is derived from the current CVS version, starting a branch from it. For example, if the current CVS version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in the RCS master will be identical to version 1.23 under CVS; your first changes are checked in as 1.23.1.1. (If the unmodified file is not available locally, VC will check in the modified file twice, both as 1.23 and 1.23.1.1, to make the revision numbers consistent.)

If you do not use locking under CVS (the default), locking is also disabled for RCS, so that editing under RCS works exactly as under CVS.

When you are done with local editing, you can commit the final version back to the CVS repository by typing C-u C-x v v cvs RET. This initializes the log entry buffer (see section M.7.3.4 Features of the Log Entry Buffer) to contain all the log entries you have recorded in the RCS master; you can edit them as you wish, and then commit in CVS by typing C-c C-c. If the commit is successful, VC removes the RCS master, so that the file is once again registered under CVS only. (The RCS master is not actually deleted, just renamed by appending `~' to the name, so that you can refer to it later if you wish.)

While using local RCS, you can pick up recent changes from the CVS repository into your local file, or commit some of your changes back to CVS, without terminating local RCS version control. To do this, switch to the CVS back end temporarily, with the C-x v b command:

C-x v b
Switch to another back end that the current file is registered under (vc-switch-backend).

C-u C-x v b backend RET
Switch to backend for the current file.

C-x v b does not change the buffer contents, or any files; it only changes VC's perspective on how to handle the file. Any subsequent VC commands for that file will operate on the back end that is currently selected.

If the current file is registered in more than one back end, typing C-x v b "cycles" through all of these back ends. With a prefix argument, it asks for the back end to use in the minibuffer.

Thus, if you are using local RCS, and you want to pick up some recent changes in the file from remote CVS, first visit the file, then type C-x v b to switch to CVS, and finally use C-x v m RET to merge the news (see section M.7.6.3 Merging Branches). You can then switch back to RCS by typing C-x v b again, and continue to edit locally.

But if you do this, the revision numbers in the RCS master no longer correspond to those of CVS. Technically, this is not a problem, but it can become difficult to keep track of what is in the CVS repository and what is not. So we suggest that you return from time to time to CVS-only operation, using C-u C-x v v cvs RET.


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M.7.8 Snapshots

A snapshot is a named set of file versions (one for each registered file) that you can treat as a unit. One important kind of snapshot is a release, a (theoretically) stable version of the system that is ready for distribution to users.

M.7.8.1 Making and Using Snapshots  The snapshot facilities.
M.7.8.2 Snapshot Caveats  Things to be careful of when using snapshots.


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M.7.8.1 Making and Using Snapshots

There are two basic commands for snapshots; one makes a snapshot with a given name, the other retrieves a named snapshot.

C-x v s name RET
Define the last saved versions of every registered file in or under the current directory as a snapshot named name (vc-create-snapshot).

C-x v r name RET
For all registered files at or below the current directory level, select whatever versions correspond to the snapshot name (vc-retrieve-snapshot).

This command reports an error if any files are locked at or below the current directory, without changing anything; this is to avoid overwriting work in progress.

A snapshot uses a very small amount of resources--just enough to record the list of file names and which version belongs to the snapshot. Thus, you need not hesitate to create snapshots whenever they are useful.

You can give a snapshot name as an argument to C-x v = or C-x v ~ (see section M.7.4 Examining And Comparing Old Versions). Thus, you can use it to compare a snapshot against the current files, or two snapshots against each other, or a snapshot against a named version.


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M.7.8.2 Snapshot Caveats

VC's snapshot facilities are modeled on RCS's named-configuration support. They use RCS's native facilities for this, so under VC snapshots made using RCS are visible even when you bypass VC.

For SCCS, VC implements snapshots itself. The files it uses contain name/file/version-number triples. These snapshots are visible only through VC.

A snapshot is a set of checked-in versions. So make sure that all the files are checked in and not locked when you make a snapshot.

File renaming and deletion can create some difficulties with snapshots. This is not a VC-specific problem, but a general design issue in version control systems that no one has solved very well yet.

If you rename a registered file, you need to rename its master along with it (the command vc-rename-file does this automatically). If you are using SCCS, you must also update the records of the snapshot, to mention the file by its new name (vc-rename-file does this, too). An old snapshot that refers to a master file that no longer exists under the recorded name is invalid; VC can no longer retrieve it. It would be beyond the scope of this manual to explain enough about RCS and SCCS to explain how to update the snapshots by hand.

Using vc-rename-file makes the snapshot remain valid for retrieval, but it does not solve all problems. For example, some of the files in your program probably refer to others by name. At the very least, the makefile probably mentions the file that you renamed. If you retrieve an old snapshot, the renamed file is retrieved under its new name, which is not the name that the makefile expects. So the program won't really work as retrieved.


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M.7.9 Miscellaneous Commands and Features of VC

This section explains the less-frequently-used features of VC.

M.7.9.1 Change Logs and VC  Generating a change log file from log entries.
M.7.9.2 Renaming VC Work Files and Master Files  A command to rename both the source and master file correctly.
M.7.9.3 Inserting Version Control Headers  Inserting version control headers into working files.


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M.7.9.1 Change Logs and VC

If you use RCS or CVS for a program and also maintain a change log file for it (see section W.1 Change Logs), you can generate change log entries automatically from the version control log entries:

C-x v a
Visit the current directory's change log file and, for registered files in that directory, create new entries for versions checked in since the most recent entry in the change log file. (vc-update-change-log).

This command works with RCS or CVS only, not with SCCS.

C-u C-x v a
As above, but only find entries for the current buffer's file.

M-1 C-x v a
As above, but find entries for all the currently visited files that are maintained with version control. This works only with RCS, and it puts all entries in the log for the default directory, which may not be appropriate.

For example, suppose the first line of `ChangeLog' is dated 1999-04-10, and that the only check-in since then was by Nathaniel Bowditch to `rcs2log' on 1999-05-22 with log text `Ignore log messages that start with `#'.'. Then C-x v a visits `ChangeLog' and inserts text like this:

 
1999-05-22  Nathaniel Bowditch  <nat@apn.org>

        * rcs2log: Ignore log messages that start with `#'.

You can then edit the new change log entry further as you wish.

Some of the new change log entries may duplicate what's already in ChangeLog. You will have to remove these duplicates by hand.

Normally, the log entry for file `foo' is displayed as `* foo: text of log entry'. The `:' after `foo' is omitted if the text of the log entry starts with `(functionname): '. For example, if the log entry for `vc.el' is `(vc-do-command): Check call-process status.', then the text in `ChangeLog' looks like this:

 
1999-05-06  Nathaniel Bowditch  <nat@apn.org>

        * vc.el (vc-do-command): Check call-process status.

When C-x v a adds several change log entries at once, it groups related log entries together if they all are checked in by the same author at nearly the same time. If the log entries for several such files all have the same text, it coalesces them into a single entry. For example, suppose the most recent check-ins have the following log entries:

* For `vc.texinfo': `Fix expansion typos.'
* For `vc.el': `Don't call expand-file-name.'
* For `vc-hooks.el': `Don't call expand-file-name.'

They appear like this in `ChangeLog':

 
1999-04-01  Nathaniel Bowditch  <nat@apn.org>

        * vc.texinfo: Fix expansion typos.

        * vc.el, vc-hooks.el: Don't call expand-file-name.

Normally, C-x v a separates log entries by a blank line, but you can mark several related log entries to be clumped together (without an intervening blank line) by starting the text of each related log entry with a label of the form `{clumpname} '. The label itself is not copied to `ChangeLog'. For example, suppose the log entries are:

* For `vc.texinfo': `{expand} Fix expansion typos.'
* For `vc.el': `{expand} Don't call expand-file-name.'
* For `vc-hooks.el': `{expand} Don't call expand-file-name.'

Then the text in `ChangeLog' looks like this:

 
1999-04-01  Nathaniel Bowditch  <nat@apn.org>

        * vc.texinfo: Fix expansion typos.
        * vc.el, vc-hooks.el: Don't call expand-file-name.

A log entry whose text begins with `#' is not copied to `ChangeLog'. For example, if you merely fix some misspellings in comments, you can log the change with an entry beginning with `#' to avoid putting such trivia into `ChangeLog'.


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M.7.9.2 Renaming VC Work Files and Master Files

When you rename a registered file, you must also rename its master file correspondingly to get proper results. Use vc-rename-file to rename the source file as you specify, and rename its master file accordingly. It also updates any snapshots (see section M.7.8 Snapshots) that mention the file, so that they use the new name; despite this, the snapshot thus modified may not completely work (see section M.7.8.2 Snapshot Caveats).

You cannot use vc-rename-file on a file that is locked by someone else.


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M.7.9.3 Inserting Version Control Headers

Sometimes it is convenient to put version identification strings directly into working files. Certain special strings called version headers are replaced in each successive version by the number of that version.

If you are using RCS, and version headers are present in your working files, Emacs can use them to determine the current version and the locking state of the files. This is more reliable than referring to the master files, which is done when there are no version headers. Note that in a multi-branch environment, version headers are necessary to make VC behave correctly (see section M.7.6.4 Multi-User Branching).

Searching for version headers is controlled by the variable vc-consult-headers. If it is non-nil (the default), Emacs searches for headers to determine the version number you are editing. Setting it to nil disables this feature.

You can use the C-x v h command (vc-insert-headers) to insert a suitable header string.

C-x v h
Insert headers in a file for use with your version-control system.

The default header string is `$Id$' for RCS and `%W%' for SCCS. You can specify other headers to insert by setting the variable vc-header-alist. Its value is a list of elements of the form (program . string) where program is RCS or SCCS and string is the string to use.

Instead of a single string, you can specify a list of strings; then each string in the list is inserted as a separate header on a line of its own.

It is often necessary to use "superfluous" backslashes when writing the strings that you put in this variable. For instance, you might write "$Id\$" rather than "$Id$". The extra backslash prevents the string constant from being interpreted as a header, if the Emacs Lisp file containing it is maintained with version control.

Each header is inserted surrounded by tabs, inside comment delimiters, on a new line at point. Normally the ordinary comment start and comment end strings of the current mode are used, but for certain modes, there are special comment delimiters for this purpose; the variable vc-comment-alist specifies them. Each element of this list has the form (mode starter ender).

The variable vc-static-header-alist specifies further strings to add based on the name of the buffer. Its value should be a list of elements of the form (regexp . format). Whenever regexp matches the buffer name, format is inserted as part of the header. A header line is inserted for each element that matches the buffer name, and for each string specified by vc-header-alist. The header line is made by processing the string from vc-header-alist with the format taken from the element. The default value for vc-static-header-alist is as follows:

 
(("\\.c$" .
  "\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
#endif /* lint */\n"))

It specifies insertion of text of this form:

 
#ifndef lint
static char vcid[] = "string";
#endif /* lint */

Note that the text above starts with a blank line.

If you use more than one version header in a file, put them close together in the file. The mechanism in revert-buffer that preserves markers may not handle markers positioned between two version headers.


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M.7.10 Customizing VC

The variable vc-handled-backends determines which version control systems VC should handle. The default value is (RCS CVS SCCS), so it contains all three version systems that are currently supported. If you want VC to ignore one or more of these systems, exclude its name from the list.

The order of systems in the list is significant: when you visit a file registered in more than one system (see section M.7.7.2 Local Version Control), VC uses the system that comes first in vc-handled-backends by default. The order is also significant when you register a file for the first time, see section M.7.5.1 Registering a File for Version Control for details.

M.7.10.1 General Options  Options that apply to multiple back ends.
M.7.10.2 Options for RCS and SCCS  
M.7.10.3 Options specific for CVS  Options for CVS.


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M.7.10.1 General Options

Emacs normally does not save backup files for source files that are maintained with version control. If you want to make backup files even for files that use version control, set the variable vc-make-backup-files to a non-nil value.

Normally the work file exists all the time, whether it is locked or not. If you set vc-keep-workfiles to nil, then checking in a new version with C-x C-q deletes the work file; but any attempt to visit the file with Emacs creates it again. (With CVS, work files are always kept.)

Editing a version-controlled file through a symbolic link can be dangerous. It bypasses the version control system--you can edit the file without locking it, and fail to check your changes in. Also, your changes might overwrite those of another user. To protect against this, VC checks each symbolic link that you visit, to see if it points to a file under version control.

The variable vc-follow-symlinks controls what to do when a symbolic link points to a version-controlled file. If it is nil, VC only displays a warning message. If it is t, VC automatically follows the link, and visits the real file instead, telling you about this in the echo area. If the value is ask (the default), VC asks you each time whether to follow the link.

If vc-suppress-confirm is non-nil, then C-x C-q and C-x v i can save the current buffer without asking, and C-x v u also operates without asking for confirmation. (This variable does not affect C-x v c; that operation is so drastic that it should always ask for confirmation.)

VC mode does much of its work by running the shell commands for RCS, CVS and SCCS. If vc-command-messages is non-nil, VC displays messages to indicate which shell commands it runs, and additional messages when the commands finish.

You can specify additional directories to search for version control programs by setting the variable vc-path. These directories are searched before the usual search path. It is rarely necessary to set this variable, because VC normally finds the proper files automatically.


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M.7.10.2 Options for RCS and SCCS

By default, RCS uses locking to coordinate the activities of several users, but there is a mode called non-strict locking in which you can check-in changes without locking the file first. Use `rcs -U' to switch to non-strict locking for a particular file, see the rcs manual page for details.

When deducing the version control state of an RCS file, VC first looks for an RCS version header string in the file (see section M.7.9.3 Inserting Version Control Headers). If there is no header string, VC normally looks at the file permissions of the work file; this is fast. But there might be situations when the file permissions cannot be trusted. In this case the master file has to be consulted, which is rather expensive. Also the master file can only tell you if there's any lock on the file, but not whether your work file really contains that locked version.

You can tell VC not to use version headers to determine the file status by setting vc-consult-headers to nil. VC then always uses the file permissions (if it is supposed to trust them), or else checks the master file.

You can specify the criterion for whether to trust the file permissions by setting the variable vc-mistrust-permissions. Its value can be t (always mistrust the file permissions and check the master file), nil (always trust the file permissions), or a function of one argument which makes the decision. The argument is the directory name of the `RCS' subdirectory. A non-nil value from the function says to mistrust the file permissions. If you find that the file permissions of work files are changed erroneously, set vc-mistrust-permissions to t. Then VC always checks the master file to determine the file's status.

VC determines the version control state of files under SCCS much as with RCS. It does not consider SCCS version headers, though. Thus, the variable vc-mistrust-permissions affects SCCS use, but vc-consult-headers does not.


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M.7.10.3 Options specific for CVS

By default, CVS does not use locking to coordinate the activities of several users; anyone can change a work file at any time. However, there are ways to restrict this, resulting in behavior that resembles locking.

For one thing, you can set the CVSREAD environment variable (the value you use makes no difference). If this variable is defined, CVS makes your work files read-only by default. In Emacs, you must type C-x C-q to make the file writable, so that editing works in fact similar as if locking was used. Note however, that no actual locking is performed, so several users can make their files writable at the same time. When setting CVSREAD for the first time, make sure to check out all your modules anew, so that the file protections are set correctly.

Another way to achieve something similar to locking is to use the watch feature of CVS. If a file is being watched, CVS makes it read-only by default, and you must also use C-x C-q in Emacs to make it writable. VC calls cvs edit to make the file writable, and CVS takes care to notify other developers of the fact that you intend to change the file. See the CVS documentation for details on using the watch feature.

When a file's repository is on a remote machine, VC tries to keep network interactions to a minimum. This is controlled by the variable vc-cvs-stay-local. If it is t (the default), then VC uses only the entry in the local CVS subdirectory to determine the file's state (and possibly information returned by previous CVS commands). One consequence of this is that when you have modified a file, and somebody else has already checked in other changes to the file, you are not notified of it until you actually try to commit. (But you can try to pick up any recent changes from the repository first, using C-x v m RET, see section M.7.6.3 Merging Branches).

When vc-cvs-stay-local is t, VC also makes local version backups, so that simple diff and revert operations are completely local (see section M.7.7.1 Version Backups).

On the other hand, if you set vc-cvs-stay-local to nil, then VC queries the remote repository before it decides what to do in vc-next-action (C-x v v), just as it does for local repositories. It also does not make any version backups.

You can also set vc-cvs-stay-local to a regular expression that is matched against the repository host name; VC then stays local only for repositories from hosts that match the pattern.


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M.8 File Directories

The file system groups files into directories. A directory listing is a list of all the files in a directory. Emacs provides commands to create and delete directories, and to make directory listings in brief format (file names only) and verbose format (sizes, dates, and authors included). There is also a directory browser called Dired; see AB. Dired, the Directory Editor.

C-x C-d dir-or-pattern RET
Display a brief directory listing (list-directory).
C-u C-x C-d dir-or-pattern RET
Display a verbose directory listing.
M-x make-directory RET dirname RET
Create a new directory named dirname.
M-x delete-directory RET dirname RET
Delete the directory named dirname. It must be empty, or you get an error.

The command to display a directory listing is C-x C-d (list-directory). It reads using the minibuffer a file name which is either a directory to be listed or a wildcard-containing pattern for the files to be listed. For example,

 
C-x C-d /u2/emacs/etc RET

lists all the files in directory `/u2/emacs/etc'. Here is an example of specifying a file name pattern:

 
C-x C-d /u2/emacs/src/*.c RET

Normally, C-x C-d displays a brief directory listing containing just file names. A numeric argument (regardless of value) tells it to make a verbose listing including sizes, dates, and owners (like `ls -l').

The text of a directory listing is obtained by running ls in an inferior process. Two Emacs variables control the switches passed to ls: list-directory-brief-switches is a string giving the switches to use in brief listings ("-CF" by default), and list-directory-verbose-switches is a string giving the switches to use in a verbose listing ("-l" by default).


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M.9 Comparing Files

The command M-x diff compares two files, displaying the differences in an Emacs buffer named `*diff*'. It works by running the diff program, using options taken from the variable diff-switches. The value of diff-switches should be a string; the default is "-c" to specify a context diff.

The buffer `*diff*' has Compilation mode as its major mode, so you can use C-x ` to visit successive changed locations in the two source files. You can also move to a particular hunk of changes and type RET or C-c C-c, or click Mouse-2 on it, to move to the corresponding source location. You can also use the other special commands of Compilation mode: SPC and DEL for scrolling, and M-p and M-n for cursor motion. See section V.1 Running Compilations under Emacs.

The command M-x diff-backup compares a specified file with its most recent backup. If you specify the name of a backup file, diff-backup compares it with the source file that it is a backup of.

The command M-x compare-windows compares the text in the current window with that in the next window. Comparison starts at point in each window, and each starting position is pushed on the mark ring in its respective buffer. Then point moves forward in each window, a character at a time, until a mismatch between the two windows is reached. Then the command is finished. For more information about windows in Emacs, O. Multiple Windows.

With a numeric argument, compare-windows ignores changes in whitespace. If the variable compare-ignore-case is non-nil, it ignores differences in case as well.

Differences between versions of files are often distributed as patches, which are the output from diff or a version control system that uses diff. M-x diff-mode turns on Diff mode, a major mode for viewing and editing patches, either as "unified diffs" or "context diffs."

You can use M-x smerge-mode to turn on Smerge mode, a minor mode for editing output from the diff3 program. This is typically the result of a failed merge from a version control system "update" outside VC, due to conflicting changes to a file. Smerge mode provides commands to resolve conflicts by selecting specific changes.

See also W.3 Merging Files with Emerge, and section `Top' in The Ediff Manual, for convenient facilities for merging two similar files.


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M.10 Miscellaneous File Operations

Emacs has commands for performing many other operations on files. All operate on one file; they do not accept wildcard file names.

M-x view-file allows you to scan or read a file by sequential screenfuls. It reads a file name argument using the minibuffer. After reading the file into an Emacs buffer, view-file displays the beginning. You can then type SPC to scroll forward one windowful, or DEL to scroll backward. Various other commands are provided for moving around in the file, but none for changing it; type ? while viewing for a list of them. They are mostly the same as normal Emacs cursor motion commands. To exit from viewing, type q. The commands for viewing are defined by a special major mode called View mode.

A related command, M-x view-buffer, views a buffer already present in Emacs. See section N.3 Miscellaneous Buffer Operations.

M-x insert-file (also C-x i) inserts a copy of the contents of the specified file into the current buffer at point, leaving point unchanged before the contents and the mark after them.

M-x write-region is the inverse of M-x insert-file; it copies the contents of the region into the specified file. M-x append-to-file adds the text of the region to the end of the specified file. See section H.9 Accumulating Text.

M-x delete-file deletes the specified file, like the rm command in the shell. If you are deleting many files in one directory, it may be more convenient to use Dired (see section AB. Dired, the Directory Editor).

M-x rename-file reads two file names old and new using the minibuffer, then renames file old as new. If the file name new already exists, you must confirm with yes or renaming is not done; this is because renaming causes the old meaning of the name new to be lost. If old and new are on different file systems, the file old is copied and deleted.

The similar command M-x add-name-to-file is used to add an additional name to an existing file without removing its old name. The new name is created as a "hard link" to the existing file. The new name must belong on the same file system that the file is on. On Windows, this command works only if the file resides in an NTFS file system. On MS-DOS, it works by copying the file.

M-x copy-file reads the file old and writes a new file named new with the same contents. Confirmation is required if a file named new already exists, because copying has the consequence of overwriting the old contents of the file new.

M-x make-symbolic-link reads two file names target and linkname, then creates a symbolic link named linkname, which points at target. The effect is that future attempts to open file linkname will refer to whatever file is named target at the time the opening is done, or will get an error if the name target is not in use at that time. This command does not expand the argument target, so that it allows you to specify a relative name as the target of the link.

Confirmation is required when creating the link if linkname is in use. Note that not all systems support symbolic links; on systems that don't support them, this command is not defined.


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M.11 Accessing Compressed Files

Emacs comes with a library that can automatically uncompress compressed files when you visit them, and automatically recompress them if you alter them and save them. To enable this feature, type the command M-x auto-compression-mode. You can enable it permanently by customizing the option auto-compression-mode.

When automatic compression (which implies automatic uncompression as well) is enabled, Emacs recognizes compressed files by their file names. File names ending in `.gz' indicate a file compressed with gzip. Other endings indicate other compression programs.

Automatic uncompression and compression apply to all the operations in which Emacs uses the contents of a file. This includes visiting it, saving it, inserting its contents into a buffer, loading it, and byte compiling it.


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M.12 File Archives

A file whose name ends in `.tar' is normally an archive made by the tar program. Emacs views these files in a special mode called Tar mode which provides a Dired-like list of the contents (see section AB. Dired, the Directory Editor). You can move around through the list just as you would in Dired, and visit the subfiles contained in the archive. However, not all Dired commands are available in Tar mode.

If you enable Auto Compression mode (see section M.11 Accessing Compressed Files), then Tar mode is used also for compressed archives--files with extensions `.tgz', .tar.Z and .tar.gz.

The keys e, f and RET all extract a component file into its own buffer. You can edit it there and when you save the buffer the edited version will replace the version in the Tar buffer. v extracts a file into a buffer in View mode. o extracts the file and displays it in another window, so you could edit the file and operate on the archive simultaneously. d marks a file for deletion when you later use x, and u unmarks a file, as in Dired. C copies a file from the archive to disk and R renames a file. g reverts the buffer from the archive on disk.

The keys M, G, and O change the file's permission bits, group, and owner, respectively.

If your display supports colors and the mouse, moving the mouse pointer across a file name highlights that file name, indicating that you can click on it. Clicking Mouse-2 on the highlighted file name extracts the file into a buffer and displays that buffer.

Saving the Tar buffer writes a new version of the archive to disk with the changes you made to the components.

You don't need the tar program to use Tar mode--Emacs reads the archives directly. However, accessing compressed archives requires the appropriate uncompression program.

A separate but similar Archive mode is used for archives produced by the programs arc, jar, lzh, zip, and zoo, which have extensions corresponding to the program names.

The key bindings of Archive mode are similar to those in Tar mode, with the addition of the m key which marks a file for subsequent operations, and M-DEL which unmarks all the marked files. Also, the a key toggles the display of detailed file information, for those archive types where it won't fit in a single line. Operations such as renaming a subfile, or changing its mode or owner, are supported only for some of the archive formats.

Unlike Tar mode, Archive mode runs the archiving program to unpack and repack archives. Details of the program names and their options can be set in the `Archive' Customize group. However, you don't need these programs to look at the archive table of contents, only to extract or manipulate the subfiles in the archive.


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M.13 Remote Files

You can refer to files on other machines using a special file name syntax:

 
/host:filename
/user@host:filename
/user@host#port:filename

When you do this, Emacs uses the FTP program to read and write files on the specified host. It logs in through FTP using your user name or the name user. It may ask you for a password from time to time; this is used for logging in on host. The form using port allows you to access servers running on a non-default TCP port.

If you want to disable backups for remote files, set the variable ange-ftp-make-backup-files to nil.

Normally, if you do not specify a user name in a remote file name, that means to use your own user name. But if you set the variable ange-ftp-default-user to a string, that string is used instead. (The Emacs package that implements FTP file access is called ange-ftp.)

To visit files accessible by anonymous FTP, you use special user names `anonymous' or `ftp'. Passwords for these user names are handled specially. The variable ange-ftp-generate-anonymous-password controls what happens: if the value of this variable is a string, then that string is used as the password; if non-nil (the default), then the value of user-mail-address is used; if nil, the user is prompted for a password as normal.

Sometimes you may be unable to access files on a remote machine because a firewall in between blocks the connection for security reasons. If you can log in on a gateway machine from which the target files are accessible, and whose FTP server supports gatewaying features, you can still use remote file names; all you have to do is specify the name of the gateway machine by setting the variable ange-ftp-gateway-host, and set ange-ftp-smart-gateway to t. Otherwise you may be able to make remote file names work, but the procedure is complex. You can read the instructions by typing M-x finder-commentary RET ange-ftp RET.

You can entirely turn off the FTP file name feature by removing the entries ange-ftp-completion-hook-function and ange-ftp-hook-function from the variable file-name-handler-alist. You can turn off the feature in individual cases by quoting the file name with `/:' (see section M.14 Quoted File Names).


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M.14 Quoted File Names

You can quote an absolute file name to prevent special characters and syntax in it from having their special effects. The way to do this is to add `/:' at the beginning.

For example, you can quote a local file name which appears remote, to prevent it from being treated as a remote file name. Thus, if you have a directory named `/foo:' and a file named `bar' in it, you can refer to that file in Emacs as `/:/foo:/bar'.

`/:' can also prevent `~' from being treated as a special character for a user's home directory. For example, `/:/tmp/~hack' refers to a file whose name is `~hack' in directory `/tmp'.

Likewise, quoting with `/:' is one way to enter in the minibuffer a file name that contains `$'. However, the `/:' must be at the beginning of the minibuffer in order to quote `$'.

You can also quote wildcard characters with `/:', for visiting. For example, `/:/tmp/foo*bar' visits the file `/tmp/foo*bar'. However, in most cases you can simply type the wildcard characters for themselves. For example, if the only file name in `/tmp' that starts with `foo' and ends with `bar' is `foo*bar', then specifying `/tmp/foo*bar' will visit just `/tmp/foo*bar'. Another way is to specify `/tmp/foo[*]bar'.


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M.15 File Name Cache

You can use the file name cache to make it easy to locate a file by name, without having to remember exactly where it is located. When typing a file name in the minibuffer, C-tab (file-cache-minibuffer-complete) completes it using the file name cache. If you repeat C-tab, that cycles through the possible completions of what you had originally typed. Note that the C-tab character cannot be typed on most text-only terminals.

The file name cache does not fill up automatically. Instead, you load file names into the cache using these commands:

M-x file-cache-add-directory RET directory RET
Add each file name in directory to the file name cache.
M-x file-cache-add-directory-using-find RET directory RET
Add each file name in directory and all of its nested subdirectories to the file name cache.
M-x file-cache-add-directory-using-locate RET directory RET
Add each file name in directory and all of its nested subdirectories to the file name cache, using locate to find them all.
M-x file-cache-add-directory-list RET variable RET
Add each file name in each directory listed in variable to the file name cache. variable should be a Lisp variable such as load-path or exec-path, whose value is a list of directory names.
M-x file-cache-clear-cache RET
Clear the cache; that is, remove all file names from it.


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M.16 Convenience Features for Finding Files

If you enable Recentf mode, with M-x recentf-mode, the `File' menu includes a submenu containing a list of recently opened files. M-x recentf-save-list saves the current recent-file-list to a file, and M-x recentf-edit-list edits it.

When Auto-image-file minor mode is enabled, visiting an image file displays it as an image, not as text. Likewise, inserting an image file into a buffer inserts it as an image. This works only when Emacs can display the relevant image type. The variables image-file-name-extensions or image-file-name-regexps control which file names are recognized as containing images.

The M-x ffap command generalizes find-file with more powerful heuristic defaults (see section AC.28.3 Finding Files and URLs at Point), often based on the text at point. Partial Completion mode offers other features extending find-file, which can be used with ffap. See section E.3.4 Completion Options.


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N. Using Multiple Buffers

The text you are editing in Emacs resides in an object called a buffer. Each time you visit a file, a buffer is created to hold the file's text. Each time you invoke Dired, a buffer is created to hold the directory listing. If you send a message with C-x m, a buffer named `*mail*' is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer called `*Help*'.

At any time, one and only one buffer is current. It is also called the selected buffer. Often we say that a command operates on "the buffer" as if there were only one; but really this means that the command operates on the current buffer (most commands do).

When Emacs has multiple windows, each window has its own chosen buffer and displays it; at any time, only one of the windows is selected, and its chosen buffer is the current buffer. Each window's mode line normally displays the name of the window's chosen buffer (see section O. Multiple Windows).

Each buffer has a name, which can be of any length, and you can select any buffer by giving its name. Most buffers are made by visiting files, and their names are derived from the files' names. But you can also create an empty buffer with any name you want. A newly started Emacs has a buffer named `*scratch*' which can be used for evaluating Lisp expressions in Emacs. The distinction between upper and lower case matters in buffer names.

Each buffer records individually what file it is visiting, whether it is modified, and what major mode and minor modes are in effect in it (see section R. Major Modes). Any Emacs variable can be made local to a particular buffer, meaning its value in that buffer can be different from the value in other buffers. See section AD.2.4 Local Variables.

A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by the Emacs integer data type. This is because Emacs tracks buffer positions using that data type. For 32-bit machines, the largest buffer size is 128 megabytes.

N.1 Creating and Selecting Buffers  Creating a new buffer or reselecting an old one.
N.2 Listing Existing Buffers  Getting a list of buffers that exist.
N.3 Miscellaneous Buffer Operations  Renaming; changing read-onlyness; copying text.
N.4 Killing Buffers  Killing buffers you no longer need.
N.5 Operating on Several Buffers  How to go through the list of all buffers and operate variously on several of them.
N.6 Indirect Buffers  An indirect buffer shares the text of another buffer.
N.7 Convenience Features and Customization of Buffer Handling  Convenience and customization features for buffer handling.


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N.1 Creating and Selecting Buffers

C-x b buffer RET
Select or create a buffer named buffer (switch-to-buffer).
C-x 4 b buffer RET
Similar, but select buffer in another window (switch-to-buffer-other-window).
C-x 5 b buffer RET
Similar, but select buffer in a separate frame (switch-to-buffer-other-frame).

To select the buffer named bufname, type C-x b bufname RET. This runs the command switch-to-buffer with argument bufname. You can use completion on an abbreviation for the buffer name you want (see section E.3 Completion). An empty argument to C-x b specifies the buffer that was current most recently among those not now displayed in any window.

To select a buffer in a window other than the current one, type C-x 4 b bufname RET. This runs the command switch-to-buffer-other-window which displays the buffer bufname in another window. By default, if displaying the buffer causes two vertically adjacent windows to be displayed, the heights of those windows are evened out; to countermand that and preserve the window configuration, set the variable even-window-heights to nil.

Similarly, C-x 5 b buffer RET runs the command switch-to-buffer-other-frame which selects a buffer in another frame.

You can control how certain buffers are handled by these commands by customizing the variables special-display-buffer-names, special-display-regexps, same-window-buffer-names, and same-window-regexps. See O.5 Forcing Display in the Same Window, and P.11 Special Buffer Frames, for more about these variables. In addition, if the value of display-buffer-reuse-frames is non-nil, and the buffer you want to switch to is already displayed in some frame, Emacs will raise that frame.

Most buffers are created by visiting files, or by Emacs commands that want to display some text, but you can also create a buffer explicitly by typing C-x b bufname RET. This makes a new, empty buffer that is not visiting any file, and selects it for editing. Such buffers are used for making notes to yourself. If you try to save one, you are asked for the file name to use. The new buffer's major mode is determined by the value of default-major-mode (see section R. Major Modes).

Note that C-x C-f, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. See section M.2 Visiting Files.

Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways--for example, by default they do not record undo information. It is best to avoid using such buffer names yourself.


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N.2 Listing Existing Buffers

C-x C-b
List the existing buffers (list-buffers).

To display a list of all the buffers that exist, type C-x C-b. Each line in the list shows one buffer's name, major mode and visited file. The buffers are listed in the order that they were current; the buffers that were current most recently come first.

`*' at the beginning of a line indicates the buffer is "modified." If several buffers are modified, it may be time to save some with C-x s (see section M.3 Saving Files). `%' indicates a read-only buffer. `.' marks the current buffer. Here is an example of a buffer list:

 
 MR Buffer         Size  Mode           File
 -- ------         ----  ----           ----
.*  emacs.tex      383402 Texinfo       /u2/emacs/man/emacs.tex
    *Help*         1287  Fundamental	
    files.el       23076 Emacs-Lisp     /u2/emacs/lisp/files.el
  % RMAIL          64042 RMAIL          /u/rms/RMAIL
 *% man            747   Dired          /u2/emacs/man/		
    net.emacs      343885 Fundamental   /u/rms/net.emacs
    fileio.c       27691 C              /u2/emacs/src/fileio.c
    NEWS           67340 Text           /u2/emacs/etc/NEWS
    *scratch*	   0	 Lisp Interaction

Note that the buffer `*Help*' was made by a help request; it is not visiting any file. The buffer man was made by Dired on the directory `/u2/emacs/man/'. You can list only buffers that are visiting files by giving the command a prefix; for instance, by typing C-u C-x C-b.


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N.3 Miscellaneous Buffer Operations

C-x C-q
Toggle read-only status of buffer (vc-toggle-read-only).
M-x rename-buffer RET name RET
Change the name of the current buffer.
M-x rename-uniquely
Rename the current buffer by adding `<number>' to the end.
M-x view-buffer RET buffer RET
Scroll through buffer buffer.

A buffer can be read-only, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with `%%' or `%*' near the left margin. Read-only buffers are usually made by subsystems such as Dired and Rmail that have special commands to operate on the text; also by visiting a file whose access control says you cannot write it.

If you wish to make changes in a read-only buffer, use the command C-x C-q (vc-toggle-read-only). It makes a read-only buffer writable, and makes a writable buffer read-only. In most cases, this works by setting the variable buffer-read-only, which has a local value in each buffer and makes the buffer read-only if its value is non-nil. If the file is maintained with version control, C-x C-q works through the version control system to change the read-only status of the file as well as the buffer. See section M.7 Version Control.

M-x rename-buffer changes the name of the current buffer. Specify the new name as a minibuffer argument. There is no default. If you specify a name that is in use for some other buffer, an error happens and no renaming is done.

M-x rename-uniquely renames the current buffer to a similar name with a numeric suffix added to make it both different and unique. This command does not need an argument. It is useful for creating multiple shell buffers: if you rename the `*Shell*' buffer, then do M-x shell again, it makes a new shell buffer named `*Shell*'; meanwhile, the old shell buffer continues to exist under its new name. This method is also good for mail buffers, compilation buffers, and most Emacs features that create special buffers with particular names.

M-x view-buffer is much like M-x view-file (see section M.10 Miscellaneous File Operations) except that it examines an already existing Emacs buffer. View mode provides commands for scrolling through the buffer conveniently but not for changing it. When you exit View mode with q, that switches back to the buffer (and the position) which was previously displayed in the window. Alternatively, if you exit View mode with e, the buffer and the value of point that resulted from your perusal remain in effect.

The commands M-x append-to-buffer and M-x insert-buffer can be used to copy text from one buffer to another. See section H.9 Accumulating Text.


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N.4 Killing Buffers

If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:

C-x k bufname RET
Kill buffer bufname (kill-buffer).
M-x kill-some-buffers
Offer to kill each buffer, one by one.

C-x k (kill-buffer) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just RET in the minibuffer, is to kill the current buffer. If you kill the current buffer, another buffer becomes current: one that was current in the recent past but is not displayed in any window now. If you ask to kill a file-visiting buffer that is modified (has unsaved editing), then you must confirm with yes before the buffer is killed.

The command M-x kill-some-buffers asks about each buffer, one by one. An answer of y means to kill the buffer. Killing the current buffer or a buffer containing unsaved changes selects a new buffer or asks for confirmation just like kill-buffer.

The buffer menu feature (see section N.5 Operating on Several Buffers) is also convenient for killing various buffers.

If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (see section AD.2.3 Hooks).

If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour.

You can also have this buffer purging done for you, every day at midnight, by enabling Midnight mode. Midnight mode operates each day at midnight; at that time, it runs clean-buffer-list, or whichever functions you have placed in the normal hook midnight-hook (see section AD.2.3 Hooks).

To enable Midnight mode, use the Customization buffer to set the variable midnight-mode to t. See section AD.2.2 Easy Customization Interface.


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N.5 Operating on Several Buffers

The buffer-menu facility is like a "Dired for buffers"; it allows you to request operations on various Emacs buffers by editing an Emacs buffer containing a list of them. You can save buffers, kill them (here called deleting them, for consistency with Dired), or display them.

M-x buffer-menu
Begin editing a buffer listing all Emacs buffers.

The command buffer-menu writes a list of all Emacs buffers into the buffer `*Buffer List*', and selects that buffer in Buffer Menu mode. The buffer is read-only, and can be changed only through the special commands described in this section. The usual Emacs cursor motion commands can be used in the `*Buffer List*' buffer. The following commands apply to the buffer described on the current line.

d
Request to delete (kill) the buffer, then move down. The request shows as a `D' on the line, before the buffer name. Requested deletions take place when you type the x command.
C-d
Like d but move up afterwards instead of down.
s
Request to save the buffer. The request shows as an `S' on the line. Requested saves take place when you type the x command. You may request both saving and deletion for the same buffer.
x
Perform previously requested deletions and saves.
u
Remove any request made for the current line, and move down.
DEL
Move to previous line and remove any request made for that line.

The d, C-d, s and u commands to add or remove flags also move down (or up) one line. They accept a numeric argument as a repeat count.

These commands operate immediately on the buffer listed on the current line:

~
Mark the buffer "unmodified." The command ~ does this immediately when you type it.
%
Toggle the buffer's read-only flag. The command % does this immediately when you type it.
t
Visit the buffer as a tags table. See section W.2.4 Selecting a Tags Table.

There are also commands to select another buffer or buffers:

q
Quit the buffer menu--immediately display the most recent formerly visible buffer in its place.
RET
f
Immediately select this line's buffer in place of the `*Buffer List*' buffer.
o
Immediately select this line's buffer in another window as if by C-x 4 b, leaving `*Buffer List*' visible.
C-o
Immediately display this line's buffer in another window, but don't select the window.
1
Immediately select this line's buffer in a full-screen window.
2
Immediately set up two windows, with this line's buffer in one, and the previously current buffer (aside from the buffer `*Buffer List*') in the other.
b
Bury the buffer listed on this line.
m
Mark this line's buffer to be displayed in another window if you exit with the v command. The request shows as a `>' at the beginning of the line. (A single buffer may not have both a delete request and a display request.)
v
Immediately select this line's buffer, and also display in other windows any buffers previously marked with the m command. If you have not marked any buffers, this command is equivalent to 1.

All that buffer-menu does directly is create and switch to a suitable buffer, and turn on Buffer Menu mode. Everything else described above is implemented by the special commands provided in Buffer Menu mode. One consequence of this is that you can switch from the `*Buffer List*' buffer to another Emacs buffer, and edit there. You can reselect the `*Buffer List*' buffer later, to perform the operations already requested, or you can kill it, or pay no further attention to it.

The only difference between buffer-menu and list-buffers is that buffer-menu switches to the `*Buffer List*' buffer in the selected window; list-buffers displays it in another window. If you run list-buffers (that is, type C-x C-b) and select the buffer list manually, you can use all of the commands described here.

The buffer `*Buffer List*' is not updated automatically when buffers are created and killed; its contents are just text. If you have created, deleted or renamed buffers, the way to update `*Buffer List*' to show what you have done is to type g (revert-buffer) or repeat the buffer-menu command.


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N.6 Indirect Buffers

An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link between files.

M-x make-indirect-buffer RET base-buffer RET indirect-name RET
Create an indirect buffer named indirect-name whose base buffer is base-buffer.
M-x clone-indirect-buffer RET
Create an indirect buffer that is a twin copy of the current buffer.
C-x 4 c
Create an indirect buffer that is a twin copy of the current buffer, and select it in another window (clone-indirect-buffer-other-window).

The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. But in all other respects, the indirect buffer and its base buffer are completely separate. They have different names, different values of point, different narrowing, different markers, different major modes, and different local variables.

An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing the base buffer effectively kills the indirect buffer, but killing an indirect buffer has no effect on its base buffer.

One way to use indirect buffers is to display multiple views of an outline. See section T.8.4 Viewing One Outline in Multiple Views.

A quick and handy way to make an indirect buffer is with the command M-x clone-indirect-buffer. It creates and selects an indirect buffer whose base buffer is the current buffer. With a numeric argument, it prompts for the name of the indirect buffer; otherwise it defaults to the name of the current buffer, modifying it by adding a `<n>' prefix if required. C-x 4 c (clone-indirect-buffer-other-window) works like M-x clone-indirect-buffer, but it selects the cloned buffer in another window. These commands come in handy if you want to create new `*info*' or `*Help*' buffers, for example.

The more general way is with the command M-x make-indirect-buffer. It creates an indirect buffer from buffer base-buffer, under the name indirect-name. It prompts for both base-buffer and indirect-name using the minibuffer.


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N.7 Convenience Features and Customization of Buffer Handling

This section describes several modes and features that make it more convenient to switch between buffers.

N.7.1 Making Buffer Names Unique  Buffer names can contain directory parts.
N.7.2 Switching Between Buffers using Substrings  Switching between buffers with substrings.
N.7.3 Customizing Buffer Menus  Configurable buffer menu.


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N.7.1 Making Buffer Names Unique

When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds `<2>', `<3>', etc. to the end of the buffer names (all but one of them).

Other methods work by adding parts of each file's directory to the buffer name. To select one, customize the variable uniquify-buffer-name-style (see section AD.2.2 Easy Customization Interface).

For instance, the forward naming method puts part of the directory name at the beginning of the buffer name; using this method, buffers visiting `/u/mernst/tmp/Makefile' and `/usr/projects/zaphod/Makefile' would be named `tmp/Makefile' and `zaphod/Makefile', respectively (instead of `Makefile' and `Makefile<2>').

By contrast, the post-forward naming method would call the buffers `Makefile|tmp' and `Makefile|zaphod', and the reverse naming method would call them `Makefile\tmp' and `Makefile\zaphod'. The nontrivial difference between post-forward and reverse occurs when just one directory name is not enough to distinguish two files; then reverse puts the directory names in reverse order, so that `/top/middle/file' becomes `file\middle\top', while post-forward puts them in forward order after the file name, as in `file|top/middle'.

Which rule to follow for putting the directory names in the buffer name is not very important if you are going to look at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and utilize fast.


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N.7.2 Switching Between Buffers using Substrings

Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of C-x b, C-x 4 b, C-x 5 b, and C-x 4 C-o with alternative commands that are somewhat "smarter."

When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed.

At any time, you can type RET to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use C-s and C-r to rotate the list until the desired buffer is first.

TAB while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers.

To enable Iswitchb mode, type M-x iswitchb-mode, or customize the variable iswitchb-mode to t (see section AD.2.2 Easy Customization Interface).


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N.7.3 Customizing Buffer Menus

M-x bs-show
Make a list of buffers similarly to M-x list-buffers but customizable.

M-x bs-show pops up a buffer list similar to the one normally displayed by C-x C-b but which you can customize. If you prefer this to the usual buffer list, you can bind this command to C-x C-b. To customize this buffer list, use the bs Custom group (see section AD.2.2 Easy Customization Interface).

MSB global minor mode ("MSB" stands for "mouse select buffer") provides a different and customizable mouse buffer menu which you may prefer. It replaces the bindings of mouse-buffer-menu, normally on C-Down-Mouse-1, and the menu bar buffer menu. You can customize the menu in the msb Custom group.


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O. Multiple Windows

Emacs can split a frame into two or many windows. Multiple windows can display parts of different buffers, or different parts of one buffer. Multiple frames always imply multiple windows, because each frame has its own set of windows. Each window belongs to one and only one frame.

O.1 Concepts of Emacs Windows  Introduction to Emacs windows.
O.2 Splitting Windows  New windows are made by splitting existing windows.
O.3 Using Other Windows  Moving to another window or doing something to it.
O.4 Displaying in Another Window  Finding a file or buffer in another window.
O.5 Forcing Display in the Same Window  Forcing certain buffers to appear in the selected window rather than in another window.
O.6 Deleting and Rearranging Windows  Deleting windows and changing their sizes.
O.7 Window Handling Convenience Features and Customization  Convenience functions for window handling.


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O.1 Concepts of Emacs Windows

Each Emacs window displays one Emacs buffer at any time. A single buffer may appear in more than one window; if it does, any changes in its text are displayed in all the windows where it appears. But the windows showing the same buffer can show different parts of it, because each window has its own value of point.

At any time, one of the windows is the selected window; the buffer this window is displaying is the current buffer. The terminal's cursor shows the location of point in this window. Each other window has a location of point as well, but since the terminal has only one cursor there is no way to show where those locations are. When multiple frames are visible in X, each frame has a cursor which appears in the frame's selected window. The cursor in the selected frame is solid; the cursor in other frames is a hollow box.

Commands to move point affect the value of point for the selected Emacs window only. They do not change the value of point in any other Emacs window, even one showing the same buffer. The same is true for commands such as C-x b to change the current buffer in the selected window; they do not affect other windows at all. However, there are other commands such as C-x 4 b that select a different window and switch buffers in it. Also, all commands that display information in a window, including (for example) C-h f (describe-function) and C-x C-b (list-buffers), work by switching buffers in a nonselected window without affecting the selected window.

When multiple windows show the same buffer, they can have different regions, because they can have different values of point. However, they all have the same value for the mark, because each buffer has only one mark position.

Each window has its own mode line, which displays the buffer name, modification status and major and minor modes of the buffer that is displayed in the window. See section B.3 The Mode Line, for full details on the mode line.


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O.2 Splitting Windows

C-x 2
Split the selected window into two windows, one above the other (split-window-vertically).
C-x 3
Split the selected window into two windows positioned side by side (split-window-horizontally).
C-Mouse-2
In the mode line or scroll bar of a window, split that window.

The command C-x 2 (split-window-vertically) breaks the selected window into two windows, one above the other. Both windows start out displaying the same buffer, with the same value of point. By default the two windows each get half the height of the window that was split; a numeric argument specifies how many lines to give to the top window.

C-x 3 (split-window-horizontally) breaks the selected window into two side-by-side windows. A numeric argument specifies how many columns to give the one on the left. A line of vertical bars separates the two windows. Windows that are not the full width of the screen have mode lines, but they are truncated. On terminals where Emacs does not support highlighting, truncated mode lines sometimes do not appear in inverse video.

You can split a window horizontally or vertically by clicking C-Mouse-2 in the mode line or the scroll bar. (This does not work in scroll bars implemented by X toolkits.) The line of splitting goes through the place where you click: if you click on the mode line, the new scroll bar goes above the spot; if you click in the scroll bar, the mode line of the split window is side by side with your click.

When a window is less than the full width, text lines too long to fit are frequent. Continuing all those lines might be confusing. The variable truncate-partial-width-windows can be set non-nil to force truncation in all windows less than the full width of the screen, independent of the buffer being displayed and its value for truncate-lines. See section D.8 Continuation Lines.

Horizontal scrolling is often used in side-by-side windows. See section J. Controlling the Display.

If split-window-keep-point is non-nil, the default, both of the windows resulting from C-x 2 inherit the value of point from the window that was split. This means that scrolling is inevitable. If this variable is nil, then C-x 2 tries to avoid scrolling the text currently visible on the screen, by putting point in each window at a position already visible in the window. It also selects whichever window contain the screen line that the cursor was previously on. Some users prefer the latter mode on slow terminals.


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O.3 Using Other Windows

C-x o
Select another window (other-window). That is o, not zero.
C-M-v
Scroll the next window (scroll-other-window).
M-x compare-windows
Find next place where the text in the selected window does not match the text in the next window.
Mouse-1
Mouse-1, in a window's mode line, selects that window but does not move point in it (mouse-select-window).

To select a different window, click with Mouse-1 on its mode line. With the keyboard, you can switch windows by typing C-x o (other-window). That is an o, for "other," not a zero. When there are more than two windows, this command moves through all the windows in a cyclic order, generally top to bottom and left to right. After the rightmost and bottommost window, it goes back to the one at the upper left corner. A numeric argument means to move several steps in the cyclic order of windows. A negative argument moves around the cycle in the opposite order. When the minibuffer is active, the minibuffer is the last window in the cycle; you can switch from the minibuffer window to one of the other windows, and later switch back and finish supplying the minibuffer argument that is requested. See section E.2 Editing in the Minibuffer.

The usual scrolling commands (see section J. Controlling the Display) apply to the selected window only, but there is one command to scroll the next window. C-M-v (scroll-other-window) scrolls the window that C-x o would select. It takes arguments, positive and negative, like C-v. (In the minibuffer, C-M-v scrolls the window that contains the minibuffer help display, if any, rather than the next window in the standard cyclic order.)

The command M-x compare-windows lets you compare two files or buffers visible in two windows, by moving through them to the next mismatch. See section M.9 Comparing Files, for details.


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O.4 Displaying in Another Window

C-x 4 is a prefix key for commands that select another window (splitting the window if there is only one) and select a buffer in that window. Different C-x 4 commands have different ways of finding the buffer to select.

C-x 4 b bufname RET
Select buffer bufname in another window. This runs switch-to-buffer-other-window.
C-x 4 C-o bufname RET
Display buffer bufname in another window, but don't select that buffer or that window. This runs display-buffer.
C-x 4 f filename RET
Visit file filename and select its buffer in another window. This runs find-file-other-window. See section M.2 Visiting Files.
C-x 4 d directory RET
Select a Dired buffer for directory directory in another window. This runs dired-other-window. See section AB. Dired, the Directory Editor.
C-x 4 m
Start composing a mail message in another window. This runs mail-other-window; its same-window analogue is C-x m (see section Z. Sending Mail).
C-x 4 .
Find a tag in the current tags table, in another window. This runs find-tag-other-window, the multiple-window variant of M-. (see section W.2 Tags Tables).
C-x 4 r filename RET
Visit file filename read-only, and select its buffer in another window. This runs find-file-read-only-other-window. See section M.2 Visiting Files.


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O.5 Forcing Display in the Same Window

Certain Emacs commands switch to a specific buffer with special contents. For example, M-x shell switches to a buffer named `*Shell*'. By convention, all these commands are written to pop up the buffer in a separate window. But you can specify that certain of these buffers should appear in the selected window.

If you add a buffer name to the list same-window-buffer-names, the effect is that such commands display that particular buffer by switching to it in the selected window. For example, if you add the element "*grep*" to the list, the grep command will display its output buffer in the selected window.

The default value of same-window-buffer-names is not nil: it specifies buffer names `*info*', `*mail*' and `*shell*' (as well as others used by more obscure Emacs packages). This is why M-x shell normally switches to the `*shell*' buffer in the selected window. If you delete this element from the value of same-window-buffer-names, the behavior of M-x shell will change--it will pop up the buffer in another window instead.

You can specify these buffers more generally with the variable same-window-regexps. Set it to a list of regular expressions; then any buffer whose name matches one of those regular expressions is displayed by switching to it in the selected window. (Once again, this applies only to buffers that normally get displayed for you in a separate window.) The default value of this variable specifies Telnet and rlogin buffers.

An analogous feature lets you specify buffers which should be displayed in their own individual frames. See section P.11 Special Buffer Frames.


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O.6 Deleting and Rearranging Windows

C-x 0
Delete the selected window (delete-window). The last character in this key sequence is a zero.
C-x 1
Delete all windows in the selected frame except the selected window (delete-other-windows).
C-x 4 0
Delete the selected window and kill the buffer that was showing in it (kill-buffer-and-window). The last character in this key sequence is a zero.
C-x ^
Make selected window taller (enlarge-window).
C-x }
Make selected window wider (enlarge-window-horizontally).
C-x {
Make selected window narrower (shrink-window-horizontally).
C-x -
Shrink this window if its buffer doesn't need so many lines (shrink-window-if-larger-than-buffer).
C-x +
Make all windows the same height (balance-windows).
Drag-Mouse-1
Dragging a window's mode line up or down with Mouse-1 changes window heights.
Mouse-2
Mouse-2 in a window's mode line deletes all other windows in the frame (mouse-delete-other-windows).
Mouse-3
Mouse-3 in a window's mode line deletes that window (mouse-delete-window), unless the frame has only one window, in which case it buries the current buffer instead and switches to another buffer.

To delete a window, type C-x 0 (delete-window). (That is a zero.) The space occupied by the deleted window is given to an adjacent window (but not the minibuffer window, even if that is active at the time). Once a window is deleted, its attributes are forgotten; only restoring a window configuration can bring it back. Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can select it in any window with C-x b.

C-x 4 0 (kill-buffer-and-window) is a stronger command than C-x 0; it kills the current buffer and then deletes the selected window.

C-x 1 (delete-other-windows) is more powerful in a different way; it deletes all the windows except the selected one (and the minibuffer); the selected window expands to use the whole frame except for the echo area.

You can also delete a window by clicking on its mode line with Mouse-2, and delete all the windows in a frame except one window by clicking on that window's mode line with Mouse-3.

The easiest way to adjust window heights is with a mouse. If you press Mouse-1 on a mode line, you can drag that mode line up or down, changing the heights of the windows above and below it.

To readjust the division of space among vertically adjacent windows, use C-x ^ (enlarge-window). It makes the currently selected window get one line bigger, or as many lines as is specified with a numeric argument. With a negative argument, it makes the selected window smaller. C-x } (enlarge-window-horizontally) makes the selected window wider by the specified number of columns. C-x { (shrink-window-horizontally) makes the selected window narrower by the specified number of columns.

When you make a window bigger, the space comes from one of its neighbors. If this makes any window too small, it is deleted and its space is given to an adjacent window. The minimum size is specified by the variables window-min-height and window-min-width.

The command C-x - (shrink-window-if-larger-than-buffer) reduces the height of the selected window, if it is taller than necessary to show the whole text of the buffer it is displaying. It gives the extra lines to other windows in the frame.

You can also use C-x + (balance-windows) to even out the heights of all the windows in the selected frame.


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O.7 Window Handling Convenience Features and Customization

M-x winner-mode is a global minor mode that records the changes in the window configuration (i.e. how the frames are partitioned into windows), so that you can "undo" them. To undo, use C-x left (winner-undo). If you change your mind while undoing, you can redo the changes you had undone using C-x right (M-x winner-redo). Another way to enable Winner mode is by customizing the variable winner-mode.

The Windmove commands move directionally between neighboring windows in a frame. M-x windmove-right selects the window immediately to the right of the currently selected one, and similarly for the "left," "up," and "down" counterparts. M-x windmove-default-keybindings binds these commands to S-right etc. (Not all terminals support shifted arrow keys, however.)

Follow minor mode (M-x follow-mode) synchronizes several windows on the same buffer so that they always display adjacent sections of that buffer. See section J.8 Follow Mode.

M-x scroll-all-mode provides commands to scroll all visible windows together. You can also turn it on by customizing the variable scroll-all-mode. The commands provided are M-x scroll-all-scroll-down-all, M-x scroll-all-page-down-all and their corresponding "up" equivalents. To make this mode useful, you should bind these commands to appropriate keys.


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P. Frames and X Windows

When using the X Window System, you can create multiple windows at the X level in a single Emacs session. Each X window that belongs to Emacs displays a frame which can contain one or several Emacs windows. A frame initially contains a single general-purpose Emacs window which you can subdivide vertically or horizontally into smaller windows. A frame normally contains its own echo area and minibuffer, but you can make frames that don't have these--they use the echo area and minibuffer of another frame.

Editing you do in one frame also affects the other frames. For instance, if you put text in the kill ring in one frame, you can yank it in another frame. If you exit Emacs through C-x C-c in one frame, it terminates all the frames. To delete just one frame, use C-x 5 0 (that is zero, not o).

To avoid confusion, we reserve the word "window" for the subdivisions that Emacs implements, and never use it to refer to a frame.

Emacs compiled for MS-DOS emulates some aspects of the window system so that you can use many of the features described in this chapter. See section AH.1 Keyboard and Mouse on MS-DOS, for more information.

Emacs compiled for MS Windows mostly supports the same features as under X. However, images, tool bars, and tooltips are not yet available in Emacs version 21.1 on MS-Windows.

P.1 Mouse Commands for Editing  Moving, cutting, and pasting, with the mouse.
P.2 Secondary Selection  Cutting without altering point and mark.
P.3 Using the Clipboard  Using the clipboard for selections.
P.4 Following References with the Mouse  Using the mouse to select an item from a list.
P.5 Mouse Clicks for Menus  Mouse clicks that bring up menus.
P.6 Mode Line Mouse Commands  Mouse clicks on the mode line.
P.7 Creating Frames  Creating additional Emacs frames with various contents.
P.8 Frame Commands  Iconifying, deleting, and switching frames.
P.9 Making and Using a Speedbar Frame  How to make and use a speedbar frame.
P.10 Multiple Displays  How one Emacs job can talk to several displays.
P.11 Special Buffer Frames  You can make certain buffers have their own frames.
P.12 Setting Frame Parameters  Changing the colors and other modes of frames.
P.13 Scroll Bars  How to enable and disable scroll bars; how to use them.
P.14 Scrolling With "Wheeled" Mice  Using mouse wheels for scrolling.
P.15 Menu Bars  Enabling and disabling the menu bar.
P.16 Tool Bars  Enabling and disabling the tool bar.
P.17 Using Dialog Boxes  Controlling use of dialog boxes.
P.18 Tooltips (or "Balloon Help")  Showing "tooltips", AKA "balloon help" for active text.
P.19 Mouse Avoidance  Moving the mouse pointer out of the way.
P.20 Non-Window Terminals  Multiple frames on terminals that show only one.
P.21 Using a Mouse in Terminal Emulators  Using the mouse in an XTerm terminal emulator.


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P.1 Mouse Commands for Editing

The mouse commands for selecting and copying a region are mostly compatible with the xterm program. You can use the same mouse commands for copying between Emacs and other X client programs.

If you select a region with any of these mouse commands, and then immediately afterward type the DELETE function key, it deletes the region that you selected. The BACKSPACE function key and the ASCII character DEL do not do this; if you type any other key in between the mouse command and DELETE, it does not do this.

Mouse-1
Move point to where you click (mouse-set-point). This is normally the left button.

Drag-Mouse-1
Set the region to the text you select by dragging, and copy it to the kill ring (mouse-set-region). You can specify both ends of the region with this single command.

If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can select regions that don't fit entirely on the screen. The number of lines scrolled per step depends on how far away from the window edge the mouse has gone; the variable mouse-scroll-min-lines specifies a minimum step size.

Mouse-2
Yank the last killed text, where you click (mouse-yank-at-click). This is normally the middle button.

Mouse-3
This command, mouse-save-then-kill, has several functions depending on where you click and the status of the region.

The most basic case is when you click Mouse-1 in one place and then Mouse-3 in another. This selects the text between those two positions as the region. It also copies the new region to the kill ring, so that you can copy it to someplace else.

If you click Mouse-1 in the text, scroll with the scroll bar, and then click Mouse-3, it remembers where point was before scrolling (where you put it with Mouse-1), and uses that position as the other end of the region. This is so that you can select a region that doesn't fit entirely on the screen.

More generally, if you do not have a highlighted region, Mouse-3 selects the text between point and the click position as the region. It does this by setting the mark where point was, and moving point to where you click.

If you have a highlighted region, or if the region was set just before by dragging button 1, Mouse-3 adjusts the nearer end of the region by moving it to where you click. The adjusted region's text also replaces the old region's text in the kill ring.

If you originally specified the region using a double or triple Mouse-1, so that the region is defined to consist of entire words or lines, then adjusting the region with Mouse-3 also proceeds by entire words or lines.

If you use Mouse-3 a second time consecutively, at the same place, that kills the region already selected.

Double-Mouse-1
This key sets the region around the word which you click on. If you click on a character with "symbol" syntax (such as underscore, in C mode), it sets the region around the symbol surrounding that character.

If you click on a character with open-parenthesis or close-parenthesis syntax, it sets the region around the parenthetical grouping which that character starts or ends. If you click on a character with string-delimiter syntax (such as a singlequote or doublequote in C), it sets the region around the string constant (using heuristics to figure out whether that character is the beginning or the end of it).

Double-Drag-Mouse-1
This key selects a region made up of the words you drag across.

Triple-Mouse-1
This key sets the region around the line you click on.

Triple-Drag-Mouse-1
This key selects a region made up of the lines you drag across.

The simplest way to kill text with the mouse is to press Mouse-1 at one end, then press Mouse-3 twice at the other end. See section H.7 Deletion and Killing. To copy the text into the kill ring without deleting it from the buffer, press Mouse-3 just once--or just drag across the text with Mouse-1. Then you can copy it elsewhere by yanking it.

To yank the killed or copied text somewhere else, move the mouse there and press Mouse-2. See section H.8 Yanking. However, if mouse-yank-at-point is non-nil, Mouse-2 yanks at point. Then it does not matter where you click, or even which of the frame's windows you click on. The default value is nil. This variable also affects yanking the secondary selection.

To copy text to another X window, kill it or save it in the kill ring. Under X, this also sets the primary selection. Then use the "paste" or "yank" command of the program operating the other window to insert the text from the selection.

To copy text from another X window, use the "cut" or "copy" command of the program operating the other window, to select the text you want. Then yank it in Emacs with C-y or Mouse-2.

The standard coding system for X selections is compound-text. To specify another coding system for X selections, use C-x RET x or C-x RET X. See section Q.9 Specifying a Coding System.

These cutting and pasting commands also work on MS-Windows.

When Emacs puts text into the kill ring, or rotates text to the front of the kill ring, it sets the primary selection in the X server. This is how other X clients can access the text. Emacs also stores the text in the cut buffer, but only if the text is short enough (the value of x-cut-buffer-max specifies the maximum number of characters); putting long strings in the cut buffer can be slow.

The commands to yank the first entry in the kill ring actually check first for a primary selection in another program; after that, they check for text in the cut buffer. If neither of those sources provides text to yank, the kill ring contents are used.


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P.2 Secondary Selection

The secondary selection is another way of selecting text using X. It does not use point or the mark, so you can use it to kill text without setting point or the mark.

M-Drag-Mouse-1
Set the secondary selection, with one end at the place where you press down the button, and the other end at the place where you release it (mouse-set-secondary). The highlighting appears and changes as you drag. You can control the appearance of the highlighting by customizing the secondary-selection face (see section AD.2.2.3 Customizing Faces).

If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can mark regions that don't fit entirely on the screen.

M-Mouse-1
Set one endpoint for the secondary selection (mouse-start-secondary).

M-Mouse-3
Make a secondary selection, using the place specified with M-Mouse-1 as the other end (mouse-secondary-save-then-kill). A second click at the same place kills the secondary selection just made.

M-Mouse-2
Insert the secondary selection where you click (mouse-yank-secondary). This places point at the end of the yanked text.

Double or triple clicking of M-Mouse-1 operates on words and lines, much like Mouse-1.

If mouse-yank-at-point is non-nil, M-Mouse-2 yanks at point. Then it does not matter precisely where you click; all that matters is which window you click on. See section P.1 Mouse Commands for Editing.


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P.3 Using the Clipboard

As well as the primary and secondary selection types, X supports a clipboard selection type which is used by some applications, particularly under OpenWindows and Gnome.

The command M-x menu-bar-enable-clipboard makes the Cut, Paste and Copy menu items, as well as the keys of the same names, all use the clipboard. You can customize the option x-select-enable-clipboard to make the Emacs yank functions consult the clipboard before the primary selection, and to make the kill functions to store in the clipboard as well as the primary selection. Otherwise they do not access the clipboard at all. Using the clipboard is the default on MS-Windows, unlike most systems.


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P.4 Following References with the Mouse

Some Emacs buffers display lists of various sorts. These include lists of files, of buffers, of possible completions, of matches for a pattern, and so on.

Since yanking text into these buffers is not very useful, most of them define Mouse-2 specially, as a command to use or view the item you click on.

For example, if you click Mouse-2 on a file name in a Dired buffer, you visit that file. If you click Mouse-2 on an error message in the `*Compilation*' buffer, you go to the source code for that error message. If you click Mouse-2 on a completion in the `*Completions*' buffer, you choose that completion.

You can usually tell when Mouse-2 has this special sort of meaning because the sensitive text highlights when you move the mouse over it.


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P.5 Mouse Clicks for Menus

Mouse clicks modified with the CTRL and SHIFT keys bring up menus.

C-Mouse-1
This menu is for selecting a buffer.

The MSB ("mouse select buffer") global minor mode makes this menu smarter and more customizable. See section N.7.3 Customizing Buffer Menus.

C-Mouse-2
This menu is for specifying faces and other text properties for editing formatted text. See section T.11 Editing Formatted Text.

C-Mouse-3
This menu is mode-specific. For most modes if Menu-bar mode is on, this menu has the same items as all the mode-specific menu-bar menus put together. Some modes may specify a different menu for this button.(2) If Menu-bar mode is off, this menu contains all the items which would be present in the menu bar--not just the mode-specific ones--so that you can access them without having to display the menu bar.

S-Mouse-1
This menu is for specifying the frame's principal font.


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P.6 Mode Line Mouse Commands

You can use mouse clicks on window mode lines to select and manipulate windows.

Mouse-1
Mouse-1 on a mode line selects the window above. By dragging Mouse-1 on the mode line, you can move it, thus changing the height of the windows above and below.

Mouse-2
Mouse-2 on a mode line expands that window to fill its frame.

Mouse-3
Mouse-3 on a mode line deletes the window above. If the frame has only one window, it buries the current buffer instead and switches to another buffer.

C-Mouse-2
C-Mouse-2 on a mode line splits the window above horizontally, above the place in the mode line where you click.

C-Mouse-2 on a scroll bar splits the corresponding window vertically, unless you are using an X toolkit's implementation of scroll bars. See section O.2 Splitting Windows.

The commands above apply to areas of the mode line which do not have special mouse bindings of their own. Some areas, such as the buffer name and the major mode name, have their own special mouse bindings. Emacs displays information about these bindings when you hold the mouse over such a place (see section P.18 Tooltips (or "Balloon Help")).


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P.7 Creating Frames

The prefix key C-x 5 is analogous to C-x 4, with parallel subcommands. The difference is that C-x 5 commands create a new frame rather than just a new window in the selected frame (see section O.4 Displaying in Another Window). If an existing visible or iconified frame already displays the requested material, these commands use the existing frame, after raising or deiconifying as necessary.

The various C-x 5 commands differ in how they find or create the buffer to select:

C-x 5 2
Create a new frame (make-frame-command).
C-x 5 b bufname RET
Select buffer bufname in another frame. This runs switch-to-buffer-other-frame.
C-x 5 f filename RET
Visit file filename and select its buffer in another frame. This runs find-file-other-frame. See section M.2 Visiting Files.
C-x 5 d directory RET
Select a Dired buffer for directory directory in another frame. This runs dired-other-frame. See section AB. Dired, the Directory Editor.
C-x 5 m
Start composing a mail message in another frame. This runs mail-other-frame. It is the other-frame variant of C-x m. See section Z. Sending Mail.
C-x 5 .
Find a tag in the current tag table in another frame. This runs find-tag-other-frame, the multiple-frame variant of M-.. See section W.2 Tags Tables.
C-x 5 r filename RET
Visit file filename read-only, and select its buffer in another frame. This runs find-file-read-only-other-frame. See section M.2 Visiting Files.

You can control the appearance of new frames you create by setting the frame parameters in default-frame-alist. You can use the variable initial-frame-alist to specify parameters that affect only the initial frame. See section `Initial Parameters' in The Emacs Lisp Reference Manual, for more information.

The easiest way to specify the principal font for all your Emacs frames is with an X resource (see section AE.7 Font Specification Options), but you can also do it by modifying default-frame-alist to specify the font parameter, as shown here:

 
(add-to-list 'default-frame-alist '(font . "10x20"))

Here's a similar example for specifying a foreground color:

 
(add-to-list 'default-frame-alist '(background-color . "blue"))


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P.8 Frame Commands

The following commands let you create, delete and operate on frames:

C-z
Iconify the selected Emacs frame (iconify-or-deiconify-frame). The normal meaning of C-z, to suspend Emacs, is not useful under a window system, so it has a different binding in that case.

If you type this command on an Emacs frame's icon, it deiconifies the frame.

C-x 5 0
Delete the selected frame (delete-frame). This is not allowed if there is only one frame.

C-x 5 o
Select another frame, raise it, and warp the mouse to it so that it stays selected. If you repeat this command, it cycles through all the frames on your terminal.

C-x 5 1
Delete all frames except the selected one.


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P.9 Making and Using a Speedbar Frame

An Emacs frame can have a speedbar, which is a vertical window that serves as a scrollable menu of files you could visit and tags within those files. To create a speedbar, type M-x speedbar; this creates a speedbar window for the selected frame. From then on, you can click on a file name in the speedbar to visit that file in the corresponding Emacs frame, or click on a tag name to jump to that tag in the Emacs frame.

Initially the speedbar lists the immediate contents of the current directory, one file per line. Each line also has a box, `[+]' or `<+>', that you can click on with Mouse-2 to "open up" the contents of that item. If the line names a directory, opening it adds the contents of that directory to the speedbar display, underneath the directory's own line. If the line lists an ordinary file, opening it up adds a list of the tags in that file to the speedbar display. When a file is opened up, the `[+]' changes to `[-]'; you can click on that box to "close up" that file (hide its contents).

Some major modes, including Rmail mode, Info, and GUD, have specialized ways of putting useful items into the speedbar for you to select. For example, in Rmail mode, the speedbar shows a list of Rmail files, and lets you move the current message to another Rmail file by clicking on its `<M>' box.

A speedbar belongs to one Emacs frame, and always operates on that frame. If you use multiple frames, you can make a speedbar for some or all of the frames; type M-x speedbar in any given frame to make a speedbar for it.


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P.10 Multiple Displays

A single Emacs can talk to more than one X display. Initially, Emacs uses just one display--the one specified with the DISPLAY environment variable or with the `--display' option (see section AE.2 Initial Options). To connect to another display, use the command make-frame-on-display:

M-x make-frame-on-display RET display RET
Create a new frame on display display.

A single X server can handle more than one screen. When you open frames on two screens belonging to one server, Emacs knows they share a single keyboard, and it treats all the commands arriving from these screens as a single stream of input.

When you open frames on different X servers, Emacs makes a separate input stream for each server. This way, two users can type simultaneously on the two displays, and Emacs will not garble their input. Each server also has its own selected frame. The commands you enter with a particular X server apply to that server's selected frame.

Despite these features, people using the same Emacs job from different displays can still interfere with each other if they are not careful. For example, if any one types C-x C-c, that exits the Emacs job for all of them!


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P.11 Special Buffer Frames

You can make certain chosen buffers, for which Emacs normally creates a second window when you have just one window, appear in special frames of their own. To do this, set the variable special-display-buffer-names to a list of buffer names; any buffer whose name is in that list automatically gets a special frame, when an Emacs command wants to display it "in another window."

For example, if you set the variable this way,

 
(setq special-display-buffer-names
      '("*Completions*" "*grep*" "*tex-shell*"))

then completion lists, grep output and the TeX mode shell buffer get individual frames of their own. These frames, and the windows in them, are never automatically split or reused for any other buffers. They continue to show the buffers they were created for, unless you alter them by hand. Killing the special buffer deletes its frame automatically.

More generally, you can set special-display-regexps to a list of regular expressions; then a buffer gets its own frame if its name matches any of those regular expressions. (Once again, this applies only to buffers that normally get displayed for you in a separate window.)

The variable special-display-frame-alist specifies the frame parameters for these frames. It has a default value, so you don't need to set it.

For those who know Lisp, an element of special-display-buffer-names or special-display-regexps can also be a list. Then the first element is the buffer name or regular expression; the rest of the list specifies how to create the frame. It can be an association list specifying frame parameter values; these values take precedence over parameter values specified in special-display-frame-alist. Alternatively, it can have this form:

 
(function args...)

where function is a symbol. Then the frame is constructed by calling function; its first argument is the buffer, and its remaining arguments are args.

An analogous feature lets you specify buffers which should be displayed in the selected window. See section O.5 Forcing Display in the Same Window. The same-window feature takes precedence over the special-frame feature; therefore, if you add a buffer name to special-display-buffer-names and it has no effect, check to see whether that feature is also in use for the same buffer name.


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P.12 Setting Frame Parameters

This section describes commands for altering the display style and window management behavior of the selected frame.

M-x set-foreground-color RET color RET
Specify color color for the foreground of the selected frame. (This also changes the foreground color of the default face.)

M-x set-background-color RET color RET
Specify color color for the background of the selected frame. (This also changes the background color of the default face.)

M-x set-cursor-color RET color RET
Specify color color for the cursor of the selected frame.

M-x set-mouse-color RET color RET
Specify color color for the mouse cursor when it is over the selected frame.

M-x set-border-color RET color RET
Specify color color for the border of the selected frame.

M-x list-colors-display
Display the defined color names and show what the colors look like. This command is somewhat slow.

M-x auto-raise-mode
Toggle whether or not the selected frame should auto-raise. Auto-raise means that every time you move the mouse onto the frame, it raises the frame.

Note that this auto-raise feature is implemented by Emacs itself. Some window managers also implement auto-raise. If you enable auto-raise for Emacs frames in your X window manager, it should work, but it is beyond Emacs's control and therefore auto-raise-mode has no effect on it.

M-x auto-lower-mode
Toggle whether or not the selected frame should auto-lower. Auto-lower means that every time you move the mouse off the frame, the frame moves to the bottom of the stack of X windows.

The command auto-lower-mode has no effect on auto-lower implemented by the X window manager. To control that, you must use the appropriate window manager features.

M-x set-frame-font RET font RET
Specify font font as the principal font for the selected frame. The principal font controls several face attributes of the default face (see section J.1 Using Multiple Typefaces). For example, if the principal font has a height of 12 pt, all text will be drawn in 12 pt fonts, unless you use another face that specifies a different height. See section AE.7 Font Specification Options, for ways to list the available fonts on your system.

You can also set a frame's principal font through a pop-up menu. Press S-Mouse-1 to activate this menu.

In Emacs versions that use an X toolkit, the color-setting and font-setting functions don't affect menus and the menu bar, since they are displayed by their own widget classes. To change the appearance of the menus and menu bar, you must use X resources (see section AE.13 X Resources). See section AE.8 Window Color Options, regarding colors. See section AE.7 Font Specification Options, regarding choice of font.

Colors, fonts, and other attributes of the frame's display can also be customized by setting frame parameters in the variable default-frame-alist (see section P.7 Creating Frames). For a detailed description of frame parameters and customization, see section `Frame Parameters' in The Emacs Lisp Reference Manual.


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P.13 Scroll Bars

When using X, Emacs normally makes a scroll bar at the left of each Emacs window.(3) The scroll bar runs the height of the window, and shows a moving rectangular inner box which represents the portion of the buffer currently displayed. The entire height of the scroll bar represents the entire length of the buffer.

You can use Mouse-2 (normally, the middle button) in the scroll bar to move or drag the inner box up and down. If you move it to the top of the scroll bar, you see the top of the buffer. If you move it to the bottom of the scroll bar, you see the bottom of the buffer.

The left and right buttons in the scroll bar scroll by controlled increments. Mouse-1 (normally, the left button) moves the line at the level where you click up to the top of the window. Mouse-3 (normally, the right button) moves the line at the top of the window down to the level where you click. By clicking repeatedly in the same place, you can scroll by the same distance over and over.

If you are using Emacs's own implementation of scroll bars, as opposed to scroll bars from an X toolkit, you can also click C-Mouse-2 in the scroll bar to split a window vertically. The split occurs on the line where you click.

You can enable or disable Scroll Bar mode with the command M-x scroll-bar-mode. With no argument, it toggles the use of scroll bars. With an argument, it turns use of scroll bars on if and only if the argument is positive. This command applies to all frames, including frames yet to be created. Customize the option scroll-bar-mode to control the use of scroll bars at startup. You can use it to specify that they are placed at the right of windows if you prefer that. You can use the X resource `verticalScrollBars' to control the initial setting of Scroll Bar mode similarly. See section AE.13 X Resources.

To enable or disable scroll bars for just the selected frame, use the M-x toggle-scroll-bar command.

You can control the scroll bar width by changing the value of the scroll-bar-width frame parameter.


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P.14 Scrolling With "Wheeled" Mice

Some mice have a "wheel" instead of a third button. You can usually click the wheel to act as either Mouse-2 or Mouse-3, depending on the setup. You can also use the wheel to scroll windows instead of using the scroll bar or keyboard commands. To do so, turn on Mouse Wheel global minor mode with the command M-x mouse-wheel-mode or by customizing the option mouse-wheel-mode. Support for the wheel depends on the system generating appropriate events for Emacs.

The variables mouse-wheel-follow-mouse and mouse-wheel-scroll-amount determine where and by how much buffers are scrolled.


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P.15 Menu Bars

You can turn display of menu bars on or off with M-x menu-bar-mode or by customizing the option menu-bar-mode. With no argument, this command toggles Menu Bar mode, a minor mode. With an argument, the command turns Menu Bar mode on if the argument is positive, off if the argument is not positive. You can use the X resource `menuBarLines' to control the initial setting of Menu Bar mode. See section AE.13 X Resources.

Expert users often turn off the menu bar, especially on text-only terminals, where this makes one additional line available for text. If the menu bar is off, you can still pop up a menu of its contents with C-Mouse-3 on a display which supports pop-up menus. See section P.5 Mouse Clicks for Menus.

See section B.4 The Menu Bar, for information on how to invoke commands with the menu bar.


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P.16 Tool Bars

The tool bar is a line (or multiple lines) of icons at the top of the Emacs window. You can click on these icons with the mouse to do various jobs.

The global tool bar contains general commands. Some major modes define their own tool bars to replace it. A few "special" modes that are not designed for ordinary editing remove some items from the global tool bar.

Tool bars work only on a graphical display. The tool bar uses colored XPM icons if Emacs was built with XPM support. Otherwise, the tool bar uses monochrome icons (PBM or XBM format).

You can turn display of tool bars on or off with M-x tool-bar-mode.


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P.17 Using Dialog Boxes

A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command to begin with.

You can customize the option use-dialog-box to suppress the use of dialog boxes. This also controls whether to use file selection windows (but those are not supported on all platforms).


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P.18 Tooltips (or "Balloon Help")

Tooltips are small X windows displaying a help string at the current mouse position, typically over text--including the mode line--which can be activated with the mouse or other keys. (This facility is sometimes known as balloon help.) Help text may be available for menu items too.

To use tooltips, enable Tooltip mode with the command M-x tooltip-mode. The customization group tooltip controls various aspects of how tooltips work. When Tooltip mode is disabled, the help text is displayed in the echo area instead.

As of Emacs 21.1, tooltips are not supported on MS-Windows. So help text always appears in the echo area.


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P.19 Mouse Avoidance

Mouse Avoidance mode keeps the window system mouse pointer away from point, to avoid obscuring text. Whenever it moves the mouse, it also raises the frame. To use Mouse Avoidance mode, customize the option mouse-avoidance-mode. You can set this to various values to move the mouse in several ways:

banish
Move the mouse to the upper-right corner on any key-press;
exile
Move the mouse to the corner only if the cursor gets too close, and allow it to return once the cursor is out of the way;
jump
If the cursor gets too close to the mouse, displace the mouse a random distance & direction;
animate
As jump, but shows steps along the way for illusion of motion;
cat-and-mouse
The same as animate;
proteus
As animate, but changes the shape of the mouse pointer too.

You can also use the command M-x mouse-avoidance-mode to enable the mode.


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P.20 Non-Window Terminals

If your terminal does not have a window system that Emacs supports, then it can display only one Emacs frame at a time. However, you can still create multiple Emacs frames, and switch between them. Switching frames on these terminals is much like switching between different window configurations.

Use C-x 5 2 to create a new frame and switch to it; use C-x 5 o to cycle through the existing frames; use C-x 5 0 to delete the current frame.

Each frame has a number to distinguish it. If your terminal can display only one frame at a time, the selected frame's number n appears near the beginning of the mode line, in the form `Fn'.

`Fn' is actually the frame's name. You can also specify a different name if you wish, and you can select a frame by its name. Use the command M-x set-frame-name RET name RET to specify a new name for the selected frame, and use M-x select-frame-by-name RET name RET to select a frame according to its name. The name you specify appears in the mode line when the frame is selected.


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P.21 Using a Mouse in Terminal Emulators

Some terminal emulators under X support mouse clicks in the terminal window. In a terminal emulator which is compatible with xterm, you can use M-x xterm-mouse-mode to enable simple use of the mouse--only single clicks are supported. The normal xterm mouse functionality is still available by holding down the SHIFT key when you press the mouse button. The Linux console supports this mode if it has support for the mouse enabled, e.g. using the gpm daemon.


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Q. International Character Set Support

Emacs supports a wide variety of international character sets, including European variants of the Latin alphabet, as well as Chinese, Cyrillic, Devanagari (Hindi and Marathi), Ethiopic, Greek, Hebrew, IPA, Japanese, Korean, Lao, Thai, Tibetan, and Vietnamese scripts. These features have been merged from the modified version of Emacs known as MULE (for "MULti-lingual Enhancement to GNU Emacs")

Emacs also supports various encodings of these characters used by other internationalized software, such as word processors and mailers.

Emacs allows editing text with international characters by supporting all the related activities:

The rest of this chapter describes these issues in detail.

Q.1 Introduction to International Character Sets  Basic concepts of multibyte characters.
Q.2 Enabling Multibyte Characters  Controlling whether to use multibyte characters.
Q.3 Language Environments  Setting things up for the language you use.
Q.4 Input Methods  Entering text characters not on your keyboard.
Q.5 Selecting an Input Method  Specifying your choice of input methods.
Q.6 Unibyte and Multibyte Non-ASCII characters  How single-byte characters convert to multibyte.
Q.7 Coding Systems  Character set conversion when you read and write files, and so on.
Q.8 Recognizing Coding Systems  How Emacs figures out which conversion to use.
Q.9 Specifying a Coding System  Various ways to choose which conversion to use.
Q.10 Fontsets  Fontsets are collections of fonts that cover the whole spectrum of characters.
Q.11 Defining fontsets  Defining a new fontset.
Q.12 Undisplayable Characters  When characters don't display.
Q.13 Single-byte Character Set Support  You can pick one European character set to use without multibyte characters.


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Q.1 Introduction to International Character Sets

The users of international character sets and scripts have established many more-or-less standard coding systems for storing files. Emacs internally uses a single multibyte character encoding, so that it can intermix characters from all these scripts in a single buffer or string. This encoding represents each non-ASCII character as a sequence of bytes in the range 0200 through 0377. Emacs translates between the multibyte character encoding and various other coding systems when reading and writing files, when exchanging data with subprocesses, and (in some cases) in the C-q command (see section Q.6 Unibyte and Multibyte Non-ASCII characters).

The command C-h h (view-hello-file) displays the file `etc/HELLO', which shows how to say "hello" in many languages. This illustrates various scripts. If some characters can't be displayed on your terminal, they appear as `?' or as hollow boxes (see section Q.12 Undisplayable Characters).

Keyboards, even in the countries where these character sets are used, generally don't have keys for all the characters in them. So Emacs supports various input methods, typically one for each script or language, to make it convenient to type them.

The prefix key C-x RET is used for commands that pertain to multibyte characters, coding systems, and input methods.


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Q.2 Enabling Multibyte Characters

You can enable or disable multibyte character support, either for Emacs as a whole, or for a single buffer. When multibyte characters are disabled in a buffer, then each byte in that buffer represents a character, even codes 0200 through 0377. The old features for supporting the European character sets, ISO Latin-1 and ISO Latin-2, work as they did in Emacs 19 and also work for the other ISO 8859 character sets.

However, there is no need to turn off multibyte character support to use ISO Latin; the Emacs multibyte character set includes all the characters in these character sets, and Emacs can translate automatically to and from the ISO codes.

By default, Emacs starts in multibyte mode, because that allows you to use all the supported languages and scripts without limitations.

To edit a particular file in unibyte representation, visit it using find-file-literally. See section M.2 Visiting Files. To convert a buffer in multibyte representation into a single-byte representation of the same characters, the easiest way is to save the contents in a file, kill the buffer, and find the file again with find-file-literally. You can also use C-x RET c (universal-coding-system-argument) and specify `raw-text' as the coding system with which to find or save a file. See section Q.9 Specifying a Coding System. Finding a file as `raw-text' doesn't disable format conversion, uncompression and auto mode selection as find-file-literally does.

To turn off multibyte character support by default, start Emacs with the `--unibyte' option (see section AE.2 Initial Options), or set the environment variable EMACS_UNIBYTE. You can also customize enable-multibyte-characters or, equivalently, directly set the variable default-enable-multibyte-characters to nil in your init file to have basically the same effect as `--unibyte'.

To convert a unibyte session to a multibyte session, set default-enable-multibyte-characters to t. Buffers which were created in the unibyte session before you turn on multibyte support will stay unibyte. You can turn on multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer.

With `--unibyte', multibyte strings are not created during initialization from the values of environment variables, `/etc/passwd' entries etc. that contain non-ASCII 8-bit characters.

Emacs normally loads Lisp files as multibyte, regardless of whether you used `--unibyte'. This includes the Emacs initialization file, `.emacs', and the initialization files of Emacs packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by putting `-*-unibyte: t;-*-' in a comment on the first line. Then that file is always loaded as unibyte text, even if you did not start Emacs with `--unibyte'. The motivation for these conventions is that it is more reliable to always load any particular Lisp file in the same way. However, you can load a Lisp file as unibyte, on any one occasion, by typing C-x RET c raw-text RET immediately before loading it.

The mode line indicates whether multibyte character support is enabled in the current buffer. If it is, there are two or more characters (most often two dashes) before the colon near the beginning of the mode line. When multibyte characters are not enabled, just one dash precedes the colon.


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Q.3 Language Environments

All supported character sets are supported in Emacs buffers whenever multibyte characters are enabled; there is no need to select a particular language in order to display its characters in an Emacs buffer. However, it is important to select a language environment in order to set various defaults. The language environment really represents a choice of preferred script (more or less) rather than a choice of language.

The language environment controls which coding systems to recognize when reading text (see section Q.8 Recognizing Coding Systems). This applies to files, incoming mail, netnews, and any other text you read into Emacs. It may also specify the default coding system to use when you create a file. Each language environment also specifies a default input method.

To select a language environment, customize the option current-language-environment or use the command M-x set-language-environment. It makes no difference which buffer is current when you use this command, because the effects apply globally to the Emacs session. The supported language environments include:

Chinese-BIG5, Chinese-CNS, Chinese-GB, Cyrillic-ALT, Cyrillic-ISO, Cyrillic-KOI8, Czech, Devanagari, Dutch, English, Ethiopic, German, Greek, Hebrew, IPA, Japanese, Korean, Lao, Latin-1, Latin-2, Latin-3, Latin-4, Latin-5, Latin-8 (Celtic), Latin-9 (updated Latin-1, with the Euro sign), Polish, Romanian, Slovak, Slovenian, Spanish, Thai, Tibetan, Turkish, and Vietnamese.

To display the script(s) used by your language environment on a graphical display, you need to have a suitable font. If some of the characters appear as empty boxes, you should install the GNU Intlfonts package, which includes fonts for all supported scripts.(4) See section Q.10 Fontsets, for more details about setting up your fonts.

Some operating systems let you specify the character-set locale you are using by setting the locale environment variables LC_ALL, LC_CTYPE, or LANG.(5) During startup, Emacs looks up your character-set locale's name in the system locale alias table, matches its canonical name against entries in the value of the variables locale-charset-language-names and locale-language-names, and selects the corresponding language environment if a match is found. (The former variable overrides the latter.) It also adjusts the display table and terminal coding system, the locale coding system, the preferred coding system as needed for the locale, and--last but not least--the way Emacs decodes non-ASCII characters sent by your keyboard.

If you modify the LC_ALL, LC_CTYPE, or LANG environment variables while running Emacs, you may want to invoke the set-locale-environment function afterwards to readjust the language environment from the new locale.

The set-locale-environment function normally uses the preferred coding system established by the language environment to decode system messages. But if your locale matches an entry in the variable locale-preferred-coding-systems, Emacs uses the corresponding coding system instead. For example, if the locale `ja_JP.PCK' matches japanese-shift-jis in locale-preferred-coding-systems, Emacs uses that encoding even though it might normally use japanese-iso-8bit.

You can override the language environment chosen at startup with explicit use of the command set-language-environment, or with customization of current-language-environment in your init file.

To display information about the effects of a certain language environment lang-env, use the command C-h L lang-env RET (describe-language-environment). This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts used in this language environment. By default, this command describes the chosen language environment.

You can customize any language environment with the normal hook set-language-environment-hook. The command set-language-environment runs that hook after setting up the new language environment. The hook functions can test for a specific language environment by checking the variable current-language-environment. This hook is where you should put non-default settings for specific language environment, such as coding systems for keyboard input and terminal output, the default input method, etc.

Before it starts to set up the new language environment, set-language-environment first runs the hook exit-language-environment-hook. This hook is useful for undoing customizations that were made with set-language-environment-hook. For instance, if you set up a special key binding in a specific language environment using set-language-environment-hook, you should set up exit-language-environment-hook to restore the normal binding for that key.


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Q.4 Input Methods

An input method is a kind of character conversion designed specifically for interactive input. In Emacs, typically each language has its own input method; sometimes several languages which use the same characters can share one input method. A few languages support several input methods.

The simplest kind of input method works by mapping ASCII letters into another alphabet; this allows you to use one other alphabet instead of ASCII. The Greek and Russian input methods work this way.

A more powerful technique is composition: converting sequences of characters into one letter. Many European input methods use composition to produce a single non-ASCII letter from a sequence that consists of a letter followed by accent characters (or vice versa). For example, some methods convert the sequence a' into a single accented letter. These input methods have no special commands of their own; all they do is compose sequences of printing characters.

The input methods for syllabic scripts typically use mapping followed by composition. The input methods for Thai and Korean work this way. First, letters are mapped into symbols for particular sounds or tone marks; then, sequences of these which make up a whole syllable are mapped into one syllable sign.

Chinese and Japanese require more complex methods. In Chinese input methods, first you enter the phonetic spelling of a Chinese word (in input method chinese-py, among others), or a sequence of portions of the character (input methods chinese-4corner and chinese-sw, and others). One input sequence typically corresponds to many possible Chinese characters. You select the one you mean using keys such as C-f, C-b, C-n, C-p, and digits, which have special meanings in this situation.

The possible characters are conceptually arranged in several rows, with each row holding up to 10 alternatives. Normally, Emacs displays just one row at a time, in the echo area; (i/j) appears at the beginning, to indicate that this is the ith row out of a total of j rows. Type C-n or C-p to display the next row or the previous row.

Type C-f and C-b to move forward and backward among the alternatives in the current row. As you do this, Emacs highlights the current alternative with a special color; type C-SPC to select the current alternative and use it as input. The alternatives in the row are also numbered; the number appears before the alternative. Typing a digit n selects the nth alternative of the current row and uses it as input.

TAB in these Chinese input methods displays a buffer showing all the possible characters at once; then clicking Mouse-2 on one of them selects that alternative. The keys C-f, C-b, C-n, C-p, and digits continue to work as usual, but they do the highlighting in the buffer showing the possible characters, rather than in the echo area.

In Japanese input methods, first you input a whole word using phonetic spelling; then, after the word is in the buffer, Emacs converts it into one or more characters using a large dictionary. One phonetic spelling corresponds to a number of different Japanese words; to select one of them, use C-n and C-p to cycle through the alternatives.

Sometimes it is useful to cut off input method processing so that the characters you have just entered will not combine with subsequent characters. For example, in input method latin-1-postfix, the sequence e ' combines to form an `e' with an accent. What if you want to enter them as separate characters?

One way is to type the accent twice; this is a special feature for entering the separate letter and accent. For example, e ' ' gives you the two characters `e''. Another way is to type another letter after the e---something that won't combine with that--and immediately delete it. For example, you could type e e DEL ' to get separate `e' and `''.

Another method, more general but not quite as easy to type, is to use C-\ C-\ between two characters to stop them from combining. This is the command C-\ (toggle-input-method) used twice. See section Q.5 Selecting an Input Method.

C-\ C-\ is especially useful inside an incremental search, because it stops waiting for more characters to combine, and starts searching for what you have already entered.

The variables input-method-highlight-flag and input-method-verbose-flag control how input methods explain what is happening. If input-method-highlight-flag is non-nil, the partial sequence is highlighted in the buffer (for most input methods--some disable this feature). If input-method-verbose-flag is non-nil, the list of possible characters to type next is displayed in the echo area (but not when you are in the minibuffer).

Input methods are implemented in the separate Leim package: they are available only if the system administrator used Leim when building Emacs. If Emacs was built without Leim, you will find that no input methods are defined.


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Q.5 Selecting an Input Method

C-\
Enable or disable use of the selected input method.

C-x RET C-\ method RET
Select a new input method for the current buffer.

C-h I method RET
C-h C-\ method RET
Describe the input method method (describe-input-method). By default, it describes the current input method (if any). This description should give you the full details of how to use any particular input method.

M-x list-input-methods
Display a list of all the supported input methods.

To choose an input method for the current buffer, use C-x RET C-\ (set-input-method). This command reads the input method name from the minibuffer; the name normally starts with the language environment that it is meant to be used with. The variable current-input-method records which input method is selected. Input methods use various sequences of ASCII characters to stand for non-ASCII characters. Sometimes it is useful to turn off the input method temporarily. To do this, type C-\ (toggle-input-method). To reenable the input method, type C-\ again.

If you type C-\ and you have not yet selected an input method, it prompts for you to specify one. This has the same effect as using C-x RET C-\ to specify an input method.

When invoked with a numeric argument, as in C-u C-\, toggle-input-method always prompts you for an input method, suggesting the most recently selected one as the default.

Selecting a language environment specifies a default input method for use in various buffers. When you have a default input method, you can select it in the current buffer by typing C-\. The variable default-input-method specifies the default input method (nil means there is none).

In some language environments, which support several different input methods, you might want to use an input method different from the default chosen by set-language-environment. You can instruct Emacs to select a different default input method for a certain language environment, if you wish, by using set-language-environment-hook (see section set-language-environment-hook). For example:

 
(defun my-chinese-setup ()
  "Set up my private Chinese environment."
  (if (equal current-language-environment "Chinese-GB")
      (setq default-input-method "chinese-tonepy")))
(add-hook 'set-language-environment-hook 'my-chinese-setup)

This sets the default input method to be chinese-tonepy whenever you choose a Chinese-GB language environment.

Some input methods for alphabetic scripts work by (in effect) remapping the keyboard to emulate various keyboard layouts commonly used for those scripts. How to do this remapping properly depends on your actual keyboard layout. To specify which layout your keyboard has, use the command M-x quail-set-keyboard-layout.

To display a list of all the supported input methods, type M-x list-input-methods. The list gives information about each input method, including the string that stands for it in the mode line.


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Q.6 Unibyte and Multibyte Non-ASCII characters

When multibyte characters are enabled, character codes 0240 (octal) through 0377 (octal) are not really legitimate in the buffer. The valid non-ASCII printing characters have codes that start from 0400.

If you type a self-inserting character in the range 0240 through 0377, or if you use C-q to insert one, Emacs assumes you intended to use one of the ISO Latin-n character sets, and converts it to the Emacs code representing that Latin-n character. You select which ISO Latin character set to use through your choice of language environment (see section Q.3 Language Environments). If you do not specify a choice, the default is Latin-1.

If you insert a character in the range 0200 through 0237, which forms the eight-bit-control character set, it is inserted literally. You should normally avoid doing this since buffers containing such characters have to be written out in either the emacs-mule or raw-text coding system, which is usually not what you want.


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Q.7 Coding Systems

Users of various languages have established many more-or-less standard coding systems for representing them. Emacs does not use these coding systems internally; instead, it converts from various coding systems to its own system when reading data, and converts the internal coding system to other coding systems when writing data. Conversion is possible in reading or writing files, in sending or receiving from the terminal, and in exchanging data with subprocesses.

Emacs assigns a name to each coding system. Most coding systems are used for one language, and the name of the coding system starts with the language name. Some coding systems are used for several languages; their names usually start with `iso'. There are also special coding systems no-conversion, raw-text and emacs-mule which do not convert printing characters at all.

A special class of coding systems, collectively known as codepages, is designed to support text encoded by MS-Windows and MS-DOS software. To use any of these systems, you need to create it with M-x codepage-setup. See section AH.6 International Support on MS-DOS. After creating the coding system for the codepage, you can use it as any other coding system. For example, to visit a file encoded in codepage 850, type C-x RET c cp850 RET C-x C-f filename RET.

In addition to converting various representations of non-ASCII characters, a coding system can perform end-of-line conversion. Emacs handles three different conventions for how to separate lines in a file: newline, carriage-return linefeed, and just carriage-return.

C-h C coding RET
Describe coding system coding.

C-h C RET
Describe the coding systems currently in use.

M-x list-coding-systems
Display a list of all the supported coding systems.

The command C-h C (describe-coding-system) displays information about particular coding systems. You can specify a coding system name as the argument; alternatively, with an empty argument, it describes the coding systems currently selected for various purposes, both in the current buffer and as the defaults, and the priority list for recognizing coding systems (see section Q.8 Recognizing Coding Systems).

To display a list of all the supported coding systems, type M-x list-coding-systems. The list gives information about each coding system, including the letter that stands for it in the mode line (see section B.3 The Mode Line).

Each of the coding systems that appear in this list--except for no-conversion, which means no conversion of any kind--specifies how and whether to convert printing characters, but leaves the choice of end-of-line conversion to be decided based on the contents of each file. For example, if the file appears to use the sequence carriage-return linefeed to separate lines, DOS end-of-line conversion will be used.

Each of the listed coding systems has three variants which specify exactly what to do for end-of-line conversion:

...-unix
Don't do any end-of-line conversion; assume the file uses newline to separate lines. (This is the convention normally used on Unix and GNU systems.)

...-dos
Assume the file uses carriage-return linefeed to separate lines, and do the appropriate conversion. (This is the convention normally used on Microsoft systems.(6))

...-mac
Assume the file uses carriage-return to separate lines, and do the appropriate conversion. (This is the convention normally used on the Macintosh system.)

These variant coding systems are omitted from the list-coding-systems display for brevity, since they are entirely predictable. For example, the coding system iso-latin-1 has variants iso-latin-1-unix, iso-latin-1-dos and iso-latin-1-mac.

The coding system raw-text is good for a file which is mainly ASCII text, but may contain byte values above 127 which are not meant to encode non-ASCII characters. With raw-text, Emacs copies those byte values unchanged, and sets enable-multibyte-characters to nil in the current buffer so that they will be interpreted properly. raw-text handles end-of-line conversion in the usual way, based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion to use.

In contrast, the coding system no-conversion specifies no character code conversion at all--none for non-ASCII byte values and none for end of line. This is useful for reading or writing binary files, tar files, and other files that must be examined verbatim. It, too, sets enable-multibyte-characters to nil.

The easiest way to edit a file with no conversion of any kind is with the M-x find-file-literally command. This uses no-conversion, and also suppresses other Emacs features that might convert the file contents before you see them. See section M.2 Visiting Files.

The coding system emacs-mule means that the file contains non-ASCII characters stored with the internal Emacs encoding. It handles end-of-line conversion based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion.


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Q.8 Recognizing Coding Systems

Emacs tries to recognize which coding system to use for a given text as an integral part of reading that text. (This applies to files being read, output from subprocesses, text from X selections, etc.) Emacs can select the right coding system automatically most of the time--once you have specified your preferences.

Some coding systems can be recognized or distinguished by which byte sequences appear in the data. However, there are coding systems that cannot be distinguished, not even potentially. For example, there is no way to distinguish between Latin-1 and Latin-2; they use the same byte values with different meanings.

Emacs handles this situation by means of a priority list of coding systems. Whenever Emacs reads a file, if you do not specify the coding system to use, Emacs checks the data against each coding system, starting with the first in priority and working down the list, until it finds a coding system that fits the data. Then it converts the file contents assuming that they are represented in this coding system.

The priority list of coding systems depends on the selected language environment (see section Q.3 Language Environments). For example, if you use French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use Czech, you probably want Latin-2 to be preferred. This is one of the reasons to specify a language environment.

However, you can alter the priority list in detail with the command M-x prefer-coding-system. This command reads the name of a coding system from the minibuffer, and adds it to the front of the priority list, so that it is preferred to all others. If you use this command several times, each use adds one element to the front of the priority list.

If you use a coding system that specifies the end-of-line conversion type, such as iso-8859-1-dos, what this means is that Emacs should attempt to recognize iso-8859-1 with priority, and should use DOS end-of-line conversion when it does recognize iso-8859-1.

Sometimes a file name indicates which coding system to use for the file. The variable file-coding-system-alist specifies this correspondence. There is a special function modify-coding-system-alist for adding elements to this list. For example, to read and write all `.txt' files using the coding system china-iso-8bit, you can execute this Lisp expression:

 
(modify-coding-system-alist 'file "\\.txt\\'" 'china-iso-8bit)

The first argument should be file, the second argument should be a regular expression that determines which files this applies to, and the third argument says which coding system to use for these files.

Emacs recognizes which kind of end-of-line conversion to use based on the contents of the file: if it sees only carriage-returns, or only carriage-return linefeed sequences, then it chooses the end-of-line conversion accordingly. You can inhibit the automatic use of end-of-line conversion by setting the variable inhibit-eol-conversion to non-nil. If you do that, DOS-style files will be displayed with the `^M' characters visible in the buffer; some people prefer this to the more subtle `(DOS)' end-of-line type indication near the left edge of the mode line (see section eol-mnemonic).

By default, the automatic detection of coding system is sensitive to escape sequences. If Emacs sees a sequence of characters that begin with an escape character, and the sequence is valid as an ISO-2022 code, that tells Emacs to use one of the ISO-2022 encodings to decode the file.

However, there may be cases that you want to read escape sequences in a file as is. In such a case, you can set the variable inhibit-iso-escape-detection to non-nil. Then the code detection ignores any escape sequences, and never uses an ISO-2022 encoding. The result is that all escape sequences become visible in the buffer.

The default value of inhibit-iso-escape-detection is nil. We recommend that you not change it permanently, only for one specific operation. That's because many Emacs Lisp source files in the Emacs distribution contain non-ASCII characters encoded in the coding system iso-2022-7bit, and they won't be decoded correctly when you visit those files if you suppress the escape sequence detection.

You can specify the coding system for a particular file using the `-*-...-*-' construct at the beginning of a file, or a local variables list at the end (see section AD.2.5 Local Variables in Files). You do this by defining a value for the "variable" named coding. Emacs does not really have a variable coding; instead of setting a variable, this uses the specified coding system for the file. For example, `-*-mode: C; coding: latin-1;-*-' specifies use of the Latin-1 coding system, as well as C mode. When you specify the coding explicitly in the file, that overrides file-coding-system-alist.

The variables auto-coding-alist and auto-coding-regexp-alist are the strongest way to specify the coding system for certain patterns of file names, or for files containing certain patterns; these variables even override `-*-coding:-*-' tags in the file itself. Emacs uses auto-coding-alist for tar and archive files, to prevent it from being confused by a `-*-coding:-*-' tag in a member of the archive and thinking it applies to the archive file as a whole. Likewise, Emacs uses auto-coding-regexp-alist to ensure that RMAIL files, whose names in general don't match any particular pattern, are decoded correctly.

If Emacs recognizes the encoding of a file incorrectly, you can reread the file using the correct coding system by typing C-x RET c coding-system RET M-x revert-buffer RET. To see what coding system Emacs actually used to decode the file, look at the coding system mnemonic letter near the left edge of the mode line (see section B.3 The Mode Line), or type C-h C RET.

Once Emacs has chosen a coding system for a buffer, it stores that coding system in buffer-file-coding-system and uses that coding system, by default, for operations that write from this buffer into a file. This includes the commands save-buffer and write-region. If you want to write files from this buffer using a different coding system, you can specify a different coding system for the buffer using set-buffer-file-coding-system (see section Q.9 Specifying a Coding System).

You can insert any possible character into any Emacs buffer, but most coding systems can only handle some of the possible characters. This means that it is possible for you to insert characters that cannot be encoded with the coding system that will be used to save the buffer. For example, you could start with an ASCII file and insert a few Latin-1 characters into it, or you could edit a text file in Polish encoded in iso-8859-2 and add some Russian words to it. When you save the buffer, Emacs cannot use the current value of buffer-file-coding-system, because the characters you added cannot be encoded by that coding system.

When that happens, Emacs tries the most-preferred coding system (set by M-x prefer-coding-system or M-x set-language-environment), and if that coding system can safely encode all of the characters in the buffer, Emacs uses it, and stores its value in buffer-file-coding-system. Otherwise, Emacs displays a list of coding systems suitable for encoding the buffer's contents, and asks you to choose one of those coding systems.

If you insert the unsuitable characters in a mail message, Emacs behaves a bit differently. It additionally checks whether the most-preferred coding system is recommended for use in MIME messages; if not, Emacs tells you that the most-preferred coding system is not recommended and prompts you for another coding system. This is so you won't inadvertently send a message encoded in a way that your recipient's mail software will have difficulty decoding. (If you do want to use the most-preferred coding system, you can still type its name in response to the question.)

When you send a message with Mail mode (see section Z. Sending Mail), Emacs has four different ways to determine the coding system to use for encoding the message text. It tries the buffer's own value of buffer-file-coding-system, if that is non-nil. Otherwise, it uses the value of sendmail-coding-system, if that is non-nil. The third way is to use the default coding system for new files, which is controlled by your choice of language environment, if that is non-nil. If all of these three values are nil, Emacs encodes outgoing mail using the Latin-1 coding system.

When you get new mail in Rmail, each message is translated automatically from the coding system it is written in, as if it were a separate file. This uses the priority list of coding systems that you have specified. If a MIME message specifies a character set, Rmail obeys that specification, unless rmail-decode-mime-charset is nil.

For reading and saving Rmail files themselves, Emacs uses the coding system specified by the variable rmail-file-coding-system. The default value is nil, which means that Rmail files are not translated (they are read and written in the Emacs internal character code).


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Q.9 Specifying a Coding System

In cases where Emacs does not automatically choose the right coding system, you can use these commands to specify one:

C-x RET f coding RET
Use coding system coding for the visited file in the current buffer.

C-x RET c coding RET
Specify coding system coding for the immediately following command.

C-x RET k coding RET
Use coding system coding for keyboard input.

C-x RET t coding RET
Use coding system coding for terminal output.

C-x RET p input-coding RET output-coding RET
Use coding systems input-coding and output-coding for subprocess input and output in the current buffer.

C-x RET x coding RET
Use coding system coding for transferring selections to and from other programs through the window system.

C-x RET X coding RET
Use coding system coding for transferring one selection--the next one--to or from the window system.

The command C-x RET f (set-buffer-file-coding-system) specifies the file coding system for the current buffer--in other words, which coding system to use when saving or rereading the visited file. You specify which coding system using the minibuffer. Since this command applies to a file you have already visited, it affects only the way the file is saved.

Another way to specify the coding system for a file is when you visit the file. First use the command C-x RET c (universal-coding-system-argument); this command uses the minibuffer to read a coding system name. After you exit the minibuffer, the specified coding system is used for the immediately following command.

So if the immediately following command is C-x C-f, for example, it reads the file using that coding system (and records the coding system for when the file is saved). Or if the immediately following command is C-x C-w, it writes the file using that coding system. Other file commands affected by a specified coding system include C-x C-i and C-x C-v, as well as the other-window variants of C-x C-f.

C-x RET c also affects commands that start subprocesses, including M-x shell (see section AC.15 Running Shell Commands from Emacs).

However, if the immediately following command does not use the coding system, then C-x RET c ultimately has no effect.

An easy way to visit a file with no conversion is with the M-x find-file-literally command. See section M.2 Visiting Files.

The variable default-buffer-file-coding-system specifies the choice of coding system to use when you create a new file. It applies when you find a new file, and when you create a buffer and then save it in a file. Selecting a language environment typically sets this variable to a good choice of default coding system for that language environment.

The command C-x RET t (set-terminal-coding-system) specifies the coding system for terminal output. If you specify a character code for terminal output, all characters output to the terminal are translated into that coding system.

This feature is useful for certain character-only terminals built to support specific languages or character sets--for example, European terminals that support one of the ISO Latin character sets. You need to specify the terminal coding system when using multibyte text, so that Emacs knows which characters the terminal can actually handle.

By default, output to the terminal is not translated at all, unless Emacs can deduce the proper coding system from your terminal type or your locale specification (see section Q.3 Language Environments).

The command C-x RET k (set-keyboard-coding-system) or the Custom option keyboard-coding-system specifies the coding system for keyboard input. Character-code translation of keyboard input is useful for terminals with keys that send non-ASCII graphic characters--for example, some terminals designed for ISO Latin-1 or subsets of it.

By default, keyboard input is not translated at all.

There is a similarity between using a coding system translation for keyboard input, and using an input method: both define sequences of keyboard input that translate into single characters. However, input methods are designed to be convenient for interactive use by humans, and the sequences that are translated are typically sequences of ASCII printing characters. Coding systems typically translate sequences of non-graphic characters.

The command C-x RET x (set-selection-coding-system) specifies the coding system for sending selected text to the window system, and for receiving the text of selections made in other applications. This command applies to all subsequent selections, until you override it by using the command again. The command C-x RET X (set-next-selection-coding-system) specifies the coding system for the next selection made in Emacs or read by Emacs.

The command C-x RET p (set-buffer-process-coding-system) specifies the coding system for input and output to a subprocess. This command applies to the current buffer; normally, each subprocess has its own buffer, and thus you can use this command to specify translation to and from a particular subprocess by giving the command in the corresponding buffer.

The default for translation of process input and output depends on the current language environment.

The variable file-name-coding-system specifies a coding system to use for encoding file names. If you set the variable to a coding system name (as a Lisp symbol or a string), Emacs encodes file names using that coding system for all file operations. This makes it possible to use non-ASCII characters in file names--or, at least, those non-ASCII characters which the specified coding system can encode.

If file-name-coding-system is nil, Emacs uses a default coding system determined by the selected language environment. In the default language environment, any non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation.

Warning: if you change file-name-coding-system (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and cannot be encoded (or are encoded differently) under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may get an error. If such a problem happens, use C-x C-w to specify a new file name for that buffer.

The variable locale-coding-system specifies a coding system to use when encoding and decoding system strings such as system error messages and format-time-string formats and time stamps. That coding system is also used for decoding non-ASCII keyboard input on X Window systems. You should choose a coding system that is compatible with the underlying system's text representation, which is normally specified by one of the environment variables LC_ALL, LC_CTYPE, and LANG. (The first one, in the order specified above, whose value is nonempty is the one that determines the text representation.)


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Q.10 Fontsets

A font for X typically defines shapes for a single alphabet or script. Therefore, displaying the entire range of scripts that Emacs supports requires a collection of many fonts. In Emacs, such a collection is called a fontset. A fontset is defined by a list of fonts, each assigned to handle a range of character codes.

Each fontset has a name, like a font. The available X fonts are defined by the X server; fontsets, however, are defined within Emacs itself. Once you have defined a fontset, you can use it within Emacs by specifying its name, anywhere that you could use a single font. Of course, Emacs fontsets can use only the fonts that the X server supports; if certain characters appear on the screen as hollow boxes, this means that the fontset in use for them has no font for those characters.(7)

Emacs creates two fontsets automatically: the standard fontset and the startup fontset. The standard fontset is most likely to have fonts for a wide variety of non-ASCII characters; however, this is not the default for Emacs to use. (By default, Emacs tries to find a font that has bold and italic variants.) You can specify use of the standard fontset with the `-fn' option, or with the `Font' X resource (see section AE.7 Font Specification Options). For example,

 
emacs -fn fontset-standard

A fontset does not necessarily specify a font for every character code. If a fontset specifies no font for a certain character, or if it specifies a font that does not exist on your system, then it cannot display that character properly. It will display that character as an empty box instead.

The fontset height and width are determined by the ASCII characters (that is, by the font used for ASCII characters in that fontset). If another font in the fontset has a different height, or a different width, then characters assigned to that font are clipped to the fontset's size. If highlight-wrong-size-font is non-nil, a box is displayed around these wrong-size characters as well.


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Q.11 Defining fontsets

Emacs creates a standard fontset automatically according to the value of standard-fontset-spec. This fontset's name is

 
-*-fixed-medium-r-normal-*-16-*-*-*-*-*-fontset-standard

or just `fontset-standard' for short.

Bold, italic, and bold-italic variants of the standard fontset are created automatically. Their names have `bold' instead of `medium', or `i' instead of `r', or both.

If you specify a default ASCII font with the `Font' resource or the `-fn' argument, Emacs generates a fontset from it automatically. This is the startup fontset and its name is fontset-startup. It does this by replacing the foundry, family, add_style, and average_width fields of the font name with `*', replacing charset_registry field with `fontset', and replacing charset_encoding field with `startup', then using the resulting string to specify a fontset.

For instance, if you start Emacs this way,

 
emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"

Emacs generates the following fontset and uses it for the initial X window frame:

 
-*-*-medium-r-normal-*-14-140-*-*-*-*-fontset-startup

With the X resource `Emacs.Font', you can specify a fontset name just like an actual font name. But be careful not to specify a fontset name in a wildcard resource like `Emacs*Font'---that wildcard specification matches various other resources, such as for menus, and menus cannot handle fontsets.

You can specify additional fontsets using X resources named `Fontset-n', where n is an integer starting from 0. The resource value should have this form:

 
fontpattern, [charsetname:fontname]...

fontpattern should have the form of a standard X font name, except for the last two fields. They should have the form `fontset-alias'.

The fontset has two names, one long and one short. The long name is fontpattern. The short name is `fontset-alias'. You can refer to the fontset by either name.

The construct `charset:font' specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in defining one fontset.

For the other character sets, Emacs chooses a font based on fontpattern. It replaces `fontset-alias' with values that describe the character set. For the ASCII character font, `fontset-alias' is replaced with `ISO8859-1'.

In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which is what Emacs does.

Thus if fontpattern is this,

 
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

the font specification for ASCII characters would be this:

 
-*-fixed-medium-r-normal-*-24-*-ISO8859-1

and the font specification for Chinese GB2312 characters would be this:

 
-*-fixed-medium-r-normal-*-24-*-gb2312*-*

You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have `song ti' or `fangsong ti' in family field. In such a case, `Fontset-n' can be specified as below:

 
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
        chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*

Then, the font specifications for all but Chinese GB2312 characters have `fixed' in the family field, and the font specification for Chinese GB2312 characters has a wild card `*' in the family field.

The function that processes the fontset resource value to create the fontset is called create-fontset-from-fontset-spec. You can also call this function explicitly to create a fontset.

See section AE.7 Font Specification Options, for more information about font naming in X.


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Q.12 Undisplayable Characters

Your terminal may be unable to display some non-ASCII characters. Most non-windowing terminals can only use a single character set (use the variable default-terminal-coding-system (see section Q.9 Specifying a Coding System) to tell Emacs which one); characters which can't be encoded in that coding system are displayed as `?' by default.

Windowing terminals can display a broader range of characters, but you may not have fonts installed for all of them; characters that have no font appear as a hollow box.

If you use Latin-1 characters but your terminal can't display Latin-1, you can arrange to display mnemonic ASCII sequences instead, e.g. `"o' for o-umlaut. Load the library `iso-ascii' to do this.

If your terminal can display Latin-1, you can display characters from other European character sets using a mixture of equivalent Latin-1 characters and ASCII mnemonics. Use the Custom option latin1-display to enable this. The mnemonic ASCII sequences mostly correspond to those of the prefix input methods.


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Q.13 Single-byte Character Set Support

The ISO 8859 Latin-n character sets define character codes in the range 0240 to 0377 octal (160 to 255 decimal) to handle the accented letters and punctuation needed by various European languages (and some non-European ones). If you disable multibyte characters, Emacs can still handle one of these character codes at a time. To specify which of these codes to use, invoke M-x set-language-environment and specify a suitable language environment such as `Latin-n'.

For more information about unibyte operation, see Q.2 Enabling Multibyte Characters. Note particularly that you probably want to ensure that your initialization files are read as unibyte if they contain non-ASCII characters.

Emacs can also display those characters, provided the terminal or font in use supports them. This works automatically. Alternatively, if you are using a window system, Emacs can also display single-byte characters through fontsets, in effect by displaying the equivalent multibyte characters according to the current language environment. To request this, set the variable unibyte-display-via-language-environment to a non-nil value.

If your terminal does not support display of the Latin-1 character set, Emacs can display these characters as ASCII sequences which at least give you a clear idea of what the characters are. To do this, load the library iso-ascii. Similar libraries for other Latin-n character sets could be implemented, but we don't have them yet.

Normally non-ISO-8859 characters (decimal codes between 128 and 159 inclusive) are displayed as octal escapes. You can change this for non-standard "extended" versions of ISO-8859 character sets by using the function standard-display-8bit in the disp-table library.

There are several ways you can input single-byte non-ASCII characters:


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R. Major Modes

Emacs provides many alternative major modes, each of which customizes Emacs for editing text of a particular sort. The major modes are mutually exclusive, and each buffer has one major mode at any time. The mode line normally shows the name of the current major mode, in parentheses (see section B.3 The Mode Line).

The least specialized major mode is called Fundamental mode. This mode has no mode-specific redefinitions or variable settings, so that each Emacs command behaves in its most general manner, and each option is in its default state. For editing text of a specific type that Emacs knows about, such as Lisp code or English text, you should switch to the appropriate major mode, such as Lisp mode or Text mode.

Selecting a major mode changes the meanings of a few keys to become more specifically adapted to the language being edited. The ones that are changed frequently are TAB, DEL, and C-j. The prefix key C-c normally contains mode-specific commands. In addition, the commands which handle comments use the mode to determine how comments are to be delimited. Many major modes redefine the syntactical properties of characters appearing in the buffer. See section AD.6 The Syntax Table.

The major modes fall into three major groups. The first group contains modes for normal text, either plain or with mark-up. It includes Text mode, HTML mode, SGML mode, TeX mode and Outline mode. The second group contains modes for specific programming languages. These include Lisp mode (which has several variants), C mode, Fortran mode, and others. The remaining major modes are not intended for use on users' files; they are used in buffers created for specific purposes by Emacs, such as Dired mode for buffers made by Dired (see section AB. Dired, the Directory Editor), Mail mode for buffers made by C-x m (see section Z. Sending Mail), and Shell mode for buffers used for communicating with an inferior shell process (see section AC.15.2 Interactive Inferior Shell).

Most programming-language major modes specify that only blank lines separate paragraphs. This is to make the paragraph commands useful. (See section T.3 Paragraphs.) They also cause Auto Fill mode to use the definition of TAB to indent the new lines it creates. This is because most lines in a program are usually indented (see section S. Indentation).

R.1 How Major Modes are Chosen  How major modes are specified or chosen.


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R.1 How Major Modes are Chosen

You can select a major mode explicitly for the current buffer, but most of the time Emacs determines which mode to use based on the file name or on special text in the file.

Explicit selection of a new major mode is done with a M-x command. From the name of a major mode, add -mode to get the name of a command to select that mode. Thus, you can enter Lisp mode by executing M-x lisp-mode.

When you visit a file, Emacs usually chooses the right major mode based on the file's name. For example, files whose names end in `.c' are edited in C mode. The correspondence between file names and major modes is controlled by the variable auto-mode-alist. Its value is a list in which each element has this form,

 
(regexp . mode-function)

or this form,

 
(regexp mode-function flag)

For example, one element normally found in the list has the form ("\\.c\\'" . c-mode), and it is responsible for selecting C mode for files whose names end in `.c'. (Note that `\\' is needed in Lisp syntax to include a `\' in the string, which must be used to suppress the special meaning of `.' in regexps.) If the element has the form (regexp mode-function flag) and flag is non-nil, then after calling mode-function, the suffix that matched regexp is discarded and the list is searched again for another match.

You can specify which major mode should be used for editing a certain file by a special sort of text in the first nonblank line of the file. The mode name should appear in this line both preceded and followed by `-*-'. Other text may appear on the line as well. For example,

 
;-*-Lisp-*-

tells Emacs to use Lisp mode. Such an explicit specification overrides any defaults based on the file name. Note how the semicolon is used to make Lisp treat this line as a comment.

Another format of mode specification is

 
-*- mode: modename;-*-

which allows you to specify local variables as well, like this:

 
-*- mode: modename; var: value; ... -*-

See section AD.2.5 Local Variables in Files, for more information about this.

When a file's contents begin with `#!', it can serve as an executable shell command, which works by running an interpreter named on the file's first line. The rest of the file is used as input to the interpreter.

When you visit such a file in Emacs, if the file's name does not specify a major mode, Emacs uses the interpreter name on the first line to choose a mode. If the first line is the name of a recognized interpreter program, such as `perl' or `tcl', Emacs uses a mode appropriate for programs for that interpreter. The variable interpreter-mode-alist specifies the correspondence between interpreter program names and major modes.

When the first line starts with `#!', you cannot (on many systems) use the `-*-' feature on the first line, because the system would get confused when running the interpreter. So Emacs looks for `-*-' on the second line in such files as well as on the first line.

When you visit a file that does not specify a major mode to use, or when you create a new buffer with C-x b, the variable default-major-mode specifies which major mode to use. Normally its value is the symbol fundamental-mode, which specifies Fundamental mode. If default-major-mode is nil, the major mode is taken from the previously current buffer.

If you change the major mode of a buffer, you can go back to the major mode Emacs would choose automatically: use the command M-x normal-mode to do this. This is the same function that find-file calls to choose the major mode. It also processes the file's local variables list (if any).

The commands C-x C-w and set-visited-file-name change to a new major mode if the new file name implies a mode (see section M.3 Saving Files). However, this does not happen if the buffer contents specify a major mode, and certain "special" major modes do not allow the mode to change. You can turn off this mode-changing feature by setting change-major-mode-with-file-name to nil.


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S. Indentation

This chapter describes the Emacs commands that add, remove, or adjust indentation.

TAB
Indent the current line "appropriately" in a mode-dependent fashion.
C-j
Perform RET followed by TAB (newline-and-indent).
M-^
Merge the previous and the current line (delete-indentation). This would cancel out the effect of C-j.
C-M-o
Split the current line at point; text on the line after point becomes a new line indented to the same column where point is located (split-line).
M-m
Move (forward or back) to the first nonblank character on the current line (back-to-indentation).
C-M-\
Indent several lines to the same column (indent-region).
C-x TAB
Shift a block of lines rigidly right or left (indent-rigidly).
M-i
Indent from point to the next prespecified tab stop column (tab-to-tab-stop).
M-x indent-relative
Indent from point to under an indentation point in the previous line.

Most programming languages have some indentation convention. For Lisp code, lines are indented according to their nesting in parentheses. The same general idea is used for C code, though many details are different.

Whatever the language, to indent a line, use the TAB command. Each major mode defines this command to perform the sort of indentation appropriate for the particular language. In Lisp mode, TAB aligns the line according to its depth in parentheses. No matter where in the line you are when you type TAB, it aligns the line as a whole. In C mode, TAB implements a subtle and sophisticated indentation style that knows about many aspects of C syntax.

In Text mode, TAB runs the command tab-to-tab-stop, which indents to the next tab stop column. You can set the tab stops with M-x edit-tab-stops.

Normally, TAB inserts an optimal mix of tabs and spaces for the intended indentation. See section S.3 Tabs vs. Spaces, for how to prevent use of tabs.

S.1 Indentation Commands and Techniques  Various commands and techniques for indentation.
S.2 Tab Stops  You can set arbitrary "tab stops" and then indent to the next tab stop when you want to.
S.3 Tabs vs. Spaces  You can request indentation using just spaces.


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S.1 Indentation Commands and Techniques

To move over the indentation on a line, do M-m (back-to-indentation). This command, given anywhere on a line, positions point at the first nonblank character on the line.

To insert an indented line before the current line, do C-a C-o TAB. To make an indented line after the current line, use C-e C-j.

If you just want to insert a tab character in the buffer, you can type C-q TAB.

C-M-o (split-line) moves the text from point to the end of the line vertically down, so that the current line becomes two lines. C-M-o first moves point forward over any spaces and tabs. Then it inserts after point a newline and enough indentation to reach the same column point is on. Point remains before the inserted newline; in this regard, C-M-o resembles C-o.

To join two lines cleanly, use the M-^ (delete-indentation) command. It deletes the indentation at the front of the current line, and the line boundary as well, replacing them with a single space. As a special case (useful for Lisp code) the single space is omitted if the characters to be joined are consecutive open parentheses or closing parentheses, or if the junction follows another newline. To delete just the indentation of a line, go to the beginning of the line and use M-\ (delete-horizontal-space), which deletes all spaces and tabs around the cursor.

If you have a fill prefix, M-^ deletes the fill prefix if it appears after the newline that is deleted. See section T.5.4 The Fill Prefix.

There are also commands for changing the indentation of several lines at once. C-M-\ (indent-region) applies to all the lines that begin in the region; it indents each line in the "usual" way, as if you had typed TAB at the beginning of the line. A numeric argument specifies the column to indent to, and each line is shifted left or right so that its first nonblank character appears in that column. C-x TAB (indent-rigidly) moves all of the lines in the region right by its argument (left, for negative arguments). The whole group of lines moves rigidly sideways, which is how the command gets its name.

M-x indent-relative indents at point based on the previous line (actually, the last nonempty line). It inserts whitespace at point, moving point, until it is underneath an indentation point in the previous line. An indentation point is the end of a sequence of whitespace or the end of the line. If point is farther right than any indentation point in the previous line, the whitespace before point is deleted and the first indentation point then applicable is used. If no indentation point is applicable even then, indent-relative runs tab-to-tab-stop (see section S.2 Tab Stops), unless it is called with a numeric argument, in which case it does nothing.

indent-relative is the definition of TAB in Indented Text mode. See section T. Commands for Human Languages.

See section T.11.6 Indentation in Formatted Text, for another way of specifying the indentation for part of your text.


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S.2 Tab Stops

For typing in tables, you can use Text mode's definition of TAB, tab-to-tab-stop. This command inserts indentation before point, enough to reach the next tab stop column. If you are not in Text mode, this command can be found on the key M-i.

You can specify the tab stops used by M-i. They are stored in a variable called tab-stop-list, as a list of column-numbers in increasing order.

The convenient way to set the tab stops is with M-x edit-tab-stops, which creates and selects a buffer containing a description of the tab stop settings. You can edit this buffer to specify different tab stops, and then type C-c C-c to make those new tab stops take effect. edit-tab-stops records which buffer was current when you invoked it, and stores the tab stops back in that buffer; normally all buffers share the same tab stops and changing them in one buffer affects all, but if you happen to make tab-stop-list local in one buffer then edit-tab-stops in that buffer will edit the local settings.

Here is what the text representing the tab stops looks like for ordinary tab stops every eight columns.

 
        :       :       :       :       :       :
0         1         2         3         4
0123456789012345678901234567890123456789012345678
To install changes, type C-c C-c

The first line contains a colon at each tab stop. The remaining lines are present just to help you see where the colons are and know what to do.

Note that the tab stops that control tab-to-tab-stop have nothing to do with displaying tab characters in the buffer. See section J.12 Customization of Display, for more information on that.


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S.3 Tabs vs. Spaces

Emacs normally uses both tabs and spaces to indent lines. If you prefer, all indentation can be made from spaces only. To request this, set indent-tabs-mode to nil. This is a per-buffer variable, so altering the variable affects only the current buffer, but there is a default value which you can change as well. See section AD.2.4 Local Variables.

There are also commands to convert tabs to spaces or vice versa, always preserving the columns of all nonblank text. M-x tabify scans the region for sequences of spaces, and converts sequences of at least three spaces to tabs if that can be done without changing indentation. M-x untabify changes all tabs in the region to appropriate numbers of spaces.


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T. Commands for Human Languages

The term text has two widespread meanings in our area of the computer field. One is data that is a sequence of characters. Any file that you edit with Emacs is text, in this sense of the word. The other meaning is more restrictive: a sequence of characters in a human language for humans to read (possibly after processing by a text formatter), as opposed to a program or commands for a program.

Human languages have syntactic/stylistic conventions that can be supported or used to advantage by editor commands: conventions involving words, sentences, paragraphs, and capital letters. This chapter describes Emacs commands for all of these things. There are also commands for filling, which means rearranging the lines of a paragraph to be approximately equal in length. The commands for moving over and killing words, sentences and paragraphs, while intended primarily for editing text, are also often useful for editing programs.

Emacs has several major modes for editing human-language text. If the file contains text pure and simple, use Text mode, which customizes Emacs in small ways for the syntactic conventions of text. Outline mode provides special commands for operating on text with an outline structure.

For text which contains embedded commands for text formatters, Emacs has other major modes, each for a particular text formatter. Thus, for input to TeX, you would use TeX mode. For input to nroff, use Nroff mode.

Instead of using a text formatter, you can edit formatted text in WYSIWYG style ("what you see is what you get"), with Enriched mode. Then the formatting appears on the screen in Emacs while you edit.

The "automatic typing" features may be useful when writing text. See section `Autotyping' in Features for Automatic Typing.

T.1 Words  Moving over and killing words.
T.2 Sentences  Moving over and killing sentences.
T.3 Paragraphs  Moving over paragraphs.
T.4 Pages  Moving over pages.
T.5 Filling Text  Filling or justifying text.
T.6 Case Conversion Commands  Changing the case of text.
T.7 Text Mode  The major modes for editing text files.
T.8 Outline Mode  Editing outlines.
T.9 TeX Mode  Editing input to the formatter TeX.
T.10 Nroff Mode  Editing input to the formatter nroff.
T.11 Editing Formatted Text  Editing formatted text directly in WYSIWYG fashion.


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T.1 Words

Emacs has commands for moving over or operating on words. By convention, the keys for them are all Meta characters.

M-f
Move forward over a word (forward-word).
M-b
Move backward over a word (backward-word).
M-d
Kill up to the end of a word (kill-word).
M-DEL
Kill back to the beginning of a word (backward-kill-word).
M-@
Mark the end of the next word (mark-word).
M-t
Transpose two words or drag a word across other words (transpose-words).

Notice how these keys form a series that parallels the character-based C-f, C-b, C-d, DEL and C-t. M-@ is cognate to C-@, which is an alias for C-SPC.

The commands M-f (forward-word) and M-b (backward-word) move forward and backward over words. These Meta characters are thus analogous to the corresponding control characters, C-f and C-b, which move over single characters in the text. The analogy extends to numeric arguments, which serve as repeat counts. M-f with a negative argument moves backward, and M-b with a negative argument moves forward. Forward motion stops right after the last letter of the word, while backward motion stops right before the first letter.

M-d (kill-word) kills the word after point. To be precise, it kills everything from point to the place M-f would move to. Thus, if point is in the middle of a word, M-d kills just the part after point. If some punctuation comes between point and the next word, it is killed along with the word. (If you wish to kill only the next word but not the punctuation before it, simply do M-f to get the end, and kill the word backwards with M-DEL.) M-d takes arguments just like M-f.

M-DEL (backward-kill-word) kills the word before point. It kills everything from point back to where M-b would move to. If point is after the space in `FOO, BAR', then `FOO, ' is killed. (If you wish to kill just `FOO', and not the comma and the space, use M-b M-d instead of M-DEL.)

M-t (transpose-words) exchanges the word before or containing point with the following word. The delimiter characters between the words do not move. For example, `FOO, BAR' transposes into `BAR, FOO' rather than `BAR FOO,'. See section L.2 Transposing Text, for more on transposition and on arguments to transposition commands.

To operate on the next n words with an operation which applies between point and mark, you can either set the mark at point and then move over the words, or you can use the command M-@ (mark-word) which does not move point, but sets the mark where M-f would move to. M-@ accepts a numeric argument that says how many words to scan for the place to put the mark. In Transient Mark mode, this command activates the mark.

The word commands' understanding of syntax is completely controlled by the syntax table. Any character can, for example, be declared to be a word delimiter. See section AD.6 The Syntax Table.


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T.2 Sentences

The Emacs commands for manipulating sentences and paragraphs are mostly on Meta keys, so as to be like the word-handling commands.

M-a
Move back to the beginning of the sentence (backward-sentence).
M-e
Move forward to the end of the sentence (forward-sentence).
M-k
Kill forward to the end of the sentence (kill-sentence).
C-x DEL
Kill back to the beginning of the sentence (backward-kill-sentence).

The commands M-a and M-e (backward-senten