This chapter talks about various topics relevant to adapting the behavior of Emacs in minor ways. See The Emacs Lisp Reference Manual for how to make more far-reaching changes.
All kinds of customization affect only the particular Emacs session that you do them in. They are completely lost when you kill the Emacs session, and have no effect on other Emacs sessions you may run at the same time or later. The only way an Emacs session can affect anything outside of it is by writing a file; in particular, the only way to make a customization `permanent' is to put something in your `.emacs' file or other appropriate file to do the customization in each session. See section The Init File, `~/.emacs'.
Minor modes are optional features which you can turn on or off. For example, Auto Fill mode is a minor mode in which SPC breaks lines between words as you type. All the minor modes are independent of each other and of the selected major mode. Most minor modes say in the mode line when they are on; for example, `Fill' in the mode line means that Auto Fill mode is on.
-mode to the name of a minor mode to get the name of a
command function that turns the mode on or off. Thus, the command to
enable or disable Auto Fill mode is called M-x auto-fill-mode. These
commands are usually invoked with M-x, but you can bind keys to them
if you wish. With no argument, the function turns the mode on if it was
off and off if it was on. This is known as toggling. A positive
argument always turns the mode on, and an explicit zero argument or a
negative argument always turns it off.
Enabling or disabling some minor modes applies only to the current buffer; each buffer is independent of the other buffers. Therefore, you can enable the mode in particular buffers and disable it in others. The per-buffer minor modes include Auto Fill mode, Outline minor mode, Auto Save mode, Font-Lock mode, and ISO Accents mode.
Auto Fill mode allows you to enter filled text without breaking lines explicitly. Emacs inserts newlines as necessary to prevent lines from becoming too long. See section Filling Text.
Outline minor mode provides the same facilities as the major mode called Outline mode; but since it is a minor mode instead, you can combine it with any major mode. See section Outline Mode.
Overwrite mode causes ordinary printing characters to replace existing text instead of shoving it to the right. For example, if point is in front of the `B' in `FOOBAR', then in Overwrite mode typing a G changes it to `FOOGAR', instead of producing it `FOOGBAR' as usual.
Auto Save mode causes the contents of a buffer to be saved periodically to reduce the amount of work you can lose in case of a system crash. See section Auto-Saving: Protection Against Disasters.
Font-Lock mode automatically highlights certain textual units found in programs, such as comments, strings, and function names being defined. This requires a window system that can display multiple fonts. See section Using Multiple Typefaces.
ISO Accents mode makes the characters ``', `'', `"', `^', `/' and `~' combine with the following letter, to produce an accented letter in the ISO Latin-1 character set. See section European Character Set Display.
The following minor modes normally apply to all buffers at once. Since each is enabled or disabled by the value of a variable, you can set them differently for particular buffers, by explicitly making the corresponding variables local in those buffers. See section Local Variables.
Abbrev mode allows you to define abbreviations that automatically expand as you type them. For example, `amd' might expand to `abbrev mode'. See section Abbrevs, for full information.
Line Number mode enables continuous display in the mode line of the line number of point. See section The Mode Line.
Resize-Minibuffer mode makes the minibuffer expand as necessary to hold the text that you put in it. See section Editing in the Minibuffer.
Scroll Bar mode gives each window a scroll bar (see section Scroll Bars). Menu Bar mode gives each frame a menu bar (see section Menu Bars). Both of these modes are enabled by default when you use the X Window System.
In Transient Mark mode, every change in the buffer contents "deactivates" the mark, so that commands that operate on the region will get an error. This means you must either set the mark, or explicitly "reactivate" it, before each command that uses the region. The advantage of Transient Mark mode is that Emacs can display the region highlighted (currently only when using X). See section Setting the Mark.
A variable is a Lisp symbol which has a value. The symbol's name is also called the name of the variable. A variable name can contain any characters that can appear in a file, but conventionally variable names consist of words separated by hyphens. A variable can have a documentation string which describes what kind of value it should have and how the value will be used.
Lisp allows any variable to have any kind of value, but most variables
that Emacs uses require a value of a certain type. Often the value should
always be a string, or should always be a number. Sometimes we say that a
certain feature is turned on if a variable is "non-
that if the variable's value is
nil, the feature is off, but the
feature is on for any other value. The conventional value to use to
turn on the feature--since you have to pick one particular value when you
set the variable--is
Emacs uses many Lisp variables for internal record keeping, as any Lisp program must, but the most interesting variables for you are the ones that exist for the sake of customization. Emacs does not (usually) change the values of these variables; instead, you set the values, and thereby alter and control the behavior of certain Emacs commands. These variables are called options. Most options are documented in this manual, and appear in the Variable Index (see section Variable Index).
One example of a variable which is an option is
specifies the position of the right margin (as a number of characters from
the left margin) to be used by the fill commands (see section Filling Text).
To examine the value of a single variable, use C-h v
describe-variable), which reads a variable name using the
minibuffer, with completion. It displays both the value and the
documentation of the variable. For example,
C-h v fill-column RET
displays something like this:
fill-column's value is 75 Documentation: *Column beyond which automatic line-wrapping should happen. Automatically becomes buffer-local when set in any fashion.
The star at the beginning of the documentation indicates that this variable is an option. C-h v is not restricted to options; it allows any variable name.
The most convenient way to set a specific option is with M-x set-variable. This reads the variable name with the minibuffer (with completion), and then reads a Lisp expression for the new value using the minibuffer a second time. For example,
M-x set-variable RET fill-column RET 75 RET
fill-column to 75.
You can set any variable with a Lisp expression using the function
setq. Here's how to use it to set
(setq fill-column 75)
Setting variables, like all means of customizing Emacs except where otherwise stated, affects only the current Emacs session.
These two functions make it easy to display all the Emacs option variables, and to change some of them if you wish.
M-x list-options displays a list of all Emacs option variables, in an Emacs buffer named `*List Options*'. Each option is shown with its documentation and its current value. Here is what a portion of it might look like:
;; exec-path: ("." "/usr/local/bin" "/usr/ucb" "/bin" "/usr/bin" "/u2/emacs/etc") *List of directories to search programs to run in subprocesses. Each element is a string (directory name) or nil (try the default directory). ;; ;; fill-column: 75 *Column beyond which automatic line-wrapping should happen. Automatically becomes buffer-local when set in any fashion. ;;
M-x edit-options goes one step further and immediately selects the `*List Options*' buffer; this buffer uses the major mode Options mode, which provides commands that allow you to point at an option and change its value:
nil, it becomes
t; otherwise it becomes
Any changes take effect immediately, and last until you exit from Emacs.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides a number of hooks for the sake of customization.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. The reason most hooks are normal hooks is so that you can use them in a uniform way. Every variable in Emacs whose name ends in `-hook' is a normal hook.
Most major modes run hooks as the last step of initialization. This
makes it easy for a user to customize the behavior of the mode, by
overriding the local variable assignments already made by the mode. But
hooks may also be used in other contexts. For example, the hook
suspend-hook runs just before Emacs suspends itself
(see section Exiting Emacs).
The recommended way to add a hook function to a normal hook is by
add-hook. You can use any valid Lisp function as the
hook function. For example, here's how to set up a hook to turn on Auto
Fill mode when entering Text mode and other modes based on Text mode:
(add-hook 'text-mode-hook 'turn-on-auto-fill)
The next example shows how to use a hook to customize the indentation of C code. (People often have strong personal preferences for one format compared to another.) Here the hook function is an anonymous lambda expression.
(add-hook 'c-mode-hook (function (lambda () (setq c-indent-level 4 c-argdecl-indent 0 c-label-offset -4 c-continued-statement-indent 0 c-brace-offset 0 comment-column 40)))) (setq c++-mode-hook c-mode-hook)
It is best to design your hook functions so that the order in which they are executed does not matter. Any dependence on the order is "asking for trouble." However, the order is predictable: the most recently added hook functions are executed first.
Any variable can be made local to a specific Emacs buffer. This means that its value in that buffer is independent of its value in other buffers. A few variables are always local in every buffer. Every other Emacs variable has a global value which is in effect in all buffers that have not made the variable local.
M-x make-local-variable reads the name of a variable and makes it local to the current buffer. Further changes in this buffer will not affect others, and further changes in the global value will not affect this buffer.
M-x make-variable-buffer-local reads the name of a variable and
changes the future behavior of the variable so that it will become local
automatically when it is set. More precisely, once a variable has been
marked in this way, the usual ways of setting the variable automatically
make-local-variable first. We call such variables
Major modes (see section Major Modes) always make variables local to the
buffer before setting the variables. This is why changing major modes
in one buffer has no effect on other buffers. Minor modes also work by
setting variables--normally, each minor mode has one controlling
variable which is non-
nil when the mode is enabled (see section Minor Modes). For most minor modes, the controlling variable is per buffer.
Emacs contains a number of variables that are always per-buffer.
truncate-lines. Some other variables are
always local in every buffer, but they are used for internal
M-x kill-local-variable reads the name of a variable and makes it cease to be local to the current buffer. The global value of the variable henceforth is in effect in this buffer. Setting the major mode kills all the local variables of the buffer except for a few variables specially marked as permanent locals.
To set the global value of a variable, regardless of whether the
variable has a local value in the current buffer, you can use the Lisp
setq-default. This construct is used just like
setq, but it sets variables' global values instead of their local
values (if any). When the current buffer does have a local value, the
new global value may not be visible until you switch to another buffer.
Here is an example:
(setq-default fill-column 75)
setq-default is the only way to set the global value of a variable
that has been marked with
Lisp programs can use
default-value to look at a variable's
default value. This function takes a symbol as argument and returns its
default value. The argument is evaluated; usually you must quote it
explicitly. For example, here's how to obtain the default value of
A file can specify local variable values for use when you edit the file with Emacs. Visiting the file checks for local variables specifications; it automatically makes these variables local to the buffer, and sets them to the values specified in the file.
There are two ways to specify local variable values: in the first line, or with a local variables list. Here's how to specify them in the first line:
-*- mode: modename; var: value; ... -*-
You can specify any number of variables/value pairs in this way, each
pair with a colon and semicolon as shown above.
modename; specifies the major mode; this should come first in the
line. The values are not evaluated; they are used literally.
Here is an example that specifies Lisp mode and sets two variables with
;; -*-Mode: Lisp; fill-column: 75; comment-column: 50; -*-
A local variables list goes near the end of the file, in the last page. (It is often best to put it on a page by itself.) The local variables list starts with a line containing the string `Local Variables:', and ends with a line containing the string `End:'. In between come the variable names and values, one set per line, as `variable: value'. The values are not evaluated; they are used literally.
Here is an example of a local variables list:
;;; Local Variables: *** ;;; mode:lisp *** ;;; comment-column:0 *** ;;; comment-start: ";;; " *** ;;; comment-end:"***" *** ;;; End: ***
As you see, each line starts with the prefix `;;; ' and each line ends with the suffix ` ***'. Emacs recognizes these as the prefix and suffix based on the first line of the list, by finding them surrounding the magic string `Local Variables:'; then it automatically discards them from the other lines of the list.
The usual reason for using a prefix and/or suffix is to embed the
local variables list in a comment, so it won't confuse other programs
that the file is intended as input for. The example above is for a
language where comment lines start with `;;; ' and end with
`***'; the local values for
comment-end customize the rest of Emacs for this unusual syntax.
Don't use a prefix (or a suffix) if you don't need one.
Two "variable names" have special meanings in a local variables
list: a value for the variable
mode really sets the major mode,
and a value for the variable
eval is simply evaluated as an
expression and the value is ignored.
not real variables; setting variables named
in any other context has no special meaning. If
mode is used in
a local variables list, it should be the first entry in the list.
The start of the local variables list must be no more than 3000 characters from the end of the file, and must be in the last page if the file is divided into pages. Otherwise, Emacs will not notice it is there. The purpose of this rule is so that a stray `Local Variables:' not in the last page does not confuse Emacs, and so that visiting a long file that is all one page and has no local variables list need not take the time to search the whole file.
You may be tempted to try to turn on Auto Fill mode with a local variable list. That is a mistake. The choice of Auto Fill mode or not is a matter of individual taste, not a matter of the contents of particular files. If you want to use Auto Fill, set up major mode hooks with your `.emacs' file to turn it on (when appropriate) for you alone (see section The Init File, `~/.emacs'). Don't try to use a local variable list that would impose your taste on everyone.
enable-local-variables controls whether to process
local variables lists, and thus gives you a chance to override them.
Its default value is
t, which means do process local variables
lists. If you set the value to
nil, Emacs simply ignores local
variables lists. Any other value says to query you about each local
variables list, showing you the local variables list to consider.
eval "variable", and certain actual variables, create a
special risk; when you visit someone else's file, local variable
specifications for these could affect your Emacs in arbitrary ways.
Therefore, the option
enable-local-eval controls whether Emacs
eval variables, as well variables with names that end
in `-hook', `-hooks', `-function' or `-functions',
and certain other variables. The three possibilities for the option's
nil, and anything else, just as for
enable-local-variables. The default is
maybe, which is
nil, so normally Emacs does ask for
confirmation about file settings for these variables.
Use the command
normal-mode to reset the local variables and
major mode of a buffer according to the file name and contents,
including the local variables list if any. See section How Major Modes are Chosen.
A keyboard macro is a command defined by the user to stand for another sequence of keys. For example, if you discover that you are about to type C-n C-d forty times, you can speed your work by defining a keyboard macro to do C-n C-d and calling it with a repeat count of forty.
Keyboard macros differ from ordinary Emacs commands in that they are written in the Emacs command language rather than in Lisp. This makes it easier for the novice to write them, and makes them more convenient as temporary hacks. However, the Emacs command language is not powerful enough as a programming language to be useful for writing anything intelligent or general. For such things, Lisp must be used.
You define a keyboard macro while executing the commands which are the definition. Put differently, as you define a keyboard macro, the definition is being executed for the first time. This way, you can see what the effects of your commands are, so that you don't have to figure them out in your head. When you are finished, the keyboard macro is defined and also has been, in effect, executed once. You can then do the whole thing over again by invoking the macro.
To start defining a keyboard macro, type the C-x ( command
start-kbd-macro). From then on, your keys continue to be
executed, but also become part of the definition of the macro. `Def'
appears in the mode line to remind you of what is going on. When you are
finished, the C-x ) command (
end-kbd-macro) terminates the
definition (without becoming part of it!). For example,
C-x ( M-f foo C-x )
defines a macro to move forward a word and then insert `foo'.
The macro thus defined can be invoked again with the C-x e
call-last-kbd-macro), which may be given a repeat count
as a numeric argument to execute the macro many times. C-x ) can
also be given a repeat count as an argument, in which case it repeats
the macro that many times right after defining it, but defining the
macro counts as the first repetition (since it is executed as you define
it). Therefore, giving C-x ) an argument of 4 executes the macro
immediately 3 additional times. An argument of zero to C-x e or
C-x ) means repeat the macro indefinitely (until it gets an error
or you type C-g).
If you wish to repeat an operation at regularly spaced places in the text, define a macro and include as part of the macro the commands to move to the next place you want to use it. For example, if you want to change each line, you should position point at the start of a line, and define a macro to change that line and leave point at the start of the next line. Then repeating the macro will operate on successive lines.
After you have terminated the definition of a keyboard macro, you can add to the end of its definition by typing C-u C-x (. This is equivalent to plain C-x ( followed by retyping the whole definition so far. As a consequence it re-executes the macro as previously defined.
You can use function keys in a keyboard macro, just like keyboard keys. You can even use mouse events, but be careful about that: when the macro replays the mouse event, it uses the original mouse position of that event, the position that the mouse had while you were defining the macro. The effect of this may be hard to predict. (Using the current mouse position would be even less predictable.)
One thing that doesn't always work well in a keyboard macro is the
command C-M-c (
exit-recursive-edit). When this command
exits a recursive edit that started within the macro, it works as you'd
expect. But if it exits a recursive edit that started before you
invoked the keyboard macro, it also necessarily exits the keyboard macro
as part of the process.
You can edit a keyboard macro already defined by typing C-x C-k
edit-kbd-macro). Follow that with the keyboard input that you
would use to invoke the macro---C-x e or M-x name or
some other key sequence. This formats the macro definition in a buffer
and enters a specialized major mode for editing it. Type C-h m
once in that buffer to display details of how to edit the macro. When
you are finished editing, type C-c C-c.
If you wish to save a keyboard macro for longer than until you define the
next one, you must give it a name using M-x name-last-kbd-macro.
This reads a name as an argument using the minibuffer and defines that name
to execute the macro. The macro name is a Lisp symbol, and defining it in
this way makes it a valid command name for calling with M-x or for
binding a key to with
global-set-key (see section Keymaps). If you
specify a name that has a prior definition other than another keyboard
macro, an error message is printed and nothing is changed.
Once a macro has a command name, you can save its definition in a file. Then it can be used in another editing session. First, visit the file you want to save the definition in. Then use this command:
M-x insert-kbd-macro RET macroname RET
This inserts some Lisp code that, when executed later, will define the
same macro with the same definition it has now. (You need not
understand Lisp code to do this, because
the Lisp code for you.) Then save the file. You can load the file
load-file (see section Libraries of Lisp Code for Emacs). If the file you
save in is your init file `~/.emacs' (see section The Init File, `~/.emacs') then the
macro will be defined each time you run Emacs.
If you give
insert-kbd-macro a numeric argument, it makes
additional Lisp code to record the keys (if any) that you have bound to the
keyboard macro, so that the macro will be reassigned the same keys when you
load the file.
Using C-x q (
kbd-macro-query), you can get an effect
similar to that of
query-replace, where the macro asks you each
time around whether to make a change. While defining the macro,
type C-x q at the point where you want the query to occur. During
macro definition, the C-x q does nothing, but when you run the
macro later, C-x q asks you interactively whether to continue.
The valid responses when C-x q asks are SPC (or y),
DEL (or n), ESC (or q), C-l and C-r.
The answers are the same as in
query-replace, though not all of
query-replace options are meaningful.
These responses include SPC to continue, and DEL to skip the remainder of this repetition of the macro and start right away with the next repetition. ESC means to skip the remainder of this repetition and cancel further repetitions. C-l redraws the screen and asks you again for a character to say what to do.
C-r enters a recursive editing level, in which you can perform editing which is not part of the macro. When you exit the recursive edit using C-M-c, you are asked again how to continue with the keyboard macro. If you type a SPC at this time, the rest of the macro definition is executed. It is up to you to leave point and the text in a state such that the rest of the macro will do what you want.
C-u C-x q, which is C-x q with a numeric argument, performs a completely different function. It enters a recursive edit reading input from the keyboard, both when you type it during the definition of the macro, and when it is executed from the macro. During definition, the editing you do inside the recursive edit does not become part of the macro. During macro execution, the recursive edit gives you a chance to do some particularized editing on each repetition. See section Recursive Editing Levels.
This section describes key bindings which map keys to commands, and the keymaps which record key bindings. It also explains how to customize key bindings.
Recall that a command is a Lisp function whose definition provides for interactive use. Like every Lisp function, a command has a function name which usually consists of lower case letters and hyphens.
The bindings between key sequences and command functions are recorded in data structures called keymaps. Emacs has many of these, each used on particular occasions.
Recall that a key sequence (key, for short) is a sequence of input events that have a meaning as a unit. Input events include characters, function keys and mouse buttons--all the inputs that you can send to the computer with your terminal. A key sequence gets its meaning from its binding, which says what command it runs. The function of keymaps is to record these bindings.
The global keymap is the most important keymap because it is always in effect. The global keymap defines keys for Fundamental mode; most of these definitions are common to most or all major modes. Each major or minor mode can have its own keymap which overrides the global definitions of some keys.
For example, a self-inserting character such as g is
self-inserting because the global keymap binds it to the command
self-insert-command. The standard Emacs editing characters such
as C-a also get their standard meanings from the global keymap.
Commands to rebind keys, such as M-x global-set-key, actually work
by storing the new binding in the proper place in the global map.
See section Changing Key Bindings Interactively.
Meta characters work differently; Emacs translates each Meta character into a pair of characters starting with ESC. When you type the character M-a in a key sequence, Emacs replaces it with ESC a. A meta key comes in as a single input event, but becomes two events for purposes of key bindings. The reason for this is historical, and we might change it someday.
Most modern keyboards have function keys as well as character keys. Function keys send input events just as character keys do, and keymaps can have bindings for them.
On many terminals, typing a function key actually sends the computer a sequence of characters; the precise details of the sequence depends on which function key and on the model of terminal you are using. (Often the sequence starts with ESC [.) If Emacs understands your terminal type properly, it recognizes the character sequences forming function keys wherever they occur in a key sequence (not just at the beginning). Thus, for most purposes, you can pretend the function keys reach Emacs directly and ignore their encoding as character sequences.
Mouse buttons also produce input events. These events come with other data--the window and position where you pressed or released the button, and a time stamp. But only the choice of button matters for key bindings; the other data matters only if a command looks at it. (Commands designed for mouse invocation usually do look at the other data.)
A keymap records definitions for single events. Interpreting a key sequence of multiple events involves a chain of keymaps. The first keymap gives a definition for the first event; this definition is another keymap, which is used to look up the second event in the sequence, and so on.
Key sequences can mix function keys and characters. For example, C-x SELECT makes sense. If you make SELECT a prefix key, then SELECT C-n makes sense. You can even mix mouse events with keyboard events, but we recommend against it, because such sequences are inconvenient to type in.
A prefix key such as C-x or ESC has its own keymap, which holds the definition for the event that immediately follows that prefix.
The definition of a prefix key is usually the keymap to use for
looking up the following event. The definition can also be a Lisp
symbol whose function definition is the following keymap; the effect is
the same, but it provides a command name for the prefix key that can be
used as a description of what the prefix key is for. Thus, the binding
of C-x is the symbol
Ctl-X-Prefix, whose function
definition is the keymap for C-x commands. The definitions of
C-c, C-x, C-h and ESC as prefix keys appear in
the global map, so these prefix keys are always available.
Some prefix keymaps are stored in variables with names:
ctl-x-mapis the variable name for the map used for characters that follow C-x.
help-mapis for characters that follow C-h.
esc-mapis for characters that follow ESC. Thus, all Meta characters are actually defined by this map.
ctl-x-4-mapis for characters that follow C-x 4.
mode-specific-mapis for characters that follow C-c.
So far we have explained the ins and outs of the global map. Major modes customize Emacs by providing their own key bindings in local keymaps. For example, C mode overrides TAB to make it indent the current line for C code. Portions of text in the buffer can specify their own keymaps to substitute for the keymap of the buffer's major mode.
Minor modes can also have local keymaps. Whenever a minor mode is in effect, the definitions in its keymap override both the major mode's local keymap and the global keymap.
The local keymaps for Lisp mode, C mode, and several other major modes
always exist even when not in use. These are kept in variables named
c-mode-map, and so on. For major modes
less often used, the local keymap is normally constructed only when the
mode is used for the first time in a session. This is to save space.
All minor mode keymaps are created in advance. There is no way to defer their creation until the first time the minor mode is enabled.
A local keymap can locally redefine a key as a prefix key by defining it as a prefix keymap. If the key is also defined globally as a prefix, then its local and global definitions (both keymaps) effectively combine: both of them are used to look up the event that follows the prefix key. Thus, if the mode's local keymap defines C-c as another keymap, and that keymap defines C-z as a command, this provides a local meaning for C-c C-z. This does not affect other sequences that start with C-c; if those sequences don't have their own local bindings, their global bindings remain in effect.
Another way to think of this is that Emacs handles a multi-event key sequence by looking in several keymaps, one by one, for a binding of the whole key sequence. First it checks the minor mode keymaps for minor modes that are enabled, then it checks the major mode's keymap, and then it checks the global keymap. This is not precisely how key lookup works, but it's good enough for understanding ordinary circumstances.
The minibuffer has its own set of local keymaps; they contain various completion and exit commands.
minibuffer-local-mapis used for ordinary input (no completion).
minibuffer-local-ns-mapis similar, except that SPC exits just like RET. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-mapis for permissive completion.
minibuffer-local-must-match-mapis for strict completion and for cautious completion.
The way to redefine an Emacs key is to change its entry in a keymap. You can change the global keymap, in which case the change is effective in all major modes (except those that have their own overriding local definitions for the same key). Or you can change the current buffer's local map, which affects all buffers using the same major mode.
For example, suppose you like to execute commands in a subshell within
an Emacs buffer, instead of suspending Emacs and executing commands in
your login shell. Normally, C-z is bound to the function
suspend-emacs (when not using the X Window System), but you can
change C-z to invoke an interactive subshell within Emacs, by
binding it to
shell as follows:
M-x global-set-key RET C-z shell RET
global-set-key reads the command name after the key. After you
press the key, a message like this appears so that you can confirm that
you are binding the key you want:
Set key C-z to command:
You can redefine function keys and mouse events in the same way; just type the function key or click the mouse when it's time to specify the key to rebind.
You can rebind a key that contains more than one event in the same way. Emacs keeps reading the key to rebind until it is a complete key (that is, not a prefix key). Thus, if you type C-f for key, that's the end; the minibuffer is entered immediately to read cmd. But if you type C-x, another character is read; if that is 4, another character is read, and so on. For example,
M-x global-set-key RET C-x 4 $ spell-other-window RET
redefines C-x 4 $ to run the (fictitious) command
The two-character keys consisting of C-c followed by a letter are reserved for user customizations. Lisp programs are not supposed to define these keys, so the bindings you make for them will be available in all major modes and will never get in the way of anything.
You can remove the global definition of a key with
global-unset-key. This makes the key undefined; if you
type it, Emacs will just beep. Similarly,
a key undefined in the current major mode keymap, which makes the global
definition (or lack of one) come back into effect in that major mode.
If you have redefined (or undefined) a key and you subsequently wish to retract the change, undefining the key will not do the job--you need to redefine the key with its standard definition. To find the name of the standard definition of a key, go to a Fundamental mode buffer and use C-h c. The documentation of keys in this manual also lists their command names.
If you want to prevent yourself from invoking a command by mistake, it is better to disable the command than to undefine the key. A disabled command is less work to invoke when you really want to. See section Disabling Commands.
If you have a set of key bindings that you like to use all the time,
you can specify them in your `.emacs' file by using their Lisp
syntax. Thus, the first
global-set-key command in this section
could be put in an `.emacs' file in either of the two following
(global-set-key "\C-z" 'shell)
(global-set-key [?\C-z] 'shell)
When the key sequence consists of ASCII characters and Meta-modified
ASCII characters, like this one, you can write it as a string or as a
vector. The first format specifies the key sequence as a string,
"\C-z". The second format uses a vector to specify the key
sequence. The square brackets (`[...]') delimit the contents
of the vector. The vector in this example contains just one element,
which is the integer code corresponding to C-z. The question mark
is the Lisp syntax for a character constant; the character must follow
with no intervening spaces.
The single-quote before
shell marks it as a constant symbol
rather than a variable. If you omit the quote, Emacs tries to evaluate
shell immediately as a variable. This probably causes an error;
it certainly isn't what you want.
Here is another example that binds a key sequence two characters long:
(global-set-key "\C-xl" 'make-symbolic-link)
(global-set-key [?\C-x ?l] 'make-symbolic-link)
When the key sequence includes function keys or mouse button events,
or non-ASCII characters such as
H-a, you must use a
(global-set-key [?\C-=] 'make-symbolic-link) (global-set-key [?\H-a] 'make-symbolic-link) (global-set-key [C-H-mouse-1] 'make-symbolic-link)
Key sequences can contain function keys as well as ordinary characters. Just as Lisp characters (actually integers) represent keyboard characters, Lisp symbols represent function keys. If the function key has a word as its label, then that word is also the name of the corresponding Lisp symbol. Here are the conventional Lisp names for common function keys:
These names are conventional, but some systems (especially when using X windows) may use different names. To make certain what symbol is used for a given function key on your terminal, type C-h c followed by that key.
A key sequence which contains non-characters must be a vector rather than a string. To write a vector, write square brackets containing the vector elements. Write spaces to separate the elements. If an element is a symbol, simply write the symbol's name--no delimiters or punctuation are needed. If an element is a character, write a Lisp character constant, which is `?' followed by the character as it would appear in a string.
Thus, to bind function key `f1' to the command
(global-set-key [f1] 'rmail)
To bind the right-arrow key to the command
forward-char, you can
use this expression:
(global-set-key [right] 'forward-char)
This uses the Lisp syntax for a vector containing the symbol
right. (This binding is present in Emacs by default.)
You can mix function keys and characters in a key sequence. This
example binds C-x RIGHT to the command
(global-set-key [?\C-x right] 'forward-page)
?\C-x is the Lisp character constant for the character
C-x. The vector element
right is a symbol and therefore
does not take a question mark.
You can use the modifier keys CTRL, META, HYPER, SUPER, ALT and SHIFT with function keys. To represent these modifiers, add the strings `C-', `M-', `H-', `s-', `A-' and `S-' at the front of the symbol name. Thus, here is how to make Hyper-Meta-RIGHT move forward a word:
(global-set-key [H-M-right] 'forward-word)
TAB, RET, BS, LFD, ESC and DEL started out as names for certain ASCII control characters, used so often that they have special keys of their own. Later, users found it convenient to distinguish in Emacs between these keys and the "same" control characters typed with the CTRL key.
Emacs 19 distinguishes these two kinds of input, when used with the X
Window System. It treats the "special" keys as function keys named
delete. These function keys translate
automatically into the corresponding ASCII characters if they
have no bindings of their own. As a result, neither users nor Lisp
programs need to pay attention to the distinction unless they care to.
If you do not want to distinguish between (for example) TAB and
C-i, make just one binding, for the ASCII character TAB
(octal code 011). If you do want to distinguish, make one binding for
this ASCII character, and another for the "function key"
With an ordinary ASCII terminal, there is no way to distinguish between TAB and C-i (and likewise for other such pairs), because the terminal sends the same character in both cases.
Emacs uses Lisp symbols to designate mouse buttons, too. The ordinary mouse events in Emacs are click events; these happen when you press a button and release it without moving the mouse. You can also get drag events, when you move the mouse while holding the button down. Drag events happen when you finally let go of the button.
The symbols for basic click events are
mouse-1 for the leftmost
mouse-2 for the next, and so on. Here is how you can
redefine the second mouse button to split the current window:
(global-set-key [mouse-2] 'split-window-vertically)
The symbols for drag events are similar, but have the prefix
`drag-' before the word `mouse'. For example, dragging the
first button generates a
You can also define bindings for events that occur when a mouse button is pressed down. These events start with `down-' instead of `drag-'. Such events are generated only if they have key bindings. When you get a button-down event, a corresponding click or drag event will always follow.
If you wish, you can distinguish single, double, and triple clicks. A
double click means clicking a mouse button twice in approximately the
same place. The first click generates an ordinary click event. The
second click, if it comes soon enough, generates a double-click event
instead. The event type for a double click event starts with
`double-': for example,
This means that you can give a special meaning to the second click at the same place, but it must act on the assumption that the ordinary single click definition has run when the first click was received.
This constrains what you can do with double clicks, but user interface designers say that this constraint ought to be followed in any case. A double click should do something similar to the single click, only "more so". The command for the double-click event should perform the extra work for the double click.
If a double-click event has no binding, it changes to the corresponding single-click event. Thus, if you don't define a particular double click specially, it executes the single-click command twice.
Emacs also supports triple-click events whose names start with `triple-'. Emacs does not distinguish quadruple clicks as event types; clicks beyond the third generate additional triple-click events. However, the full number of clicks is recorded in the event list, so you can distinguish if you really want to. We don't recommend distinct meanings for more than three clicks, but sometimes it is useful for subsequent clicks to cycle through the same set of three meanings, so that four clicks are equivalent to one click, five are equivalent to two, and six are equivalent to three.
Emacs also records multiple presses in drag and button-down events. For example, when you press a button twice, then move the mouse while holding the button, Emacs gets a `double-drag-' event. And at the moment when you press it down for the second time, Emacs gets a `double-down-' event (which is ignored, like all button-down events, if it has no binding).
double-click-time specifies how long may elapse
between clicks that are recognized as a pair. Its value is measured
in milliseconds. If the value is
nil, double clicks are not
detected at all. If the value is
t, then there is no time
The symbols for mouse events also indicate the status of the modifier keys, with the usual prefixes `C-', `M-', `H-', `s-', `A-' and `S-'. These always precede `double-' or `triple-', which always precede `drag-' or `down-'.
A frame includes areas that don't show text from the buffer, such as
the mode line and the scroll bar. You can tell whether a mouse button
comes from a special area of the screen by means of dummy "prefix
keys." For example, if you click the mouse in the mode line, you get
the prefix key
mode-line before the ordinary mouse-button symbol.
Thus, here is how to define the command for clicking the first button in
a mode line to run
(global-set-key [mode-line mouse-1] 'scroll-up)
Here is the complete list of these dummy prefix keys and their meanings:
You can put more than one mouse button in a key sequence, but it isn't usual to do so.
Disabling a command marks the command as requiring confirmation before it can be executed. The purpose of disabling a command is to prevent beginning users from executing it by accident and being confused.
An attempt to invoke a disabled command interactively in Emacs displays a window containing the command's name, its documentation, and some instructions on what to do immediately; then Emacs asks for input saying whether to execute the command as requested, enable it and execute it, or cancel. If you decide to enable the command, you are asked whether to do this permanently or just for the current session. Enabling permanently works by automatically editing your `.emacs' file.
The direct mechanism for disabling a command is to put a
disabled property on the Lisp symbol for the
command. Here is the Lisp program to do this:
(put 'delete-region 'disabled t)
If the value of the
disabled property is a string, that string
is included in the message printed when the command is used:
(put 'delete-region 'disabled "It's better to use `kill-region' instead.\n")
You can make a command disabled either by editing the `.emacs' file directly or with the command M-x disable-command, which edits the `.emacs' file for you. Likewise, M-x enable-command edits `.emacs' to enable a command permanently. See section The Init File, `~/.emacs'.
Whether a command is disabled is independent of what key is used to invoke it; disabling also applies if the command is invoked using M-x. Disabling a command has no effect on calling it as a function from Lisp programs.
Some keyboards do not make it convenient to send all the special characters that Emacs uses. The most common problem case is the DEL character. Some keyboards provide no convenient way to type this very important character--usually because they were designed to expect the character C-h to be used for deletion. On these keyboard, if you press the key normally used for deletion, Emacs handles the C-h as a prefix character and offers you a list of help options, which is not what you want.
You can work around this problem within Emacs by setting up keyboard translations to turn C-h into DEL and DEL into C-h, as follows:
;; Translate C-h to DEL. (keyboard-translate ?\C-h ?\C-?) ;; Translate DEL to C-h. (keyboard-translate ?\C-? ?\C-h)
Keyboard translations are not the same as key bindings in keymaps (see section Keymaps). Emacs contains numerous keymaps that apply in different situations, but there is only one set of keyboard translations, and it applies to every character that Emacs reads from the terminal. Keyboard translations take place at the lowest level of input processing; the keys that are looked up in keymaps contain the characters that result from keyboard translation.
Under X, the keyboard key named DEL acts like a function key and
is distinct from the ASCII character named DEL. See section Named ASCII Control Characters. Keyboard translations affect only ASCII character input, not
function keys; thus, the above example used under X will not do what you
probably want. However, you can remap the keyboard keys using
xmodmap when using X.
For full information about how to use keyboard translations, see section `Translating Input' in The Emacs Lisp Reference Manual.
All the Emacs commands which parse words or balance parentheses are controlled by the syntax table. The syntax table says which characters are opening delimiters, which are parts of words, which are string quotes, and so on. Each major mode has its own syntax table (though sometimes related major modes use the same one) which it installs in each buffer that uses that major mode. The syntax table installed in the current buffer is the one that all commands use, so we call it "the" syntax table. A syntax table is a Lisp object, a vector of length 256 whose elements are numbers.
To display a description of the contents of the current syntax table,
type C-h s (
describe-syntax). The description of each
character includes both the string you would have to give to
modify-syntax-entry to set up that character's current syntax,
and some English to explain that string if necessary.
For full information on the syntax table, see section `Syntax Tables' in The Emacs Lisp Reference Manual.
When Emacs is started, it normally loads a Lisp program from the file `.emacs' in your home directory. We call this file your init file because it specifies how to initialize Emacs for you. You can use the command line switches `-q' and `-u' to tell Emacs whether to load an init file, and which one (see section Entering and Exiting Emacs).
There can also be a default init file, which is the library
named `default.el', found via the standard search path for
libraries. The Emacs distribution contains no such library; your site
may create one for local customizations. If this library exists, it is
loaded whenever you start Emacs (except when you specify `-q').
But your init file, if any, is loaded first; if it sets
nil, then `default' is not
Your site may also have a site startup file; this is named `site-start.el', if it exists. Emacs loads this library before it loads your init file. To inhibit loading of this library, use the option `-no-site-file'.
If you have a large amount of code in your `.emacs' file, you
should move it into another file such as `~/something.el',
byte-compile it, and make your `.emacs' file load it with
(load "~/something"). See section `Byte Compilation' in the Emacs Lisp Reference Manual, for more
information about compiling Emacs Lisp programs.
The `.emacs' file contains one or more Lisp function call
expressions. Each of these consists of a function name followed by
arguments, all surrounded by parentheses. For example,
fill-column 60) calls the function
setq to set the variable
fill-column (see section Filling Text) to 60.
The second argument to
setq is an expression for the new value of
the variable. This can be a constant, a variable, or a function call
expression. In `.emacs', constants are used most of the time. They can be:
?\). Note that strings and characters are not interchangeable in Lisp; some contexts require one and some contexts require the other.
tstands for `true'.
nilstands for `false'.
Here are some examples of doing certain commonly desired things with Lisp expressions:
(setq c-tab-always-indent nil)Here we have a variable whose value is normally
tfor `true' and the alternative is
(setq-default case-fold-search nil)This sets the default value, which is effective in all buffers that do not have local values for the variable. Setting
setqaffects only the current buffer's local value, which is not what you probably want to do in an init file.
(setq user-mail-address "email@example.com")Various Emacs packages that need to use your own email address use the value of
(setq default-major-mode 'text-mode)Note that
text-modeis used because it is the command for entering Text mode. The single-quote before it makes the symbol a constant; otherwise,
text-modewould be treated as a variable name.
(add-hook 'text-mode-hook '(lambda () (auto-fill-mode 1)))This shows how to add a hook function to a normal hook variable (see section Hooks). The function we supply is a list starting with
lambda, with a single-quote in front of it to make it a list constant rather than an expression. It's beyond the scope of this manual to explain Lisp functions, but for this example it is enough to know that the effect is to execute
(auto-fill-mode 1)when Text mode is entered. You can replace that with any other expression that you like, or with several expressions in a row. Emacs comes with a function named
turn-on-auto-fillwhose definition is
(lambda () (auto-fill-mode 1)). Thus, a simpler way to write the above example is as follows:
(add-hook 'text-mode-hook 'turn-on-auto-fill)
(load "foo")When the argument to
loadis a relative file name, not starting with `/' or `~',
loadsearches the directories in
load-path(see section Libraries of Lisp Code for Emacs).
(load "~/foo.elc")Here an absolute file name is used, so no searching is done.
(global-set-key "\C-xl" 'make-symbolic-link)or
(define-key global-map "\C-xl" 'make-symbolic-link)Note once again the single-quote used to refer to the symbol
make-symbolic-linkinstead of its value as a variable.
(define-key c-mode-map "\C-xl" 'make-symbolic-link)
next-linein Fundamental mode so that they run
(substitute-key-definition 'next-line 'forward-line global-map)
(global-unset-key "\C-x\C-v")One reason to undefine a key is so that you can make it a prefix. Simply defining C-x C-v anything will make C-x C-v a prefix, but C-x C-v must first be freed of its usual non-prefix definition.
(modify-syntax-entry ?\$ "." text-mode-syntax-table)
(put 'eval-expression 'disabled nil)
Each terminal type can have a Lisp library to be loaded into Emacs when
it is run on that type of terminal. For a terminal type named
termtype, the library is called `term/termtype' and it is
found by searching the directories
load-path as usual and trying the
suffixes `.elc' and `.el'. Normally it appears in the
subdirectory `term' of the directory where most Emacs libraries are
The usual purpose of the terminal-specific library is to map the
escape sequences used by the terminal's function keys onto more
meaningful names, using
function-key-map. See the file
`term/lk201.el' for an example of how this is done. Many function
keys are mapped automatically according to the information in the
Termcap data base; the terminal-specific library needs to map only the
function keys that Termcap does not specify.
When the terminal type contains a hyphen, only the part of the name
before the first hyphen is significant in choosing the library name.
Thus, terminal types `aaa-48' and `aaa-30-rv' both use
the library `term/aaa'. The code in the library can use
(getenv "TERM") to find the full terminal type name.
The library's name is constructed by concatenating the value of the
term-file-prefix and the terminal type. Your `.emacs'
file can prevent the loading of the terminal-specific library by setting
Emacs runs the hook
term-setup-hook at the end of
initialization, after both your `.emacs' file and any
terminal-specific library have been read in. Add hook functions to this
hook if you wish to override part of any of the terminal-specific
libraries and to define initializations for terminals that do not have a
library. See section Hooks.
Normally Emacs uses the environment variable
HOME to find
`.emacs'; that's what `~' means in a file name. But if you
su, Emacs tries to find your own `.emacs', not
that of the user you are currently pretending to be. The idea is
that you should get your own editor customizations even if you are
running as the super user.
More precisely, Emacs first determines which user's init file to use.
It gets the user name from the environment variables
USER; if neither of those exists, it uses effective user-ID.
If that user name matches the real user-ID, then Emacs uses
otherwise, it looks up the home directory corresponding to that user
name in the system's data base of users.