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Copyright (C) 1985,1986,1987,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "The GNU Manifesto", "Distribution" and "GNU GENERAL PUBLIC LICENSE", with the Front-Cover texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License."
(a) The FSF's Back-Cover Text is: "You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development."
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 21.3.
For information on extending Emacs, see Emacs Lisp.
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.
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Copyright © 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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Ty Coon, President of Vice
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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 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 Real-time.
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 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 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 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.
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 Frames.
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 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.
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 Cursor Display, 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."
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 Display Custom).
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
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 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 Minibuffer.
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 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 Optional Mode Line.
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 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 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 Narrowing. Def means that a keyboard macro is being
defined. See 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 Recursive Edit.
Non-windowing terminals can only show a single Emacs frame at a time
(see Frames). 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 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 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 Enabling Multibyte.
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 Variables, for an explanation of how to set variables.
See Optional Mode Line, 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 Mode Line Mouse.
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 Key Help).
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.
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 International), 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 Input Events, 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 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.
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 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.
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 What Is a Function. (The definition we use in this manual is
simplified slightly.)
The bindings between keys and commands are recorded in various tables called keymaps. See 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 Variables.
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 Text Display.
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 International. 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 Single-Byte Character Support.
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 Init File.)
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 Command 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 yo