Under certain circumstances you will find yourself typing similar things over and over again. This is especially true of form letters and programming language constructs. Project-specific header comments, flow-control constructs or magic numbers are essentially the same every time. Emacs has various features for doing tedious and repetitive typing chores for you in addition to the Abbrev features (see Abbrevs in The GNU Emacs Manual).
One solution is using skeletons, flexible rules that say what to insert, and how to do it. Various programming language modes offer some ready-to-use skeletons, and you can adapt them to suit your needs or taste, or define new ones.
Another feature is automatic insertion of what you want into empty files, depending on the file-name or the mode as appropriate. You can have a file or a skeleton inserted, or you can call a function. Then there is the possibility to have Un*x interpreter scripts automatically take on a magic number and be executable as soon as they are saved. Or you can have a copyright notice’s year updated, if necessary, every time you save a file. Similarly for time stamps in the file.
URLs can be inserted based on a word at point. Flexible templates can be defined for inserting and navigating between text more generally. A sort of meta-expansion facility can be used to try a set of alternative completions and expansions of text at point.
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(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”
When you want Emacs to insert a form letter or a typical construct of the programming language you are using, skeletons are a means of accomplishing this. Normally skeletons each have a command of their own, that, when called, will insert the skeleton. These commands can be issued in the usual ways (see Commands in The GNU Emacs Manual). Modes that offer various skeletons will often bind these to key-sequences on the C-c prefix, as well as having an Insert menu and maybe even predefined abbrevs for them (see Skeletons as Abbrev Expansions).
The simplest kind of skeleton will simply insert some text indented according to the major mode and leave the cursor at a likely place in the middle. Interactive skeletons may prompt you for a string that will be part of the inserted text.
Skeletons may ask for input several times. They even have a looping mechanism in which you will be asked for input as long as you are willing to furnish it. An example would be multiple “else if” conditions. You can recognize this situation by a prompt ending in RET, C-g or C-h. This means that entering an empty string will simply assume that you are finished. Typing quit on the other hand terminates the loop but also the rest of the skeleton, e.g., an “else” clause is skipped. Only a syntactically necessary termination still gets inserted.
Often you will find yourself with some code that for whatever reason suddenly becomes conditional. Or you have written a bit of text and want to put it in the middle of a form letter. Skeletons provide a means for accomplishing this, and can even, in the case of programming languages, reindent the wrapped code for you.
Skeleton commands take an optional numeric prefix argument (see Arguments in The GNU Emacs Manual). This is interpreted in two different ways depending on whether the prefix is positive, i.e., forwards oriented, or negative, i.e., backwards oriented.
A positive prefix means to wrap the skeleton around that many following words. This is accomplished by putting the words there where the point is normally left after that skeleton is inserted (see Using Skeletons). The point (see Point in The GNU Emacs Manual) is left at the next interesting spot in the skeleton instead.
A negative prefix means to do something similar with that many previously marked interregions (see Mark in The GNU Emacs Manual). In the simplest case, if you type M-- just before issuing the skeleton command, that will wrap the skeleton around the current region, just like a positive argument would have wrapped it around a number of words.
Smaller negative arguments will wrap that many interregions into successive interesting spots within the skeleton, again leaving the point at the next one. We speak about interregions rather than regions here, because we treat them in the order they appear in the buffer, which coincides with successive regions only if they were marked in order.
That is, if you marked in alphabetical order the points A B C [] (where [] represents the point) and call a skeleton command with M-- 3, you will wrap the text from A to B into the first interesting spot of the skeleton, the text from B to C into the next one, the text from C to the point into the third one, and leave the point in the fourth one. If there are less marks in the buffer, or if the skeleton defines less interesting points, the surplus is ignored.
If, on the other hand, you marked in alphabetical order the points [] A C B, and call a skeleton command with M-- 3, you will wrap the text from point to A, then the text from A to C and finally the text from C to B. This is done because the regions overlap and Emacs would be helplessly lost if it tried to follow the order in which you marked these points.
Rather than use a key binding for every skeleton command, you can also define an abbreviation (see Defining Abbrevs in The GNU Emacs Manual) that will expand (see Expanding Abbrevs in The GNU Emacs Manual) into the skeleton.
Say you want ‘ifst’ to be an abbreviation for the C language if
statement. You will tell Emacs that ‘ifst’ expands to the empty string
and then calls the skeleton command. In Emacs Lisp you can say something like
(define-abbrev c-mode-abbrev-table "ifst" "" 'c-if). Or you can edit
the output from M-x list-abbrevs to make it look like this:
(c-mode-abbrev-table) "ifst" 0 "" c-if
(Some blank lines of no semantic significance, and other abbrev tables, have been omitted.)
Various characters usually appear in pairs. When, for example, you insert an open parenthesis, no matter whether you are programming or writing prose, you will surely enter a closing one later. By entering both at the same time and leaving the cursor in between, Emacs can guarantee you that such parentheses are always balanced. And if you have a non-qwerty keyboard, where typing some of the stranger programming language symbols makes you bend your fingers backwards, this can be quite relieving too.
This is done by binding the first key (see Rebinding in The GNU Emacs Manual) of
the pair to skeleton-pair-insert-maybe instead of
self-insert-command. The “maybe” comes from the fact that
this at-first surprising behavior is initially turned off. To enable
it, you must set skeleton-pair to some non-nil value.
And even then, a positive argument (see Arguments in The GNU Emacs Manual) will
make this key behave like a self-inserting key
(see Inserting Text in The GNU Emacs Manual).
While this breaks with the stated intention of always balancing pairs, it
turns out that one often doesn’t want pairing to occur, when the following
character is part of a word. If you want pairing to occur even then, set
skeleton-pair-on-word to some non-nil value.
Pairing is possible for all visible characters. By default the
parenthesis ‘(’, the square bracket ‘[’, the brace
‘{’ and the pointed bracket ‘<’ all
pair with the symmetrical character, and the grave accent ‘`’
pairs with the apostrophe ‘'’. All other characters pair
themselves. This behavior can be modified by the variable
skeleton-pair-alist. This is in fact an alist of skeletons
(see Skeleton Language), with the first part of each sublist
matching the typed character. This is the position of the interactor,
but since pairs don’t need the str element, this is ignored.
Some modes have bound the command skeleton-pair-insert-maybe
to relevant keys. These modes also configure the pairs as
appropriate. For example, when typing TeX input, you’d expect the
grave accent (‘`’) to pair with the apostrophe (‘'’), while in Shell
script mode it must pair to itself. They can also inhibit pairing in
certain contexts. For example an escaped character stands for itself.
M-x auto-insert will put some predefined text at the beginning of
the buffer. The main application for this function, as its name suggests,
is to have it be called automatically every time an empty, and only an
empty file is visited. This is accomplished by putting
(auto-insert-mode t) into your init file
(see Init File in The GNU Emacs Manual).
What gets inserted, if anything, is determined by the variable
auto-insert-alist. The CAR of each element of this list
is either a mode name, making the element applicable when a buffer is
in that mode, or a string, which is a regexp matched against a
buffer’s file name (the latter allows to distinguish between different
kinds of files that have the same mode in Emacs). The CAR of an
element may also be a cons cell, consisting of mode name or regexp, as
above, and an additional descriptive string.
When a matching element is found, the CDR says what to do. It may
be a string, which is a file name, whose contents are to be inserted, if
that file is found in the directory auto-insert-directory or under a
absolute file name. Or it can be a skeleton (see Skeleton Language) to
be inserted.
It can also be a function, which allows doing various things. The function can simply insert some text, indeed, it can be skeleton command (see Using Skeletons). It can be a lambda function which will for example conditionally call another function. Or it can even reset the mode for the buffer. If you want to perform several such actions in order, you use a vector, i.e., several of the above elements between square brackets (‘[…]’).
By default C and C++ headers insert a definition of a symbol derived from the filename to prevent multiple inclusions. C and C++ sources insert an include of the header. Makefiles insert the file makefile.inc if it exists.
TeX and bibTeX mode files insert the file tex-insert.tex if it exists, while
LaTeX mode files insert a typical \documentclass frame. HTML
files insert a skeleton with the usual frame.
Ada mode files call the Ada header skeleton command. Emacs Lisp
source files insert the usual header, with a copyright of your
environment variable $ORGANIZATION or else the name of the
current user, and prompt for valid keywords describing the contents.
Files in a bin directory for which Emacs could determine no
specialized mode (see Choosing Modes in The GNU Emacs
Manual) are set to Shell script mode.
In Lisp (see Init File in The GNU Emacs Manual) you can use the function
define-auto-insert to add to or modify
auto-insert-alist. See its documentation with C-h f
define-auto-insert.
The variable auto-insert says what to do when auto-insert is
called non-interactively, e.g., when a newly found file is empty (see above):
nilDo nothing.
tInsert something if possible, i.e., there is a matching entry in
auto-insert-alist.
Insert something if possible, but mark as unmodified.
The variable auto-insert-query controls whether to ask about
inserting something. When this is nil, inserting is only done with
M-x auto-insert. When this is function, you are queried
whenever auto-insert is called as a function, such as when Emacs
visits an empty file and you have set the above-mentioned hook. Otherwise
you are always queried.
When querying, the variable auto-insert-prompt’s value is used as a
prompt for a y-or-n-type question. If this includes a ‘%s’ construct,
that is replaced by what caused the insertion rule to be chosen. This is
either a descriptive text, the mode-name of the buffer or the regular
expression that matched the filename.
M-x copyright is a skeleton inserting command, that adds a copyright
notice at the point. The “by” part is taken from your environment variable
$ORGANIZATION or if that isn’t set you are prompted for it. If the
buffer has a comment syntax (see Comments in The GNU Emacs Manual), this is inserted as a comment.
M-x copyright-update looks for a copyright notice in the first
copyright-limit characters of the buffer and updates it when necessary.
The current year (variable copyright-current-year) is added to the
existing ones, in the same format as the preceding year, i.e., 1994, ’94 or 94.
If a dash-separated year list up to last year is found, that is extended to
current year, else the year is added separated by a comma. Or it replaces
them when this is called with a prefix argument. If a header referring to a
wrong version of the GNU General Public License (see Copying in The GNU Emacs Manual) is found,
that is updated too.
An interesting application for this function is to have it be called
automatically every time a file is saved. This is accomplished by
putting (add-hook 'before-save-hook 'copyright-update) into
your ~/.emacs file (see Init File in The GNU Emacs Manual). Alternative,
you can do M-x customize-variable RET before-save-hook
RET. copyright-update is conveniently listed as an
option in the customization buffer.
The variable copyright-query controls whether to update the
copyright or whether to ask about it. When this is nil updating is
only done with M-x copyright-update. When this is function
you are queried whenever copyright-update is called as a function,
such as in the before-save-hook feature mentioned above. Otherwise
you are always queried.
Various interpreter modes such as Shell script mode or AWK mode will
automatically insert or update the buffer’s magic number, a special
comment on the first line that makes the exec systemcall know
how to execute the script. To this end the script is automatically
made executable upon saving, with executable-chmod as argument
to the system chmod command. The magic number is prefixed by
the value of executable-prefix.
Any file whose name matches executable-magicless-file-regexp is not
furnished with a magic number, nor is it made executable. This is mainly
intended for resource files, which are only meant to be read in.
The variable executable-insert says what to do when
executable-set-magic is called non-interactively, e.g., when file has no
or the wrong magic number:
nilDo nothing.
tInsert or update magic number.
Insert or update magic number, but mark as unmodified.
The variable executable-query controls whether to ask about
inserting or updating the magic number. When this is nil updating
is only done with M-x executable-set-magic. When this is
function you are queried whenever executable-set-magic is
called as a function, such as when Emacs puts a buffer in Shell script
mode. Otherwise you are always queried.
The time-stamp command can be used to update automatically a
template in a file with a new time stamp every time you save the file.
Customize the hook before-save-hook to add the function
time-stamp to arrange this. It you use Custom to do this,
then time-stamp is conveniently listed as an option in the
customization buffer.
The time stamp is updated only if the customizable variable
time-stamp-active is on, which it is by default; the command
time-stamp-toggle-active can be used to toggle it. The format of
the time stamp is set by the customizable variables
time-stamp-format and time-stamp-time-zone.
The variables time-stamp-line-limit, time-stamp-start,
time-stamp-end, time-stamp-count, and
time-stamp-inserts-lines control finding the template. Do not
change these in your init file or you will be incompatible with other
people’s files. If you must change them, do so only in the local
variables section of the file itself.
Normally the template must appear in the first 8 lines of a file and look like one of the following:
Time-stamp: <> Time-stamp: " "
The time stamp is written between the brackets or quotes:
Time-stamp: <1998-02-18 10:20:51 gildea>
The Tempo package provides a simple way to define powerful templates, or macros, if you wish. It is mainly intended for, but not limited to, programmers to be used for creating shortcuts for editing certain kinds of documents.
A template is defined as a list of items to be inserted in the current buffer at point. Some can be simple strings, while others can control formatting or define special points of interest in the inserted text. M-x tempo-backward-mark and M-x tempo-forward-mark can be used to jump between such points.
More flexible templates can be created by including Lisp symbols, which will be evaluated as variables, or lists, which will be evaluated as Lisp expressions. Automatic completion of specified tags to expanded templates can be provided.
See the documentation for tempo-define-template for the different
items that can be used to define a tempo template with a command for
inserting it.
See the commentary in tempo.el for more information on using the Tempo package.
M-x hippie-expand is a single command providing a variety of completions and expansions. Called repeatedly, it tries all possible completions in succession.
Which ones to try, and in which order, is determined by the contents of
the customizable option hippie-expand-try-functions-list. Much
customization of the expansion behavior can be made by changing the
order of, removing, or inserting new functions in this list. Given a
positive numeric argument, M-x hippie-expand jumps directly that
number of functions forward in this list. Given some other argument (a
negative argument or just C-u) it undoes the tried completion.
See the commentary in hippie-exp.el for more information on the possibilities.
Typically you would bind hippie-expand to M-/ with
dabbrev-expand, the standard binding of M-/, providing one
of the expansion possibilities.
Skeletons are a shorthand extension to the Lisp language, where various
atoms directly perform either actions on the current buffer or rudimentary
flow control mechanisms. Skeletons are interpreted by the function
skeleton-insert.
A skeleton is a list starting with an interactor, which is usually a
prompt-string, or nil when not needed, but can also be a Lisp
expression for complex read functions or for returning some calculated value.
The rest of the list are any number of elements as described in the following
table:
"string", ?c, ?\c ¶Insert string or character. Literal strings and characters are passed through
skeleton-transformation when that is non-nil.
\nInsert a newline and align under current line, but not if this is the
last element of a skeleton and the newline would be inserted at end of
line, or this is the first element and the newline would be inserted
at beginning of line. Use newline character ?\n to prevent
alignment. Use "\n" as the first or last string element of a
skeleton to insert a newline unconditionally.
_Interesting point. When wrapping skeletons around successive regions, they are
put at these places. Point is left at first _ where nothing is
wrapped.
-Interesting point with no inter-region interaction; overrides
interesting point set by _.
>Indent line according to major mode. When following element is _, and
there is an interregion that will be wrapped here, indent that interregion.
&Logical and. If preceding element moved point, i.e., usually inserted something, do following element.
|Logical xor. If preceding element didn’t move point, i.e., usually inserted nothing, do following element.
@Add position to skeleton-positions.
-numberDelete preceding number characters. Depends on value of
skeleton-untabify.
() or nilIgnored.
Evaluated, and the return value is again interpreted as a skeleton element.
strA special variable that, when evaluated the first time, usually prompts for input according to the skeleton’s interactor. It is then set to the return value resulting from the interactor. Each subskeleton has its local copy of this variable.
v1, v2Skeleton-local user variables.
'expressionEvaluate following Lisp expression for its side-effect, but prevent it from being interpreted as a skeleton element.
Subskeletons are inserted recursively, not once, but as often as the user
enters something at the subskeletons interactor. Thus there must be a
str in the subskeleton. They can also be used non-interactively, when
prompt is a lisp-expression that returns successive list-elements.
resume:Ignored. Execution resumes here if the user quits during skeleton interpretation.
helpHelp form during interaction with the user or nil.
inputInitial input (a string or a cons with index) while reading the input.
quitA constant which is non-nil when the resume: section was entered
because the user quit.
Some modes also use other skeleton elements they themselves defined. For
example in shell script mode’s skeletons you will find < which does a
rigid indentation backwards, or in CC mode’s skeletons you find the
self-inserting elements { and }. These are defined by the
buffer-local variable skeleton-further-elements which is a list of
variables bound while interpreting a skeleton.
The macro define-skeleton defines a command for interpreting a
skeleton. The first argument is the command name, the second is a
documentation string, and the rest is an interactor and any number of skeleton
elements together forming a skeleton. This skeleton is assigned to a variable
of the same name as the command and can thus be overridden from your
~/.emacs file (see Init File in The GNU Emacs Manual).
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