AD. Customization

This chapter talks about various topics relevant to adapting the behavior of Emacs in minor ways. See The Emacs Lisp Reference Manual for how to make more far-reaching changes.

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 `.emacs' or `.Xdefaults' that will affect future sessions. See section AD.7 The Init File, `~/.emacs'. In the customization buffer, when you save customizations for future sessions, this actually works by editing `.emacs' for you.

AD.1 Minor Modes

Minor modes are optional features which you can turn on or off. For example, Auto Fill mode is a minor mode in which SPC breaks lines between words as you type. All the minor modes are independent of each other and of the selected major mode. Most minor modes say in the mode line when they are on; for example, `Fill' in the mode line means that Auto Fill mode is on.

Append -mode to the name of a minor mode to get the name of a command function that turns the mode on or off. Thus, the command to enable or disable Auto Fill mode is called M-x auto-fill-mode. These commands are usually invoked with M-x, but you can bind keys to them if you wish. With no argument, the function turns the mode on if it was off and off if it was on. This is known as toggling. A positive argument always turns the mode on, and an explicit zero argument or a negative argument always turns it off.

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 which directly controls the mode. The mode is enabled whenever this variable's value is non-nil, and the minor-mode command works by setting the variable. For example, the command outline-minor-mode works by setting the value of outline-minor-mode as a variable; it is this variable that directly turns Outline minor mode on and off. To check whether a given minor mode works this way, use C-h v to ask for documentation on the variable name.

These minor-mode variables provide a good way for Lisp programs to turn minor modes on and off; they are also useful in a file's local variables list. But please think twice before setting minor modes with a local variables list, because most minor modes are matter of user preference--other users editing the same file might not want the same minor modes you prefer.

The buffer-local minor modes include Abbrev mode, Auto Fill mode, Auto Save mode, Font-Lock mode, Glasses mode, ISO Accents 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 X. 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 T.5 Filling Text.

Auto Save mode causes the contents of a buffer to be saved periodically to reduce the amount of work you can lose in case of a system crash. See section M.5 Auto-Saving: Protection Against Disasters.

Enriched mode enables editing and saving of formatted text. See section T.11 Editing Formatted Text.

Flyspell mode automatically highlights misspelled words. See section L.4 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 window system that can display multiple fonts. See section J.1 Using Multiple Typefaces.

ISO Accents mode makes the characters ``', `'', `"', `^', `/' and `~' combine with the following letter, to produce an accented letter in the ISO Latin-1 character set. The newer and more general feature of input methods more or less supersedes ISO Accents mode. See section Q.13 Single-byte Character Set Support.

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 T.8 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.

The following minor modes normally apply to all buffers at once. Since each is enabled or disabled by the value of a variable, you can set them differently for particular buffers, by explicitly making the corresponding variables local in those buffers. See section AD.2.4 Local Variables.

Icomplete mode displays an indication of available completions when you are in the minibuffer and completion is active. See section E.3.4 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 B.3 The Mode Line.

Scroll Bar mode gives each window a scroll bar (see section P.13 Scroll Bars). Menu Bar mode gives each frame a menu bar (see section P.15 Menu Bars). Both of these modes are enabled by default when you use the X Window System.

In Transient Mark mode, every change in the buffer contents "deactivates" the mark, so that commands that operate on the region will get an error. This means you must either set the mark, or explicitly "reactivate" it, before each command that uses the region. The advantage of Transient Mark mode is that Emacs can display the region highlighted (currently only when using X). See section H. The Mark and the Region.

AD.2 Variables

A variable is a Lisp symbol which has a value. The symbol's name is also called the name of the variable. A variable name can contain any characters that can appear in a file, but conventionally variable names consist of words separated by hyphens. A variable can have a documentation string which describes what kind of value it should have and how the value will be used.

Lisp allows any variable to have any kind of value, but most variables that Emacs uses require a value of a certain type. Often the value should always be a string, or should always be a number. Sometimes we say that a certain feature is turned on if a variable is "non-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, as any Lisp program must, but the most interesting variables for you are the ones that exist for the sake of customization. Emacs does not (usually) change the values of these variables; instead, you set the values, and thereby alter and control the behavior of certain Emacs commands. These variables are called user options. Most user options are documented in this manual, and appear in the Variable Index (see section Variable Index).

One example of a variable which is a user option is fill-column, which specifies the position of the right margin (as a number of characters from the left margin) to be used by the fill commands (see section T.5 Filling Text).

AD.2.1 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's value is 70

Documentation:
*Column beyond which automatic line-wrapping should happen.
Automatically becomes buffer-local when set in any fashion.

The star at the beginning of the documentation indicates that this variable is 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 is with M-x set-variable. This reads the variable name with the minibuffer (with completion), and then reads a Lisp expression for the new value using the minibuffer a second time. For example,

M-x set-variable RET fill-column RET 75 RET

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 V.9 Lisp Interaction Buffers.

Setting variables, like all means of customizing Emacs except where otherwise stated, affects only the current Emacs session.

AD.2.2 Easy Customization Interface

A convenient way to find the user option variables that you want to change, and then change them, is with M-x customize. This command creates a customization buffer with which you can browse through the Emacs user options in a logically organized structure, then edit and set their values. You can also use the customization buffer to save settings permanently. (Not all Emacs user options are included in this structure as of yet, but we are adding the rest.)

The appearance of the example buffers in the following is typically different under a window system where faces can be used to indicate the active fields and other features.

AD.2.2.1 Customization Groups

For customization purposes, user options 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 settings.
   Customization of the One True Editor.
   See also [Manual].

Confirm Kill Emacs: [Hide] [Value Menu] Don't confirm
   [State]: this option is unchanged from its standard setting.
How to ask for confirmation when leaving Emacs. [More]

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 active fields; this means a field that does something when you invoke it. To invoke an active field, either click on it with Mouse-1, or move point to it and type RET.

For example, the phrase `[Go to Group]' that appears in a second-level group is an active field. Invoking the `[Go to Group]' field for a group creates a new customization buffer, which shows that group and its contents. This field is a kind of hypertext link to another group.

The Emacs group includes a few user options itself, but mainly it contains other groups, which contain more groups, which contain the user options. 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 the options and faces pertaining to that feature. You can also go straight to a particular group by name, using the command M-x customize-group.

You can view the structure of customization groups on a larger scale with M-x customize-browse. This command creates a special kind of customization buffer which shows only the names of the groups (and options and faces), and their structure.

In this buffer, you can show the contents of a group by invoking `[+]'. When the group contents are visible, this button changes to `[-]'; invoking that hides the group contents.

Each group, option or face name in this buffer has an active field which says `[Group]', `[Option]' or `[Face]'. Invoking that active field creates an ordinary customization buffer showing just that group and its contents, just that option, or just that face. This is the way to set values in it.

AD.2.2.2 Changing an Option

Here is an example of what a user option looks like in the customization buffer:

Kill Ring Max: [Hide] 60
   [State]: this option is unchanged from its standard setting.
Maximum length of kill ring before oldest elements are thrown away.

The text following `[Hide]', `60' in this case, indicates the current value of the option. If you see `[Show]' instead of `[Hide]', it means that the value is hidden; the customization buffer initially hides values that take up several lines. Invoke `[Show]' to show the value.

The line after the option name indicates the customization state of the option: in the example above, it says you have not changed the option yet. The word `[State]' at the beginning of this line is active; you can get a menu of various operations by invoking it with Mouse-1 or RET. These operations are essential for customizing the variable.

The line after the `[State]' line displays the beginning of the option's documentation string. If there are more lines of documentation, this line ends with `[More]'; invoke this 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.

When you begin to alter the text, you will see the `[State]' line change to say that you have edited the value:

[State]: you have edited the value as text, but not set the option.

Editing the value does not actually set the option variable. To do that, you must set the option. To do this, invoke the word `[State]' and choose `Set for Current Session'.

The state of the option changes visibly when you set it:

[State]: you have set this option, but not saved it for future sessions.

You don't have to worry about specifying a value that is not valid; setting the option checks for validity and will not really install an unacceptable value.

While editing a value or 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.

Some options have a small fixed set of possible legitimate values. These options don't let you edit the value textually. Instead, an active field `[Value Menu]' appears before the value; invoke this field to edit the value. For a boolean "on or off" value, the active field says `[Toggle]', and it changes to the other value. `[Value Menu]' and `[Toggle]' edit the buffer; the changes take effect when you use the `Set for Current Session' operation.

Some options 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]
[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]: this option is unchanged from its standard setting.
Alist to decide a coding system to use for a file I/O operation. [Hide]
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 or "active" fields. You can edit the regexps and coding systems using ordinary editing commands. You can also invoke `[Value Menu]' to switch to a 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 association, another at the beginning and another at the end, so you can add the 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 active or editable field; S-TAB (widget-backward) moves backward to the previous active 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 option changes its value in the current Emacs session; saving the value changes it for future sessions as well. This works by writing code into your `~/.emacs' file so as to set the option variable again each time you start Emacs. To save the option, invoke `[State]' and select the `Save for Future Sessions' operation.

If Emacs was invoked with the `-q' or `--no-init-file' options (see section AE.2 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.

You can also restore the option to its standard value by invoking `[State]' and selecting the `Erase Customization' operation. There are actually three reset operations:

`Reset'

If you have made some modifications and not yet set the option, this restores the text in the customization buffer to match the actual value.

`Reset to Saved'

This restores the value of the option to the last saved value, and updates the text accordingly.

`Erase Customization'

This sets the option to its standard value, and updates the text accordingly. This also eliminates any saved value for the option, so that you will get the standard value in future Emacs sessions.

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 option 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. You can select `Set for Current Session', `Save for Future Sessions' and the various kinds of `Reset' operation for the group; these operations on the group apply to all options in the group and its subgroups.

Near the top of the customization buffer there are two lines containing several active fields:

 [Set for Current Session] [Save for Future Sessions]
 [Reset] [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-function; the default is to bury the buffer. Each of the other fields performs an operation--set, save or reset--on each of the items in the buffer that could meaningfully be set, saved or reset.

AD.2.2.3 Customizing Faces

In addition to user options, some customization groups also include faces. When you show the contents of a group, both the user options 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]
   [State]: this face is unchanged from its standard setting.
Parent groups: [Custom Magic Faces]
Attributes: [ ] Font family: [Value Menu] *
            [ ] Width: [Value Menu] *
            [ ] Height: [Value Menu] *
            [ ] Weight: [Value Menu] *
            [ ] Slant: [Value Menu] *
            [ ] Underline: [Value Menu] *
            [ ] Overline: [Value Menu] *
            [ ] Strike-through: [Value Menu] *
            [ ] Box around text: [Value Menu] *
            [ ] Inverse-video: [Value Menu] *
            [X] Foreground: [Value Menu] Color: white       (sample)
            [X] Background: [Value Menu] Color: blue        (sample)
            [ ] Stipple: [Value Menu] *
            [ ] Inherit:

Each face attribute has its own line. The `[x]' field before the attribute name indicates whether the attribute is enabled; `X' means that it is. You can enable or disable the attribute by invoking that field. When the attribute is enabled, you can change the attribute value in the usual ways.

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 options (see section AD.2.2.2 Changing an Option).

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 `Show all display specs' 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.

AD.2.2.4 Customizing Specific Items

Instead of finding the options you want to change by moving down through the structure of groups, you can specify the particular option, face or group that you want to customize.

M-x customize-option RET option RET

Set up a customization buffer with just one option, 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 options, faces and groups that match regexp.

M-x customize-changed-options RET version RET

Set up a customization buffer with all the options, faces and groups whose meaning has changed since Emacs version version.

M-x customize-saved

Set up a customization buffer containing all options and faces that you have saved with customization buffers.

M-x customize-customized

Set up a customization buffer containing all options and faces that you have customized but not saved.

If you want to alter a particular user option variable with the customization buffer, and you know its name, you can use the command M-x customize-option and specify the option name. This sets up the customization buffer with just one option--the one that you asked for. Editing, setting and saving the value work as described above, but only for the specified option.

Likewise, you can modify a specific face, chosen by name, using M-x customize-face.

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 option variables, faces, and other groups, all appear as well. However, these subgroups' own contents start out hidden. You can show their contents in the usual way, by invoking `[Show]'.

To control more precisely what to customize, you can use M-x customize-apropos. You specify a regular expression as argument; then all options, faces 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 groups, options and faces in the customization buffer (but that takes a long time).

When you upgrade to a new Emacs version, you might want to customize new options and options whose meanings or default values have changed. To do this, use M-x customize-changed-options and specify a previous Emacs version number using the minibuffer. It creates a customization buffer which shows all the options (and groups) whose definitions have been changed since the specified version.

If you change option values 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 options and faces that you have saved. Use M-x customize-customized to look at the options and faces that you have set but not saved.

AD.2.3 Hooks

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 C.1 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-hooks (see section M.2 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.

The recommended way to add a hook function to a hook (either normal or abnormal) is by calling add-hook. You can use any valid Lisp function as the hook function, provided it can handle the proper number of arguments (zero arguments, in the case of a normal hook). Of course, not every Lisp function is useful in any particular hook.

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.

AD.2.4 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. Further changes in this buffer will not affect others, and further changes in the global value will not affect this buffer.

M-x make-variable-buffer-local reads the name of a variable and changes the future behavior of the variable so that it will become local automatically when it is set. More precisely, once a variable has been marked in this way, the usual ways of setting the variable automatically do make-local-variable first. We call such variables per-buffer variables.

Major modes (see section R. 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 AD.1 Minor Modes). For most minor modes, the controlling variable is per buffer.

Emacs contains a number of variables that are always per-buffer. These include abbrev-mode, auto-fill-function, case-fold-search, comment-column, ctl-arrow, fill-column, fill-prefix, indent-tabs-mode, left-margin, mode-line-format, overwrite-mode, selective-display-ellipses, selective-display, tab-width, and truncate-lines. Some other variables are always local in every buffer, but they are used for internal purposes.

A few variables cannot be local to a buffer because they are always local to each display instead (see section P.10 Multiple Displays). If you try to make one of these variables buffer-local, you'll get an error message.

M-x kill-local-variable reads the name of a variable and makes it cease to be local to the current buffer. The global value of the variable henceforth is in effect in this buffer. Setting the major mode kills all the local variables of the buffer except for a few variables specially marked as permanent locals.

To set the global value of a variable, regardless of whether the variable has a local value in the current buffer, you can use the Lisp 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)

AD.2.5 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.

There are two ways to specify local variable values: in the first line, or with a local variables list. Here's how to specify them in the first line:

-*- mode: modename; var: value; ... -*-

You can specify any number of variables/value pairs in this way, each pair with a colon and semicolon as shown above. 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 Q.7 Coding Systems.

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 for this, when Emacs visits a shell script, it looks for local variable specifications in the second line.

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: ***

As you see, each line starts with the prefix `;;; ' and each line ends with the suffix ` ***'. Emacs recognizes these as the prefix and suffix based on the first line of the list, by finding them surrounding the magic string `Local Variables:'; then it automatically discards them from the other lines of the list.

The usual reason for using a prefix and/or suffix is to embed the local variables list in a comment, so it won't confuse other programs that the file is intended as input for. The example above is for a language where comment lines start with `;;; ' and end with `***'; the local values for comment-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.

Two "variable names" have special meanings in a local variables list: a value for the variable mode really sets the major mode, and a value for the variable eval is simply evaluated as an expression and the value is ignored. mode and eval are not real variables; setting variables named mode and eval 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 in the list of the local variables are likely to 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 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 in any fashion, 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 AD.7 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 R.1 How Major Modes are Chosen.

The variable enable-local-variables controls whether to process local variables in files, and thus gives you a chance to override them. Its default value is t, which means do process local variables in files. If you set the value to nil, Emacs simply ignores local variables in files. Any other value says to query you about each file that has local variables, showing you the local variable specifications so you can judge.

The eval "variable," and certain actual variables, create a special risk; when you visit someone else's file, local variable specifications for these could affect your Emacs in arbitrary ways. Therefore, the option enable-local-eval controls whether Emacs processes eval variables, as well variables with names that end in `-hook', `-hooks', `-function' or `-functions', and certain other variables. The three possibilities for the option's 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 file settings for these variables.

AD.3 Keyboard Macros

A keyboard macro is a command defined by the user to stand for another sequence of keys. For example, if you discover that you are about to type C-n C-d forty times, you can speed your work by defining a keyboard macro to do C-n C-d and calling it with a repeat count of forty.

C-x (

Start defining a keyboard macro (start-kbd-macro).

C-x )

End the definition of a keyboard macro (end-kbd-macro).

C-x e

Execute the most recent keyboard macro (call-last-kbd-macro).

C-u C-x (

Re-execute last keyboard macro, then add more keys to its definition.

C-x q

When this point is reached during macro execution, ask for confirmation (kbd-macro-query).

M-x name-last-kbd-macro

Give a command name (for the duration of the session) to the most recently defined keyboard macro.

M-x insert-kbd-macro

Insert in the buffer a keyboard macro's definition, as Lisp code.

C-x C-k

Edit a previously defined keyboard macro (edit-kbd-macro).

M-x apply-macro-to-region-lines

Run the last keyboard macro on each complete line in the region.

Keyboard macros differ from ordinary Emacs commands in that they are written in the Emacs command language rather than in Lisp. This makes it easier for the novice to write them, and makes them more convenient as temporary hacks. However, the Emacs command language is not powerful enough as a programming language to be useful for writing anything intelligent or general. For such things, Lisp must be used.

You define a keyboard macro while executing the commands which are the definition. Put differently, as you define a keyboard macro, the definition is being executed for the first time. This way, you can see what the effects of your commands are, so that you don't have to figure them out in your head. When you are finished, the keyboard macro is defined and also has been, in effect, executed once. You can then do the whole thing over again by invoking the macro.

AD.3.1 Basic Use

To start defining a keyboard macro, type the C-x ( command (start-kbd-macro). From then on, your keys continue to be executed, but also become part of the definition of the macro. `Def' appears in the mode line to remind you of what is going on. When you are finished, the C-x ) command (end-kbd-macro) terminates the definition (without becoming part of it!). For example,

C-x ( M-f foo C-x )

defines a macro to move forward a word and then insert `foo'.

The macro thus defined can be invoked again with the C-x e command (call-last-kbd-macro), which may be given a repeat count as a numeric argument to execute the macro many times. C-x ) can also be given a repeat count as an argument, in which case it repeats the macro that many times right after defining it, but defining the macro counts as the first repetition (since it is executed as you define it). Therefore, giving C-x ) an argument of 4 executes the macro immediately 3 additional times. An argument of zero to C-x e or C-x ) means repeat the macro indefinitely (until it gets an error or you type C-g or, on MS-DOS, C-BREAK).

If you wish to repeat an operation at regularly spaced places in the text, define a macro and include as part of the macro the commands to move to the next place you want to use it. For example, if you want to change each line, you should position point at the start of a line, and define a macro to change that line and leave point at the start of the next line. Then repeating the macro will operate on successive lines.

When a command reads an argument with the minibuffer, your minibuffer input becomes part of the macro along with the command. So when you replay the macro, the command gets the same argument as when you entered the macro. For example,

C-x ( C-a C-SPC C-n M-w C-x b f o o RET C-y C-x b RET C-x )

defines a macro that copies the current line into the buffer `foo', then returns to the original buffer.

You can use function keys in a keyboard macro, just like keyboard keys. You can even use mouse events, but be careful about that: when the macro replays the mouse event, it uses the original mouse position of that event, the position that the mouse had while you were defining the macro. The effect of this may be hard to predict. (Using the current mouse position would be even less predictable.)

One thing that doesn't always work well in a keyboard macro is the command C-M-c (exit-recursive-edit). When this command exits a recursive edit that started within the macro, it works as you'd expect. But if it exits a recursive edit that started before you invoked the keyboard macro, it also necessarily exits the keyboard macro as part of the process.

After you have terminated the definition of a keyboard macro, you can add to the end of its definition by typing C-u C-x (. This is equivalent to plain C-x ( followed by retyping the whole definition so far. As a consequence it re-executes the macro as previously defined.

You can edit a keyboard macro already defined by typing C-x C-k (edit-kbd-macro). Follow that with the keyboard input that you would use to invoke the macro---C-x e or M-x name or some other key sequence. This formats the macro definition in a buffer and enters a specialized major mode for editing it. Type C-h m once in that buffer to display details of how to edit the macro. When you are finished editing, type C-c C-c.

The command M-x apply-macro-to-region-lines repeats the last defined keyboard macro on each complete line within the current region. It does this line by line, by moving point to the beginning of the line and then executing the macro.

AD.3.2 Naming and Saving Keyboard Macros

If you wish to save a keyboard macro for longer than until you define the next one, you must give it a name using M-x name-last-kbd-macro. This reads a name as an argument using the minibuffer and defines that name to execute the macro. The macro name is a Lisp symbol, and defining it in this way makes it a valid command name for calling with M-x or for binding a key to with global-set-key (see section AD.4.1 Keymaps). If you specify a name that has a prior definition other than another keyboard macro, an error message is shown and nothing is changed.

Once a macro has a command name, you can save its definition in a file. Then it can be used in another editing session. First, visit the file you want to save the definition in. Then use this command:

M-x insert-kbd-macro RET macroname RET

This inserts some Lisp code that, when executed later, will define the same macro with the same definition it has now. (You need not understand Lisp code to do this, because insert-kbd-macro writes the Lisp code for you.) Then save the file. You can load the file later with load-file (see section V.7 Libraries of Lisp Code for Emacs). If the file you save in is your init file `~/.emacs' (see section AD.7 The Init File, `~/.emacs') then the macro will be defined each time you run Emacs.

If you give insert-kbd-macro a numeric argument, it makes additional Lisp code to record the keys (if any) that you have bound to the keyboard macro, so that the macro will be reassigned the same keys when you load the file.

AD.3.3 Executing Macros with Variations

Using C-x q (kbd-macro-query), you can get an effect similar to that of query-replace, where the macro asks you each time around whether to make a change. While defining the macro, type C-x q at the point where you want the query to occur. During macro definition, the C-x q does nothing, but when you run the macro later, C-x q asks you interactively whether to continue.

The valid responses when C-x q asks are SPC (or y), DEL (or n), RET (or q), C-l and C-r. The answers are the same as in query-replace, though not all of the query-replace options are meaningful.

These responses include SPC to continue, and DEL to skip the remainder of this repetition of the macro and start right away with the next repetition. RET means to skip the remainder of this repetition and cancel further repetitions. C-l redraws the screen and asks you again for a character to say what to do.

C-r enters a recursive editing level, in which you can perform editing which is not part of the macro. When you exit the recursive edit using C-M-c, you are asked again how to continue with the keyboard macro. If you type a SPC at this time, the rest of the macro definition is executed. It is up to you to leave point and the text in a state such that the rest of the macro will do what you want.

C-u C-x q, which is C-x q with a numeric argument, performs a completely different function. It enters a recursive edit reading input from the keyboard, both when you type it during the definition of the macro, and when it is executed from the macro. During definition, the editing you do inside the recursive edit does not become part of the macro. During macro execution, the recursive edit gives you a chance to do some particularized editing on each repetition. See section AC.26 Recursive Editing Levels.

Another way to vary the behavior of a keyboard macro is to use a register as a counter, incrementing it on each repetition of the macro. See section I.5 Keeping Numbers in Registers.

AD.4 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.

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.

AD.4.1 Keymaps

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 AD.4.5 Changing Key Bindings Interactively.

Meta characters work differently; Emacs translates each Meta character into a pair of characters starting with ESC. When you type the character M-a in a key sequence, Emacs replaces it with ESC a. A meta key comes in as a single input event, but becomes two events for purposes of key bindings. The reason for this is historical, and we might change it someday.

Most modern keyboards have function keys as well as character keys. Function keys send input events just as character keys do, and keymaps can have bindings for them.

On many terminals, typing a function key actually sends the computer a sequence of characters; the precise details of the sequence depends on which function key and on the model of terminal you are using. (Often the sequence starts with ESC [.) If Emacs understands your terminal type properly, it recognizes the character sequences forming function keys wherever they occur in a key sequence (not just at the beginning). Thus, for most purposes, you can pretend the function keys reach Emacs directly and ignore their encoding as character sequences.

Mouse buttons also produce input events. These events come with other data--the window and position where you pressed or released the button, and a time stamp. But only the choice of button matters for key bindings; the other data matters only if a command looks at it. (Commands designed for mouse invocation usually do look at the other data.)

A keymap records definitions for single events. Interpreting a key sequence of multiple events involves a chain of keymaps. The first keymap gives a definition for the first event; this definition is another keymap, which is used to look up the second event in the sequence, and so on.

Key sequences can mix function keys and characters. For example, C-x SELECT 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. 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.

AD.4.2 Prefix Keymaps

A prefix key such as C-x or ESC has its own keymap, which holds the definition for the event that immediately follows that prefix.

The definition of a prefix key is usually the keymap to use for looking up the following event. The definition can also be a Lisp symbol whose function definition is the following keymap; the effect is the same, but it provides a command name for the prefix key that can be used as a description of what the prefix key is for. Thus, the binding of C-x is the symbol Ctl-X-Prefix, whose function definition is the keymap for C-x commands. The definitions of C-c, C-x, C-h and ESC as prefix keys appear in the global map, so these prefix keys are always available.

Aside from ordinary prefix keys, there is a fictitious "prefix key" which represents the menu bar; see 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 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.

AD.4.3 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. Portions of text in the buffer can specify their own keymaps to substitute for the keymap of the buffer's major mode.

Minor modes can also have local keymaps. Whenever a minor mode is in effect, the definitions in its keymap override both the major mode's local keymap and the global keymap.

The local keymaps for Lisp mode and several other major modes always exist even when not in use. These are kept in variables named lisp-mode-map and so on. For major modes less often used, the local keymap is normally constructed only when the mode is used for the first time in a session. This is to save space. If you wish to change one of these keymaps, you must use the major mode's mode hook---see below.

All minor mode keymaps are created in advance. There is no way to defer their creation until the first time the minor mode is enabled.

A local keymap can locally redefine a key as a prefix key by defining it as a prefix keymap. If the key is also defined globally as a prefix, then its local and global definitions (both keymaps) effectively combine: both of them are used to look up the event that follows the prefix key. Thus, if the mode's local keymap defines C-c as another keymap, and that keymap defines C-z as a command, this provides a local meaning for C-c C-z. This does not affect other sequences that start with C-c; if those sequences don't have their own local bindings, their global bindings remain in effect.

Another way to think of this is that Emacs handles a multi-event key sequence by looking in several keymaps, one by one, for a binding of the whole key sequence. First it checks the minor mode keymaps for minor modes that are enabled, then it checks the major mode's keymap, and then it checks the global keymap. This is not precisely how key lookup works, but it's good enough for understanding ordinary circumstances.

To change the local bindings of a major mode, you must change the mode's local keymap. Normally you must wait until the first time the mode is used, because most major modes don't create their keymaps until then. If you want to specify something in your `~/.emacs' file to change a major mode's bindings, you must use the mode's mode hook to delay the change until the mode is first used.

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)))

See section AD.2.3 Hooks.

AD.4.4 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. 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.

AD.4.5 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 definitions for the same key). Or you can change the current buffer's local map, which affects all buffers using the same major mode.

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, suppose you like to execute commands in a subshell within an Emacs buffer, instead of suspending Emacs and executing commands in your login shell. Normally, C-z is bound to the function suspend-emacs (when not using the X Window System), but you can change C-z to invoke an interactive subshell within Emacs, by binding it to shell as follows:

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

global-set-key reads the command name after the key. After you press the key, a message like this appears so that you can confirm that you are binding the key you want:

Set key C-z to command: 

You can redefine function keys and mouse events in the same way; just type the function key or click the mouse when it's time to specify the key to rebind.

You can rebind a key that contains more than one event in the same way. Emacs keeps reading the key to rebind until it is a complete key (that is, not a prefix key). Thus, if you type C-f for key, that's the end; the minibuffer is entered immediately to read cmd. But if you type C-x, another character is read; if that is 4, another character is read, and so on. For example,

M-x global-set-key RET C-x 4 $ spell-other-window RET

redefines C-x 4 $ to run the (fictitious) command 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 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 AD.4.11 Disabling Commands.

AD.4.6 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 `.emacs' file by using their Lisp syntax. (See section AD.7 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. 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 a key sequence two characters long:

(global-set-key "\C-xl" '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 three examples above, using vectors to bind C-z, C-x l, and C-x TAB:

(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 each of the characters within the square brackets that delimit the vector.

AD.4.7 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.

A key sequence which contains function key symbols (or anything but ASCII characters) must be a vector rather than a string. The vector syntax uses spaces between the elements, and square brackets around the whole vector. 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 AD.4.6 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)

AD.4.8 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. Later, users found it convenient to distinguish in Emacs between these keys and the "same" control characters typed with the CTRL key.

Emacs distinguishes these two kinds of input, when the keyboard reports these keys to Emacs. 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.

AD.4.9 Non-ASCII Characters on the Keyboard

If your keyboard has keys that send non-ASCII characters, such as accented letters, rebinding these keys is a bit tricky. There are two solutions you can use. One is to specify a keyboard coding system, using set-keyboard-coding-system (see section Q.9 Specifying a Coding System). Then you can bind these keys in the usual way(16), like this:

(global-set-key [?char] 'some-function)

Type C-q followed by the key you want to bind, to insert char.

If you don't specify the keyboard coding system, that approach won't work. Instead, you need to find out the actual code that the terminal sends. The easiest way to do this in Emacs is to create an empty buffer with C-x b temp RET, make it unibyte with M-x toggle-enable-multibyte-characters RET, then type the key to insert the character into this buffer.

Move point before the character, then type C-x =. This displays a message in the minibuffer, showing the character code in three ways, octal, decimal and hexadecimal, all within a set of parentheses. Use the second of the three numbers, the decimal one, inside the vector to bind:

(global-set-key [decimal-code] 'some-function)

If you bind 8-bit characters like this in your init file, you may find it convenient to specify that it is unibyte. See section Q.2 Enabling Multibyte Characters.

AD.4.10 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 you can distinguish if you really want to. We don't recommend distinct meanings for more than three clicks, but sometimes it is useful for subsequent clicks to cycle through the same set of three meanings, so that four clicks are equivalent to one click, five are equivalent to two, and six are equivalent to three.

Emacs also records multiple presses in drag and button-down events. For example, when you press a button twice, then move the mouse while holding the button, Emacs gets a `double-drag-' event. And at the moment when you press it down for the second time, Emacs gets a `double-down-' event (which is ignored, like all button-down events, if it has no binding).

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 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.)

You can put more than one mouse button in a key sequence, but it isn't usual to do so.

AD.4.11 Disabling Commands

Disabling a command marks the command as requiring confirmation before it can be executed. The purpose of disabling a command is to prevent beginning users from executing it by accident and being confused.

An attempt to invoke a disabled command interactively in Emacs displays a window containing the command's name, its documentation, and some instructions on what to do immediately; then Emacs asks for input saying whether to execute the command as requested, enable it and execute it, or cancel. If you decide to enable the command, you are asked whether to do this permanently or just for the current session. (Enabling permanently works by automatically editing your `.emacs' file.) 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 AD.7 The Init File, `~/.emacs'.

Whether a command is disabled is independent of what key is used to invoke it; disabling also applies if the command is invoked using M-x. Disabling a command has no effect on calling it as a function from Lisp programs.

AD.5 Keyboard Translations

Some keyboards do not make it convenient to send all the special characters that Emacs uses. The most common problem case is the DEL character. Some keyboards provide no convenient way to type this very important character--usually because they were designed to expect the character C-h to be used for deletion. On these keyboards, if you press the key normally used for deletion, Emacs handles the C-h as a prefix character and offers you a list of help options, which is not what you want.

You can work around this problem within Emacs by setting up keyboard translations to turn C-h into DEL and DEL into C-h, as follows:

;; Translate C-h to DEL.
(keyboard-translate ?\C-h ?\C-?)

;; Translate DEL to C-h.
(keyboard-translate ?\C-? ?\C-h)

Keyboard translations are not the same as key bindings in keymaps (see section AD.4.1 Keymaps). Emacs contains numerous keymaps that apply in different situations, but there is only one set of keyboard translations, and it applies to every character that Emacs reads from the terminal. Keyboard translations take place at the lowest level of input processing; the keys that are looked up in keymaps contain the characters that result from keyboard translation.

On a window system, the keyboard key named DELETE is a function key and is distinct from the ASCII character named DEL. See section AD.4.8 Named ASCII Control Characters. Keyboard translations affect only ASCII character input, not function keys; thus, the above example used on a window system does not affect the DELETE key. However, the translation above isn't necessary on window systems, because Emacs can also distinguish between the BACKSPACE key and C-h; and it normally treats BACKSPACE as DEL.

For full information about how to use keyboard translations, see section `Translating Input' in The Emacs Lisp Reference Manual.

AD.6 The Syntax Table

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 both 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 section `Syntax Tables' in The Emacs Lisp Reference Manual.

AD.7 The Init File, `~/.emacs'

When Emacs is started, it normally loads a Lisp program from the file `.emacs' or `.emacs.el' in your home directory. We call this file your init file because it specifies how to initialize Emacs for you. You can use the command line switch `-q' to prevent loading your init file, and `-u' (or `--user') to specify a different user's init file (see section C. Entering and Exiting Emacs).

There can also be a default init file, which is the library named `default.el', found via the standard search path for libraries. The Emacs distribution contains no such library; your site may create one for local customizations. If this library exists, it is loaded whenever you start Emacs (except when you specify `-q'). But your init file, if any, is loaded first; if it sets 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 AE.2 Initial Options.

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 V.7 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 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 section `Emacs Lisp' in the Emacs Lisp Reference Manual.

AD.7.1 Init File Syntax

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 T.5 Filling Text) to 60.

The second argument to setq is an expression for the new value of the variable. This can be a constant, a variable, or a function call expression. In `.emacs', constants are used most of the time. They can be:

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.

If you want to include non-ASCII characters in strings in your init file, you should consider putting a `-*-coding: coding-system-*-' tag on the first line which states the coding system used to save your `.emacs', as explained in Q.8 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.

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 section AD.4.9 Non-ASCII Characters on the Keyboard, 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.

AD.7.2 Init File Examples

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 "[email protected]")

  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 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 AD.2.3 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 V.7 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.

  (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)

AD.7.3 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 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 AD.2.3 Hooks.

AD.7.4 How Emacs Finds Your Init File

Normally Emacs uses the environment variable HOME to find `.emacs'; that's what `~' means in a file name. But 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 the 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.

AD.8 Quitting and Aborting

C-g

C-BREAK (MS-DOS only)

Quit: cancel running or partially typed command.

C-]

Abort innermost recursive editing level and cancel the command which invoked it (abort-recursive-edit).

ESC ESC ESC

Either quit or abort, whichever makes sense (keyboard-escape-quit).

M-x top-level

Abort all recursive editing levels that are currently executing.

C-x u

Cancel a previously made change in the buffer contents (undo).

There are two ways of canceling commands which are not finished executing: quitting with C-g, and aborting with C-] or M-x top-level. Quitting cancels a partially typed command or one which is already running. Aborting exits a recursive editing level and cancels the command that invoked the recursive edit. (See section AC.26 Recursive Editing Levels.)

Quitting with C-g is used for getting rid of a partially typed command, or a numeric argument that you don't want. It also stops a running command in the middle in a relatively safe way, so you can use it if you accidentally give a command which takes a long time. In particular, it is safe to quit out of killing; either your text will all still be in the buffer, or it will all be in the kill ring (or maybe both). Quitting an incremental search does special things documented under searching; in general, it may take two successive C-g characters to get out of a search (see section K.1 Incremental Search).

On MS-DOS, the character C-BREAK serves as a quit character like C-g. The reason is that it is not feasible, on MS-DOS, to recognize C-g while a command is running, between interactions with the user. By contrast, it is feasible to recognize C-BREAK at all times. See section AH.1 Keyboard and Mouse on MS-DOS.

C-g works by setting the variable quit-flag to t the instant C-g is typed; Emacs Lisp checks this variable frequently and quits if it is non-nil. C-g is only actually executed as a command if you type it while Emacs is waiting for input. In that case, the command it runs is keyboard-quit.

If you quit with C-g a second time before the first C-g is recognized, you activate the "emergency escape" feature and return to the shell. See section AD.9.8 Emergency Escape.

There may be times when you cannot quit. When Emacs is waiting for the operating system to do something, quitting is impossible unless special pains are taken for the particular system call within Emacs where the waiting occurs. We have done this for the system calls that users are likely to want to quit from, but it's possible you will find another. In one very common case--waiting for file input or output using NFS--Emacs itself knows how to quit, but many NFS implementations simply do not allow user programs to stop waiting for NFS when the NFS server is hung.

Aborting with C-] (abort-recursive-edit) is used to get out of a recursive editing level and cancel the command which invoked it. Quitting with C-g does not do this, and could not do this, because it is used to cancel a partially typed command within the recursive editing level. Both operations are useful. For example, if you are in a recursive edit and type C-u 8 to enter a numeric argument, you can cancel that argument with C-g and remain in the recursive edit.

The command ESC ESC ESC (keyboard-escape-quit) can either quit or abort. This key was defined because ESC is used to "get out" in many PC programs. It can cancel a prefix argument, clear a selected region, or get out of a Query Replace, like C-g. It can get out of the minibuffer or a recursive edit, like C-]. It can also get out of splitting the frame into multiple windows, like C-x 1. One thing it cannot do, however, is stop a command that is running. That's because it executes as an ordinary command, and Emacs doesn't notice it until it is ready for a command.

The command M-x top-level is equivalent to "enough" C-] commands to get you out of all the levels of recursive edits that you are in. C-] gets you out one level at a time, but M-x top-level goes out all levels at once. Both C-] and M-x top-level are like all other commands, and unlike C-g, in that they take effect only when Emacs is ready for a command. C-] is an ordinary key and has its meaning only because of its binding in the keymap. See section AC.26 Recursive Editing Levels.

C-x u (undo) is not strictly speaking a way of canceling a command, but you can think of it as canceling a command that already finished executing. See section D.4 Undoing Changes, for more information about the undo facility.

AD.9 Dealing with Emacs Trouble

This section describes various conditions in which Emacs fails to work normally, and how to recognize them and correct them. For a list of additional problems you might encounter, see section `Bugs and problems' in GNU Emacs FAQ, and the file `etc/PROBLEMS' in the Emacs distribution. Type C-h F to read the FAQ; type C-h P to read the `PROBLEMS' file.

AD.9.1 If DEL Fails to Delete

Every keyboard has a large key, a little ways above the RET or ENTER key, which you normally use outside Emacs to erase the last character that you typed. We call this key the usual erasure key. In Emacs, it is supposed to be equivalent to DEL, and when Emacs is properly configured for your terminal, it translates that key into the character DEL.

When Emacs starts up using a window system, it determines automatically which key should be DEL. In some unusual cases Emacs gets the wrong information from the system. If the usual erasure key deletes forwards instead of backwards, that is probably what happened--Emacs ought to be treating the DELETE key as DEL, but it isn't.

With a window system, if the usual erasure key is labeled BACKSPACE and there is a DELETE key elsewhere, but the DELETE key deletes backward instead of forward, that too suggests Emacs got the wrong information--but in the opposite sense. It ought to be treating the BACKSPACE key as DEL, and treating DELETE differently, but it isn't.

On a text-only terminal, if you find the usual erasure key prompts for a Help command, like Control-h, instead of deleting a character, it means that key is actually sending the BS character. Emacs ought to be treating BS as DEL, but it isn't.

In all of those cases, the immediate remedy is the same: use the command M-x normal-erase-is-backspace-mode. This toggles between the two modes that Emacs supports for handling DEL, so if Emacs starts in the wrong mode, it should switch to the right mode. On a text-only terminal, if you want to ask for help when BS is treated as DEL, use F1; C-? may also work, if it sends character code 127.

To fix the problem automatically for every Emacs session, you can put one of the following lines into your `.emacs' file (see section AD.7 The Init File, `~/.emacs'). For the first case above, where DELETE deletes forwards instead of backwards, use this line to make DELETE act as DEL (resulting in behavior compatible with Emacs 20 and previous versions):

(normal-erase-is-backspace-mode 0)

For the other two cases, where BACKSPACE ought to act as DEL, use this line:

(normal-erase-is-backspace-mode 1)

Another way to fix the problem for every Emacs session is to customize the variable normal-erase-is-backspace: the value t specifies the mode where BS or BACKSPACE is DEL, and nil specifies the other mode. See section AD.2.2 Easy Customization Interface.

With a window system, it can also happen that the usual erasure key is labeled BACKSPACE, there is a DELETE key elsewhere, and both keys delete forward. This probably means that someone has redefined your BACKSPACE key as a DELETE key. With X, this is typically done with a command to the xmodmap program when you start the server or log in. The most likely motive for this customization was to support old versions of Emacs, so we recommend you simply remove it now.

AD.9.2 Recursive Editing Levels

Recursive editing levels are important and useful features of Emacs, but they can seem like malfunctions to the user who does not understand them.

If the mode line has square brackets `[...]' around the parentheses that contain the names of the major and minor modes, you have entered a recursive editing level. If you did not do this on purpose, or if you don't understand what that means, you should just get out of the recursive editing level. To do so, type M-x top-level. This is called getting back to top level. See section AC.26 Recursive Editing Levels.

AD.9.3 Garbage on the Screen

If the data on the screen looks wrong, the first thing to do is see whether the text is really wrong. Type C-l to redisplay the entire screen. If the screen appears correct after this, the problem was entirely in the previous screen update. (Otherwise, see the following section.)

Display updating problems often result from an incorrect termcap entry for the terminal you are using. The file `etc/TERMS' in the Emacs distribution gives the fixes for known problems of this sort. `INSTALL' contains general advice for these problems in one of its sections. Very likely there is simply insufficient padding for certain display operations. To investigate the possibility that you have this sort of problem, try Emacs on another terminal made by a different manufacturer. If problems happen frequently on one kind of terminal but not another kind, it is likely to be a bad termcap entry, though it could also be due to a bug in Emacs that appears for terminals that have or that lack specific features.

AD.9.4 Garbage in the Text

If C-l shows that the text is wrong, try undoing the changes to it using C-x u until it gets back to a state you consider correct. Also try C-h l to find out what command you typed to produce the observed results.

If a large portion of text appears to be missing at the beginning or end of the buffer, check for the word `Narrow' in the mode line. If it appears, the text you don't see is probably still present, but temporarily off-limits. To make it accessible again, type C-x n w. See section AC.22 Narrowing.

AD.9.5 Spontaneous Entry to Incremental Search

If Emacs spontaneously displays `I-search:' at the bottom of the screen, it means that the terminal is sending C-s and C-q according to the poorly designed xon/xoff "flow control" protocol.

If this happens to you, your best recourse is to put the terminal in a mode where it will not use flow control, or give it so much padding that it will never send a C-s. (One way to increase the amount of padding is to set the variable baud-rate to a larger value. Its value is the terminal output speed, measured in the conventional units of baud.)

If you don't succeed in turning off flow control, the next best thing is to tell Emacs to cope with it. To do this, call the function enable-flow-control.

Typically there are particular terminal types with which you must use flow control. You can conveniently ask for flow control on those terminal types only, using enable-flow-control-on. For example, if you find you must use flow control on VT-100 and H19 terminals, put the following in your `.emacs' file:

(enable-flow-control-on "vt100" "h19")

When flow control is enabled, you must type C-\ to get the effect of a C-s, and type C-^ to get the effect of a C-q. (These aliases work by means of keyboard translations; see AD.5 Keyboard Translations.)

AD.9.6 Running out of Memory

If you get the error message `Virtual memory exceeded', save your modified buffers with C-x s. This method of saving them has the smallest need for additional memory. Emacs keeps a reserve of memory which it makes available when this error happens; that should be enough to enable C-x s to complete its work.

Once you have saved your modified buffers, you can exit this Emacs job and start another, or you can use M-x kill-some-buffers to free space in the current Emacs job. If you kill buffers containing a substantial amount of text, you can safely go on editing. Emacs refills its memory reserve automatically when it sees sufficient free space available, in case you run out of memory another time.

Do not use M-x buffer-menu to save or kill buffers when you run out of memory, because the buffer menu needs a fair amount of memory itself, and the reserve supply may not be enough.

AD.9.7 Recovery After a Crash

If Emacs or the computer crashes, you can recover the files you were editing at the time of the crash from their auto-save files. To do this, start Emacs again and type the command M-x recover-session.

This command initially displays a buffer which lists interrupted session files, each with its date. You must choose which session to recover from. Typically the one you want is the most recent one. Move point to the one you choose, and type C-c C-c.

Then recover-session asks about each of the files that you were editing during that session; it asks whether to recover that file. If you answer y for a file, it shows the dates of that file and its auto-save file, then asks once again whether to recover that file. For the second question, you must confirm with yes. If you do, Emacs visits the file but gets the text from the auto-save file.

When recover-session is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this--saving them--updates the files themselves.

AD.9.8 Emergency Escape

Because at times there have been bugs causing Emacs to loop without checking quit-flag, a special feature causes Emacs to be suspended immediately if you type a second C-g while the flag is already set, so you can always get out of GNU Emacs. Normally Emacs recognizes and clears quit-flag (and quits!) quickly enough to prevent this from happening. (On MS-DOS and compatible systems, type C-BREAK twice.)

When you resume Emacs after a suspension caused by multiple C-g, it asks two questions before going back to what it had been doing:

Auto-save? (y or n)
Abort (and dump core)? (y or n)

Answer each one with y or n followed by RET.

Saying y to `Auto-save?' causes immediate auto-saving of all modified buffers in which auto-saving is enabled.

Saying y to `Abort (and dump core)?' causes an illegal instruction to be executed, dumping core. This is to enable a wizard to figure out why Emacs was failing to quit in the first place. Execution does not continue after a core dump. If you answer n, execution does continue. With luck, GNU Emacs will ultimately check quit-flag and quit normally. If not, and you type another C-g, it is suspended again.

If Emacs is not really hung, just slow, you may invoke the double C-g feature without really meaning to. Then just resume and answer n to both questions, and you will arrive at your former state. Presumably the quit you requested will happen soon.

The double C-g feature is turned off when Emacs is running under the X Window System, since you can use the window manager to kill Emacs or to create another window and run another program.

On MS-DOS and compatible systems, the emergency escape feature is sometimes unavailable, even if you press C-BREAK twice, when some system call (MS-DOS or BIOS) hangs, or when Emacs is stuck in a very tight endless loop (in C code, not in Lisp code).

AD.9.9 Help for Total Frustration

If using Emacs (or something else) becomes terribly frustrating and none of the techniques described above solve the problem, Emacs can still help you.

First, if the Emacs you are using is not responding to commands, type C-g C-g to get out of it and then start a new one.

Second, type M-x doctor RET.

The doctor will help you feel better. Each time you say something to the doctor, you must end it by typing RET RET. This lets the doctor know you are finished.

AD.10 Reporting Bugs

Sometimes you will encounter a bug in Emacs. Although we cannot promise we can or will fix the bug, and we might not even agree that it is a bug, we want to hear about problems you encounter. Often we agree they are bugs and want to fix them.

To make it possible for us to fix a bug, you must report it. In order to do so effectively, you must know when and how to do it.

Before reporting a bug, it is a good idea to see if it is already known. You can find the list of known problems in the file `etc/PROBLEMS' in the Emacs distribution; type C-h P to read it. Some additional user-level problems can be found in section `Bugs and problems' in GNU Emacs FAQ. Looking up your problem in these two documents might provide you with a solution or a work-around, or give you additional information about related issues.

AD.10.1 When Is There a Bug

If Emacs executes an illegal instruction, or dies with an operating system error message that indicates a problem in the program (as opposed to something like "disk full"), then it is certainly a bug.

If Emacs updates the display in a way that does not correspond to what is in the buffer, then it is certainly a bug. If a command seems to do the wrong thing but the problem corrects itself if you type C-l, it is a case of incorrect display updating.

Taking forever to complete a command can be a bug, but you must make certain that it was really Emacs's fault. Some commands simply take a long time. Type C-g (C-BREAK on MS-DOS) and then C-h l to see whether the input Emacs received was what you intended to type; if the input was such that you know it should have been processed quickly, report a bug. If you don't know whether the command should take a long time, find out by looking in the manual or by asking for assistance.

If a command you are familiar with causes an Emacs error message in a case where its usual definition ought to be reasonable, it is probably a bug.

If a command does the wrong thing, that is a bug. But be sure you know for certain what it ought to have done. If you aren't familiar with the command, or don't know for certain how the command is supposed to work, then it might actually be working right. Rather than jumping to conclusions, show the problem to someone who knows for certain.

Finally, a command's intended definition may not be the best possible definition for editing with. This is a very important sort of problem, but it is also a matter of judgment. Also, it is easy to come to such a conclusion out of ignorance of some of the existing features. It is probably best not to complain about such a problem until you have checked the documentation in the usual ways, feel confident that you understand it, and know for certain that what you want is not available. If you are not sure what the command is supposed to do after a careful reading of the manual, check the index and glossary for any terms that may be unclear.

If after careful rereading of the manual you still do not understand what the command should do, that indicates a bug in the manual, which you should report. The manual's job is to make everything clear to people who are not Emacs experts--including you. It is just as important to report documentation bugs as program bugs.

If the on-line documentation string of a function or variable disagrees with the manual, one of them must be wrong; that is a bug.

AD.10.2 Understanding Bug Reporting

When you decide that there is a bug, it is important to report it and to report it in a way which is useful. What is most useful is an exact description of what commands you type, starting with the shell command to run Emacs, until the problem happens.

The most important principle in reporting a bug is to report facts. Hypotheses and verbal descriptions are no substitute for the detailed raw data. Reporting the facts is straightforward, but many people strain to posit explanations and report them instead of the facts. If the explanations are based on guesses about how Emacs is implemented, they will be useless; meanwhile, lacking the facts, we will have no real information about the bug.

For example, suppose that you type C-x C-f /glorp/baz.ugh RET, visiting a file which (you know) happens to be rather large, and Emacs displayed `I feel pretty today'. The best way to report the bug is with a sentence like the preceding one, because it gives all the facts.

A bad way would be to assume that the problem is due to the size of the file and say, "I visited a large file, and Emacs displayed `I feel pretty today'." This is what we mean by "guessing explanations." The problem is just as likely to be due to the fact that there is a `z' in the file name. If this is so, then when we got your report, we would try out the problem with some "large file," probably with no `z' in its name, and not see any problem. There is no way in the world that we could guess that we should try visiting a file with a `z' in its name.

Alternatively, the problem might be due to the fact that the file starts with exactly 25 spaces. For this reason, you should make sure that you inform us of the exact contents of any file that is needed to reproduce the bug. What if the problem only occurs when you have typed the C-x C-a command previously? This is why we ask you to give the exact sequence of characters you typed since starting the Emacs session.

You should not even say "visit a file" instead of C-x C-f unless you know that it makes no difference which visiting command is used. Similarly, rather than saying "if I have three characters on the line," say "after I type RET A B C RET C-p," if that is the way you entered the text.

So please don't guess any explanations when you report a bug. If you want to actually debug the problem, and report explanations that are more than guesses, that is useful--but please include the facts as well.

AD.10.3 Checklist for Bug Reports

The best way to send a bug report is to mail it electronically to the Emacs maintainers at [email protected], or to [email protected] if you are pretesting an Emacs beta release. (If you want to suggest a change as an improvement, use the same address.)

If you'd like to read the bug reports, you can find them on the newsgroup `gnu.emacs.bug'; keep in mind, however, that as a spectator you should not criticize anything about what you see there. The purpose of bug reports is to give information to the Emacs maintainers. Spectators are welcome only as long as they do not interfere with this. In particular, some bug reports contain fairly large amounts of data; spectators should not complain about this.

Please do not post bug reports using netnews; mail is more reliable than netnews about reporting your correct address, which we may need in order to ask you for more information. If your data is more than 500,000 bytes, please don't include it directly in the bug report; instead, offer to send it on request, or make it available by ftp and say where.

If you can't send electronic mail, then mail the bug report on paper or machine-readable media to this address:

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

We do not promise to fix the bug; but if the bug is serious, or ugly, or easy to fix, chances are we will want to.

A convenient way to send a bug report for Emacs is to use the command M-x report-emacs-bug. This sets up a mail buffer (see section Z. Sending Mail) and automatically inserts some of the essential information. However, it cannot supply all the necessary information; you should still read and follow the guidelines below, so you can enter the other crucial information by hand before you send the message.

To enable maintainers to investigate a bug, your report should include all these things:

• The version number of Emacs. Without this, we won't know whether there is any point in looking for the bug in the current version of GNU Emacs.

  You can get the version number by typing M-x emacs-version RET. If that command does not work, you probably have something other than GNU Emacs, so you will have to report the bug somewhere else.

• The type of machine you are using, and the operating system name and version number. M-x emacs-version RET provides this information too. Copy its output from the `*Messages*' buffer, so that you get it all and get it accurately.

• The operands given to the configure command when Emacs was installed.

• A complete list of any modifications you have made to the Emacs source. (We may not have time to investigate the bug unless it happens in an unmodified Emacs. But if you've made modifications and you don't tell us, you are sending us on a wild goose chase.)

  Be precise about these changes. A description in English is not enough--send a context diff for them.

  Adding files of your own, or porting to another machine, is a modification of the source.

• Details of any other deviations from the standard procedure for installing GNU Emacs.

• The complete text of any files needed to reproduce the bug.

  If you can tell us a way to cause the problem without visiting any files, please do so. This makes it much easier to debug. If you do need files, make sure you arrange for us to see their exact contents. For example, it can often matter whether there are spaces at the ends of lines, or a newline after the last line in the buffer (nothing ought to care whether the last line is terminated, but try telling the bugs that).

• The precise commands we need to type to reproduce the bug.

  The easy way to record the input to Emacs precisely is to write a dribble file. To start the file, execute the Lisp expression

  (open-dribble-file "~/dribble")

  using M-: or from the `*scratch*' buffer just after starting Emacs. From then on, Emacs copies all your input to the specified dribble file until the Emacs process is killed.

• For possible display bugs, the terminal type (the value of environment variable TERM), the complete termcap entry for the terminal from `/etc/termcap' (since that file is not identical on all machines), and the output that Emacs actually sent to the terminal.

  The way to collect the terminal output is to execute the Lisp expression

  (open-termscript "~/termscript")

  using M-: or from the `*scratch*' buffer just after starting Emacs. From then on, Emacs copies all terminal output to the specified termscript file as well, until the Emacs process is killed. If the problem happens when Emacs starts up, put this expression into your `.emacs' file so that the termscript file will be open when Emacs displays the screen for the first time.

  Be warned: it is often difficult, and sometimes impossible, to fix a terminal-dependent bug without access to a terminal of the type that stimulates the bug.

• If non-ASCII text or internationalization is relevant, the locale that was current when you started Emacs. On GNU/Linux and Unix systems, or if you use a Posix-style shell such as Bash, you can use this shell command to view the relevant values:

  echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_TYPE=$LC_TYPE \ LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG

  Alternatively, use the locale command, if your system has it, to display your locale settings.

  You can use the M-! command to execute these commands from Emacs, and then copy the output from the `*Messages*' buffer into the bug report. Alternatively, M-x getenv RET LC_ALL RET will display the value of LC_ALL in the echo area, and you can copy its output from the `*Messages*' buffer.

• A description of what behavior you observe that you believe is incorrect. For example, "The Emacs process gets a fatal signal," or, "The resulting text is as follows, which I think is wrong."

  Of course, if the bug is that Emacs gets a fatal signal, then one can't miss it. But if the bug is incorrect text, the maintainer might fail to notice what is wrong. Why leave it to chance?

  Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of the source is out of sync, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and the copy here might not. If you said to expect a crash, then when Emacs here fails to crash, we would know that the bug was not happening. If you don't say to expect a crash, then we would not know whether the bug was happening--we would not be able to draw any conclusion from our observations.

• If the bug is that the Emacs Manual or the Emacs Lisp Reference Manual fails to describe the actual behavior of Emacs, or that the text is confusing, copy in the text from the online manual which you think is at fault. If the section is small, just the section name is enough.

• If the manifestation of the bug is an Emacs error message, it is important to report the precise text of the error message, and a backtrace showing how the Lisp program in Emacs arrived at the error.

  To get the error message text accurately, copy it from the `*Messages*' buffer into the bug report. Copy all of it, not just part.

  To make a backtrace for the error, use M-x toggle-debug-on-error before the error happens (that is to say, you must give that command and then make the bug happen). This causes the error to run the Lisp debugger, which shows you a backtrace. Copy the text of the debugger's backtrace into the bug report. See section `The Lisp Debugger' in the Emacs Lisp Reference Manual, for information on debugging Emacs Lisp programs with the Edebug package.

  This use of the debugger is possible only if you know how to make the bug happen again. If you can't make it happen again, at least copy the whole error message.

• Check whether any programs you have loaded into the Lisp world, including your `.emacs' file, set any variables that may affect the functioning of Emacs. Also, see whether the problem happens in a freshly started Emacs without loading your `.emacs' file (start Emacs with the -q switch to prevent loading the init file). If the problem does not occur then, you must report the precise contents of any programs that you must load into the Lisp world in order to cause the problem to occur.

• If the problem does depend on an init file or other Lisp programs that are not part of the standard Emacs system, then you should make sure it is not a bug in those programs by complaining to their maintainers first. After they verify that they are using Emacs in a way that is supposed to work, they should report the bug.

• If you wish to mention something in the GNU Emacs source, show the line of code with a few lines of context. Don't just give a line number.

  The line numbers in the development sources don't match those in your sources. It would take extra work for the maintainers to determine what code is in your version at a given line number, and we could not be certain.

• Additional information from a C debugger such as GDB might enable someone to find a problem on a machine which he does not have available. If you don't know how to use GDB, please read the GDB manual--it is not very long, and using GDB is easy. You can find the GDB distribution, including the GDB manual in online form, in most of the same places you can find the Emacs distribution. To run Emacs under GDB, you should switch to the `src' subdirectory in which Emacs was compiled, then do `gdb emacs'. It is important for the directory `src' to be current so that GDB will read the `.gdbinit' file in this directory.

  However, you need to think when you collect the additional information if you want it to show what causes the bug.

  For example, many people send just a backtrace, but that is not very useful by itself. A simple backtrace with arguments often conveys little about what is happening inside GNU Emacs, because most of the arguments listed in the backtrace are pointers to Lisp objects. The numeric values of these pointers have no significance whatever; all that matters is the contents of the objects they point to (and most of the contents are themselves pointers).

  To provide useful information, you need to show the values of Lisp objects in Lisp notation. Do this for each variable which is a Lisp object, in several stack frames near the bottom of the stack. Look at the source to see which variables are Lisp objects, because the debugger thinks of them as integers.

  To show a variable's value in Lisp syntax, first print its value, then use the user-defined GDB command pr to print the Lisp object in Lisp syntax. (If you must use another debugger, call the function debug_print with the object as an argument.) The pr command is defined by the file `.gdbinit', and it works only if you are debugging a running process (not with a core dump).

  To make Lisp errors stop Emacs and return to GDB, put a breakpoint at Fsignal.

  For a short listing of Lisp functions running, type the GDB command xbacktrace.

  The file `.gdbinit' defines several other commands that are useful for examining the data types and contents of Lisp objects. Their names begin with `x'. These commands work at a lower level than pr, and are less convenient, but they may work even when pr does not, such as when debugging a core dump or when Emacs has had a fatal signal.

  More detailed advice and other useful techniques for debugging Emacs are available in the file `etc/DEBUG' in the Emacs distribution. That file also includes instructions for investigating problems whereby Emacs stops responding (many people assume that Emacs is "hung," whereas in fact it might be in an infinite loop).

  To find the file `etc/DEBUG' in your Emacs installation, use the directory name stored in the variable data-directory.

Here are some things that are not necessary in a bug report:

• A description of the envelope of the bug--this is not necessary for a reproducible bug.

  Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.

  This is often time-consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. You might as well save time by not searching for additional examples. It is better to send the bug report right away, go back to editing, and find another bug to report.

  Of course, if you can find a simpler example to report instead of the original one, that is a convenience. Errors in the output will be easier to spot, running under the debugger will take less time, etc.

  However, simplification is not vital; if you can't do this or don't have time to try, please report the bug with your original test case.

• A core dump file.

  Debugging the core dump might be useful, but it can only be done on your machine, with your Emacs executable. Therefore, sending the core dump file to the Emacs maintainers won't be useful. Above all, don't include the core file in an email bug report! Such a large message can be extremely inconvenient.

• A system-call trace of Emacs execution.

  System-call traces are very useful for certain special kinds of debugging, but in most cases they give little useful information. It is therefore strange that many people seem to think that the way to report information about a crash is to send a system-call trace. Perhaps this is a habit formed from experience debugging programs that don't have source code or debugging symbols.

  In most programs, a backtrace is normally far, far more informative than a system-call trace. Even in Emacs, a simple backtrace is generally more informative, though to give full information you should supplement the backtrace by displaying variable values and printing them as Lisp objects with pr (see above).

• A patch for the bug.

  A patch for the bug is useful if it is a good one. But don't omit the other information that a bug report needs, such as the test case, on the assumption that a patch is sufficient. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all. And if we can't understand what bug you are trying to fix, or why your patch should be an improvement, we mustn't install it.

  See section AD.10.4 Sending Patches for GNU Emacs, for guidelines on how to make it easy for us to understand and install your patches.

• A guess about what the bug is or what it depends on.

  Such guesses are usually wrong. Even experts can't guess right about such things without first using the debugger to find the facts.

AD.10.4 Sending Patches for GNU Emacs

If you would like to write bug fixes or improvements for GNU Emacs, that is very helpful. When you send your changes, please follow these guidelines to make it easy for the maintainers to use them. If you don't follow these guidelines, your information might still be useful, but using it will take extra work. Maintaining GNU Emacs is a lot of work in the best of circumstances, and we can't keep up unless you do your best to help.

• Send an explanation with your changes of what problem they fix or what improvement they bring about. For a bug fix, just include a copy of the bug report, and explain why the change fixes the bug.

  (Referring to a bug report is not as good as including it, because then we will have to look it up, and we have probably already deleted it if we've already fixed the bug.)

• Always include a proper bug report for the problem you think you have fixed. We need to convince ourselves that the change is right before installing it. Even if it is correct, we might have trouble understanding it if we don't have a way to reproduce the problem.

• Include all the comments that are appropriate to help people reading the source in the future understand why this change was needed.

• Don't mix together changes made for different reasons. Send them individually.

  If you make two changes for separate reasons, then we might not want to install them both. We might want to install just one. If you send them all jumbled together in a single set of diffs, we have to do extra work to disentangle them--to figure out which parts of the change serve which purpose. If we don't have time for this, we might have to ignore your changes entirely.

  If you send each change as soon as you have written it, with its own explanation, then two changes never get tangled up, and we can consider each one properly without any extra work to disentangle them.

• Send each change as soon as that change is finished. Sometimes people think they are helping us by accumulating many changes to send them all together. As explained above, this is absolutely the worst thing you could do.

  Since you should send each change separately, you might as well send it right away. That gives us the option of installing it immediately if it is important.

• Use `diff -c' to make your diffs. Diffs without context are hard to install reliably. More than that, they are hard to study; we must always study a patch to decide whether we want to install it. Unidiff format is better than contextless diffs, but not as easy to read as `-c' format.

  If you have GNU diff, use `diff -c -F'^[_a-zA-Z0-9$]+ *('' when making diffs of C code. This shows the name of the function that each change occurs in.

• Avoid any ambiguity as to which is the old version and which is the new. Please make the old version the first argument to diff, and the new version the second argument. And please give one version or the other a name that indicates whether it is the old version or your new changed one.

• Write the change log entries for your changes. This is both to save us the extra work of writing them, and to help explain your changes so we can understand them.

  The purpose of the change log is to show people where to find what was changed. So you need to be specific about what functions you changed; in large functions, it's often helpful to indicate where within the function the change was.

  On the other hand, once you have shown people where to find the change, you need not explain its purpose in the change log. Thus, if you add a new function, all you need to say about it is that it is new. If you feel that the purpose needs explaining, it probably does--but put the explanation in comments in the code. It will be more useful there.

  Please read the `ChangeLog' files in the `src' and `lisp' directories to see what sorts of information to put in, and to learn the style that we use. If you would like your name to appear in the header line, showing who made the change, send us the header line. See section W.1 Change Logs.

• When you write the fix, keep in mind that we can't install a change that would break other systems. Please think about what effect your change will have if compiled on another type of system.

  Sometimes people send fixes that might be an improvement in general--but it is hard to be sure of this. It's hard to install such changes because we have to study them very carefully. Of course, a good explanation of the reasoning by which you concluded the change was correct can help convince us.

  The safest changes are changes to the configuration files for a particular machine. These are safe because they can't create new bugs on other machines.

  Please help us keep up with the workload by designing the patch in a form that is clearly safe to install.

AD.11 Contributing to Emacs Development

If you would like to help pretest Emacs releases to assure they work well, or if you would like to work on improving Emacs, please contact the maintainers at [email protected]. A pretester should be prepared to investigate bugs as well as report them. If you'd like to work on improving Emacs, please ask for suggested projects or suggest your own ideas.

If you have already written an improvement, please tell us about it. If you have not yet started work, it is useful to contact [email protected] before you start; it might be possible to suggest ways to make your extension fit in better with the rest of Emacs.

AD.12 How To Get Help with GNU Emacs

If you need help installing, using or changing GNU Emacs, there are two ways to find it:

• Send a message to the mailing list [email protected], or post your request on newsgroup gnu.emacs.help. (This mailing list and newsgroup interconnect, so it does not matter which one you use.)

• Look in the service directory for someone who might help you for a fee. The service directory is found in the file named `etc/SERVICE' in the Emacs distribution.