36. Abbrevs and Abbrev Expansion

An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.

The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.

An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function to do the expansion (see section 36.3 Defining Abbrevs); its property list cell contains the use count, the number of times the abbreviation has been expanded. Because these symbols are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See section 8.3 Creating and Interning Symbols.

For the user-level commands for abbrevs, see section `Abbrev Mode' in The GNU Emacs Manual.

36.1 Setting Up Abbrev Mode

Abbrev mode is a minor mode controlled by the value of the variable abbrev-mode.

Variable: abbrev-mode

A non-nil value of this variable turns on the automatic expansion of abbrevs when their abbreviations are inserted into a buffer. If the value is nil, abbrevs may be defined, but they are not expanded automatically.

This variable automatically becomes buffer-local when set in any fashion.

Variable: default-abbrev-mode

This is the value of abbrev-mode for buffers that do not override it. This is the same as (default-value 'abbrev-mode).

36.2 Abbrev Tables

This section describes how to create and manipulate abbrev tables.

Function: make-abbrev-table

This function creates and returns a new, empty abbrev table--an obarray containing no symbols. It is a vector filled with zeros.

Function: clear-abbrev-table table

This function undefines all the abbrevs in abbrev table table, leaving it empty. It always returns nil.

Function: define-abbrev-table tabname definitions

This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to definitions, a list of elements of the form (abbrevname expansion hook usecount). The return value is always nil.

Variable: abbrev-table-name-list

This is a list of symbols whose values are abbrev tables. define-abbrev-table adds the new abbrev table name to this list.

Function: insert-abbrev-table-description name &optional human

This function inserts before point a description of the abbrev table named name. The argument name is a symbol whose value is an abbrev table. The return value is always nil.

If human is non-nil, the description is human-oriented. Otherwise the description is a Lisp expression--a call to define-abbrev-table that would define name exactly as it is currently defined.

36.3 Defining Abbrevs

These functions define an abbrev in a specified abbrev table. define-abbrev is the low-level basic function, while add-abbrev is used by commands that ask for information from the user.

Function: add-abbrev table type arg

This function adds an abbreviation to abbrev table table based on information from the user. The argument type is a string describing in English the kind of abbrev this will be (typically, "global" or "mode-specific"); this is used in prompting the user. The argument arg is the number of words in the expansion.

The return value is the symbol that internally represents the new abbrev, or nil if the user declines to confirm redefining an existing abbrev.

Function: define-abbrev table name expansion &optional hook count

This function defines an abbrev named name, in table, to expand to expansion and call hook. The value of count, if specified, initializes the abbrev's usage-count. If count is not specified or nil, the use count is initialized to zero. The return value is a symbol that represents the abbrev inside Emacs; its name is name.

The argument name should be a string. The argument expansion is normally the desired expansion (a string), or nil to undefine the abbrev. If it is anything but a string or nil, then the abbreviation "expands" solely by running hook.

The argument hook is a function or nil. If hook is non-nil, then it is called with no arguments after the abbrev is replaced with expansion; point is located at the end of expansion when hook is called.

If hook is a non-nil symbol whose no-self-insert property is non-nil, hook can explicitly control whether to insert the self-inserting input character that triggered the expansion. If hook returns non-nil in this case, that inhibits insertion of the character. By contrast, if hook returns nil, expand-abbrev also returns nil, as if expansion had not really occurred.

User Option: only-global-abbrevs

If this variable is non-nil, it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the behavior of the functions in this section; it is examined by their callers.

36.4 Saving Abbrevs in Files

A file of saved abbrev definitions is actually a file of Lisp code. The abbrevs are saved in the form of a Lisp program to define the same abbrev tables with the same contents. Therefore, you can load the file with load (see section 15.1 How Programs Do Loading). However, the function quietly-read-abbrev-file is provided as a more convenient interface.

User-level facilities such as save-some-buffers can save abbrevs in a file automatically, under the control of variables described here.

User Option: abbrev-file-name

This is the default file name for reading and saving abbrevs.

Function: quietly-read-abbrev-file &optional filename

This function reads abbrev definitions from a file named filename, previously written with write-abbrev-file. If filename is omitted or nil, the file specified in abbrev-file-name is used. save-abbrevs is set to t so that changes will be saved.

This function does not display any messages. It returns nil.

User Option: save-abbrevs

A non-nil value for save-abbrev means that Emacs should save abbrevs when files are saved. abbrev-file-name specifies the file to save the abbrevs in.

Variable: abbrevs-changed

This variable is set non-nil by defining or altering any abbrevs. This serves as a flag for various Emacs commands to offer to save your abbrevs.

Command: write-abbrev-file &optional filename

Save all abbrev definitions, in all abbrev tables, in the file filename, in the form of a Lisp program that when loaded will define the same abbrevs. If filename is nil or omitted, abbrev-file-name is used. This function returns nil.

36.5 Looking Up and Expanding Abbreviations

Abbrevs are usually expanded by certain interactive commands, including self-insert-command. This section describes the subroutines used in writing such commands, as well as the variables they use for communication.

Function: abbrev-symbol abbrev &optional table

This function returns the symbol representing the abbrev named abbrev. The value returned is nil if that abbrev is not defined. The optional second argument table is the abbrev table to look it up in. If table is nil, this function tries first the current buffer's local abbrev table, and second the global abbrev table.

Function: abbrev-expansion abbrev &optional table

This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). The optional argument table specifies the abbrev table to use, as in abbrev-symbol.

Command: expand-abbrev

This command expands the abbrev before point, if any. If point does not follow an abbrev, this command does nothing. The command returns the abbrev symbol if it did expansion, nil otherwise.

If the abbrev symbol has a hook function which is a symbol whose no-self-insert property is non-nil, and if the hook function returns nil as its value, then expand-abbrev returns nil even though expansion did occur.

Command: abbrev-prefix-mark &optional arg

Mark current point as the beginning of an abbrev. The next call to expand-abbrev will use the text from here to point (where it is then) as the abbrev to expand, rather than using the previous word as usual.

User Option: abbrev-all-caps

When this is set non-nil, an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion.

Variable: abbrev-start-location

This is the buffer position for expand-abbrev to use as the start of the next abbrev to be expanded. (nil means use the word before point instead.) abbrev-start-location is set to nil each time expand-abbrev is called. This variable is also set by abbrev-prefix-mark.

Variable: abbrev-start-location-buffer

The value of this variable is the buffer for which abbrev-start-location has been set. Trying to expand an abbrev in any other buffer clears abbrev-start-location. This variable is set by abbrev-prefix-mark.

Variable: last-abbrev

This is the abbrev-symbol of the most recent abbrev expanded. This information is left by expand-abbrev for the sake of the unexpand-abbrev command (see section `Expanding Abbrevs' in The GNU Emacs Manual).

Variable: last-abbrev-location

This is the location of the most recent abbrev expanded. This contains information left by expand-abbrev for the sake of the unexpand-abbrev command.

Variable: last-abbrev-text

This is the exact expansion text of the most recent abbrev expanded, after case conversion (if any). Its value is nil if the abbrev has already been unexpanded. This contains information left by expand-abbrev for the sake of the unexpand-abbrev command.

Variable: pre-abbrev-expand-hook

This is a normal hook whose functions are executed, in sequence, just before any expansion of an abbrev. See section 23.6 Hooks. Since it is a normal hook, the hook functions receive no arguments. However, they can find the abbrev to be expanded by looking in the buffer before point. Running the hook is the first thing that expand-abbrev does, and so a hook function can be used to change the current abbrev table before abbrev lookup happens.

The following sample code shows a simple use of pre-abbrev-expand-hook. If the user terminates an abbrev with a punctuation character, the hook function asks for confirmation. Thus, this hook allows the user to decide whether to expand the abbrev, and aborts expansion if it is not confirmed.

(add-hook 'pre-abbrev-expand-hook 'query-if-not-space)

;; This is the function invoked by pre-abbrev-expand-hook.

;; If the user terminated the abbrev with a space, the function does
;; nothing (that is, it returns so that the abbrev can expand).  If the
;; user entered some other character, this function asks whether
;; expansion should continue.

;; If the user answers the prompt with y, the function returns
;; nil (because of the not function), but that is
;; acceptable; the return value has no effect on expansion.

(defun query-if-not-space ()
  (if (/= ?\  (preceding-char))
      (if (not (y-or-n-p "Do you want to expand this abbrev? "))
          (error "Not expanding this abbrev"))))

36.6 Standard Abbrev Tables

Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.

Variable: global-abbrev-table

This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.

Variable: local-abbrev-table

The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer.

Variable: fundamental-mode-abbrev-table

This is the local abbrev table used in Fundamental mode; in other words, it is the local abbrev table in all buffers in Fundamental mode.

Variable: text-mode-abbrev-table

This is the local abbrev table used in Text mode.

Variable: lisp-mode-abbrev-table

This is the local abbrev table used in Lisp mode and Emacs Lisp mode.