Customization
*************

This chapter describes some simple methods to customize the behavior of Emacs.

Apart from the methods described here, see X Resources for information about using X resources to customize Emacs, and see Keyboard Macros for information about recording and replaying keyboard macros.  Making more far-reaching and open-ended changes involves writing Emacs Lisp code; see Emacs Lisp (The Emacs Lisp Reference Manual).

Easy Customization Interface
============================

Emacs has many settings which have values that you can change. Many are documented in this manual.  Most settings are user options---that is to say, Lisp variables (see Variables)---and their names appear in the Variable Index (see Variable Index). The other settings are faces and their attributes (see Faces).

You can browse settings and change them using M-x customize. This creates a customization buffer, which lets you navigate through a logically organized list of settings, edit and set their values, and save them permanently in your initialization file (see Init File).

Customization Groups
--------------------

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: Customization of the One True Editor. -------------\
           [State]: visible group members are all at standard values.

        See also [Manual].

     [Editing] : Basic text editing facilities.

     [External] : 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.  Each group name, such as [Editing], is a hypertext link to that group; invoking it creates a new customization buffer, showing the group and its contents.

The Emacs group only contains other groups.  These groups, in turn, can contain settings or still more groups.  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.

Browsing and Searching for Options and Faces
--------------------------------------------

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 Customizing Specific Items.

Changing a Variable
-------------------

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.  You can thus type RET when you are finished editing a field, to move on to the next button or 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 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:

Undo Edits
     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.

Reset to Saved
     This restores the value of the variable to the last saved value, and updates the text accordingly.

Erase Customization
     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.

Set to Backup Value
     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.

Saving Customizations
---------------------

Saving customizations from the customization buffer works by writing code to a file.  By reading this code, future sessions can set up the customizations again.  Normally, the code is saved in your initialization file (see Init File).

You can choose to save your customizations in a file other than your initialization file.  To make this work, you must add a couple of lines of code to your initialization file, to set the variable custom-file to the name of the desired file, and to load that file.  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 22)
            ;; Emacs 21 customization.
            (setq custom-file "~/.custom-21.el"))
           ((and (= emacs-major-version 22)
                 (< emacs-minor-version 3))
            ;; Emacs 22 customization, before version 22.3.
            (setq custom-file "~/.custom-22.el"))
           (t
            ;; Emacs version 22.3 or later.
            (setq custom-file "~/.emacs-custom.el")))

     (load custom-file)

If Emacs was invoked with the -q or --no-init-file options (see Initial Options), it will not let you save your customizations in your initialization file.  This is because saving customizations from such a session would wipe out all the other customizations you might have on your initialization file.

Customizing Faces
-----------------

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.

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 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.

Customizing Specific Items
--------------------------

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.

M-x customize-option RET OPTION RET
     Set up a customization buffer with just one user option variable, OPTION.

M-x customize-face RET FACE RET
     Set up a customization buffer with just one face, FACE.

M-x customize-group RET GROUP RET
     Set up a customization buffer with just one group, GROUP.

M-x customize-apropos RET REGEXP RET
     Set up a customization buffer with all the settings and groups that match REGEXP.

M-x customize-changed RET VERSION RET
     Set up a customization buffer with all the settings and groups whose meaning has changed since Emacs version VERSION.

M-x customize-saved
     Set up a customization buffer containing all settings that you have saved with customization buffers.

M-x customize-unsaved
     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.

Customization Themes
--------------------

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.)

Variables
=========

A variable is a Lisp symbol which has a value.  The symbol's name is also called the variable name.  A variable name can contain any characters that can appear in a file, but most variable names consist of ordinary words separated by hyphens.

The name of the variable serves as a compact description of its role.  Most variables also have a documentation string, which describes what the variable's purpose is, what kind of value it should have, and how the value will be used.  You can view this documentation using the help command C-h v (describe-variable). See Examining.

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.  See Easy Customization, for information about using the Customize facility to set user options.  In the following sections, we will describe other aspects of Emacs variables, such as how to set them outside Customize.

Emacs Lisp allows any variable (with a few exceptions) to have any kind of value.  However, many variables are meaningful only if assigned values of a certain type.  For example, only numbers are meaningful values for kill-ring-max, which specifies the maximum length of the kill ring (see Earlier Kills); if you give kill-ring-max a string value, commands such as C-y (yank) will signal an error.  On the other hand, some variables don't care about type; for instance, if a variable has one effect for nil values and another effect for ``non-nil'' values, then any value that is not the symbol nil induces the second effect, regardless of its type (by convention, we usually use the value t---a symbol which stands for ``true''---to specify a non-nil value).  If you set a variable using the customization buffer, you need not worry about giving it an invalid type: the customization buffer usually only allows you to enter meaningful values.  When in doubt, use C-h v (describe-variable) to check the variable's documentation string to see kind of value it expects (see Examining).

Examining and Setting Variables
-------------------------------

C-h v VAR RET
     Display the value and documentation of variable VAR (describe-variable).

M-x set-variable RET VAR RET VALUE RET
     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.

       Automatically becomes buffer-local when set in any fashion.
       This variable is safe as a file local variable 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.  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 Lisp Interaction.

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 your initialization file to set it those sessions (see Init File).

Hooks
-----

Hooks are an important mechanism for customizing 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.  For example, the hook kill-emacs-hook runs just before exiting Emacs (see Exiting).

Most hooks are normal hooks.  This means that when Emacs runs the hook, it calls each hook function in turn, 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 whose name ends in -hook is a normal hook.

A few hooks are abnormal hooks.  Their names end in -hooks or -functions, instead of -hook.  What makes these hooks abnormal is 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 is abnormal because as soon as one hook function returns a non-nil value, the rest are not called at all (see Visiting).  The documentation of each abnormal hook variable explains how its functions are used.

You can set a hook variable with setq like any other Lisp variable, but the recommended way to add a function to a hook (either normal or abnormal) is to use add-hook, as shown by the following examples.  See Hooks (The Emacs Lisp Reference Manual), for details.

Most major modes run one or more mode hooks as the last step of initialization.  Mode hooks are a convenient way to customize the behavior of individual modes; they are always normal.  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)

Here is another example, showing how to use a hook to customize the indentation of C code.  The hook function uses an anonymous lambda expression (see Lambda Expressions (The Emacs Lisp Reference Manual)).

     (setq my-c-style
       '((c-comment-only-line-offset . 4)

         (c-cleanup-list . (scope-operator
                            empty-defun-braces
                            defun-close-semi))))

     (add-hook 'c-mode-common-hook
       (lambda () (c-add-style "my-style" my-c-style t)))

Major mode hooks also apply to other major modes derived from the original mode (see Derived Modes (The Emacs Lisp Reference Manual)).  For instance, HTML mode (see HTML Mode) inherits from Text mode; when HTML mode is enabled, it runs text-mode-hook before running html-mode-hook.  This provides a convenient way to use a single hook to affect several related modes.  In particular, if you want to apply a hook function to any programming language mode, add it to prog-mode-hook; Prog mode is a major mode that does little else than to let other major modes inherit from it, exactly for this purpose.

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 hook functions are executed in the order they appear in the hook.

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.

If the hook variable is buffer-local, the buffer-local variable will be used instead of the global variable.  However, if the buffer-local variable contains the element t, the global hook variable will be run as well.

Local Variables
---------------

M-x make-local-variable RET VAR RET
     Make variable VAR have a local value in the current buffer.

M-x kill-local-variable RET VAR RET
     Make variable VAR use its global value in the current buffer.

M-x make-variable-buffer-local RET VAR RET
     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 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 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 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)

Local Variables in Files
------------------------

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.

Specifying File Variables
.........................

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 variable/value pairs in this way, each pair with a colon and semicolon as shown above.  The special variable/value pair mode: MODENAME;, if present, specifies a major mode, and should come first in the line.  The VALUEs are used literally, and not evaluated.

You can use the command add-file-local-variable-prop-line instead of adding entries by hand.  It prompts for a variable and value, and adds them to the first line in the appropriate way. The command delete-file-local-variable-prop-line deletes a variable from the line.  The command copy-dir-locals-to-file-locals-prop-line copies directory-local variables (see Directory Variables) to the first line.

Here is an example first line that specifies Lisp mode and sets two variables with numeric values:

     ;; -*- mode: Lisp; fill-column: 75; comment-column: 50; -*-

Aside from mode, other keywords that have special meanings as file variables are coding, unibyte, and eval. These are described below.

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 if the first line specifies an interpreter.  The same is true for man pages which start with the magic string '\" to specify a list of troff preprocessors (not all do, however).

Instead of using a -*- line, you can define file local variables using a local variables list near the end of the file. The start of the local variables list should be no more than 3000 characters from the end of the file, and must be on the last page if the file is divided into pages.

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.  The exception to this is a major mode specification.  Emacs applies this first, wherever it appears, since most major modes kill all local variables as part of their initialization.

A 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, like this:

     /* Local Variables: */
     /* mode:c           */
     /* comment-column:0 */
     /* End:             */

In this example, each line starts with the prefix /* and ends with the suffix */.  Emacs recognizes the prefix and suffix by finding them surrounding the magic string Local Variables:, on the first line of the list; it then 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 for.  The example above is for the C programming language, where comment lines start with /* and end with */.

You can construct the local variables list yourself, or use the command add-file-local-variable.  This prompts for a variable and value, and adds them to the list.  If necessary, it also adds the start and end markers.  The command delete-file-local-variable deletes a variable from the list.  The command copy-dir-locals-to-file-locals copies directory-local variables (see Directory Variables) to the list.

As with the -*- line, the variables in a local variables list are used literally, and are not evaluated first.  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; you should put the prefix and suffix on each line, even lines that start or end within the string, as they will be stripped off when processing the list.  Here is an example:

     # 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:

  * mode enables the specified major mode.

  * eval evaluates the specified Lisp expression (the value returned by that expression is ignored).

  * coding specifies the coding system for character code conversion of this file.  See Coding Systems.

  * unibyte says to visit the file in a unibyte buffer, if the value is t.  See Enabling Multibyte.

These four ``variables'' are not really variables; setting them in any other context has no special meaning.

You can use the mode ``variable'' to enable 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 enable minor modes which are specific to particular buffers.  Using mode for minor modes is deprecated, though---instead, use eval: (minor-mode 1).

Often, however, it is a mistake to enable minor modes in file local variables.  Most minor modes, like Auto Fill mode, represent individual user preferences.  If you want to use a minor mode, it is better to set up major mode hooks with your init file to turn that minor mode on for yourself alone (see Init File), instead of using a local variable list to impose your taste on everyone.

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 Choosing Modes.

Safety of File Variables
........................

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 Initial Options), it can't really ask you, so it assumes the answer n.

Emacs normally recognizes certain variable/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.  If a file contains only risky local variables, Emacs neither offers nor accepts ! as input at the confirmation prompt.  If some of the local variables in a file are risky, and some are only potentially unsafe, you can enter ! at the prompt.  It applies all the variables, but only marks the non-risky ones as safe for the future.  If you really want to record safe values for risky variables, do it directly by customizing safe-local-variable-values (see Easy Customization).

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.

As an exception, Emacs never asks for confirmation to evaluate any eval form if that form occurs within the variable safe-local-eval-forms.

Per-Directory Local Variables
-----------------------------

A project is a collection of files on which you work together. Usually, the project's files are kept in one or more directories. Occasionally, you may wish to define Emacs settings that are common to all the files that belong to the project.

Emacs provides two ways to specify settings that are applicable to files in a specific directory: you can put a special file in that directory, or you can define a project class for that directory.

If you put a file with a special name .dir-locals.el (On MS-DOS, the name of this file should be _dir-locals.el, due to limitations of the DOS filesystems.  If the filesystem is limited to 8+3 file names, the name of the file will be truncated by the OS to _dir-loc.el.) in a directory, Emacs will read it when it visits any file in that directory or any of its subdirectories, and apply the settings it specifies to the file's buffer.  Emacs searches for .dir-locals.el starting in the directory of the visited file, and moving up the directory tree.  (To avoid slowdown, this search is skipped for remote files.)

The .dir-locals.el file should hold a specially-constructed list.  This list maps Emacs mode names (symbols) to alists; each alist specifies values for variables to use when the respective mode is turned on.  The special mode name nil means that its alist applies to any mode.  Instead of a mode name, you can specify a string that is a name of a subdirectory of the project's directory; then the corresponding alist applies to all the files in that subdirectory.

Here's an example of a .dir-locals.el file:

     ((nil . ((indent-tabs-mode . t)
              (tab-width . 4)
              (fill-column . 80)))
      (c-mode . ((c-file-style . "BSD")))
      (java-mode . ((c-file-style . "BSD")
                    (subdirs . nil)))
      ("src/imported"
       . ((nil . ((change-log-default-name .
                   "ChangeLog.local"))))))

This example shows some settings for a hypothetical project.  It sets indent-tabs-mode, tab-width, and fill-column for any file in the project's directory tree, and it sets the indentation style for any C or Java source file.  The special subdirs element indicates that the Java mode settings are only to be applied in the current directory, not in any subdirectories.  Finally, it specifies a different ChangeLog file name for any file in the src/imported subdirectory of the directory where you put the .dir-locals.el file.

You can edit the .dir-locals.el file by hand, or use the command add-dir-local-variable.  This prompts for a mode (or subdirectory), variable and value, and adds an entry to the file. The command delete-dir-local-variable deletes an entry.  The command copy-file-locals-to-dir-locals copies file local variables (see File Variables) to the .dir-locals.el file.

Another method of specifying directory-local variables is to explicitly define a project class using dir-locals-set-class-variables, and then tell Emacs which directories correspond to that class, using dir-locals-set-directory-class.  You can put calls to these functions in your ~/.emacs init file; this can be useful when you can't put .dir-locals.el in the directory for some reason, or if you want to keep in a single place settings for several directories that don't have a common parent.  For example, you could apply settings to an unwritable directory this way:

     (dir-locals-set-class-variables 'unwritable-directory
        '((nil . ((some-useful-setting . value)))))

     (dir-locals-set-directory-class
        "/usr/include/" 'unwritable-directory)

Unsafe directory-local variables are handled in the same way as unsafe file-local variables (see Safe File Variables).

Customizing Key Bindings
========================

This section describes key bindings, which map keys to commands, and keymaps, which record key bindings.  It also explains how to customize key bindings, which is done by editing your init file (see Init Rebinding).

Keymaps
-------

As described in Commands, each Emacs 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.

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.  A key sequence gets its meaning from its binding, which says what command it runs.

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.

The global keymap is the most important keymap because it is always in effect.  The global keymap defines keys for Fundamental mode (see Major Modes); 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, work by storing the new binding in the proper place in the global map (see Rebinding).

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.  Key sequences can mix function keys and characters.  For example, if your keyboard has a Home function key, Emacs can recognize key sequences like C-x Home.  You can even mix mouse events with keyboard events, such as S-down-mouse-1.

On text terminals, typing a function key actually sends the computer a sequence of characters; the precise details of the sequence depends on the function key and on the terminal type.  (Often the sequence starts with ESC [.)  If Emacs understands your terminal type properly, it automatically handles such sequences as single input events.

Prefix Keymaps
--------------

Internally, Emacs records only single events in each keymap. Interpreting a key sequence of multiple events involves a chain of keymaps: the first keymap gives a definition for the first event, which is another keymap, which is used to look up the second event in the sequence, and so on.  Thus, 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 Menu Bar (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 Menu Keymaps (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.

Local Keymaps
-------------

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.  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.  In addition, portions of text in the buffer can specify their own keymaps, which override all other keymaps.

A local keymap can redefine a key as a prefix key by defining it as a prefix keymap.  If the key is also defined globally as a prefix, its local and global definitions (both keymaps) effectively combine: both definitions are used to look up the event that follows the prefix key. For example, if a local keymap defines C-c as a prefix 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.

Minibuffer Keymaps
------------------

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.

  * minibuffer-local-completion-map is for permissive completion.

  * minibuffer-local-must-match-map is for strict completion and for cautious completion.

  * 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.

Changing Key Bindings Interactively
-----------------------------------

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 bindings for the same key).  Or you can change a local keymap, which affects all buffers using the same major mode.

In this section, we describe how to rebind keys for the present Emacs session.  See Init Rebinding, for a description of how to make key rebindings affect future Emacs sessions.

M-x global-set-key RET KEY CMD RET
     Define KEY globally to run CMD.

M-x local-set-key RET KEY CMD RET
     Define KEY locally (in the major mode now in effect) to run CMD.

M-x global-unset-key RET KEY
     Make KEY undefined in the global map.

M-x local-unset-key RET KEY
     Make KEY undefined locally (in the major mode now in effect).

For example, the following binds C-z to the shell command (see Interactive Shell), replacing the normal global definition of C-z:

     M-x global-set-key RET C-z shell RET

The global-set-key command 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.

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 Disabling.

Rebinding Keys in Your Init File
--------------------------------

If you have a set of key bindings that you like to use all the time, you can specify them in your initialization file by writing Lisp code. See Init File, for a description of the initialization file.

There are several ways to write a key binding using Lisp.  The simplest is to use the kbd macro, which converts a textual representation of a key sequence---similar to how we have written key sequences in this manual---into a form that can be passed as an argument to global-set-key.  For example, here's how to bind C-z to the shell command (see Interactive Shell):

     (global-set-key (kbd "C-z") 'shell)

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 as a variable.  This probably causes an error; it certainly isn't what you want.

Here are some additional examples, including binding function keys and mouse events:

     (global-set-key (kbd "C-c y") 'clipboard-yank)
     (global-set-key (kbd "C-M-q") 'query-replace)
     (global-set-key (kbd "<f5>") 'flyspell-mode)
     (global-set-key (kbd "C-<f5>") 'linum-mode)
     (global-set-key (kbd "C-<right>") 'forward-sentence)
     (global-set-key (kbd "<mouse-2>") 'mouse-save-then-kill)

Instead of using the kbd macro, you can use a Lisp string or vector to specify the key sequence.  Using a string is simpler, but only works for ASCII characters and Meta-modified ASCII characters.  For example, here's how to bind C-x M-l to make-symbolic-link (see Misc File Ops):

     (global-set-key "\C-x\M-l" 'make-symbolic-link)

To put TAB, RET, ESC, or DEL in the string, use the Emacs Lisp escape sequences \t, \r, \e, and \d respectively.  Here is an example which binds C-x TAB to indent-rigidly (see Indentation):

     (global-set-key "\C-x\t" 'indent-rigidly)

When the key sequence includes function keys or mouse button events, or non-ASCII characters such as C-= or H-a, you can use a vector to specify the key sequence.  Each element in the vector stands for an input event; the elements are separated by spaces and surrounded by a pair of square brackets.  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.  Function keys are represented by symbols (see Function Keys); simply write the symbol's name, with no other delimiters or punctuation.  Here are some examples:

     (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:

     (global-set-key [?\C-z ?\M-l] 'make-symbolic-link)

Language and coding systems may cause problems with key bindings for non-ASCII characters.  See Init Non-ASCII.

As described in Local Keymaps, major modes and minor modes can define local keymaps.  These keymaps are constructed 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 mode hook (see Hooks).

For example, Texinfo mode runs the hook texinfo-mode-hook. Here's how you can use the hook to add local bindings 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)))

Modifier Keys
-------------

The default key bindings in Emacs are set up so that modified alphabetical characters are case-insensitive.  In other words, C-A does the same thing as C-a, and M-A does the same thing as M-a.  This concerns only alphabetical characters, and does not apply to ``shifted'' versions of other keys; for instance, C-@ is not the same as C-2.

A Control-modified alphabetical character is always considered case-insensitive: Emacs always treats C-A as C-a, C-B as C-b, and so forth.  The reason for this is historical.

For all other modifiers, you can make the modified alphabetical characters case-sensitive when you customize Emacs.  For instance, you could make M-a and M-A run different commands.

Although only the Control and Meta modifier keys are commonly used, Emacs supports three other modifier keys.  These are called Super, Hyper and Alt.  Few terminals provide ways to use these modifiers; the key labeled Alt on most keyboards usually issues the Meta modifier, not Alt.  The standard key bindings in Emacs do not include any characters with these modifiers.  However, you can customize Emacs to assign meanings to them.  The modifier bits are labelled as s-, H- and A- respectively.

Even if your keyboard lacks these additional modifier keys, you can enter it using C-x @: C-x @ h adds the ``hyper'' flag to the next character, C-x @ s adds the ``super'' flag, and C-x @ a adds the ``alt'' flag.  For instance, C-x @ h C-a is a way to enter Hyper-Control-a.  (Unfortunately, there is no way to add two modifiers by using C-x @ twice for the same character, because the first one goes to work on the C-x.)

Rebinding Function Keys
-----------------------

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, down
     Cursor arrow keys.

begin, end, home, next, prior
     Other cursor repositioning keys.

select, print, execute, backtab
insert, undo, redo, clearline
insertline, deleteline, insertchar, deletechar
     Miscellaneous function keys.

f1, f2, ... f35
     Numbered function keys (across the top of the keyboard).

kp-add, kp-subtract, kp-multiply, kp-divide
kp-backtab, kp-space, kp-tab, kp-enter
kp-separator, kp-decimal, kp-equal
     Keypad keys (to the right of the regular keyboard), with names or punctuation.

kp-0, kp-1, ... kp-9
     Keypad keys with digits.

kp-f1, kp-f2, kp-f3, kp-f4
     Keypad 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.

See Init Rebinding, for examples of binding function keys.

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.  Note that the modified keys are not translated: for instance, if you hold down the META key while pressing the 8 key on the numeric keypad, that generates M-kp-8.

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 Easy Customization).  You can rebind the keys to perform other tasks, such as issuing numeric prefix arguments.

Named ASCII Control Characters
------------------------------

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: TAB is different 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.

Rebinding Mouse Buttons
-----------------------

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 Click Events (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-line
     The mouse was in the mode line of a window.

vertical-line
     The 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-bar
     The mouse was in a vertical scroll bar.  (This is the only kind of scroll bar Emacs currently supports.)

menu-bar
     The mouse was in the menu bar.

header-line
     The 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.

Disabling Commands
------------------

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 Init File.

If Emacs was invoked with the -q or --no-init-file options (see 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.

The Init File, ~/.emacs
=======================

When Emacs is started, it normally tries to load a Lisp program from an initialization file, or init file for short.  This file, if it exists, specifies how to initialize Emacs for you.  Emacs looks for your init file using the filenames ~/.emacs, ~/.emacs.el, or ~/.emacs.d/init.el; you can choose to use any one of these three names (see Find Init).  Here, ~/ stands for your home directory.

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 Initial Options).

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 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 Lisp Libraries) 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.

Byte-compiling your init file is not recommended (see Byte Compilation (the Emacs Lisp Reference Manual)).  It generally does not speed up startup very much, and often leads to problems when you forget to recompile the file.  A better solution is to use the Emacs server to reduce the number of times you have to start Emacs (see Emacs Server).  If your init file defines many functions, consider moving them to a separate (byte-compiled) file that you load in your init file.

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 (the Emacs Lisp Reference Manual).

Init File Syntax
----------------

The init file contains one or more Lisp 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 Filling) 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:
     Numbers are written in decimal, with an optional initial minus sign.

Strings:
     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 Init Non-ASCII, for information about including non-ASCII in your init file.

Characters:
     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 Init Non-ASCII, for information about binding commands to keys which send non-ASCII characters.

True:
     t stands for `true'.

False:
     nil stands for `false'.

Other Lisp objects:
     Write a single-quote (') followed by the Lisp object you want.

Init File Examples
------------------

Here are some examples of doing certain commonly desired things with Lisp expressions:

  * Add a directory to the variable load-path.  You can then put Lisp libraries that are not included with Emacs in this directory, and load them with M-x load-library.  See Lisp Libraries.

          (add-to-list 'load-path "/path/to/lisp/libraries")

  * 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 (see Locals).  Setting case-fold-search with setq affects only the current buffer's local value, which is probably not what you want to do in an init file.

  * Specify your own email address, if Emacs can't figure it out correctly.

          (setq user-mail-address "cheney@torture.gov")

     Various Emacs packages, such as Message mode, consult user-mail-address when they need to know your email address. See Mail Headers.

  * 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 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 Lisp Libraries).

  * 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 Init Rebinding).

          (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.

Terminal-specific Initialization
--------------------------------

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 input-decode-map (or function-key-map before it).  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 Hooks.

How Emacs Finds Your Init File
------------------------------

Normally Emacs uses the environment variable HOME (see 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.

Non-ASCII Characters in Init Files
----------------------------------

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 Recognize Coding.  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 Init Rebinding).  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 key binding 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.