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# Abbrevs

A defined abbrev is a word which expands, if you insert it, into some different text. Abbrevs are defined by the user to expand in specific ways. For example, you might define ``foo'` as an abbrev expanding to ``find outer otter'`. Then you would be able to insert ``find outer otter '` into the buffer by typing `f o o `SPC``.

A second kind of abbreviation facility is called dynamic abbrev expansion. You use dynamic abbrev expansion with an explicit command to expand the letters in the buffer before point by looking for other words in the buffer that start with those letters. See section Dynamic Abbrev Expansion.

- Abbrev Concepts: Fundamentals of defined abbrevs.
- Defining Abbrevs: Defining an abbrev, so it will expand when typed.
- Expanding Abbrevs: Controlling expansion: prefixes, canceling expansion.
- Editing Abbrevs: Viewing or editing the entire list of defined abbrevs.
- Saving Abbrevs: Saving the entire list of abbrevs for another session.
- Dynamic Abbrevs: Abbreviations for words already in the buffer.
- Dabbrev Customization: What is a word, for dynamic abbrevs. Case handling.

## Abbrev Concepts

An abbrev is a word which has been defined to expand into a specified expansion. When you insert a word-separator character following the abbrev, that expands the abbrev--replacing the abbrev with its expansion. For example, if ``foo'` is defined as an abbrev expanding to ``find outer otter'`, then you can insert ``find outer otter.'` into the buffer by typing `f o o .`.

Abbrevs expand only when Abbrev mode (a minor mode) is enabled. Disabling Abbrev mode does not cause abbrev definitions to be forgotten, but they do not expand until Abbrev mode is enabled again. The command `M-x abbrev-mode` toggles Abbrev mode; with a numeric argument, it turns Abbrev mode on if the argument is positive, off otherwise. See section Minor Modes. `abbrev-mode` is also a variable; Abbrev mode is on when the variable is non-`nil`. The variable `abbrev-mode` automatically becomes local to the current buffer when it is set.

Abbrev definitions can be mode-specific---active only in one major mode. Abbrevs can also have global definitions that are active in all major modes. The same abbrev can have a global definition and various mode-specific definitions for different major modes. A mode specific definition for the current major mode overrides a global definition.

Abbrevs can be defined interactively during the editing session. Lists of abbrev definitions can also be saved in files and reloaded in later sessions. Some users keep extensive lists of abbrevs that they load in every session.

## Defining Abbrevs

`C-x a g`
  Define an abbrev, using one or more words before point as its expansion (`add-global-abbrev`).
`C-x a l`
  Similar, but define an abbrev specific to the current major mode (`add-mode-abbrev`).
`C-x a i g`
  Define a word in the buffer as an abbrev (`inverse-add-global-abbrev`).
`C-x a i l`
  Define a word in the buffer as a mode-specific abbrev (`inverse-add-mode-abbrev`).
`M-x kill-all-abbrevs`
  This command discards all abbrev definitions currently in effect, leaving a blank slate.

The usual way to define an abbrev is to enter the text you want the abbrev to expand to, position point after it, and type `C-x a g` (`add-global-abbrev`). This reads the abbrev itself using the minibuffer, and then defines it as an abbrev for one or more words before point. Use a numeric argument to say how many words before point should be taken as the expansion. For example, to define the abbrev ``foo'` as mentioned above, insert the text ``find outer otter'` and then type `C-u 3 C-x a g f o o `RET``.

An argument of zero to `C-x a g` means to use the contents of the region as the expansion of the abbrev being defined.

The command `C-x a l` (`add-mode-abbrev`) is similar, but defines a mode-specific abbrev. Mode specific abbrevs are active only in a particular major mode. `C-x a l` defines an abbrev for the major mode in effect at the time `C-x a l` is typed. The arguments work the same as for `C-x a g`.

If the text already in the buffer is the abbrev, rather than its expansion, use command `C-x a i g` (`inverse-add-global-abbrev`) instead of `C-x a g`, or use `C-x a i l` (`inverse-add-mode-abbrev`) instead of `C-x a l`. These commands are called "inverse" because they invert the meaning of the two text strings they use (one from the buffer and one read with the minibuffer).

To change the definition of an abbrev, just define a new definition. When the abbrev has a prior definition, the abbrev definition commands ask for confirmation for replacing it.

To remove an abbrev definition, give a negative argument to the abbrev definition command: `C-u - C-x a g` or `C-u - C-x a l`. The former removes a global definition, while the latter removes a mode-specific definition.

`M-x kill-all-abbrevs` removes all the abbrev definitions there are, both global and local.

## Controlling Abbrev Expansion

An abbrev expands whenever it is present in the buffer just before point and you type a self-inserting whitespace or punctuation character (`SPC`, comma, etc.). More precisely, any character that is not a word constituent expands an abbrev, and any word constituent character can be part of an abbrev. The most common way to use an abbrev is to insert it and then insert a punctuation character to expand it.

Abbrev expansion preserves case; thus, ``foo'` expands into ``find outer otter'`; ``Foo'` into ``Find outer otter'`, and ``FOO'` into ``FIND OUTER OTTER'` or ``Find Outer Otter'` according to the variable `abbrev-all-caps` (a non-`nil` value chooses the first of the two expansions).

These commands are used to control abbrev expansion:

`M-'`
  Separate a prefix from a following abbrev to be expanded (`abbrev-prefix-mark`).
`C-x a e`
  Expand the abbrev before point (`expand-abbrev`). This is effective even when Abbrev mode is not enabled.
`M-x expand-region-abbrevs`
  Expand some or all abbrevs found in the region.

You may wish to expand an abbrev with a prefix attached; for example, if ``cnst'` expands into ``construction'`, you might want to use it to enter ``reconstruction'`. It does not work to type `recnst`, because that is not necessarily a defined abbrev. What you can do is use the command `M-'` (`abbrev-prefix-mark`) in between the prefix ``re'` and the abbrev ``cnst'`. First, insert ``re'`. Then type `M-'`; this inserts a hyphen in the buffer to indicate that it has done its work. Then insert the abbrev ``cnst'`; the buffer now contains ``re-cnst'`. Now insert a non-word character to expand the abbrev ``cnst'` into ``construction'`. This expansion step also deletes the hyphen that indicated `M-'` had been used. The result is the desired ``reconstruction'`.

If you actually want the text of the abbrev in the buffer, rather than its expansion, you can accomplish this by inserting the following punctuation with `C-q`. Thus, `foo C-q ,` leaves ``foo,'` in the buffer.

If you expand an abbrev by mistake, you can undo the expansion and bring back the abbrev itself by typing `C-_` to undo (see section Undoing Changes). This also undoes the insertion of the non-word character that expanded the abbrev. If the result you want is the terminating non-word character plus the unexpanded abbrev, you must reinsert the terminating character, quoting it with `C-q`.

`M-x expand-region-abbrevs` searches through the region for defined abbrevs, and for each one found offers to replace it with its expansion. This command is useful if you have typed in text using abbrevs but forgot to turn on Abbrev mode first. It may also be useful together with a special set of abbrev definitions for making several global replacements at once. This command is effective even if Abbrev mode is not enabled.

Expanding an abbrev runs the hook `pre-abbrev-expand-hook` (see section Hooks).

## Examining and Editing Abbrevs

`M-x list-abbrevs`
  Display a list of all abbrev definitions.
`M-x edit-abbrevs`
  Edit a list of abbrevs; you can add, alter or remove definitions.

The output from `M-x list-abbrevs` looks like this:

    (lisp-mode-abbrev-table)
    "dk"	       0    "define-key"
    (global-abbrev-table)
    "dfn"	       0    "definition"

(Some blank lines of no semantic significance, and some other abbrev tables, have been omitted.)

A line containing a name in parentheses is the header for abbrevs in a particular abbrev table; `global-abbrev-table` contains all the global abbrevs, and the other abbrev tables that are named after major modes contain the mode-specific abbrevs.

Within each abbrev table, each nonblank line defines one abbrev. The word at the beginning of the line is the abbrev. The number that follows is the number of times the abbrev has been expanded. Emacs keeps track of this to help you see which abbrevs you actually use, so that you can eliminate those that you don't use often. The string at the end of the line is the expansion.

`M-x edit-abbrevs` allows you to add, change or kill abbrev definitions by editing a list of them in an Emacs buffer. The list has the same format described above. The buffer of abbrevs is called ``*Abbrevs*'`, and is in Edit-Abbrevs mode. Type `C-c C-c` in this buffer to install the abbrev definitions as specified in the buffer--and delete any abbrev definitions not listed.

The command `edit-abbrevs` is actually the same as `list-abbrevs` except that it selects the buffer ``*Abbrevs*'` whereas `list-abbrevs` merely displays it in another window.

## Saving Abbrevs

These commands allow you to keep abbrev definitions between editing sessions.

`M-x write-abbrev-file `RET` file `RET``
  Write a file file describing all defined abbrevs.
`M-x read-abbrev-file `RET` file `RET``
  Read the file file and define abbrevs as specified therein.
`M-x quietly-read-abbrev-file `RET` file `RET``
  Similar but do not display a message about what is going on.
`M-x define-abbrevs`
  Define abbrevs from definitions in current buffer.
`M-x insert-abbrevs`
  Insert all abbrevs and their expansions into current buffer.

`M-x write-abbrev-file` reads a file name using the minibuffer and then writes a description of all current abbrev definitions into that file. This is used to save abbrev definitions for use in a later session. The text stored in the file is a series of Lisp expressions that, when executed, define the same abbrevs that you currently have.

`M-x read-abbrev-file` reads a file name using the minibuffer and then reads the file, defining abbrevs according to the contents of the file. `M-x quietly-read-abbrev-file` is the same except that it does not display a message in the echo area saying that it is doing its work; it is actually useful primarily in the ``.emacs'` file. If an empty argument is given to either of these functions, they use the file name specified in the variable `abbrev-file-name`, which is by default `"~/.abbrev_defs"`.

Emacs will offer to save abbrevs automatically if you have changed any of them, whenever it offers to save all files (for `C-x s` or `C-x C-c`). This feature can be inhibited by setting the variable `save-abbrevs` to `nil`.

The commands `M-x insert-abbrevs` and `M-x define-abbrevs` are similar to the previous commands but work on text in an Emacs buffer. `M-x insert-abbrevs` inserts text into the current buffer before point, describing all current abbrev definitions; `M-x define-abbrevs` parses the entire current buffer and defines abbrevs accordingly.

## Dynamic Abbrev Expansion

The abbrev facility described above operates automatically as you insert text, but all abbrevs must be defined explicitly. By contrast, dynamic abbrevs allow the meanings of abbrevs to be determined automatically from the contents of the buffer, but dynamic abbrev expansion happens only when you request it explicitly.

`M-/`
  Expand the word in the buffer before point as a dynamic abbrev, by searching in the buffer for words starting with that abbreviation (`dabbrev-expand`).
`C-M-/`
  Complete the word before point as a dynamic abbrev (`dabbrev-completion`).

For example, if the buffer contains ``does this follow '` and you type `f o M-/`, the effect is to insert ``follow'` because that is the last word in the buffer that starts with ``fo'`. A numeric argument to `M-/` says to take the second, third, etc. distinct expansion found looking backward from point. Repeating `M-/` searches for an alternative expansion by looking farther back. After considering the entire buffer before point, it searches the text after point. The variable `dabbrev-limit`, if non-`nil`, specifies how far in the buffer to search for an expansion.

After searching all of the current buffer, `M-/` normally searches other buffers, unless you have set `dabbrev-check-all-buffers` to `nil`.

A negative argument to `M-/`, as in `C-u - M-/`, says to search first for expansions after point, and second for expansions before point. If you repeat the `M-/` to look for another expansion, do not specify an argument. This tries all the expansions after point and then the expansions before point.

After you have expanded a dynamic abbrev, you can copy additional words that follow the expansion in its original context. Simply type ``SPC` M-/` for each word you want to copy. The spacing and punctuation between words is copied along with the words.

The command `C-M-/` (`dabbrev-completion`) performs completion of a dynamic abbreviation. Instead of trying the possible expansions one by one, it finds all of them, then inserts the text that they have in common. If they have nothing in common, `C-M-/` displays a list of completions, from which you can select a choice in the usual manner. See section Completion.

Dynamic abbrev expansion is completely independent of Abbrev mode; the expansion of a word with `M-/` is completely independent of whether it has a definition as an ordinary abbrev.

## Customizing Dynamic Abbreviation

Normally, dynamic abbrev expansion ignores case when searching for expansions. That is, the expansion need not agree in case with the word you are expanding. If you set `dabbrev-case-fold-search` to `nil`, then the word and the expansion must match in case.

The value of `dabbrev-case-fold-search` may be any expression. Dynamic abbrev expansion evaluates that expression, and ignores case while searching if its value is not `nil`. The default value of `dabbrev-case-fold-search` is `case-fold-search`, so normally the value of `case-fold-search` controls the decision. The reason why dynamic abbrev expansion normally ignores case when searching for expansions is that normally the value of `case-fold-search` is `t`.

Normally, dynamic abbrev expansion preserves the case pattern of the word you are expanding, by converting the expansion to that case pattern. If you set `dabbrev-case-replace` to `nil`, the expansion is copied without conversion.

The variables `dabbrev-case-fold-search` and `dabbrev-case-replace` are handled in a special way. Their values are actually Lisp expressions which are evaluated each time a decision needs to be made. If the expression's value is non-`nil`, then case is ignored in searching, or converted on replacement, respectively. If the expression's value is `nil`, case is not ignored or not converted. The default values let the variables `case-fold-search` (see section Searching and Case) and `case-replace` (see section Replace Commands and Case) control what to do.

The variable `dabbrev-abbrev-char-regexp`, if non-`nil`, controls which characters are considered part of a word, for dynamic expansion purposes. The regular expression must match just one character, never two or more. The same regular expression also determines which characters are part of an expansion. The value `nil` has a special meaning: abbreviations are made of word characters, but expansions are made of word and symbol characters.

In shell scripts and makefiles, a variable name is sometimes prefixed with ``$'` and sometimes not. Major modes for this kind of text can customize dynamic abbreviation to handle optional prefixes by setting the variable `dabbrev-abbrev-skip-leading-regexp`. Its value should be a regular expression that matches the optional prefix that dynamic abbreviation should ignore.

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