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This chapter talks about various topics relevant to adapting the behavior of Emacs in ways we have anticipated. See Emacs Lisp: (elisp)Top section `Emacs Lisp' in The Emacs Lisp Reference Manual, for how to make more far-reaching and open-ended changes. See section X Options and Resources, for information on using X resources to customize Emacs.
Customization that you do within Emacs normally affects only the particular Emacs session that you do it in--it does not persist between sessions unless you save the customization in a file such as your init file (`.emacs') that will affect future sessions. (See section The Init File, `~/.emacs'.) When you tell the customization buffer to save customizations for future sessions, this actually works by editing `.emacs' for you.
Another means of customization is the keyboard macro, which is a sequence of keystrokes to be replayed with a single command. See section Keyboard Macros, for full instruction how to record, manage, and replay sequences of keys.
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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 enabled; for example, `Fill' in the mode line means that Auto Fill mode is enabled.
You should append -mode to the name of a minor mode to
produce the name of the command that turns the mode on or off. Thus,
the command to enable or disable Auto Fill mode is called
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 minor mode 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.
Some minor modes are global: while enabled, they affect everything you do in the Emacs session, in all buffers. Other minor modes are buffer-local; they apply only to the current buffer, so you can enable the mode in certain buffers and not others.
For most minor modes, the command name is also the name of a
variable. The variable's value is non-nil if the mode is
enabled and nil if it is disabled. Some minor-mode commands
work by just setting the variable. For example, the command
abbrev-mode works by setting the value of abbrev-mode as
a variable; it is this variable that directly turns Abbrev mode on and
off. You can directly set the variable's value instead of calling the
mode function. For other minor modes, you need to either set the
variable through the Customize interface or call the mode function to
correctly enable or disable the mode. To check which of these two
possibilities applies to a given minor mode, use C-h v to ask
for documentation on the variable name.
For minor mode commands that work by just setting the minor mode variable, that variable provides a good way for Lisp programs to turn minor modes on and off; it is also useful in a file's local variables list (see section Local Variables in Files). But please think twice before setting minor modes with a local variables list, because most minor modes are a matter of user preference--other users editing the same file might not want the same minor modes you prefer.
The most useful buffer-local minor modes include Abbrev mode, Auto Fill mode, Auto Save mode, Font-Lock mode, Glasses mode, Outline minor mode, Overwrite mode, and Binary Overwrite mode.
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.
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.
Auto Save mode saves the buffer contents periodically to reduce the amount of work you can lose in case of a crash. See section Auto-Saving: Protection Against Disasters.
Enriched mode enables editing and saving of formatted text. See section Editing Formatted Text.
Flyspell mode automatically highlights misspelled words. See section Checking and Correcting Spelling.
Font-Lock mode automatically highlights certain textual units found in programs, such as comments, strings, and function names being defined. This requires a display that can show multiple fonts or colors. See section Using Multiple Typefaces.
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 `FOOGBAR' as usual. In Overwrite mode, the command C-q inserts the next character whatever it may be, even if it is a digit--this gives you a way to insert a character instead of replacing an existing character.
The command overwrite-mode is an exception to the rule that
commands which toggle minor modes are normally not bound to keys: it is
bound to the INSERT function key. This is because many other
programs bind INSERT to similar functions.
Binary Overwrite mode is a variant of Overwrite mode for editing binary files; it treats newlines and tabs like other characters, so that they overwrite other characters and can be overwritten by them. In Binary Overwrite mode, digits after C-q specify an octal character code, as usual.
Here are some useful minor modes that normally apply to all buffers at once. Since Line Number mode and Transient Mark mode can be enabled or disabled just by setting the value of the minor mode variable, you can set them differently for particular buffers, by explicitly making the corresponding variable local in those buffers. See section Local Variables.
Icomplete mode displays an indication of available completions when you are in the minibuffer and completion is active. See section Completion Options.
Line Number mode enables continuous display in the mode line of the line number of point, and Column Number mode enables display of the column number. See section The Mode Line.
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. See section The Mark and the Region.
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Emacs has many settings which have values that you can specify in order to customize various commands. Many are documented in this manual. Most settings are user options--that is to say, Lisp variables (see section Variables)--so their names appear in the Variable Index (see section Variable Index). The other settings are faces and their attributes (see section Using Multiple Typefaces).
You can browse interactively through settings and change them using M-x customize. This command creates a customization buffer, which offers commands to navigate through a logically organized structure of the Emacs settings; you can also use it to edit and set their values, and to save settings permanently in your `~/.emacs' file (see section The Init File, `~/.emacs').
The appearance of the example buffers in this section is typically different under a graphical display, since faces are then used to indicate buttons, links and editable fields.
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For customization purposes, settings are organized into groups
to help you find them. Groups are collected into bigger groups, all
the way up to a master group called Emacs.
M-x customize creates a customization buffer that shows the
top-level Emacs group and the second-level groups immediately
under it. It looks like this, in part:
/- Emacs group: ---------------------------------------------------\
[State]: visible group members are all at standard values.
Customization of the One True Editor.
See also [Manual].
Editing group: [Go to Group]
Basic text editing facilities.
External group: [Go to Group]
Interfacing to external utilities.
more second-level groups
\- Emacs group end ------------------------------------------------/
|
This says that the buffer displays the contents of the Emacs
group. The other groups are listed because they are its contents. But
they are listed differently, without indentation and dashes, because
their contents are not included. Each group has a single-line
documentation string; the Emacs group also has a `[State]'
line.
Most of the text in the customization buffer is read-only, but it typically includes some editable fields that you can edit. There are also buttons and links, which do something when you invoke them. To invoke a button or a link, either click on it with Mouse-1, or move point to it and type RET.
For example, the phrase `[State]' that appears in a second-level group is a button. It operates on the same customization buffer. The phrase `[Go to Group]' is a kind of hypertext link to another group. Invoking it creates a new customization buffer, which shows that group and its contents.
The Emacs group includes a few settings, but mainly it
contains other groups, which contain more groups, which contain the
settings. By browsing the hierarchy of groups, you will eventually
find the feature you are interested in customizing. Then you can use
the customization buffer to set that feature's settings. You can also
go straight to a particular group by name, using the command M-x
customize-group.
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M-x customize-browse is another way to browse the available settings. This command creates a special customization buffer which shows only the names of groups and settings, and puts them in a structure.
In this buffer, you can show the contents of a group by invoking the `[+]' button. When the group contents are visible, this button changes to `[-]'; invoking that hides the group contents again.
Each group or setting in this buffer has a link which says `[Group]', `[Option]' or `[Face]'. Invoking this link creates an ordinary customization buffer showing just that group and its contents, just that user option, or just that face. This is the way to change settings that you find with M-x customize-browse.
If you can guess part of the name of the settings you are interested
in, M-x customize-apropos is another way to search for settings.
However, unlike customize and customize-browse,
customize-apropos can only find groups and settings that are
loaded in the current Emacs session. See section Customizing Specific Items.
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Here is an example of what a variable (a user option) looks like in the customization buffer:
Kill Ring Max: [Hide Value] 60 [State]: STANDARD. Maximum length of kill ring before oldest elements are thrown away. |
The text following `[Hide Value]', `60' in this case, indicates the current value of the variable. If you see `[Show Value]' instead of `[Hide Value]', it means that the value is hidden; the customization buffer initially hides values that take up several lines. Invoke `[Show Value]' to show the value.
The line after the variable name indicates the customization state of the variable: in the example above, it says you have not changed the option yet. The `[State]' button at the beginning of this line gives you a menu of various operations for customizing the variable.
The line after the `[State]' line displays the beginning of the variable's documentation string. If there are more lines of documentation, this line ends with a `[More]' button; invoke that to show the full documentation string.
To enter a new value for `Kill Ring Max', move point to the value and edit it textually. For example, you can type M-d, then insert another number. As you begin to alter the text, you will see the `[State]' line change to say that you have edited the value:
[State]: EDITED, shown value does not take effect until you set or …
save it.
|
Editing the value does not actually set the variable. To do that, you must set the variable. To do this, invoke the `[State]' button and choose `Set for Current Session'.
The state of the variable changes visibly when you set it:
[State]: SET for current session only. |
You don't have to worry about specifying a value that is not valid; the `Set for Current Session' operation checks for validity and will not install an unacceptable value.
While editing a field that is a file name, directory name,
command name, or anything else for which completion is defined, you
can type M-TAB (widget-complete) to do completion.
(ESC TAB and C-M-i do the same thing.)
Some variables have a small fixed set of possible legitimate values. These variables don't let you edit the value textually. Instead, a `[Value Menu]' button appears before the value; invoke this button to change the value. For a boolean "on or off" value, the button says `[Toggle]', and it changes to the other value. `[Value Menu]' and `[Toggle]' simply edit the buffer; the changes take real effect when you use the `Set for Current Session' operation.
Some variables have values with complex structure. For example, the
value of file-coding-system-alist is an association list. Here
is how it appears in the customization buffer:
File Coding System Alist: [Hide Value]
[INS] [DEL] File regexp: \.elc\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: emacs-mule
Encoding: emacs-mule
[INS] [DEL] File regexp: \(\`\|/\)loaddefs.el\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: raw-text
Encoding: raw-text-unix
[INS] [DEL] File regexp: \.tar\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: no-conversion
Encoding: no-conversion
[INS] [DEL] File regexp:
Choice: [Value Menu] Encoding/decoding pair:
Decoding: undecided
Encoding: nil
[INS]
[State]: STANDARD.
Alist to decide a coding system to use for a file I/O …
operation. [Hide Rest]
The format is ((PATTERN . VAL) ...),
where PATTERN is a regular expression matching a file name,
[…more lines of documentation…]
|
Each association in the list appears on four lines, with several editable fields and/or buttons. You can edit the regexps and coding systems using ordinary editing commands. You can also invoke `[Value Menu]' to switch to a different kind of value--for instance, to specify a function instead of a pair of coding systems.
To delete an association from the list, invoke the `[DEL]' button for that item. To add an association, invoke `[INS]' at the position where you want to add it. There is an `[INS]' button between each pair of associations, another at the beginning and another at the end, so you can add a new association at any position in the list.
Two special commands, TAB and S-TAB, are useful
for moving through the customization buffer. TAB
(widget-forward) moves forward to the next button or editable
field; S-TAB (widget-backward) moves backward to
the previous button or editable field.
Typing RET on an editable field also moves forward, just like TAB. We set it up this way because people often type RET when they are finished editing a field. To insert a newline within an editable field, use C-o or C-q C-j.
Setting the variable changes its value in the current Emacs session; saving the value changes it for future sessions as well. To save the variable, invoke `[State]' and select the `Save for Future Sessions' operation. This works by writing code so as to set the variable again, each time you start Emacs (see section Saving Customizations).
You can also restore the variable to its standard value by invoking `[State]' and selecting the `Erase Customization' operation. There are actually four reset operations:
If you have made some modifications and not yet set the variable, this restores the text in the customization buffer to match the actual value.
This restores the value of the variable to the last saved value, and updates the text accordingly.
This sets the variable to its standard value, and updates the text accordingly. This also eliminates any saved value for the variable, so that you will get the standard value in future Emacs sessions.
This sets the variable to a previous value that was set in the customization buffer in this session. If you customize a variable and then reset it, which discards the customized value, you can get the discarded value back again with this operation.
Sometimes it is useful to record a comment about a specific customization. Use the `Add Comment' item from the `[State]' menu to create a field for entering the comment. The comment you enter will be saved, and displayed again if you again view the same variable in a customization buffer, even in another session.
The state of a group indicates whether anything in that group has been edited, set or saved.
Near the top of the customization buffer there are two lines of buttons:
[Set for Current Session] [Save for Future Sessions] [Undo Edits] [Reset to Saved] [Erase Customization] [Finish] |
Invoking `[Finish]' either buries or kills this customization
buffer according to the setting of the option
custom-buffer-done-kill; the default is to bury the buffer.
Each of the other buttons performs an operation--set, save or
reset--on each of the settings in the buffer that could meaningfully
be set, saved or reset. They do not operate on settings whose values
are hidden, nor on subgroups which are hidden or not visible in the buffer.
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Saving customizations from the customization buffer works by writing code that future sessions will read, code to set up those customizations again.
Normally this saves customizations in your init file,
`~/.emacs'. If you wish, you can save customizations in another
file instead. To make this work, your `~/.emacs' should set
custom-file to the name of that file. Then you should load the
file by calling load. For example:
(setq custom-file "~/.emacs-custom.el") (load custom-file) |
You can use custom-file to specify different customization
files for different Emacs versions, like this:
(cond ((< emacs-major-version 21)
;; Emacs 20 customization.
(setq custom-file "~/.custom-20.el"))
((and (= emacs-major-version 21) (< emacs-minor-version 4))
;; Emacs 21 customization, before version 21.4.
(setq custom-file "~/.custom-21.el"))
((< emacs-major-version 22)
;; Emacs version 21.4 or later.
(setq custom-file "~/.custom-21.4.el"))
(t
;; Emacs version 22.1 or later.
(setq custom-file "~/.custom-22.el")))
(load custom-file)
|
If Emacs was invoked with the `-q' or `--no-init-file' options (see section Initial Options), it will not let you save your customizations in your `~/.emacs' init file. This is because saving customizations from such a session would wipe out all the other customizations you might have on your init file.
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In addition to variables, some customization groups also include faces. When you show the contents of a group, both the variables and the faces in the group appear in the customization buffer. Here is an example of how a face looks:
Custom Changed Face:(sample) [Hide Face]
[State]: STANDARD.
Face used when the customize item has been changed.
Parent groups: [Custom Magic Faces]
Attributes: [ ] Font Family: *
[ ] Width: *
[ ] Height: *
[ ] Weight: *
[ ] Slant: *
[ ] Underline: *
[ ] Overline: *
[ ] Strike-through: *
[ ] Box around text: *
[ ] Inverse-video: *
[X] Foreground: white (sample)
[X] Background: blue (sample)
[ ] Stipple: *
[ ] Inherit: *
|
Each face attribute has its own line. The `[x]' button before the attribute name indicates whether the attribute is enabled; `[X]' means that it's enabled, and `[ ]' means that it's disabled. You can enable or disable the attribute by clicking that button. When the attribute is enabled, you can change the attribute value in the usual ways.
For the colors, you can specify a color name (use M-x list-colors-display for a list of them) or a hexadecimal color specification of the form `#rrggbb'. (`#000000' is black, `#ff0000' is red, `#00ff00' is green, `#0000ff' is blue, and `#ffffff' is white.) On a black-and-white display, the colors you can use for the background are `black', `white', `gray', `gray1', and `gray3'. Emacs supports these shades of gray by using background stipple patterns instead of a color.
Setting, saving and resetting a face work like the same operations for variables (see section Changing a Variable).
A face can specify different appearances for different types of display. For example, a face can make text red on a color display, but use a bold font on a monochrome display. To specify multiple appearances for a face, select `For All Kinds of Displays' in the menu you get from invoking `[State]'.
Another more basic way to set the attributes of a specific face is with M-x modify-face. This command reads the name of a face, then reads the attributes one by one. For the color and stipple attributes, the attribute's current value is the default--type just RET if you don't want to change that attribute. Type `none' if you want to clear out the attribute.
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Instead of finding the setting you want to change by navigating the structure of groups, here are other ways to specify the settings that you want to customize.
Set up a customization buffer with just one user option variable, option.
Set up a customization buffer with just one face, face.
Set up a customization buffer with just one group, group.
Set up a customization buffer with all the settings and groups that match regexp.
Set up a customization buffer with all the settings and groups whose meaning has changed since Emacs version version.
Set up a customization buffer containing all settings that you have saved with customization buffers.
Set up a customization buffer containing all settings that you have set but not saved.
If you want to alter a particular user option with the customization buffer, and you know its name, you can use the command M-x customize-option and specify the user option (variable) name. This sets up the customization buffer with just one user option--the one that you asked for. Editing, setting and saving the value work as described above, but only for the specified user option. Minibuffer completion is handy if you only know part of the name. However, this command can only see options that have been loaded in the current Emacs session.
Likewise, you can modify a specific face, chosen by name, using M-x customize-face. By default it operates on the face used on the character after point.
You can also set up the customization buffer with a specific group, using M-x customize-group. The immediate contents of the chosen group, including settings (user options and faces), and other groups, all appear as well (even if not already loaded). However, the subgroups' own contents are not included.
For a more general way of controlling what to customize, you can use M-x customize-apropos. You specify a regular expression as argument; then all loaded settings and groups whose names match this regular expression are set up in the customization buffer. If you specify an empty regular expression, this includes all loaded groups and settings--which takes a long time to set up.
When you upgrade to a new Emacs version, you might want to consider customizing new settings, and settings whose meanings or default values have changed. To do this, use M-x customize-changed and specify a previous Emacs version number using the minibuffer. It creates a customization buffer which shows all the settings and groups whose definitions have been changed since the specified version, loading them if necessary.
If you change settings and then decide the change was a mistake, you can use two special commands to revisit your previous changes. Use M-x customize-saved to look at the settings that you have saved. Use M-x customize-unsaved to look at the settings that you have set but not saved.
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Custom themes are collections of settings that can be enabled or disabled as a unit. You can use Custom themes to switch quickly and easily between various collections of settings, and to transfer such collections from one computer to another.
To define a Custom theme, use M-x customize-create-theme, which brings up a buffer named `*New Custom Theme*'. At the top of the buffer is an editable field where you can specify the name of the theme. Click on the button labelled `Insert Variable' to add a variable to the theme, and click on `Insert Face' to add a face. You can edit these values in the `*New Custom Theme*' buffer like in an ordinary Customize buffer. To remove an option from the theme, click on its `State' button and select `Delete'.
After adding the desired options, click on `Save Theme' to save
the Custom theme. This writes the theme definition to a file
`foo-theme.el' (where foo is the theme name you
supplied), in the directory `~/.emacs.d/'. You can specify the
directory by setting custom-theme-directory.
You can view and edit the settings of a previously-defined theme by clicking on `Visit Theme' and specifying the theme name. You can also import the variables and faces that you have set using Customize by visiting the "special" theme named `user'. This theme, which records all the options that you set in the ordinary customization buffer, is always enabled, and always takes precedence over all other enabled Custom themes. Additionally, the `user' theme is recorded with code in your `.emacs' file, rather than a `user-theme.el' file.
Once you have defined a Custom theme, you can use it by customizing
the variable custom-enabled-themes. This is a list of Custom
themes that are enabled, or put into effect. If you set
custom-enabled-themes using the Customize interface, the theme
definitions are automatically loaded from the theme files, if they
aren't already. If you save the value of custom-enabled-themes
for future Emacs sessions, those Custom themes will be enabled
whenever Emacs is started up.
If two enabled themes specify different values for an option, the
theme occurring earlier in custom-enabled-themes takes effect.
You can temporarily enable a Custom theme with M-x enable-theme. This prompts for a theme name in the minibuffer, loads the theme from the theme file if necessary, and enables the theme. You can disable any enabled theme with the command M-x disable-theme; this returns the options specified in the theme to their original values. To re-enable the theme, type M-x enable-theme again. If a theme file is changed during your Emacs session, you can reload it by typing M-x load-theme. (This also enables the theme.)
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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.
Emacs Lisp allows any variable (with a few exceptions) to have any
kind of value, but most variables that Emacs uses expect 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-nil," meaning 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 t.
Emacs uses many Lisp variables for internal record keeping, but the most interesting variables for a non-programmer user are those meant for users to change--these are called user options.
Each user option that you can set with the customization buffer is in fact a Lisp variable. Emacs does not (usually) change the values of these variables on its own; instead, you set the values in order to control the behavior of certain Emacs commands. Use of the customization buffer is explained above (see section Easy Customization Interface); here we describe other aspects of Emacs variables.
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Display the value and documentation of variable var
(describe-variable).
Change the value of variable var to value.
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 is a variable defined in `C source code'. fill-column's value is 70 Local in buffer custom.texi; global value is 70 Automatically becomes buffer-local when set in any fashion. This variable is safe to use as a file local variable only if its value satisfies the predicate `integerp'. Documentation: *Column beyond which automatic line-wrapping should happen. Interactively, you can set the buffer local value using C-x f. You can customize this variable. |
The line that says you can customize the variable indicates that this variable is a user option. (The star also indicates this, but it is an obsolete indicator that may eventually disappear.) C-h v is not restricted to user options; it allows any variable name.
The most convenient way to set a specific user option variable 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 (you can insert the old value into the minibuffer for editing via M-n). For example,
M-x set-variable RET fill-column RET 75 RET |
sets fill-column to 75.
M-x set-variable is limited to user option variables, but you can
set any variable with a Lisp expression, using the function setq.
Here is a setq expression to set fill-column:
(setq fill-column 75) |
To execute an expression like this one, go to the `*scratch*' buffer, type in the expression, and then type C-j. See section Lisp Interaction Buffers.
Setting variables, like all means of customizing Emacs except where otherwise stated, affects only the current Emacs session. The only way to alter the variable in future sessions is to put something in the `~/.emacs' file to set it those sessions (see section The Init File, `~/.emacs').
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Hooks are an important mechanism for customization of Emacs. A hook is a Lisp variable which holds a list of functions, to be called on some well-defined occasion. (This is called running the hook.) The individual functions in the list are called the hook functions of the hook. With rare exceptions, hooks in Emacs are empty when Emacs starts up, so the only hook functions in any given hook are the ones you explicitly put there as customization.
Most major modes run one or more mode hooks as the last step of
initialization. This makes it easy for you to customize the behavior of
the mode, by setting up a hook function to override the local variable
assignments already made by the mode. But hooks are also used in other
contexts. For example, the hook suspend-hook runs just before
Emacs suspends itself (see section Exiting Emacs).
Most Emacs hooks are normal hooks. This means that running the hook operates by calling all the hook functions, unconditionally, with no arguments. We have made an effort to keep most hooks normal so that you can use them in a uniform way. Every variable in Emacs whose name ends in `-hook' is a normal hook.
There are also a few abnormal hooks. These variables' names end
in `-hooks' or `-functions', instead of `-hook'. What
makes these hooks abnormal is that there is something peculiar about the
way its functions are called--perhaps they are given arguments, or
perhaps the values they return are used in some way. For example,
find-file-not-found-functions (see section Visiting Files) is abnormal because
as soon as one hook function returns a non-nil value, the rest
are not called at all. The documentation of each abnormal hook variable
explains in detail what is peculiar about it.
You can set a hook variable with setq like any other Lisp
variable, but the recommended way to add a hook function to a hook
(either normal or abnormal) is by calling add-hook.
See (elisp)Hooks section `Hooks' in The Emacs Lisp Reference Manual.
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.
(setq my-c-style
'((c-comment-only-line-offset . 4)
(c-cleanup-list . (scope-operator
empty-defun-braces
defun-close-semi))
(c-offsets-alist . ((arglist-close . c-lineup-arglist)
(substatement-open . 0)))))
(add-hook 'c-mode-common-hook
'(lambda ()
(c-add-style "my-style" my-c-style t)))
|
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.
If you play with adding various different versions of a hook
function by calling add-hook over and over, remember that all
the versions you added will remain in the hook variable together. You
can clear out individual functions by calling remove-hook, or
do (setq hook-variable nil) to remove everything.
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Make variable var have a local value in the current buffer.
Make variable var use its global value in the current buffer.
Mark variable var so that setting it will make it local to the buffer that is current at that time.
Almost 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. Changing its value subsequently in this buffer will not affect others, and changes in its global value will not affect this buffer.
M-x make-variable-buffer-local marks a variable so it will
become local automatically whenever it is set. More precisely, once a
variable has been marked in this way, the usual ways of setting the
variable automatically do make-local-variable first. We call
such variables per-buffer variables. Many variables in Emacs
are normally per-buffer; the variable's document string tells you when
this is so. A per-buffer variable's global value is normally never
effective in any buffer, but it still has a meaning: it is the initial
value of the variable for each new buffer.
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 many minor modes, the controlling variable
is per buffer, and thus always buffer-local. Otherwise, you can make
it local in a specific buffer like any other variable.
A few variables cannot be local to a buffer because they are always local to each display instead (see section Multiple Displays). If you try to make one of these variables buffer-local, you'll get an error message.
M-x kill-local-variable makes a specified variable 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
construct 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 make-variable-buffer-local.
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
fill-column:
(default-value 'fill-column) |
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A file can specify local variable values for use when you edit the file with Emacs. Visiting the file checks for local variable specifications; it automatically makes these variables local to the buffer, and sets them to the values specified in the file.
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There are two ways to specify file 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. mode:
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
numeric values:
;; -*- mode: Lisp; fill-column: 75; comment-column: 50; -*- |
You can also specify the coding system for a file in this way: just
specify a value for the "variable" named coding. The "value"
must be a coding system name that Emacs recognizes. See section Coding Systems. `unibyte: t' specifies unibyte loading for a
particular Lisp file. See section Enabling Multibyte Characters.
The eval pseudo-variable, described below, can be specified in
the first line as well.
In shell scripts, the first line is used to identify the script interpreter, so you cannot put any local variables there. To accommodate this, Emacs looks for local variable specifications in the second line when the first line specifies an interpreter.
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. If a file has both a local variables list and a `-*-' line, Emacs processes everything in the `-*-' line first, and everything in the local variables list afterward.
Here is an example of a local variables list:
;; Local Variables: ** ;; mode:lisp ** ;; comment-column:0 ** ;; comment-start: ";; " ** ;; comment-end:"**" ** ;; End: ** |
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-start and
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.
If you write a multi-line string value, you should put the prefix and suffix on each line, even lines that start or end within the string. They will be stripped off for processing the list. If you want to split a long string across multiple lines of the file, you can use backslash-newline, which is ignored in Lisp string constants. Here's an example of doing this:
# Local Variables: # compile-command: "cc foo.c -Dfoo=bar -Dhack=whatever \ # -Dmumble=blaah" # End: |
Some "variable names" have special meanings in a local variables
list. Specifying the "variable" mode really sets the major
mode, while any value specified for the "variable" eval is
simply evaluated as an expression (its value is ignored). A value for
coding specifies the coding system for character code
conversion of this file, and a value of t for unibyte
says to visit the file in a unibyte buffer. These four "variables"
are not really variables; setting them in any other context has no
special meaning.
If mode is used to set a major mode, it should be the
first "variable" in the list. Otherwise, the entries that precede
it will usually be ignored, since most modes kill all local variables
as part of their initialization.
You can use the mode "variable" to set minor modes as well
as the major modes; in fact, you can use it more than once, first to
set the major mode and then to set minor modes which are specific to
particular buffers. But most minor modes should not be specified in
the file at all, because they represent user preferences.
For example, 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 use a local variable list to impose your taste on everyone.
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.
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.
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File-local variables can be dangerous; when you visit someone else's
file, there's no telling what its local variables list could do to
your Emacs. Improper values of the eval "variable," and
other variables such as load-path, could execute Lisp code you
didn't intend to run.
Therefore, whenever Emacs encounters file local variable values that are not known to be safe, it displays the file's entire local variables list, and asks you for confirmation before setting them. You can type y or SPC to put the local variables list into effect, or n to ignore it. When Emacs is run in batch mode (see section Initial Options), it can't really ask you, so it assumes the answer n.
Emacs normally recognizes certain variables/value pairs as safe.
For instance, it is safe to give comment-column or
fill-column any integer value. If a file specifies only
known-safe variable/value pairs, Emacs does not ask for confirmation
before setting them. Otherwise, you can tell Emacs to record all the
variable/value pairs in this file as safe, by typing ! at the
confirmation prompt. When Emacs encounters these variable/value pairs
subsequently, in the same file or others, it will assume they are
safe.
Some variables, such as load-path, are considered
particularly risky: there is seldom any reason to specify them
as local variables, and changing them can be dangerous. Even if you
enter ! at the confirmation prompt, Emacs will not record any
values as safe for these variables. If you really want to record safe
values for these variables, do it directly by customizing
`safe-local-variable-values' (see section Easy Customization Interface).
The variable enable-local-variables allows you to change the
way Emacs processes local variables. Its default value is t,
which specifies the behavior described above. If it is nil,
Emacs simply ignores all file local variables. :safe means use
only the safe values and ignore the rest. Any other value says to
query you about each file that has local variables, without trying to
determine whether the values are known to be safe.
The variable enable-local-eval controls whether Emacs
processes eval variables. The three possibilities for the
variable's value are t, nil, and anything else, just as
for enable-local-variables. The default is maybe, which
is neither t nor nil, so normally Emacs does ask for
confirmation about processing eval variables.
But there is an exception. The safe-local-eval-forms is a
customizable list of eval forms which are safe. Emacs does not ask
for confirmation when it finds these forms for the eval
variable.
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This section describes key bindings, which map keys to commands, and 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.
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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 text 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 is meaningful. 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 key sequences are inconvenient to use.
As a user, you can redefine any key; but it is usually best to stick to key sequences that consist of C-c followed by a letter (upper or lower case). These keys are "reserved for users," so they won't conflict with any properly designed Emacs extension. The function keys F5 through F9 are also reserved for users. If you redefine some other key, your definition may be overridden by certain extensions or major modes which redefine the same key.
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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 Control-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.
Aside from ordinary prefix keys, there is a fictitious "prefix key" which represents the menu bar; see (elisp)Menu Bar section `Menu Bar' in The Emacs Lisp Reference Manual, for special information about menu bar key bindings. Mouse button events that invoke pop-up menus are also prefix keys; see (elisp)Menu Keymaps section `Menu Keymaps' in The Emacs Lisp Reference Manual, for more details.
Some prefix keymaps are stored in variables with names:
ctl-x-map is the variable name for the map used for characters that
follow C-x.
help-map is for characters that follow C-h.
esc-map is for characters that follow ESC. Thus, all Meta
characters are actually defined by this map.
ctl-x-4-map is for characters that follow C-x 4.
mode-specific-map is for characters that follow C-c.
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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.
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 the results in ordinary circumstances.
Most major modes construct their keymaps when the mode is used for the first time in a session. If you wish to change one of these keymaps, you must use the major mode's mode hook (see section Hooks).
For example, the command texinfo-mode to select Texinfo mode
runs the hook texinfo-mode-hook. Here's how you can use the hook
to add local bindings (not very useful, we admit) for C-c n and
C-c p in Texinfo mode:
(add-hook 'texinfo-mode-hook
'(lambda ()
(define-key texinfo-mode-map "\C-cp"
'backward-paragraph)
(define-key texinfo-mode-map "\C-cn"
'forward-paragraph)))
|
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The minibuffer has its own set of local keymaps; they contain various completion and exit commands.
minibuffer-local-map is used for ordinary input (no completion).
minibuffer-local-ns-map is similar, except that SPC exits
just like RET. This is used mainly for Mocklisp compatibility.
minibuffer-local-completion-map is for permissive completion.
minibuffer-local-must-match-map is for strict completion and
for cautious completion.
Finally, minibuffer-local-filename-completion-map and
minibuffer-local-must-match-filename-map are like the two
previous ones, but they are specifically for file name completion.
They do not bind SPC.
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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.
Define key globally to run cmd.
Define key locally (in the major mode now in effect) to run cmd.
Make key undefined in the global map.
Make key undefined locally (in the major mode now in effect).
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; it enters the minibuffer immediately to read cmd. But if you type C-x, since that's a prefix, it reads another character; if that is 4, another prefix character, it reads one more character, 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
spell-other-window.
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, local-unset-key makes
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 in a fresh Emacs 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.
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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. (See section The Init File, `~/.emacs'.)
The simplest method for doing this works for ASCII characters and
Meta-modified ASCII characters only. This method uses a string to
represent the key sequence you want to rebind. For example, here's how
to bind C-z to shell:
(global-set-key "\C-z" 'shell) |
This example uses a string constant containing one character,
C-z. (`\C-' is string syntax for a control character.) The
single-quote before the command name, shell, marks it as a
constant symbol rather than a variable. If you omit the quote, Emacs
would try 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 the key sequence C-x M-l:
(global-set-key "\C-x\M-l" 'make-symbolic-link) |
To put TAB, RET, ESC, or DEL in the string, you can use the Emacs Lisp escape sequences, `\t', `\r', `\e', and `\d'. Here is an example which binds C-x TAB:
(global-set-key "\C-x\t" 'indent-rigidly) |
These examples show how to write some other special ASCII characters in strings for key bindings:
(global-set-key "\r" 'newline) ;; RET (global-set-key "\d" 'delete-backward-char) ;; DEL (global-set-key "\C-x\e\e" 'repeat-complex-command) ;; ESC |
When the key sequence includes function keys or mouse button events,
or non-ASCII characters such as C-= or H-a, you must use
the more general method of rebinding, which uses a vector to specify the
key sequence.
The way to write a vector in Emacs Lisp is with square brackets around the vector elements. Use spaces to separate the elements. If an element is a symbol, simply write the symbol's name--no other delimiters or punctuation are needed. If a vector element is a character, write it as a Lisp character constant: `?' followed by the character as it would appear in a string.
Here are examples of using vectors to rebind C-= (a control character not in ASCII), C-M-= (not in ASCII because C-= is not), H-a (a Hyper character; ASCII doesn't have Hyper at all), F7 (a function key), and C-Mouse-1 (a keyboard-modified mouse button):
(global-set-key [?\C-=] 'make-symbolic-link) (global-set-key [?\M-\C-=] 'make-symbolic-link) (global-set-key [?\H-a] 'make-symbolic-link) (global-set-key [f7] 'make-symbolic-link) (global-set-key [C-mouse-1] 'make-symbolic-link) |
You can use a vector for the simple cases too. Here's how to rewrite the first six examples above to use vectors:
(global-set-key [?\C-z] 'shell) (global-set-key [?\C-x ?l] 'make-symbolic-link) (global-set-key [?\C-x ?\t] 'indent-rigidly) (global-set-key [?\r] 'newline) (global-set-key [?\d] 'delete-backward-char) (global-set-key [?\C-x ?\e ?\e] 'repeat-complex-command) |
As you see, you represent a multi-character key sequence with a vector by listing all of the characters, in order, within the square brackets that delimit the vector.
Language and coding systems can cause problems with key bindings for non-ASCII characters. See section Non-ASCII Characters in Init Files.
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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:
left, up, right, downCursor arrow keys.
begin, end, home, next, priorOther cursor repositioning keys.
select, print, execute, backtabinsert, undo, redo, clearlineinsertline, deleteline, insertchar, deletecharMiscellaneous function keys.
f1, f2, … f35Numbered function keys (across the top of the keyboard).
kp-add, kp-subtract, kp-multiply, kp-dividekp-backtab, kp-space, kp-tab, kp-enterkp-separator, kp-decimal, kp-equalKeypad keys (to the right of the regular keyboard), with names or punctuation.
kp-0, kp-1, … kp-9Keypad keys with digits.
kp-f1, kp-f2, kp-f3, kp-f4Keypad PF keys.
These names are conventional, but some systems (especially when using X) 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 function key symbols (or anything but
ASCII characters) must be a vector rather than a string.
Thus, to bind function key `f1' to the command rmail,
write the following:
(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.)
See section Rebinding Keys in Your Init File, for more information about using vectors for rebinding.
You can mix function keys and characters in a key sequence. This
example binds C-x NEXT to the command forward-page.
(global-set-key [?\C-x next] 'forward-page) |
where ?\C-x is the Lisp character constant for the character
C-x. The vector element next 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) |
Many keyboards have a "numeric keypad" on the right hand side.
The numeric keys in the keypad double up as cursor motion keys,
toggled by a key labeled `Num Lock'. By default, Emacs
translates these keys to the corresponding keys in the main keyboard.
For example, when `Num Lock' is on, the key labeled `8' on
the numeric keypad produces kp-8, which is translated to
8; when `Num Lock' is off, the same key produces
kp-up, which is translated to UP. If you rebind a key
such as 8 or UP, it affects the equivalent keypad key too.
However, if you rebind a `kp-' key directly, that won't affect
its non-keypad equivalent.
Emacs provides a convenient method for binding the numeric keypad
keys, using the variables keypad-setup,
keypad-numlock-setup, keypad-shifted-setup, and
keypad-numlock-shifted-setup. These can be found in the
`keyboard' customization group (see section Easy Customization Interface). You
can rebind the keys to perform other tasks, such as issuing numeric
prefix arguments.
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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. For instance, TAB was another name for C-i. Later, users found it convenient to distinguish in Emacs between these keys and the "same" control characters typed with the CTRL key. Therefore, on most modern terminals, they are no longer the same, and TAB is distinguishable from C-i.
Emacs can distinguish these two kinds of input if the keyboard does.
It treats the "special" keys as function keys named tab,
return, backspace, linefeed, escape, and
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" tab.
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.
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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
button, 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 drag-mouse-1 event.
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, double-mouse-3.
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 if you know Emacs Lisp you can distinguish if you really want to (see (elisp)Accessing Events section `Accessing Events' in The Emacs Lisp Reference Manual). 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).
The variable double-click-time specifies how much time can
elapse between clicks and still allow them to be grouped as a multiple
click. Its value is in units of milliseconds. If the value is
nil, double clicks are not detected at all. If the value is
t, then there is no time limit. The default is 500.
The variable double-click-fuzz specifies how much the mouse
can move between clicks and still allow them to be grouped as a multiple
click. Its value is in units of pixels on windowed displays and in
units of 1/8 of a character cell on text-mode terminals; the default is
3.
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 scroll-up:
(global-set-key [mode-line mouse-1] 'scroll-up) |
Here is the complete list of these dummy prefix keys and their meanings:
mode-lineThe mouse was in the mode line of a window.
vertical-lineThe mouse was in the vertical line separating side-by-side windows. (If you use scroll bars, they appear in place of these vertical lines.)
vertical-scroll-barThe mouse was in a vertical scroll bar. (This is the only kind of scroll bar Emacs currently supports.)
menu-barThe mouse was in the menu bar.
header-lineThe mouse was in a header line.
You can put more than one mouse button in a key sequence, but it isn't usual to do so.
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Disabling a command means that invoking it interactively asks for confirmation from the user. The purpose of disabling a command is to prevent users from executing it by accident; we do this for commands that might be confusing to the uninitiated.
Attempting 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 must then answer another question--whether to do this permanently, or just for the current session. (Enabling permanently works by automatically editing your `.emacs' file.) You can also type ! to enable all commands, for the current session only.
The direct mechanism for disabling a command is to put a
non-nil 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 displayed 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'.
If Emacs was invoked with the `-q' or `--no-init-file' options (see section Initial Options), it will not edit your `~/.emacs' init file. Doing so could lose information because Emacs has not read your init file.
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. However, disabling a command has no effect on calling it as a function from Lisp programs.
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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. It does this by assigning each character to one of fifteen-odd syntax classes. In some cases it specifies some additional information also.
Each major mode has its own syntax table (though related major modes sometimes share one syntax table), which it installs in each buffer that uses the mode. The syntax table installed in the current buffer is the one that all commands use, so we call it "the" syntax table.
To display a description of the contents of the current syntax
table, type C-h s (describe-syntax). The description of
each character includes the string you would have to give to
modify-syntax-entry to set up that character's current syntax,
starting with the character which designates its syntax class, plus
some English text to explain its meaning.
A syntax table is actually a Lisp object, a char-table, whose elements are cons cells. For full information on the syntax table, see (elisp)Syntax Tables section `Syntax Tables' in The Emacs Lisp Reference Manual.
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When Emacs is started, it normally loads a Lisp program from the file `.emacs' or `.emacs.el' in your home directory (see section How Emacs Finds Your Init File). We call this file your init file because it specifies how to initialize Emacs for you. You can use the command line switch `-q' to prevent loading your init file, and `-u' (or `--user') to specify a different user's init file (see section Initial Options).
You can also use `~/.emacs.d/init.el' as the init file. Emacs tries this if it cannot find `~/.emacs' or `~/.emacs.el'.
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
inhibit-default-init non-nil, then `default' is not
loaded.
Your site may also have a site startup file; this is named `site-start.el', if it exists. Like `default.el', Emacs finds this file via the standard search path for Lisp libraries. Emacs loads this library before it loads your init file. To inhibit loading of this library, use the option `--no-site-file'. See section Initial Options. We recommend against using `site-start.el' for changes that some users may not like. It is better to put them in `default.el', so that users can more easily override them.
You can place `default.el' and `site-start.el' in any of
the directories which Emacs searches for Lisp libraries. The variable
load-path (see section Libraries of Lisp Code for Emacs) specifies these directories.
Many sites put these files in the `site-lisp' subdirectory of the
Emacs installation directory, typically
`/usr/local/share/emacs/site-lisp'.
If you have a large amount of code in your `.emacs' file, you should rename it to `~/.emacs.el', and byte-compile it. See (elisp)Byte Compilation section `Byte Compilation' in the Emacs Lisp Reference Manual, for more information about compiling Emacs Lisp programs.
If you are going to write actual Emacs Lisp programs that go beyond minor customization, you should read the Emacs Lisp Reference Manual. See Emacs Lisp: (elisp)Top section `Emacs Lisp' in the Emacs Lisp Reference Manual.
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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, (setq
fill-column 60) calls the function setq to set the variable
fill-column (see section Filling Text) to 60.
You can set any Lisp variable with setq, but with certain
variables setq won't do what you probably want in the
`.emacs' file. Some variables automatically become buffer-local
when set with setq; what you want in `.emacs' is to set
the default value, using setq-default. Some customizable minor
mode variables do special things to enable the mode when you set them
with Customize, but ordinary setq won't do that; to enable the
mode in your `.emacs' file, call the minor mode command. The
following section has examples of both of these methods.
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:
Numbers are written in decimal, with an optional initial minus sign.
Lisp string syntax is the same as C string syntax with a few extra features. Use a double-quote character to begin and end a string constant.
In a string, you can include newlines and special characters literally. But often it is cleaner to use backslash sequences for them: `\n' for newline, `\b' for backspace, `\r' for carriage return, `\t' for tab, `\f' for formfeed (control-L), `\e' for escape, `\\' for a backslash, `\"' for a double-quote, or `\ooo' for the character whose octal code is ooo. Backslash and double-quote are the only characters for which backslash sequences are mandatory.
`\C-' can be used as a prefix for a control character, as in `\C-s' for ASCII control-S, and `\M-' can be used as a prefix for a Meta character, as in `\M-a' for Meta-A or `\M-\C-a' for Control-Meta-A.
See section Non-ASCII Characters in Init Files, for information about including non-ASCII in your init file.
Lisp character constant syntax consists of a `?' followed by
either a character or an escape sequence starting with `\'.
Examples: ?x, ?\n, ?\", ?\). Note that
strings and characters are not interchangeable in Lisp; some contexts
require one and some contexts require the other.
See section Non-ASCII Characters in Init Files, for information about binding commands to keys which send non-ASCII characters.
t stands for `true'.
nil stands for `false'.
Write a single-quote (') followed by the Lisp object you want.
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Here are some examples of doing certain commonly desired things with Lisp expressions:
Make TAB in C mode just insert a tab if point is in the middle of a line.
(setq c-tab-always-indent nil) |
Here we have a variable whose value is normally t for `true'
and the alternative is nil for `false'.
Make searches case sensitive by default (in all buffers that do not override this).
(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 case-fold-search
with setq affects only the current buffer's local value, which
is not what you probably want to do in an init file.
Specify your own email address, if Emacs can't figure it out correctly.
(setq user-mail-address "rumsfeld@torture.gov") |
Various Emacs packages that need your own email address use the value of
user-mail-address.
Make Text mode the default mode for new buffers.
(setq default-major-mode 'text-mode) |
Note that text-mode is used because it is the command for
entering Text mode. The single-quote before it makes the symbol a
constant; otherwise, text-mode would be treated as a variable
name.
Set up defaults for the Latin-1 character set which supports most of the languages of Western Europe.
(set-language-environment "Latin-1") |
Turn off Line Number mode, a global minor mode.
(line-number-mode 0) |
Turn on Auto Fill mode automatically in Text mode and related modes.
(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-fill whose
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 the installed Lisp library named `foo' (actually a file `foo.elc' or `foo.el' in a standard Emacs directory).
(load "foo") |
When the argument to load is a relative file name, not starting
with `/' or `~', load searches the directories in
load-path (see section Libraries of Lisp Code for Emacs).
Load the compiled Lisp file `foo.elc' from your home directory.
(load "~/foo.elc") |
Here an absolute file name is used, so no searching is done.
Tell Emacs to find the definition for the function myfunction
by loading a Lisp library named `mypackage' (i.e. a file
`mypackage.elc' or `mypackage.el'):
(autoload 'myfunction "mypackage" "Do what I say." t) |
Here the string "Do what I say." is the function's
documentation string. You specify it in the autoload
definition so it will be available for help commands even when the
package is not loaded. The last argument, t, indicates that
this function is interactive; that is, it can be invoked interactively
by typing M-x myfunction RET or by binding it to a key.
If the function is not interactive, omit the t or use
nil.
Rebind the key C-x l to run the function make-symbolic-link
(see section Rebinding Keys in Your Init File).
(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-link instead of its value as a variable.
Do the same thing for Lisp mode only.
(define-key lisp-mode-map "\C-xl" 'make-symbolic-link) |
Redefine all keys which now run next-line in Fundamental mode
so that they run forward-line instead.
(substitute-key-definition 'next-line 'forward-line
global-map)
|
Make C-x C-v undefined.
(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.
Make `$' have the syntax of punctuation in Text mode. Note the use of a character constant for `$'.
(modify-syntax-entry ?\$ "." text-mode-syntax-table) |
Enable the use of the command narrow-to-region without confirmation.
(put 'narrow-to-region 'disabled nil) |
Adjusting the configuration to various platforms and Emacs versions.
Users typically want Emacs to behave the same on all systems, so the same init file is right for all platforms. However, sometimes it happens that a function you use for customizing Emacs is not available on some platforms or in older Emacs versions. To deal with that situation, put the customization inside a conditional that tests whether the function or facility is available, like this:
(if (fboundp 'blink-cursor-mode)
(blink-cursor-mode 0))
(if (boundp 'coding-category-utf-8)
(set-coding-priority '(coding-category-utf-8)))
|
You can also simply disregard the errors that occur if the function is not defined.
(condition case ()
(set-face-background 'region "grey75")
(error nil))
|
A setq on a variable which does not exist is generally
harmless, so those do not need a conditional.
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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
kept.
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
variable term-file-prefix and the terminal type. Your `.emacs'
file can prevent the loading of the terminal-specific library by setting
term-file-prefix to nil.
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.
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Normally Emacs uses the environment variable HOME
(see section HOME) to find `.emacs'; that's what
`~' means in a file name. If `.emacs' is not found inside
`~/' (nor `.emacs.el'), Emacs looks for
`~/.emacs.d/init.el' (which, like `~/.emacs.el', can be
byte-compiled).
However, if you run Emacs from a shell started by 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 your user name from the environment variables LOGNAME and
USER; if neither of those exists, it uses effective user-ID.
If that user name matches the real user-ID, then Emacs uses HOME;
otherwise, it looks up the home directory corresponding to that user
name in the system's data base of users.
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Language and coding systems may cause problems if your init file contains non-ASCII characters, such as accented letters, in strings or key bindings.
If you want to use non-ASCII characters in your init file,
you should put a `-*-coding: coding-system-*-' tag on
the first line of the init file, and specify a coding system that
supports the character(s) in question. See section Recognizing Coding Systems. This
is because the defaults for decoding non-ASCII text might
not yet be set up by the time Emacs reads those parts of your init
file which use such strings, possibly leading Emacs to decode those
strings incorrectly. You should then avoid adding Emacs Lisp code
that modifies the coding system in other ways, such as calls to
set-language-environment.
To bind non-ASCII keys, you must use a vector (see section Rebinding Keys in Your Init File). The string syntax cannot be used, since the non-ASCII characters will be interpreted as meta keys. For instance:
(global-set-key [?char] 'some-function) |
Type C-q, followed by the key you want to bind, to insert char.
Warning: if you change the keyboard encoding, or change between multibyte and unibyte mode, or anything that would alter which code C-q would insert for that character, this keybinding may stop working. It is therefore advisable to use one and only one coding system, for your init file as well as the files you edit. For example, don't mix the `latin-1' and `latin-9' coding systems.
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