Info file elisp, produced by Makeinfo, -*- Text -*- from input file
elisp.texi.
This file documents GNU Emacs Lisp.
This is edition 1.03 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 18.
Published by the Free Software Foundation, 675 Massachusetts
Avenue, Cambridge, MA 02139 USA
Copyright (C) 1990 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
This section describes the Lisp functions and variables that
pertain to printing.
Some of the Emacs printing functions add quoting characters to the
output when necessary so that it can be read properly. The quoting
characters used are `\' and `"'; they are used to distinguish strings
from symbols, and to prevent punctuation characters in strings and
symbols from being taken as delimiters. *Note Printed
Representation::, for full details. You specify quoting or no
quoting by the choice of printing function.
If the text is to be read back into Lisp, then it is best to print
with quoting characters to avoid ambiguity. Likewise, if the purpose
is to describe a Lisp object clearly for a Lisp programmer. However,
if the purpose of the output is to look nice for humans, then it is
better to print without quoting.
In the functions below, STREAM stands for an output stream. (See
the previous section for a description of output streams.) If STREAM
is `nil' or omitted, it defaults to the value of `standard-output'.
* Function: print OBJECT &optional STREAM
The `print' is a convenient way of printing. It outputs the
printed representation of OBJECT to STREAM, printing in addition
one newline before OBJECT and another after it. Quoting
characters are used. `print' returns OBJECT. For example:
(progn (print 'The\ cat\ in)
(print "the hat")
(print " came back"))
-|
-| The\ cat\ in
-|
-| "the hat"
-|
-| " came back"
-|
=> " came back"
* Function: prin1 OBJECT &optional STREAM
This function outputs the printed representation of OBJECT to
STREAM. It does not print any spaces or newlines to separate
output as `print' does, but it does use quoting characters just
like `print'. It returns OBJECT.
(progn (prin1 'The\ cat\ in)
(prin1 "the hat")
(prin1 " came back"))
-| The\ cat\ in"the hat"" came back"
=> " came back"
* Function: prin1-to-string OBJECT
This function returns a string containing the text that `prin1'
would have printed for the same argument.
(prin1-to-string 'foo)
=> "foo"
(prin1-to-string (mark-marker))
=> "#<marker at 2773 in strings.texi>"
See `format', in *Note String Conversion::, for other ways to
obtain the printed representation of a Lisp object as a string.
* Function: princ OBJECT &optional STREAM
This function outputs the printed representation of OBJECT to
STREAM. It returns OBJECT.
This function is intended to produce output that is readable by
people, not by `read', so quoting characters are not used and
double-quotes are not printed around the contents of strings.
It does not add any spacing between calls.
(progn
(princ 'The\ cat)
(princ " in the \"hat\""))
-| The cat in the "hat"
=> " in the \"hat\""
* Function: terpri &optional STREAM
This function outputs a newline to STREAM. The name stands for
"terminate print".
* Variable: standard-output
The value of this variable is the default output stream, used
when the STREAM argument is omitted or `nil'.
* Variable: print-escape-newlines
If this variable is non-`nil', then newline characters in
strings are printed as `\n'. Normally they are printed as
actual newlines.
This variable affects the print functions `prin1' and `print';
it does not affect `princ' in Emacs 18, but this may be changed.
Here is an example using `prin1':
In the second expression, the local binding of
`print-escape-newlines' is in effect during the call to `prin1',
but not during the printing of the result.
* Variable: print-length
The value of this variable is the maximum number of elements of
a list that will be printed. If the list being printed has more
than this many elements, then it is abbreviated with an ellipsis.
If the value is `nil' (the default), then there is no limit.
A "minibuffer" is a special buffer used by Emacs commands to read
arguments more complicated than the single numeric prefix argument.
These arguments include file names, buffer names, and command names
(as in `M-x'). The minibuffer is displayed on the bottom line of the
screen, in the same place as the echo area, but only while it is in
use for reading an argument.
* Menu:
* Intro to Minibuffers:: Basic information about minibuffers.
* Text from Minibuffer:: How to read a straight text string.
* Object from Minibuffer:: How to read a Lisp object or expression.
* Completion:: How to invoke and customize completion.
* Yes-or-No Queries:: Asking a question with a simple answer.
* Minibuffer Misc:: Various customization hooks and variables.
File: elisp, Node: Intro to Minibuffers, Next: Text from Minibuffer, Prev: Minibuffers, Up: Minibuffers
Introduction to Minibuffers
===========================
In most ways, a minibuffer is a normal Emacs buffer. Most
operations *within* a buffer, such as editing commands, work normally
in a minibuffer. However, many operations for managing buffers do
not apply to minibuffers. The name of a minibuffer always has the
form ` *Minibuf-NUMBER', and it cannot be changed. There is a
special window used only for minibuffers, and minibuffers cannot be
displayed in any other window. This window is normally the single
line at the bottom of the screen; it can be resized temporarily with
the window sizing commands, but reverts to its normal size when the
minibuffer is exited.
A "recursive minibuffer" may be created when there is an active
minibuffer and a command is invoked that requires input from a
minibuffer. The first minibuffer is named ` *Minibuf-0*'. Recursive
minibuffers are named by incrementing the number at the end of the
name. (The names begin with a space so that they won't show up in
normal buffer lists.) Of several recursive minibuffers, the
innermost (or most recently entered) is the active minibuffer, and is
the only one that is displayed in a window. We usually call this
"the" minibuffer. Recursive minibuffers may be allowed or disallowed
by setting the variable `enable-recursive-minibuffers'.
Like other buffers, a minibuffer may use any of several local
keymaps (*note Keymaps::.); these contain various exit commands and
in some cases completion commands. *Note Completion::.
* `minibuffer-local-map' is 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.
* `repeat-complex-command-map' is for use in `C-x ESC'.
File: elisp, Node: Text from Minibuffer, Next: Object from Minibuffer, Prev: Intro to Minibuffers, Up: Minibuffers
Reading Text Strings with the Minibuffer
========================================
The minibuffer is usually used to read text which is returned as a
string, but can also be used to read a Lisp object in textual form.
The most basic primitive for minibuffer input is
`read-from-minibuffer'.
* Function: read-from-minibuffer PROMPT-STRING &optional INITIAL
KEYMAP READ
This function is the most general way to get input through the
minibuffer. By default, it accepts arbitrary text and returns
it as a string; however, if READ is non-`nil', then it uses
`read' to convert the text into a Lisp object (*note Input
Functions::.).
The first thing this function does is to activate a minibuffer
and display it with PROMPT-STRING as the prompt. This value
must be a string.
Then, if INITIAL is non-`nil', it must be a string; its contents
are inserted into the minibuffer as initial contents. The text
thus inserted is treated as if the user had inserted it; the
user can alter it with Emacs editing commands.
If KEYMAP is non-`nil', that keymap is the local keymap to use
while reading. If KEYMAP is omitted or `nil', the value of
`minibuffer-local-map' is used as the keymap. Specifying a
keymap is the most important way to customize minibuffer input
for various applications including completion.
When the user types a command to exit the minibuffer, the
current minibuffer contents are usually made into a string which
is the value of `read-from-minibuffer'. However, if READ is
non-`nil', Emacs converts the result to a Lisp object and
`read-from-minibuffer' returns that object, unevaluated.
Suppose, for example, you are writing a search command and want
to record the last search string and provide it as a default for
the next search. Suppose that the previous search string is
stored in the variable `last-search-string'. Here is how you
can read a search string while providing the previous string as
initial input to be edited:
Assuming the value of `last-search-string' is `No', and the user
wants to search for `Nope', the interaction looks like this:
(setq last-search-string "No")
(read-from-minibuffer "Find string: " last-search-string)
---------- Buffer: Minibuffer ----------
Find string: No-!-
---------- Buffer: Minibuffer ----------
;; The user now types `pe RET':
=> "Nope"
* Function: read-string PROMPT &optional INITIAL
This function reads a string from the minibuffer and returns it.
The arguments PROMPT and INITIAL are used as in
`read-from-minibuffer'.
This function is a simplified interface to `read-from-minibuffer':
* Variable: minibuffer-local-map
This is the default local keymap for reading from the
minibuffer. It is the keymap used by the minibuffer for local
bindings in the function `read-string'. By default, it makes
the following bindings:
LFD
`exit-minibuffer'
RET
`exit-minibuffer'
`C-g'
`abort-recursive-edit'
* Function: read-no-blanks-input PROMPT INITIAL
This function reads a string from the minibuffer, but does not
allow whitespace characters as part of the input: instead, those
characters terminate the input. The arguments PROMPT and
INITIAL are used as in `read-from-minibuffer'.
This function is a simplified interface to
`read-from-minibuffer', and passes the value of
`minibuffer-local-ns-map' as the KEYMAP argument for that
function. Since the keymap `minibuffer-local-ns-map' does not
rebind `C-q', it *is* possible to put a space into the string,
by quoting it.
* Variable: minibuffer-local-ns-map
This built-in variable is the keymap used as the minibuffer
local keymap in the function `read-no-blanks-input'. By
default, it makes the following bindings:
`LFD'
`exit-minibuffer'
`SPC'
`exit-minibuffer'
`TAB'
`exit-minibuffer'
`RET'
`exit-minibuffer'
`C-g'
`abort-recursive-edit'
`?'
`self-insert-and-exit'
File: elisp, Node: Object from Minibuffer, Next: Completion, Prev: Text from Minibuffer, Up: Minibuffers
Reading Lisp Objects with the Minibuffer
========================================
This section describes functions for reading Lisp objects with the
minibuffer.
* Function: read-minibuffer PROMPT &optional INITIAL
This function reads a Lisp object in the minibuffer and returns
it, unevaluated. The arguments PROMPT and INITIAL are used as
in `read-from-minibuffer'; in particular, INITIAL must be a
string or `nil'.
This function is a simplified interface to `read-from-minibuffer':
Here is an example in which we supply the string `"(testing)"'
as initial input:
(read-minibuffer "Enter an expression: " (format "%s" '(testing)))
;; Here is how the minibuffer is displayed:
---------- Buffer: Minibuffer ----------
Enter an expression: (testing)-!-
---------- Buffer: Minibuffer ----------
The user can type RET immediately to use the initial input as a
default, or can edit the input.
* Function: eval-minibuffer PROMPT &optional INITIAL
This function reads a Lisp expression in the minibuffer,
evaluates it, then returns the result. The arguments PROMPT and
INITIAL are used as in `read-from-minibuffer'.
This function simply evaluates the result of a call to
`read-minibuffer':
* Function: edit-and-eval-command PROMPT FORM
This function reads a Lisp expression in the minibuffer, and
then evaluates it. The difference between this command and
`eval-minibuffer' is that here the initial FORM is not optional
and it is treated as a Lisp object to be converted to printed
representation rather than as a string of text. It is printed
with `prin1', so if it is a string, double-quote characters
(`"') will appear in the initial text. *Note Output Functions::.
The first thing `edit-and-eval-command' does is to activate the
minibuffer with PROMPT as the prompt. The printed
representation of FORM is then inserted in the minibuffer, and
the user is allowed to edit. When the user exits the
minibuffer, the edited text is read with `read' and then
evaluated. The resulting value becomes the value of
`edit-and-eval-command'.
In the following example, we offer the user an expression with
initial text which is a valid form already:
Typing RET right away would exit the minibuffer and evaluate the
expression, thus moving point forward one word.
`edit-and-eval-command' returns `nil' in this example.
"Completion" is a feature that fills in the rest of a name
starting from an abbreviation for it. Completion works by comparing
the user's input against a list of valid names and determining how
much of the name is determined uniquely by what the user has typed.
For example, when you type `C-x b' (`switch-to-buffer') and then
type the first few letters of the name of the buffer to which you
wish to switch, and then type TAB (`minibuffer-complete'), Emacs
extends the name as far as it can. Standard Emacs commands offer
completion for names of symbols, files, buffers, and processes; with
the functions in this section, you can implement completion for other
kinds of names.
The `try-completion' function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function `completing-read' provides a higher-level interface
for completion. A call to `completing-read' specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands
useful for completion. Other functions provide convenient simple
interfaces for reading certain kinds of names with completion.
* Menu:
* Basic Completion:: Low-level functions for completing strings.
(These are too low level to use the minibuffer.)
* Programmed Completion:: Finding the completions for a given file name.
* Minibuffer Completion:: Invoking the minibuffer with completion.
* Completion Commands:: Minibuffer commands that do completion.
* High-Level Completion:: Convenient special cases of completion
(reading buffer name, file name, etc.)
* Reading File Names:: Using completion to read file names.
* Lisp Symbol Completion:: Completing the name of a symbol.
* Function: try-completion STRING ALIST-OR-OBARRAY &optional PREDICATE
This function returns the longest common substring of all
possible completions of STRING in ALIST-OR-OBARRAY.
If ALIST-OR-OBARRAY is an association list (*note Association
Lists::.), the CAR of each cons cell in it is compared against
STRING; if the beginning of the CAR equals STRING, the cons cell
matches. If no cons cells match, `try-completion' returns
`nil'. If only one cons cell matches, and the match is exact,
then `try-completion' returns `t'. Otherwise, all matching
strings are compared, and the longest initial sequence common to
them is returned as a string.
If ALIST-OR-OBARRAY is an obarray (*note Creating Symbols::.),
the names of all symbols in the obarray form the space of
possible names. They are tested and used just like the CARs of
the elements of an association list. (The global variable
`obarray' holds an obarray containing the names of all interned
Lisp symbols.)
If the argument PREDICATE is non-`nil', then it must be a
function of one argument. It is used to test each possible
match, and the match is accepted only if PREDICATE returns
non-`nil'. The argument given to PREDICATE is either a cons
cell from the alist (the CAR of which is a string) or else it is
a symbol (*not* a symbol name) from the obarray.
It is also possible to use a function as ALIST-OR-OBARRAY. Then
the function is solely responsible for performing completion;
`try-completion' returns whatever this function returns. The
function is called with three arguments: STRING, PREDICATE and
`nil'. (The reason for the third argument is so that the same
function can be used in `all-completions' and do the appropriate
thing in either case.) *Note Programmed Completion::.
In the first of the following examples, the string `foo' is
matched by three of the alist CARs. All of the matches begin
with the characters `fooba', so that is the result. In the
second example, there is only one possible match, and it is
exact, so the value is `t'.
(try-completion "foo" '(("barfoo" 2) ("foo" 3)))
=> t
In the following example, numerous symbols begin with the
characters `forw', and all of them begin with the word
`forward'. In most of the symbols, this is followed with a `-',
but not in all, so no more than `forward' can be completed.
(try-completion "forw" obarray)
=> "forward"
Finally, in the following example, only two of the three
possible matches pass the predicate `test' (the string `foobaz'
is too short). Both of those begin with the string `foobar'.
(defun test (s)
(> (length (car s)) 6))
=> test
(try-completion "foo"
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
'test)
=> "foobar"
* Function: all-completions STRING ALIST-OR-OBARRAY &optional
PREDICATE
This function returns a list of all possible completions,
instead of the longest substring they share. The parameters to
this function are the same as to `try-completion'.
If ALIST-OR-OBARRAY is a function, it is called with three
arguments: STRING, PREDICATE and `t', and `all-completions'
returns whatever the function returns. *Note Programmed
Completion::.
Here is an example, using the same function `test' used in the
example for `try-completion':
* Variable: completion-ignore-case
If the value of this variable is non-`nil', Emacs does not
consider case significant in completion.
The two functions `try-completion' and `all-completions' have
nothing in themselves to do with minibuffers. However, completion is
most often used there, which is why it is described in this chapter.
Sometimes it is not possible to create an alist or an obarray
containing all the intended possible completions. In such a case,
you can supply your own function to compute the completion of a given
string. This is called "programmed completion".
To use this feature, pass the function as the ALIST-OR-OBARRAY
argument to `completing-read'. This command will arrange to pass the
function along to `try-completion' and `all-completions', which will
then let your function do all the work.
The completion function should accept three arguments:
* The string to be completed.
* The predicate function to filter possible matches, or `nil' if
none. Your function should call the predicale for each possible
match and ignore the possible match if the predicate returns
`nil'.
* A flag specifying the type of operation.
There are three flag values for three operations:
* `nil' specifies `try-completion'. The completion function
should return the completion of the specified string, or `t' if
the string is an exact match already, or `nil' if the string
matches no possibility.
* `t' specifies `all-completions'. The completion function should
return a list of all possible completions of the specified string.
* `lambda' specifies a test for an exact match. The completion
function should return `t' if the specified string is an exact
match for some possibility; `nil' otherwise.
Emacs uses programmed completion when completing file names.
*Note File Name Completion::.
Completion and the Minibuffer
-----------------------------
This section describes the basic interface for reading from the
minibuffer with completion.
* Function: completing-read PROMPT ALIST-OR-OBARRAY &optional
PREDICATE REQUIRE-MATCH INITIAL
This function reads a string in the minibuffer, assisting the
user by providing completion. It activates the minibuffer with
prompt PROMPT, which must be a string. If INITIAL is non-`nil',
`completing-read' inserts it into the minibuffer as part of the
input. Then it allows the user to edit the input, providing
several commands to attempt completion.
The actual completion is done by passing ALIST-OR-OBARRAY and
PREDICATE to the function `try-completion'. This happens in
certain commands bound in the local keymaps used for completion.
If REQUIRE-MATCH is `t', the user will not be allowed to exit
unless the input completes to an element of ALIST-OR-OBARRAY.
If REQUIRE-MATCH is neither `nil' nor `t', then
`completing-read' does not exit unless the input typed is itself
an element of ALIST-OR-OBARRAY. To accomplish this,
`completing-read' calls `read-minibuffer' with the keymap
`minibuffer-local-completion-map' if REQUIRE-MATCH is `nil', or
else with the keymap `minibuffer-local-must-match-map', if
REQUIRE-MATCH is non-`nil'.
Case is ignored when comparing the input against the possible
matches if the built-in variable `completion-ignore-case' is
non-`nil'. *Note Basic Completion::.
For example:
(completing-read "Complete a foo: "
'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
nil t "fo")
;; After evaluating the preceding expression,
;; the following appears in the minibuffer:
Minibuffer Commands That Do Completion
--------------------------------------
This section describes the keymaps, commands and user options used
in the minibuffer to do completion.
* Variable: minibuffer-local-completion-map
`completing-read' uses this value as the local keymap when an
exact match of one of the completions is not required. By
default, this keymap makes the following bindings:
`?'
`minibuffer-completion-help'
`SPC'
`minibuffer-complete-word'
`TAB'
`minibuffer-complete'
`LFD'
`exit-minibuffer'
`RET'
`exit-minibuffer'
`C-g'
`abort-recursive-edit'
* Variable: minibuffer-local-must-match-map
`completing-read' uses this value as the local keymap when an
exact match of one of the completions is required. Therefore,
no keys are bound to `exit-minibuffer', the command which exits
the minibuffer unconditionally. By default, this keymap makes
the following bindings:
`?'
`minibuffer-completion-help'
`SPC'
`minibuffer-complete-word'
`TAB'
`minibuffer-complete'
`LFD'
`minibuffer-complete-and-exit'
`RET'
`minibuffer-complete-and-exit'
`C-g'
`abort-recursive-edit'
* Variable: minibuffer-completion-table
The value of this variable is the alist or obarray used for
completion in the minibuffer. This is the global variable that
contains what `completing-read' passes to `try-completion'. It
is used by all the minibuffer completion functions, such as
`minibuffer-complete-word'.
* Variable: minibuffer-completion-predicate
The value of this variable is the predicate that
`completing-read' passes to `try-completion'. The variable is
also used by the other minibuffer completion functions.
* Command: minibuffer-complete-word
This function completes the minibuffer contents by at most a
single word. Even if the minibuffer contents has only one
completion, `minibuffer-complete-word' will not add any
characters beyond the first character that is not a word
constituent. *Note Syntax Tables::.
* Command: minibuffer-complete
This function completes the minibuffer contents as far as
possible.
* Command: minibuffer-complete-and-exit
This function completes the minibuffer contents, and exits if
confirmation is not required, i.e., if
`minibuffer-completion-confirm' is non-`nil'. If confirmation
*is* required, it is given by repeating this command immediately.
* Variable: minibuffer-completion-confirm
When the value of this variable is non-`nil', Emacs asks for
confirmation of a completion before exiting the minibuffer. The
function `minibuffer-complete-and-exit' checks the value of this
variable before it exits.
* Command: minibuffer-completion-help
This function creates a list of the possible completions of the
current minibuffer contents. It works by calling
`all-completions'; the values of `minibuffer-completion-table'
and `minibuffer-completion-predicate' are used as arguments.
The list of completions is displayed as text in a buffer named
`*Completions*'.
* Function: display-completion-list COMPLETIONS
This function displays COMPLETIONS to the stream
`standard-output' (usually a buffer). (*Note Streams::, for
more information about streams.) The argument COMPLETIONS is
normally a list of completions just returned by
`all-completions', but it does not have to be. Each element may
be a symbol or a string, either of which is simply printed, or a
list of two strings, which is printed as if the strings were
concatenated.
This function is called by `minibuffer-completion-help'.
* User Option: completion-auto-help
If this variable is non-`nil', the completion commands
automatically display a list of possible completions whenever
nothing can be completed because the next character is not
uniquely determined.
This section describes the higher-level convenient functions for
reading certain sorts of names with completion.
* Function: read-buffer PROMPT &optional DEFAULT EXISTING
This function reads the name of a buffer and returns it as a
string. The argument DEFAULT is the default name to use, the
value to return if the user exits with an empty minibuffer. If
non-`nil', it should be a string. It is mentioned in the
prompt, but is not inserted in the minibuffer as initial input.
If EXISTING is non-`nil', then the name specified must be that
of an existing buffer. The usual commands to exit the
minibuffer will not exit if the text is not valid, and RET will
do completion to attempt to find a valid name. (However,
DEFAULT is not checked for this; it is returned, whatever it is,
if the user exits with the minibuffer empty.)
In the following example, the user enters `minibuffer.t', and
then types RET. The argument EXISTING is `t', and the only
buffer name starting with the given input is `minibuffer.texi',
so that name is the value.
(read-buffer "Buffer name? " "foo" t)
;; After evaluating the preceding expression,
;; the following prompt appears, with an empty minibuffer:
* Function: read-command PROMPT
This function reads the name of a command and returns it as a
Lisp symbol. The argument PROMPT is used as in
`read-from-minibuffer'. Recall that a command is anything for
which `commandp' returns `t', and a command name is a symbol for
which `commandp' returns `t'. *Note Interactive Call::.
(read-command "Command name? ")
;; After evaluating the preceding expression,
;; the following appears in the minibuffer:
If the user types `forward-c RET', then this function returns
`forward-char'.
The `read-command' function is a simplified interface to
`completing-read'. It uses the `commandp' predicate to allow
only commands to be entered, and it uses the variable `obarray'
so as to be able to complete all extant Lisp symbols:
(read-command PROMPT)
==
(intern (completing-read PROMPT obarray 'commandp t nil))
* Function: read-variable PROMPT
This function reads the name of a user variable and returns it
as a symbol.
(read-variable "Variable name? ")
;; After evaluating the preceding expression,
;; the following prompt appears with an empty minibuffer:
Here is another high-level completion function, designed for
reading a file name. It provides special features including
automatic insertion of the default directory.
* Function: read-file-name PROMPT &optional DIRECTORY DEFAULT EXISTING
This function reads a file name in the minibuffer, prompting
with PROMPT and providing completion. If DEFAULT is non-`nil',
then the value of DEFAULT will be returned by the function if
the user just types RET.
If EXISTING is non-`nil', then the name must refer to an
existing file; then RET performs completion to make the name
valid if possible, and then refuses to exit if it is not valid.
If the value of EXISTING is neither `nil' nor `t', then RET also
requires confirmation after completion.
The argument DIRECTORY specifies the directory to use for
completion of relative file names. Usually it is inserted in
the minibuffer as initial input as well. It defaults to the
current buffer's default directory.
Here is an example:
(read-file-name "The file is ")
;; After evaluating the preceding expression,
;; the following appears in the minibuffer:
---------- Buffer: Minibuffer ----------
The file is /gp/gnu/elisp/-!-
---------- Buffer: Minibuffer ----------
Typing `manual TAB' results in the following:
---------- Buffer: Minibuffer ----------
The file is /gp/gnu/elisp/manual.texi-!-
---------- Buffer: Minibuffer ----------
If the user types RET, `read-file-name' returns
`"/gp/gnu/elisp/manual.texi"'.
* User Option: insert-default-directory
This variable is used by `read-file-name'. The value of this
variable controls whether `read-file-name' starts by placing the
name of the default directory in the minibuffer. If the value
of this variable is `nil', then `read-file-name' does not place
any initial input in the minibuffer. In that case, the default
directory is still used for completion of relative file names,
but is not displayed.
For example:
;; Here the minibuffer starts out containing the default directory.
(let ((insert-default-directory t))
(read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is ~lewis/manual/-!-
---------- Buffer: Minibuffer ----------
;; Here the minibuffer is empty and only the prompt appears on its line.
(let ((insert-default-directory nil))
(read-file-name "The file is "))
---------- Buffer: Minibuffer ----------
The file is -!-
---------- Buffer: Minibuffer ----------
If you type a part of a symbol, and then type `M-TAB'
(`lisp-complete-symbol'), it will attempt to fill in as much more of
the symbol name as it can. Not only does this save typing, but it
can help you with the name of a symbol that you have partially
forgotten.
* Command: lisp-complete-symbol
This function performs completion on the symbol name preceding
point. The name is completed against the symbols in the global
variable `obarray', and characters from the completion are
inserted into the buffer, making the name longer. If there is
more than one completion, a list of all possible completions is
placed in the `*Help*' buffer. The bell rings if there is no
possible completion in `obarray'.
If an open parenthesis immediately precedes the name, only
symbols with function definitions are considered. (By reducing
the number of alternatives, this may succeed in completing more
characters.) Otherwise, symbols with either a function
definition, a value, or at least one property are considered.
`lisp-complete-symbol' returns `t' if the symbol had an exact,
and unique, match; otherwise, it returns `nil'.
In the following example, the user has already inserted `(forwa'
into the buffer `foo.el'. The command `lisp-complete-symbol'
then completes the name to `(forward-'.
This section describes functions used to ask the user a yes-or-no
question. The function `y-or-n-p' can be answered with a single
character; it is useful for questions where an inadvertent wrong
answer will not have serious consequences. `yes-or-no-p' is suitable
for more momentous questions, since it requires three or four
characters to answer.
Strictly speaking, `yes-or-no-p' uses the minibuffer and
`y-or-n-p' does not; but it seems best to describe them together.
* Function: y-or-n-p PROMPT
This function asks the user a question, expecting input in the
echo area. It returns `t' if the user types `y', `nil' if the
user types `n'. This function also accepts SPC to mean yes and
DEL to mean no. The answer is a single character, with no RET
needed to terminate it. Upper and lower case are equivalent.
"Asking the question" means printing PROMPT in the echo area,
followed by the string `(y or n) '. If the input is not one of
the expected answers (`y', `n', `SPC', or `DEL'), the function
responds `Please answer y or n.', and repeats the request.
This function does not actually use the minibuffer, since it
does not allow editing of the answer. It actually uses the echo
area (*note The Echo Area::.), which uses the same screen space
as the minibuffer. The cursor moves to the echo area while the
question is being asked.
In the following example, the user first types `q', which is
invalid. At the next prompt the user types `n'.
(y-or-n-p "Do you need a lift? ")
;; After evaluating the preceding expression,
;; the following prompt appears in the echo area:
---------- Echo area ----------
Do you need a lift? (y or n)
---------- Echo area ----------
;; If the user then types `q', the following appears:
---------- Echo area ----------
Please answer y or n. Do you need a lift? (y or n)
---------- Echo area ----------
;; When the user types a valid answer, it is displayed after the question:
---------- Echo area ----------
Do you need a lift? (y or n) y
---------- Echo area ----------
Note that we show successive lines of echo area messages here.
Only one will appear on the screen at a time.
* Function: yes-or-no-p PROMPT
This function asks the user a question, expecting input in
minibuffer. It returns `t' if the user enters `yes', `nil' if
the user types `no'. The user must type RET to finalize the
response. Upper and lower case are equivalent.
`yes-or-no-p' starts by displaying PROMPT in the echo area,
followed by `(yes or no) '. The user must type one of the
expected responses; otherwise, the function responds `Please
answer yes or no.', waits about two seconds and repeats the
request.
`yes-or-no-p' requires more work from the user than `y-or-n-p'
and is appropriate for more crucial decisions.
Here is an example:
(yes-or-no-p "Do you really want to remove your entire directory? ")
;; After evaluating the preceding expression,
;; the following prompt appears with an empty minibuffer:
---------- Buffer: minibuffer ----------
Do you really want to remove your entire directory? (yes or no)
---------- Buffer: minibuffer ----------
If the user first types `y RET', which is invalid because this
function demands the entire word `yes', it responds by
displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ----------
Please answer yes or no.
Do you really want to remove your entire directory? (yes or no)
---------- Buffer: minibuffer ----------
Some basic minibuffer functions and variables are described in
this section.
* Command: exit-minibuffer
This function exits the active minibuffer. It is normally bound
to keys in minibuffer local keymaps.
* Command: self-insert-and-exit
This function exits the active minibuffer after inserting the
last character typed on the keyboard (found in
`last-command-char'; *note Command Loop Info::.).
* Variable: minibuffer-help-form
The current value of this variable is used to rebind `help-form'
locally inside the minibuffer (*note Help Functions::.).
* Function: minibuffer-window
This function returns the window that is used for the minibuffer.
There is one and only one minibuffer window in Emacs 18; this
window always exists and cannot be deleted.
* Variable: minibuffer-scroll-window
If the value of this variable is non-`nil', it should be a
window object. When the function `scroll-other-window' is
called in the minibuffer, it will scroll the
`minibuffer-scroll-window' window.
Finally, some functions and variables deal with recursive
minibuffers (*note Recursive Editing::.):
* Function: minibuffer-depth
This function returns the current depth of activations of the
minibuffer, a nonnegative integer. If no minibuffers are
active, it returns zero.
* User Option: enable-recursive-minibuffers
If this variable is non-`nil', you can invoke commands (such as
`find-file') which use minibuffers even while in the minibuffer
window. Such invocation produces a recursive editing level for
a new minibuffer. The outer-level minibuffer is invisible while
you are editing the inner one.
This variable only affects invoking the minibuffer while the
minibuffer window is selected. If you switch windows while in
the minibuffer, you can always invoke minibuffer commands while
some other window is selected.
When you run Emacs, it enters the "editor command loop" almost
immediately. This loop reads key sequences, executes their
definitions, and displays the results. In this chapter, we describe
how these things are done, and the subroutines that allow Lisp
programs to do them.
* Menu:
* Command Overview:: How the command loop reads commands.
* Defining Commands:: Specifying how a function should read arguments.
* Interactive Call:: Calling a command, so that it will read arguments.
* Command Loop Info:: Variables set by the command loop for you to examine.
* Keyboard Input:: How your program can read characters from the keyboard.
* Quitting:: How `C-g' works. How to catch or defer quitting.
* Prefix Command Arguments:: How the commands to set prefix args work.
* Recursive Editing:: Entering a recursive edit,
and why you usually shouldn't.
* Disabling Commands:: How the command loop handles disabled commands.
* Command History:: How the command history is set up, and how accessed.
* Keyboard Macros:: How keyboard macros are implemented.
The first thing the command loop must do is read a key sequence,
which is a sequence of characters that translates into a command. It
does this by calling the function `read-key-sequence'. Your Lisp
code can also call this function (*note Keyboard Input::.). Lisp
programs can also do input at a lower level with `read-char' or
discard pending input with `discard-input'.
The key sequence is translated into a command through the keymaps
of the current buffer. *Note Keymaps::, for information on how this
is done. The result should be a keyboard macro or an interactively
callable function. If the key is `M-x', then it reads the name of
another command, which is used instead. This is done by the command
`execute-extended-command' (*note Interactive Call::.).
Once the command is read, it must be executed, which includes
reading arguments to be given to it. This is done by calling
`command-execute' (*note Interactive Call::.). For commands written
in Lisp, the `interactive' specification says how to read the
arguments. This may use the prefix argument (*note Prefix Command
Arguments::.) or may read with prompting in the minibuffer (*note
Minibuffers::.). For example, the command `find-file' has an
`interactive' specification which says to read a file name using the
minibuffer. The command's function body does not use the minibuffer;
if you call this command from Lisp code as a function, you must
supply the file name string as an ordinary Lisp function argument.
If the command is a string (i.e., a keyboard macro) then the
function `execute-kbd-macro' is used to execute it. You can call
this function yourself (*note Keyboard Macros::.).
If a command runs away, typing `C-g' will terminate its execution
immediately. This is called "quitting" (*note Quitting::.).
A Lisp function becomes a command when its body contains, at top
level, a form which calls the special form `interactive'. This form
does nothing when actually executed, but its presence serves as a
flag to indicate that interactive calling is permitted. Its argument
controls the reading of arguments for an interactive call.
* Menu:
* Using Interactive:: General rules for `interactive'.
* Interactive Codes:: The standard letter-codes for reading arguments
in various ways.
* Interactive Examples:: Examples of how to read interactive arguments.
