2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software
5 @c See the file elisp.texi for copying conditions.
7 @chapter Operating System Interface
9 This chapter is about starting and getting out of Emacs, access to
10 values in the operating system environment, and terminal input, output.
12 @xref{Building Emacs}, for related information. @xref{Display}, for
13 additional operating system status information pertaining to the
14 terminal and the screen.
17 * Starting Up:: Customizing Emacs startup processing.
18 * Getting Out:: How exiting works (permanent or temporary).
19 * System Environment:: Distinguish the name and kind of system.
20 * User Identification:: Finding the name and user id of the user.
21 * Time of Day:: Getting the current time.
22 * Time Conversion:: Converting a time from numeric form to
23 calendrical data and vice versa.
24 * Time Parsing:: Converting a time from numeric form to text
26 * Processor Run Time:: Getting the run time used by Emacs.
27 * Time Calculations:: Adding, subtracting, comparing times, etc.
28 * Timers:: Setting a timer to call a function at a certain time.
29 * Idle Timers:: Setting a timer to call a function when Emacs has
30 been idle for a certain length of time.
31 * Terminal Input:: Accessing and recording terminal input.
32 * Terminal Output:: Controlling and recording terminal output.
33 * Sound Output:: Playing sounds on the computer's speaker.
34 * X11 Keysyms:: Operating on key symbols for X Windows.
35 * Batch Mode:: Running Emacs without terminal interaction.
36 * Session Management:: Saving and restoring state with X Session Management.
37 * Desktop Notifications:: Desktop notifications.
38 * File Notifications:: File notifications.
39 * Dynamic Libraries:: On-demand loading of support libraries.
43 @section Starting Up Emacs
45 This section describes what Emacs does when it is started, and how you
46 can customize these actions.
49 * Startup Summary:: Sequence of actions Emacs performs at startup.
50 * Init File:: Details on reading the init file.
51 * Terminal-Specific:: How the terminal-specific Lisp file is read.
52 * Command-Line Arguments:: How command-line arguments are processed,
53 and how you can customize them.
57 @subsection Summary: Sequence of Actions at Startup
58 @cindex initialization of Emacs
59 @cindex startup of Emacs
60 @cindex @file{startup.el}
62 When Emacs is started up, it performs the following operations
63 (see @code{normal-top-level} in @file{startup.el}):
67 It adds subdirectories to @code{load-path}, by running the file named
68 @file{subdirs.el} in each directory in the list. Normally, this file
69 adds the directory's subdirectories to the list, and those are scanned
70 in their turn. The files @file{subdirs.el} are normally generated
71 automatically when Emacs is installed.
74 It loads any @file{leim-list.el} that it finds in the @code{load-path}
75 directories. This file is intended for registering input methods.
76 The search is only for any personal @file{leim-list.el} files that you
77 may have created; it skips the directories containing the standard Emacs
78 libraries (these should contain only a single @file{leim-list.el} file,
79 which is compiled into the Emacs executable).
81 @vindex before-init-time
83 It sets the variable @code{before-init-time} to the value of
84 @code{current-time} (@pxref{Time of Day}). It also sets
85 @code{after-init-time} to @code{nil}, which signals to Lisp programs
86 that Emacs is being initialized.
88 @c set-locale-environment
90 It sets the language environment and the terminal coding system,
91 if requested by environment variables such as @env{LANG}.
94 It does some basic parsing of the command-line arguments.
96 @vindex initial-window-system@r{, and startup}
97 @vindex window-system-initialization-alist
99 If not running in batch mode, it initializes the window system that
100 the variable @code{initial-window-system} specifies (@pxref{Window
101 Systems, initial-window-system}). The initialization function for
102 each supported window system is specified by
103 @code{window-system-initialization-alist}. If the value
104 of @code{initial-window-system} is @var{windowsystem}, then the
105 appropriate initialization function is defined in the file
106 @file{term/@var{windowsystem}-win.el}. This file should have been
107 compiled into the Emacs executable when it was built.
110 It runs the normal hook @code{before-init-hook}.
113 If appropriate, it creates a graphical frame. This is not done if the
114 options @samp{--batch} or @samp{--daemon} were specified.
117 It initializes the initial frame's faces, and sets up the menu bar
118 and tool bar if needed. If graphical frames are supported, it sets up
119 the tool bar even if the current frame is not a graphical one, since a
120 graphical frame may be created later on.
123 It use @code{custom-reevaluate-setting} to re-initialize the members
124 of the list @code{custom-delayed-init-variables}. These are any
125 pre-loaded user options whose default value depends on the run-time,
126 rather than build-time, context.
127 @xref{Building Emacs, custom-initialize-delay}.
130 @c It registers the colors available for tty frames.
133 It loads the library @file{site-start}, if it exists. This is not
134 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
135 @cindex @file{site-start.el}
138 It loads your init file (@pxref{Init File}). This is not done if the
139 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
140 the @samp{-u} option was specified, Emacs looks for the init file in
141 that user's home directory instead.
144 It loads the library @file{default}, if it exists. This is not done
145 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
146 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
147 @cindex @file{default.el}
150 It loads your abbrevs from the file specified by
151 @code{abbrev-file-name}, if that file exists and can be read
152 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
153 option @samp{--batch} was specified.
156 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
157 function @code{package-initialize} to activate any optional Emacs Lisp
158 package that has been installed. @xref{Packaging Basics}.
160 @vindex after-init-time
162 It sets the variable @code{after-init-time} to the value of
163 @code{current-time}. This variable was set to @code{nil} earlier;
164 setting it to the current time signals that the initialization phase
165 is over, and, together with @code{before-init-time}, provides the
166 measurement of how long it took.
169 It runs the normal hook @code{after-init-hook}.
172 If the buffer @file{*scratch*} exists and is still in Fundamental mode
173 (as it should be by default), it sets its major mode according to
174 @code{initial-major-mode}.
177 If started on a text terminal, it loads the terminal-specific
178 Lisp library (@pxref{Terminal-Specific}), and runs the hook
179 @code{tty-setup-hook}. This is not done
180 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
182 @c Now command-line calls command-line-1.
185 It displays the initial echo area message, unless you have suppressed
186 that with @code{inhibit-startup-echo-area-message}.
189 It processes any command-line options that were not handled earlier.
191 @c This next one is back in command-line, but the remaining bits of
192 @c command-line-1 are not done if noninteractive.
194 It now exits if the option @code{--batch} was specified.
197 If @code{initial-buffer-choice} is a string, it visits the file with
198 that name. If it is a function, it calls the function and selects the
199 buffer returned by the function. It it is @code{t}, it selects the
200 @file{*scratch*} buffer. If the @file{*scratch*} buffer exists and is
201 empty, it inserts @code{initial-scratch-message} into that buffer.
203 @c To make things nice and confusing, the next three items can be
204 @c called from two places. If displaying a startup screen, they are
205 @c called in command-line-1 before the startup screen is shown.
206 @c inhibit-startup-hooks is then set and window-setup-hook set to nil.
207 @c If not displaying a startup screen, they are are called in
209 @c FIXME? So it seems they can be called before or after the
210 @c daemon/session restore step?
213 It runs @code{emacs-startup-hook}.
216 It calls @code{frame-notice-user-settings}, which modifies the
217 parameters of the selected frame according to whatever the init files
221 It runs @code{window-setup-hook}. @xref{Window Systems}.
224 @cindex startup screen
225 It displays the @dfn{startup screen}, which is a special buffer that
226 contains information about copyleft and basic Emacs usage. This is
227 not done if @code{inhibit-startup-screen} or @code{initial-buffer-choice}
228 are non-@code{nil}, or if the @samp{--no-splash} or @samp{-Q} command-line
229 options were specified.
231 @c End of command-line-1.
233 @c Back to command-line from command-line-1.
235 @c This is the point at which we actually exit in batch mode, but the
236 @c last few bits of command-line-1 are not done in batch mode.
239 If the option @code{--daemon} was specified, it calls
240 @code{server-start} and detaches from the controlling terminal.
241 @xref{Emacs Server,,, emacs, The GNU Emacs Manual}.
244 If started by the X session manager, it calls
245 @code{emacs-session-restore} passing it as argument the ID of the
246 previous session. @xref{Session Management}.
248 @c End of command-line.
250 @c Back to normal-top-level from command-line.
255 The following options affect some aspects of the startup sequence.
257 @defopt inhibit-startup-screen
258 This variable, if non-@code{nil}, inhibits the startup screen. In
259 that case, Emacs typically displays the @file{*scratch*} buffer; but
260 see @code{initial-buffer-choice}, below.
262 Do not set this variable in the init file of a new user, or in a way
263 that affects more than one user, as that would prevent new users from
264 receiving information about copyleft and basic Emacs usage.
266 @vindex inhibit-startup-message
267 @vindex inhibit-splash-screen
268 @code{inhibit-startup-message} and @code{inhibit-splash-screen} are
269 aliases for this variable.
272 @defopt initial-buffer-choice
273 If non-@code{nil}, this variable is a string that specifies a file or
274 directory for Emacs to display after starting up, instead of the
276 If its value is a function, Emacs calls that function which must
277 return a buffer which is then displayed.
278 If its value is @code{t}, Emacs displays the @file{*scratch*} buffer.
281 @defopt inhibit-startup-echo-area-message
282 This variable controls the display of the startup echo area message.
283 You can suppress the startup echo area message by adding text with this
284 form to your init file:
287 (setq inhibit-startup-echo-area-message
288 "@var{your-login-name}")
291 Emacs explicitly checks for an expression as shown above in your init
292 file; your login name must appear in the expression as a Lisp string
293 constant. You can also use the Customize interface. Other methods of
294 setting @code{inhibit-startup-echo-area-message} to the same value do
295 not inhibit the startup message. This way, you can easily inhibit the
296 message for yourself if you wish, but thoughtless copying of your init
297 file will not inhibit the message for someone else.
300 @defopt initial-scratch-message
301 This variable, if non-@code{nil}, should be a string, which is
302 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
303 is @code{nil}, the @file{*scratch*} buffer is empty.
307 The following command-line options affect some aspects of the startup
308 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
312 Do not display a splash screen.
315 Run without an interactive terminal. @xref{Batch Mode}.
318 Do not initialize any display; just start a server in the background.
322 Do not load either the init file, or the @file{default} library.
325 Do not load the @file{site-start} library.
329 Equivalent to @samp{-q --no-site-file --no-splash}.
330 @c and --no-site-lisp, but let's not mention that here.
335 @subsection The Init File
337 @cindex @file{.emacs}
338 @cindex @file{init.el}
340 When you start Emacs, it normally attempts to load your @dfn{init
341 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
342 in your home directory, or a file named @file{init.el} in a
343 subdirectory named @file{.emacs.d} in your home directory.
345 Whichever place you use, you can also compile the file (@pxref{Byte
346 Compilation}); then the actual file loaded will be @file{.emacs.elc}
350 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
351 control whether and where to find the init file; @samp{-q} (and the
352 stronger @samp{-Q}) says not to load an init file, while @samp{-u
353 @var{user}} says to load @var{user}'s init file instead of yours.
354 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
355 option is specified, Emacs uses the @env{LOGNAME} environment
356 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
357 systems) variable, to find your home directory and thus your init
358 file; this way, even if you have su'd, Emacs still loads your own init
359 file. If those environment variables are absent, though, Emacs uses
360 your user-id to find your home directory.
362 @cindex default init file
363 An Emacs installation may have a @dfn{default init file}, which is a
364 Lisp library named @file{default.el}. Emacs finds this file through
365 the standard search path for libraries (@pxref{How Programs Do
366 Loading}). The Emacs distribution does not come with this file; it is
367 intended for local customizations. If the default init file exists,
368 it is loaded whenever you start Emacs. But your own personal init
369 file, if any, is loaded first; if it sets @code{inhibit-default-init}
370 to a non-@code{nil} value, then Emacs does not subsequently load the
371 @file{default.el} file. In batch mode, or if you specify @samp{-q}
372 (or @samp{-Q}), Emacs loads neither your personal init file nor
373 the default init file.
375 Another file for site-customization is @file{site-start.el}. Emacs
376 loads this @emph{before} the user's init file. You can inhibit the
377 loading of this file with the option @samp{--no-site-file}.
379 @defopt site-run-file
380 This variable specifies the site-customization file to load before the
381 user's init file. Its normal value is @code{"site-start"}. The only
382 way you can change it with real effect is to do so before dumping
384 @c So why even mention it here. I imagine it is almost never changed.
387 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
388 examples of how to make various commonly desired customizations in your
391 @defopt inhibit-default-init
392 If this variable is non-@code{nil}, it prevents Emacs from loading the
393 default initialization library file. The default value is @code{nil}.
396 @defvar before-init-hook
397 This normal hook is run, once, just before loading all the init files
398 (@file{site-start.el}, your init file, and @file{default.el}).
399 (The only way to change it with real effect is before dumping Emacs.)
402 @defvar after-init-hook
403 This normal hook is run, once, just after loading all the init files
404 (@file{site-start.el}, your init file, and @file{default.el}),
405 before loading the terminal-specific library (if started on a text
406 terminal) and processing the command-line action arguments.
409 @defvar emacs-startup-hook
410 This normal hook is run, once, just after handling the command line
411 arguments. In batch mode, Emacs does not run this hook.
414 @defvar user-init-file
415 This variable holds the absolute file name of the user's init file. If the
416 actual init file loaded is a compiled file, such as @file{.emacs.elc},
417 the value refers to the corresponding source file.
420 @defvar user-emacs-directory
421 This variable holds the name of the @file{.emacs.d} directory. It is
422 @file{~/.emacs.d} on all platforms but MS-DOS.
425 @node Terminal-Specific
426 @subsection Terminal-Specific Initialization
427 @cindex terminal-specific initialization
429 Each terminal type can have its own Lisp library that Emacs loads when
430 run on that type of terminal. The library's name is constructed by
431 concatenating the value of the variable @code{term-file-prefix} and the
432 terminal type (specified by the environment variable @env{TERM}).
433 Normally, @code{term-file-prefix} has the value @code{"term/"};
434 changing this is not recommended. If there is an entry matching
435 @env{TERM} in the @code{term-file-aliases} association list,
436 Emacs uses the associated value in place of @env{TERM}.
437 Emacs finds the file in the normal manner, by searching the
438 @code{load-path} directories, and trying the @samp{.elc} and
442 The usual role of a terminal-specific library is to enable special
443 keys to send sequences that Emacs can recognize. It may also need to
444 set or add to @code{input-decode-map} if the Termcap or Terminfo entry
445 does not specify all the terminal's function keys. @xref{Terminal Input}.
447 When the name of the terminal type contains a hyphen or underscore,
448 and no library is found whose name is identical to the terminal's
449 name, Emacs strips from the terminal's name the last hyphen or
450 underscore and everything that follows
451 it, and tries again. This process is repeated until Emacs finds a
452 matching library, or until there are no more hyphens or underscores in the name
453 (i.e., there is no terminal-specific library). For example, if the
454 terminal name is @samp{xterm-256color} and there is no
455 @file{term/xterm-256color.el} library, Emacs tries to load
456 @file{term/xterm.el}. If necessary, the terminal library can evaluate
457 @code{(getenv "TERM")} to find the full name of the terminal type.
459 Your init file can prevent the loading of the terminal-specific
460 library by setting the variable @code{term-file-prefix} to @code{nil}.
462 You can also arrange to override some of the actions of the
463 terminal-specific library by using @code{tty-setup-hook}. This is
464 a normal hook that Emacs runs after initializing a new text terminal.
465 You could use this hook to define initializations for terminals that do not
466 have their own libraries. @xref{Hooks}.
468 @defopt term-file-prefix
469 @cindex @env{TERM} environment variable
470 If the value of this variable is non-@code{nil}, Emacs loads a
471 terminal-specific initialization file as follows:
474 (load (concat term-file-prefix (getenv "TERM")))
478 You may set the @code{term-file-prefix} variable to @code{nil} in your
479 init file if you do not wish to load the
480 terminal-initialization file.
482 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
485 @defopt term-file-aliases
486 This variable is an an association list mapping terminal types to
487 their aliases. For example, an element of the form @code{("vt102"
488 . "vt100")} means to treat a terminal of type @samp{vt102} like one of
492 @defvar tty-setup-hook
493 This variable is a normal hook that Emacs runs after initializing a
494 new text terminal. (This applies when Emacs starts up in non-windowed
495 mode, and when making a tty @command{emacsclient} connection.) The
496 hook runs after loading your init file (if applicable) and the
497 terminal-specific Lisp file, so you can use it to adjust the
498 definitions made by that file.
500 For a related feature, @pxref{Window Systems, window-setup-hook}.
503 @node Command-Line Arguments
504 @subsection Command-Line Arguments
505 @cindex command-line arguments
507 You can use command-line arguments to request various actions when
508 you start Emacs. Note that the recommended way of using Emacs is to
509 start it just once, after logging in, and then do all editing in the same
510 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
511 For this reason, you might not use command-line arguments very often;
512 nonetheless, they can be useful when invoking Emacs from session
513 scripts or debugging Emacs. This section describes how Emacs
514 processes command-line arguments.
517 This function parses the command line that Emacs was called with,
518 processes it, and (amongst other things) loads the user's init file and
519 displays the startup messages.
522 @defvar command-line-processed
523 The value of this variable is @code{t} once the command line has been
526 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
527 Emacs}), you may wish to set this variable to @code{nil} first in
528 order to cause the new dumped Emacs to process its new command-line
532 @defvar command-switch-alist
533 @cindex switches on command line
534 @cindex options on command line
535 @cindex command-line options
536 This variable is an alist of user-defined command-line options and
537 associated handler functions. By default it is empty, but you can
538 add elements if you wish.
540 A @dfn{command-line option} is an argument on the command line, which
547 The elements of the @code{command-switch-alist} look like this:
550 (@var{option} . @var{handler-function})
553 The @sc{car}, @var{option}, is a string, the name of a command-line
554 option (not including the initial hyphen). The @var{handler-function}
555 is called to handle @var{option}, and receives the option name as its
558 In some cases, the option is followed in the command line by an
559 argument. In these cases, the @var{handler-function} can find all the
560 remaining command-line arguments in the variable
561 @code{command-line-args-left} (see below). (The entire list of
562 command-line arguments is in @code{command-line-args}.)
564 The command-line arguments are parsed by the @code{command-line-1}
565 function in the @file{startup.el} file. See also @ref{Emacs
566 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
570 @defvar command-line-args
571 The value of this variable is the list of command-line arguments passed
575 @defvar command-line-args-left
577 The value of this variable is the list of command-line arguments that
578 have not yet been processed.
579 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
580 @c @code{argv} is an alias for this.
583 @defvar command-line-functions
584 This variable's value is a list of functions for handling an
585 unrecognized command-line argument. Each time the next argument to be
586 processed has no special meaning, the functions in this list are called,
587 in order of appearance, until one of them returns a non-@code{nil}
590 These functions are called with no arguments. They can access the
591 command-line argument under consideration through the variable
592 @code{argi}, which is bound temporarily at this point. The remaining
593 arguments (not including the current one) are in the variable
594 @code{command-line-args-left}.
596 When a function recognizes and processes the argument in @code{argi}, it
597 should return a non-@code{nil} value to say it has dealt with that
598 argument. If it has also dealt with some of the following arguments, it
599 can indicate that by deleting them from @code{command-line-args-left}.
601 If all of these functions return @code{nil}, then the argument is treated
602 as a file name to visit.
606 @section Getting Out of Emacs
607 @cindex exiting Emacs
609 There are two ways to get out of Emacs: you can kill the Emacs job,
610 which exits permanently, or you can suspend it, which permits you to
611 reenter the Emacs process later. (In a graphical environment, you can
612 of course simply switch to another application without doing anything
613 special to Emacs, then switch back to Emacs when you want.)
616 * Killing Emacs:: Exiting Emacs irreversibly.
617 * Suspending Emacs:: Exiting Emacs reversibly.
621 @subsection Killing Emacs
622 @cindex killing Emacs
624 Killing Emacs means ending the execution of the Emacs process.
625 If you started Emacs from a terminal, the parent process normally
626 resumes control. The low-level primitive for killing Emacs is
629 @deffn Command kill-emacs &optional exit-data
630 This command calls the hook @code{kill-emacs-hook}, then exits the
631 Emacs process and kills it.
633 If @var{exit-data} is an integer, that is used as the exit status of
634 the Emacs process. (This is useful primarily in batch operation; see
637 If @var{exit-data} is a string, its contents are stuffed into the
638 terminal input buffer so that the shell (or whatever program next reads
639 input) can read them.
645 @cindex operating system signal
646 The @code{kill-emacs} function is normally called via the
647 higher-level command @kbd{C-x C-c}
648 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
649 Emacs Manual}. It is also called automatically if Emacs receives a
650 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
651 controlling terminal is disconnected), or if it receives a
652 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
654 @defvar kill-emacs-hook
655 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
657 Because @code{kill-emacs} can be called in situations where user
658 interaction is impossible (e.g., when the terminal is disconnected),
659 functions on this hook should not attempt to interact with the user.
660 If you want to interact with the user when Emacs is shutting down, use
661 @code{kill-emacs-query-functions}, described below.
664 When Emacs is killed, all the information in the Emacs process,
665 aside from files that have been saved, is lost. Because killing Emacs
666 inadvertently can lose a lot of work, the
667 @code{save-buffers-kill-terminal} command queries for confirmation if
668 you have buffers that need saving or subprocesses that are running.
669 It also runs the abnormal hook @code{kill-emacs-query-functions}:
671 @defvar kill-emacs-query-functions
672 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
673 functions in this hook, after asking the standard questions and before
674 calling @code{kill-emacs}. The functions are called in order of
675 appearance, with no arguments. Each function can ask for additional
676 confirmation from the user. If any of them returns @code{nil},
677 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
678 the remaining functions in this hook. Calling @code{kill-emacs}
679 directly does not run this hook.
682 @node Suspending Emacs
683 @subsection Suspending Emacs
684 @cindex suspending Emacs
686 On text terminals, it is possible to @dfn{suspend Emacs}, which
687 means stopping Emacs temporarily and returning control to its superior
688 process, which is usually the shell. This allows you to resume
689 editing later in the same Emacs process, with the same buffers, the
690 same kill ring, the same undo history, and so on. To resume Emacs,
691 use the appropriate command in the parent shell---most likely
694 @cindex controlling terminal
695 Suspending works only on a terminal device from which the Emacs
696 session was started. We call that device the @dfn{controlling
697 terminal} of the session. Suspending is not allowed if the
698 controlling terminal is a graphical terminal. Suspending is usually
699 not relevant in graphical environments, since you can simply switch to
700 another application without doing anything special to Emacs.
702 @c FIXME? Are there any systems Emacs still supports that do not
705 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
706 not support suspension of jobs; on these systems, ``suspension''
707 actually creates a new shell temporarily as a subprocess of Emacs.
708 Then you would exit the shell to return to Emacs.
710 @deffn Command suspend-emacs &optional string
711 This function stops Emacs and returns control to the superior process.
712 If and when the superior process resumes Emacs, @code{suspend-emacs}
713 returns @code{nil} to its caller in Lisp.
715 This function works only on the controlling terminal of the Emacs
716 session; to relinquish control of other tty devices, use
717 @code{suspend-tty} (see below). If the Emacs session uses more than
718 one terminal, you must delete the frames on all the other terminals
719 before suspending Emacs, or this function signals an error.
720 @xref{Multiple Terminals}.
722 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
723 superior shell, to be read as terminal input.
724 @c FIXME? It seems to me that shell does echo STRING.
725 The characters in @var{string} are not echoed by the superior shell;
726 only the results appear.
728 Before suspending, @code{suspend-emacs} runs the normal hook
729 @code{suspend-hook}. After the user resumes Emacs,
730 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
733 The next redisplay after resumption will redraw the entire screen,
734 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
735 @xref{Refresh Screen}.
737 Here is an example of how you could use these hooks:
741 (add-hook 'suspend-hook
742 (lambda () (or (y-or-n-p "Really suspend? ")
743 (error "Suspend canceled"))))
745 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
748 @c The sit-for prevents the ``nil'' that suspend-emacs returns
749 @c hiding the message.
751 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
755 ---------- Buffer: Minibuffer ----------
756 Really suspend? @kbd{y}
757 ---------- Buffer: Minibuffer ----------
761 ---------- Parent Shell ----------
767 ---------- Echo Area ----------
772 @c FIXME? AFAICS, it is echoed.
773 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
774 is read and executed by the shell.
778 This variable is a normal hook that Emacs runs before suspending.
781 @defvar suspend-resume-hook
782 This variable is a normal hook that Emacs runs on resuming
786 @defun suspend-tty &optional tty
787 If @var{tty} specifies a terminal device used by Emacs, this function
788 relinquishes the device and restores it to its prior state. Frames
789 that used the device continue to exist, but are not updated and Emacs
790 doesn't read input from them. @var{tty} can be a terminal object, a
791 frame (meaning the terminal for that frame), or @code{nil} (meaning
792 the terminal for the selected frame). @xref{Multiple Terminals}.
794 If @var{tty} is already suspended, this function does nothing.
796 @vindex suspend-tty-functions
797 This function runs the hook @code{suspend-tty-functions}, passing the
798 terminal object as an argument to each function.
801 @defun resume-tty &optional tty
802 This function resumes the previously suspended terminal device
803 @var{tty}; where @var{tty} has the same possible values as it does
804 for @code{suspend-tty}.
806 @vindex resume-tty-functions
807 This function reopens the terminal device, re-initializes it, and
808 redraws it with that terminal's selected frame. It then runs the
809 hook @code{resume-tty-functions}, passing the terminal object as an
810 argument to each function.
812 If the same device is already used by another Emacs terminal, this
813 function signals an error. If @var{tty} is not suspended, this
814 function does nothing.
817 @defun controlling-tty-p &optional tty
818 This function returns non-@code{nil} if @var{tty} is the
819 controlling terminal of the Emacs session; @var{tty} can be a
820 terminal object, a frame (meaning the terminal for that frame), or
821 @code{nil} (meaning the terminal for the selected frame).
824 @deffn Command suspend-frame
825 This command @dfn{suspends} a frame. For GUI frames, it calls
826 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
827 text terminals, it calls either @code{suspend-emacs} or
828 @code{suspend-tty}, depending on whether the frame is displayed on the
829 controlling terminal device or not.
832 @node System Environment
833 @section Operating System Environment
834 @cindex operating system environment
836 Emacs provides access to variables in the operating system environment
837 through various functions. These variables include the name of the
838 system, the user's @acronym{UID}, and so on.
840 @defvar system-configuration
841 This variable holds the standard GNU configuration name for the
842 hardware/software configuration of your system, as a string. For
843 example, a typical value for a 64-bit GNU/Linux system is
844 @samp{"x86_64-unknown-linux-gnu"}.
847 @cindex system type and name
849 The value of this variable is a symbol indicating the type of operating
850 system Emacs is running on. The possible values are:
857 Berkeley BSD and its variants.
860 Cygwin, a Posix layer on top of MS-Windows.
866 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
869 A GNU/Linux system---that is, a variant GNU system, using the Linux
870 kernel. (These systems are the ones people often call ``Linux'', but
871 actually Linux is just the kernel, not the whole system.)
874 A GNU (glibc-based) system with a FreeBSD kernel.
877 Hewlett-Packard HPUX operating system.
880 Silicon Graphics Irix system.
883 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
884 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
890 Microsoft Windows NT, 9X and later. The value of @code{system-type}
891 is always @code{windows-nt}, e.g., even on Windows 7.
895 We do not wish to add new symbols to make finer distinctions unless it
896 is absolutely necessary! In fact, we hope to eliminate some of these
897 alternatives in the future. If you need to make a finer distinction
898 than @code{system-type} allows for, you can test
899 @code{system-configuration}, e.g., against a regexp.
903 This function returns the name of the machine you are running on, as a
907 The symbol @code{system-name} is a variable as well as a function. In
908 fact, the function returns whatever value the variable
909 @code{system-name} currently holds. Thus, you can set the variable
910 @code{system-name} in case Emacs is confused about the name of your
911 system. The variable is also useful for constructing frame titles
912 (@pxref{Frame Titles}).
914 @c FIXME seems like this section is not the best place for this option?
915 @defopt mail-host-address
916 If this variable is non-@code{nil}, it is used instead of
917 @code{system-name} for purposes of generating email addresses. For
918 example, it is used when constructing the default value of
919 @code{user-mail-address}. @xref{User Identification}. (Since this is
920 done when Emacs starts up, the value actually used is the one saved when
921 Emacs was dumped. @xref{Building Emacs}.)
922 @c FIXME sounds like should probably give this a :set-after and some
923 @c custom-initialize-delay voodoo.
926 @deffn Command getenv var &optional frame
927 @cindex environment variable access
928 This function returns the value of the environment variable @var{var},
929 as a string. @var{var} should be a string. If @var{var} is undefined
930 in the environment, @code{getenv} returns @code{nil}. It returns
931 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
932 variables and their values is kept in the variable @code{process-environment}.
941 The shell command @code{printenv} prints all or part of the environment:
946 PATH=/usr/local/bin:/usr/bin:/bin
958 @deffn Command setenv variable &optional value substitute
959 This command sets the value of the environment variable named
960 @var{variable} to @var{value}. @var{variable} should be a string.
961 Internally, Emacs Lisp can handle any string. However, normally
962 @var{variable} should be a valid shell identifier, that is, a sequence
963 of letters, digits and underscores, starting with a letter or
964 underscore. Otherwise, errors may occur if subprocesses of Emacs try
965 to access the value of @var{variable}. If @var{value} is omitted or
966 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
967 removes @var{variable} from the environment. Otherwise, @var{value}
970 @c FIXME: Document `substitute-env-vars'? --xfq
971 If the optional argument @var{substitute} is non-@code{nil}, Emacs
972 calls the function @code{substitute-env-vars} to expand any
973 environment variables in @var{value}.
975 @code{setenv} works by modifying @code{process-environment}; binding
976 that variable with @code{let} is also reasonable practice.
978 @code{setenv} returns the new value of @var{variable}, or @code{nil}
979 if it removed @var{variable} from the environment.
982 @defvar process-environment
983 This variable is a list of strings, each describing one environment
984 variable. The functions @code{getenv} and @code{setenv} work by means
990 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
1001 If @code{process-environment} contains ``duplicate'' elements that
1002 specify the same environment variable, the first of these elements
1003 specifies the variable, and the other ``duplicates'' are ignored.
1006 @defvar initial-environment
1007 This variable holds the list of environment variables Emacs inherited
1008 from its parent process when Emacs started.
1011 @defvar path-separator
1012 This variable holds a string that says which character separates
1013 directories in a search path (as found in an environment variable). Its
1014 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1017 @defun parse-colon-path path
1018 This function takes a search path string such as the value of
1019 the @env{PATH} environment variable, and splits it at the separators,
1020 returning a list of directory names. @code{nil} in this list means
1021 the current directory. Although the function's name says
1022 ``colon'', it actually uses the value of @code{path-separator}.
1025 (parse-colon-path ":/foo:/bar")
1026 @result{} (nil "/foo/" "/bar/")
1030 @defvar invocation-name
1031 This variable holds the program name under which Emacs was invoked. The
1032 value is a string, and does not include a directory name.
1035 @defvar invocation-directory
1036 This variable holds the directory from which the Emacs executable was
1037 invoked, or @code{nil} if that directory cannot be determined.
1040 @defvar installation-directory
1041 If non-@code{nil}, this is a directory within which to look for the
1042 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1043 it is normally @code{nil}. It is non-@code{nil}
1044 when Emacs can't find those directories in their standard installed
1045 locations, but can find them in a directory related somehow to the one
1046 containing the Emacs executable (i.e., @code{invocation-directory}).
1049 @defun load-average &optional use-float
1050 This function returns the current 1-minute, 5-minute, and 15-minute
1051 system load averages, in a list. The load average indicates the
1052 number of processes trying to run on the system.
1054 By default, the values are integers that are 100 times the system load
1055 averages, but if @var{use-float} is non-@code{nil}, then they are
1056 returned as floating-point numbers without multiplying by 100.
1058 If it is impossible to obtain the load average, this function signals
1059 an error. On some platforms, access to load averages requires
1060 installing Emacs as setuid or setgid so that it can read kernel
1061 information, and that usually isn't advisable.
1062 @c FIXME which platforms are these? Are they still relevant?
1064 If the 1-minute load average is available, but the 5- or 15-minute
1065 averages are not, this function returns a shortened list containing
1066 the available averages.
1071 @result{} (169 48 36)
1075 @result{} (1.69 0.48 0.36)
1079 The shell command @code{uptime} returns similar information.
1083 This function returns the process @acronym{ID} of the Emacs process,
1087 @defvar tty-erase-char
1088 This variable holds the erase character that was selected
1089 in the system's terminal driver, before Emacs was started.
1090 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1091 @c The value is @code{nil} if Emacs is running under a window system.
1094 @node User Identification
1095 @section User Identification
1096 @cindex user identification
1098 @defvar init-file-user
1099 This variable says which user's init files should be used by
1100 Emacs---or @code{nil} if none. @code{""} stands for the user who
1101 originally logged in. The value reflects command-line options such as
1102 @samp{-q} or @samp{-u @var{user}}.
1104 Lisp packages that load files of customizations, or any other sort of
1105 user profile, should obey this variable in deciding where to find it.
1106 They should load the profile of the user name found in this variable.
1107 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q},
1108 @samp{-Q}, or @samp{-batch} option was used, then Lisp packages should
1109 not load any customization files or user profile.
1112 @defopt user-mail-address
1113 This holds the nominal email address of the user who is using Emacs.
1114 Emacs normally sets this variable to a default value after reading your
1115 init files, but not if you have already set it. So you can set the
1116 variable to some other value in your init file if you do not
1117 want to use the default value.
1120 @defun user-login-name &optional uid
1121 This function returns the name under which the user is logged in.
1122 It uses the environment variables @env{LOGNAME} or @env{USER} if
1123 either is set. Otherwise, the value is based on the effective
1124 @acronym{UID}, not the real @acronym{UID}.
1126 If you specify @var{uid} (a number), the result is the user name that
1127 corresponds to @var{uid}, or @code{nil} if there is no such user.
1130 @defun user-real-login-name
1131 This function returns the user name corresponding to Emacs's real
1132 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1133 environment variables @env{LOGNAME} and @env{USER}.
1136 @defun user-full-name &optional uid
1137 This function returns the full name of the logged-in user---or the value
1138 of the environment variable @env{NAME}, if that is set.
1140 If the Emacs process's user-id does not correspond to any known user (and
1141 provided @code{NAME} is not set), the result is @code{"unknown"}.
1143 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1144 or a string (a login name). Then @code{user-full-name} returns the full
1145 name corresponding to that user-id or login name. If you specify a
1146 user-id or login name that isn't defined, it returns @code{nil}.
1149 @vindex user-full-name
1150 @vindex user-real-login-name
1151 @vindex user-login-name
1152 The symbols @code{user-login-name}, @code{user-real-login-name} and
1153 @code{user-full-name} are variables as well as functions. The functions
1154 return the same values that the variables hold. These variables allow
1155 you to ``fake out'' Emacs by telling the functions what to return. The
1156 variables are also useful for constructing frame titles (@pxref{Frame
1160 @defun user-real-uid
1161 This function returns the real @acronym{UID} of the user.
1162 The value may be floating point, in the (unlikely) event that
1163 the UID is too large to fit in a Lisp integer.
1167 This function returns the effective @acronym{UID} of the user.
1168 The value may be floating point.
1173 This function returns the effective @acronym{GID} of the Emacs process.
1174 The value may be floating point.
1177 @defun group-real-gid
1178 This function returns the real @acronym{GID} of the Emacs process.
1179 The value may be floating point.
1183 This function returns a list of strings, listing the user names on the
1184 system. If Emacs cannot retrieve this information, the return value
1185 is a list containing just the value of @code{user-real-login-name}.
1189 @defun system-groups
1190 This function returns a list of strings, listing the names of user
1191 groups on the system. If Emacs cannot retrieve this information, the
1192 return value is @code{nil}.
1197 @section Time of Day
1199 This section explains how to determine the current time and time
1203 Most of these functions represent time as a list of either four
1204 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
1205 @var{picosec})}, or of three
1206 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1207 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1208 @var{sec-high} and @var{sec-low} give the high and low bits of an
1209 integer number of seconds. This integer,
1211 @var{high} * 2**16 + @var{low},
1216 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1217 UTC) to the specified time. The third list element @var{microsec}, if
1218 present, gives the number of microseconds from the start of that
1219 second to the specified time.
1220 Similarly, the fourth list element @var{picosec}, if present, gives
1221 the number of picoseconds from the start of that microsecond to the
1224 The return value of @code{current-time} represents time using four
1225 integers, as do the timestamps in the return value of
1226 @code{file-attributes} (@pxref{Definition of
1227 file-attributes}). In function arguments, e.g., the @var{time-value}
1228 argument to @code{current-time-string}, two-, three-, and four-integer
1229 lists are accepted. You can convert times from the list
1230 representation into standard human-readable strings using
1231 @code{current-time-string}, or to other forms using the
1232 @code{decode-time} and @code{format-time-string} functions documented
1233 in the following sections.
1235 @defun current-time-string &optional time-value
1236 This function returns the current time and date as a human-readable
1237 string. The format does not vary for the initial part of the string,
1238 which contains the day of week, month, day of month, and time of day
1239 in that order: the number of characters used for these fields is
1240 always the same, so you can reliably
1241 use @code{substring} to extract them. You should count
1242 characters from the beginning of the string rather than from the end,
1243 as the year might not have exactly four digits, and additional
1244 information may some day be added at the end.
1246 The argument @var{time-value}, if given, specifies a time to format
1247 (represented as a list of integers), instead of the current time.
1251 (current-time-string)
1252 @result{} "Wed Oct 14 22:21:05 1987"
1258 This function returns the current time, represented as a list of four
1259 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1260 These integers have trailing zeros on systems that return time with
1261 lower resolutions. On all current machines @var{picosec} is a
1262 multiple of 1000, but this may change as higher-resolution clocks
1266 @defun float-time &optional time-value
1267 This function returns the current time as a floating-point number of
1268 seconds since the epoch. The optional argument @var{time-value}, if
1269 given, specifies a time (represented as a list of integers) to convert
1270 instead of the current time.
1272 @emph{Warning}: Since the result is floating point, it may not be
1273 exact. Do not use this function if precise time stamps are required.
1276 @defun current-time-zone &optional time-value
1277 @cindex time zone, current
1278 This function returns a list describing the time zone that the user is
1281 The value has the form @code{(@var{offset} @var{name})}. Here
1282 @var{offset} is an integer giving the number of seconds ahead of UTC
1283 (east of Greenwich). A negative value means west of Greenwich. The
1284 second element, @var{name}, is a string giving the name of the time
1285 zone. Both elements change when daylight saving time begins or ends;
1286 if the user has specified a time zone that does not use a seasonal time
1287 adjustment, then the value is constant through time.
1289 If the operating system doesn't supply all the information necessary to
1290 compute the value, the unknown elements of the list are @code{nil}.
1292 The argument @var{time-value}, if given, specifies a time (represented
1293 as a list of integers) to analyze instead of the current time.
1296 The current time zone is determined by the @env{TZ} environment
1297 variable. @xref{System Environment}. For example, you can tell Emacs
1298 to use universal time with @code{(setenv "TZ" "UTC0")}. If @env{TZ}
1299 is not in the environment, Emacs uses a platform-dependent default
1302 @node Time Conversion
1303 @section Time Conversion
1304 @cindex calendrical information
1306 These functions convert time values (lists of two to four integers,
1307 as explained in the previous section) into calendrical information and
1310 Many 32-bit operating systems are limited to time values containing
1311 32 bits of information; these systems typically handle only the times
1312 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
1313 However, 64-bit and some 32-bit operating systems have larger time
1314 values, and can represent times far in the past or future.
1316 Time conversion functions always use the Gregorian calendar, even
1317 for dates before the Gregorian calendar was introduced. Year numbers
1318 count the number of years since the year 1 B.C., and do not skip zero
1319 as traditional Gregorian years do; for example, the year number
1320 @minus{}37 represents the Gregorian year 38 B.C@.
1322 @defun decode-time &optional time
1323 This function converts a time value into calendrical information. If
1324 you don't specify @var{time}, it decodes the current time. The return
1325 value is a list of nine elements, as follows:
1328 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1331 Here is what the elements mean:
1335 The number of seconds past the minute, as an integer between 0 and 59.
1336 On some operating systems, this is 60 for leap seconds.
1338 The number of minutes past the hour, as an integer between 0 and 59.
1340 The hour of the day, as an integer between 0 and 23.
1342 The day of the month, as an integer between 1 and 31.
1344 The month of the year, as an integer between 1 and 12.
1346 The year, an integer typically greater than 1900.
1348 The day of week, as an integer between 0 and 6, where 0 stands for
1351 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1353 An integer indicating the time zone, as the number of seconds east of
1357 @strong{Common Lisp Note:} Common Lisp has different meanings for
1358 @var{dow} and @var{zone}.
1361 @defun encode-time seconds minutes hour day month year &optional zone
1362 This function is the inverse of @code{decode-time}. It converts seven
1363 items of calendrical data into a time value. For the meanings of the
1364 arguments, see the table above under @code{decode-time}.
1366 Year numbers less than 100 are not treated specially. If you want them
1367 to stand for years above 1900, or years above 2000, you must alter them
1368 yourself before you call @code{encode-time}.
1370 The optional argument @var{zone} defaults to the current time zone and
1371 its daylight saving time rules. If specified, it can be either a list
1372 (as you would get from @code{current-time-zone}), a string as in the
1373 @env{TZ} environment variable, @code{t} for Universal Time, or an
1374 integer (as you would get from @code{decode-time}). The specified
1375 zone is used without any further alteration for daylight saving time.
1377 If you pass more than seven arguments to @code{encode-time}, the first
1378 six are used as @var{seconds} through @var{year}, the last argument is
1379 used as @var{zone}, and the arguments in between are ignored. This
1380 feature makes it possible to use the elements of a list returned by
1381 @code{decode-time} as the arguments to @code{encode-time}, like this:
1384 (apply 'encode-time (decode-time @dots{}))
1387 You can perform simple date arithmetic by using out-of-range values for
1388 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1389 arguments; for example, day 0 means the day preceding the given month.
1391 The operating system puts limits on the range of possible time values;
1392 if you try to encode a time that is out of range, an error results.
1393 For instance, years before 1970 do not work on some systems;
1394 on others, years as early as 1901 do work.
1398 @section Parsing and Formatting Times
1400 These functions convert time values to text in a string, and vice versa.
1401 Time values are lists of two to four integers (@pxref{Time of Day}).
1403 @defun date-to-time string
1404 This function parses the time-string @var{string} and returns the
1405 corresponding time value.
1408 @defun format-time-string format-string &optional time universal
1409 This function converts @var{time} (or the current time, if @var{time} is
1410 omitted) to a string according to @var{format-string}. The argument
1411 @var{format-string} may contain @samp{%}-sequences which say to
1412 substitute parts of the time. Here is a table of what the
1413 @samp{%}-sequences mean:
1417 This stands for the abbreviated name of the day of week.
1419 This stands for the full name of the day of week.
1421 This stands for the abbreviated name of the month.
1423 This stands for the full name of the month.
1425 This is a synonym for @samp{%x %X}.
1427 This has a locale-specific meaning. In the default locale (named C), it
1428 is equivalent to @samp{%A, %B %e, %Y}.
1430 This stands for the day of month, zero-padded.
1432 This is a synonym for @samp{%m/%d/%y}.
1434 This stands for the day of month, blank-padded.
1436 This is a synonym for @samp{%b}.
1438 This stands for the hour (00--23).
1440 This stands for the hour (01--12).
1442 This stands for the day of the year (001--366).
1444 This stands for the hour (0--23), blank padded.
1446 This stands for the hour (1--12), blank padded.
1448 This stands for the month (01--12).
1450 This stands for the minute (00--59).
1452 This stands for a newline.
1454 This stands for the nanoseconds (000000000--999999999). To ask for
1455 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1456 microseconds, etc. Any excess digits are discarded, without rounding.
1458 This stands for @samp{AM} or @samp{PM}, as appropriate.
1460 This is a synonym for @samp{%I:%M:%S %p}.
1462 This is a synonym for @samp{%H:%M}.
1464 This stands for the seconds (00--59).
1466 This stands for a tab character.
1468 This is a synonym for @samp{%H:%M:%S}.
1470 This stands for the week of the year (01--52), assuming that weeks
1473 This stands for the numeric day of week (0--6). Sunday is day 0.
1475 This stands for the week of the year (01--52), assuming that weeks
1478 This has a locale-specific meaning. In the default locale (named
1479 @samp{C}), it is equivalent to @samp{%D}.
1481 This has a locale-specific meaning. In the default locale (named
1482 @samp{C}), it is equivalent to @samp{%T}.
1484 This stands for the year without century (00--99).
1486 This stands for the year with century.
1488 This stands for the time zone abbreviation (e.g., @samp{EST}).
1490 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1493 You can also specify the field width and type of padding for any of
1494 these @samp{%}-sequences. This works as in @code{printf}: you write
1495 the field width as digits in the middle of a @samp{%}-sequences. If you
1496 start the field width with @samp{0}, it means to pad with zeros. If you
1497 start the field width with @samp{_}, it means to pad with spaces.
1499 For example, @samp{%S} specifies the number of seconds since the minute;
1500 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1501 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1502 because that is how @samp{%S} normally pads to two positions.
1504 The characters @samp{E} and @samp{O} act as modifiers when used between
1505 @samp{%} and one of the letters in the table above. @samp{E} specifies
1506 using the current locale's ``alternative'' version of the date and time.
1507 In a Japanese locale, for example, @code{%Ex} might yield a date format
1508 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1509 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1512 @samp{O} means to use the current locale's ``alternative''
1513 representation of numbers, instead of the ordinary decimal digits. This
1514 is allowed with most letters, all the ones that output numbers.
1516 If @var{universal} is non-@code{nil}, that means to describe the time as
1517 Universal Time; @code{nil} means describe it using what Emacs believes
1518 is the local time zone (see @code{current-time-zone}).
1520 This function uses the C library function @code{strftime}
1521 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1522 Manual}) to do most of the work. In order to communicate with that
1523 function, it first encodes its argument using the coding system
1524 specified by @code{locale-coding-system} (@pxref{Locales}); after
1525 @code{strftime} returns the resulting string,
1526 @code{format-time-string} decodes the string using that same coding
1530 @defun seconds-to-time seconds
1531 This function converts @var{seconds}, the number of seconds since the
1532 epoch, to a time value and returns that. To convert back, use
1533 @code{float-time} (@pxref{Time of Day}).
1536 @defun format-seconds format-string seconds
1537 This function converts its argument @var{seconds} into a string of
1538 years, days, hours, etc., according to @var{format-string}. The
1539 argument @var{format-string} may contain @samp{%}-sequences which
1540 control the conversion. Here is a table of what the
1541 @samp{%}-sequences mean:
1546 The integer number of 365-day years.
1549 The integer number of days.
1552 The integer number of hours.
1555 The integer number of minutes.
1558 The integer number of seconds.
1560 Non-printing control flag. When it is used, other specifiers must be
1561 given in the order of decreasing size, i.e., years before days, hours
1562 before minutes, etc. Nothing will be produced in the result string to
1563 the left of @samp{%z} until the first non-zero conversion is
1564 encountered. For example, the default format used by
1565 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1566 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1567 will always be produced, but years, days, hours, and minutes will only
1568 be shown if they are non-zero.
1570 Produces a literal @samp{%}.
1573 Upper-case format sequences produce the units in addition to the
1574 numbers, lower-case formats produce only the numbers.
1576 You can also specify the field width by following the @samp{%} with a
1577 number; shorter numbers will be padded with blanks. An optional
1578 period before the width requests zero-padding instead. For example,
1579 @code{"%.3Y"} might produce @code{"004 years"}.
1581 @emph{Warning:} This function works only with values of @var{seconds}
1582 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1583 most-positive-fixnum}).
1586 @node Processor Run Time
1587 @section Processor Run time
1588 @cindex processor run time
1589 @cindex Emacs process run time
1591 Emacs provides several functions and primitives that return time,
1592 both elapsed and processor time, used by the Emacs process.
1594 @deffn Command emacs-uptime &optional format
1595 @cindex uptime of Emacs
1596 This function returns a string representing the Emacs
1597 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1598 running. The string is formatted by @code{format-seconds} according
1599 to the optional argument @var{format}. For the available format
1600 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1601 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1604 When called interactively, it prints the uptime in the echo area.
1607 @defun get-internal-run-time
1608 This function returns the processor run time used by Emacs as a list
1609 of four integers: @code{(@var{high} @var{low} @var{microsec}
1610 @var{picosec})}, using the same format as @code{current-time}
1611 (@pxref{Time of Day}).
1613 Note that the time returned by this function excludes the time Emacs
1614 was not using the processor, and if the Emacs process has several
1615 threads, the returned value is the sum of the processor times used up
1616 by all Emacs threads.
1618 If the system doesn't provide a way to determine the processor run
1619 time, @code{get-internal-run-time} returns the same time as
1620 @code{current-time}.
1623 @deffn Command emacs-init-time
1624 This function returns the duration of the Emacs initialization
1625 (@pxref{Startup Summary}) in seconds, as a string. When called
1626 interactively, it prints the duration in the echo area.
1629 @node Time Calculations
1630 @section Time Calculations
1632 These functions perform calendrical computations using time values
1633 (the kind of list that @code{current-time} returns).
1635 @defun time-less-p t1 t2
1636 This returns @code{t} if time value @var{t1} is less than time value
1640 @defun time-subtract t1 t2
1641 This returns the time difference @var{t1} @minus{} @var{t2} between
1642 two time values, in the same format as a time value.
1645 @defun time-add t1 t2
1646 This returns the sum of two time values, one of which ought to
1647 represent a time difference rather than a point in time.
1648 Here is how to add a number of seconds to a time value:
1651 (time-add @var{time} (seconds-to-time @var{seconds}))
1655 @defun time-to-days time
1656 This function returns the number of days between the beginning of year
1660 @defun time-to-day-in-year time
1661 This returns the day number within the year corresponding to @var{time}.
1664 @defun date-leap-year-p year
1665 This function returns @code{t} if @var{year} is a leap year.
1669 @section Timers for Delayed Execution
1672 You can set up a @dfn{timer} to call a function at a specified
1673 future time or after a certain length of idleness.
1675 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1676 can run them only when Emacs could accept output from a subprocess:
1677 namely, while waiting or inside certain primitive functions such as
1678 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1679 timer's execution may be delayed if Emacs is busy. However, the time of
1680 execution is very precise if Emacs is idle.
1682 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1683 function, because quitting out of many timer functions can leave
1684 things in an inconsistent state. This is normally unproblematical
1685 because most timer functions don't do a lot of work. Indeed, for a
1686 timer to call a function that takes substantial time to run is likely
1687 to be annoying. If a timer function needs to allow quitting, it
1688 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1689 a timer function calls @code{accept-process-output} to receive output
1690 from an external process, that call should be wrapped inside
1691 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1694 It is usually a bad idea for timer functions to alter buffer
1695 contents. When they do, they usually should call @code{undo-boundary}
1696 both before and after changing the buffer, to separate the timer's
1697 changes from user commands' changes and prevent a single undo entry
1698 from growing to be quite large.
1700 Timer functions should also avoid calling functions that cause Emacs
1701 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1702 unpredictable effects, since other timers (or even the same timer) can
1703 run while waiting. If a timer function needs to perform an action
1704 after a certain time has elapsed, it can do this by scheduling a new
1707 If a timer function calls functions that can change the match data,
1708 it should save and restore the match data. @xref{Saving Match Data}.
1710 @deffn Command run-at-time time repeat function &rest args
1711 This sets up a timer that calls the function @var{function} with
1712 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1713 (integer or floating point), the timer is scheduled to run again every
1714 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1715 the timer runs only once.
1717 @var{time} may specify an absolute or a relative time.
1719 Absolute times may be specified using a string with a limited variety
1720 of formats, and are taken to be times @emph{today}, even if already in
1721 the past. The recognized forms are @samp{@var{xxxx}},
1722 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1723 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1724 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1725 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1726 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1727 to separate the hour and minute parts.
1729 To specify a relative time as a string, use numbers followed by units.
1734 denotes 1 minute from now.
1736 denotes 65 seconds from now.
1737 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1738 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1741 For relative time values, Emacs considers a month to be exactly thirty
1742 days, and a year to be exactly 365.25 days.
1744 Not all convenient formats are strings. If @var{time} is a number
1745 (integer or floating point), that specifies a relative time measured in
1746 seconds. The result of @code{encode-time} can also be used to specify
1747 an absolute value for @var{time}.
1749 In most cases, @var{repeat} has no effect on when @emph{first} call
1750 takes place---@var{time} alone specifies that. There is one exception:
1751 if @var{time} is @code{t}, then the timer runs whenever the time is a
1752 multiple of @var{repeat} seconds after the epoch. This is useful for
1753 functions like @code{display-time}.
1755 The function @code{run-at-time} returns a timer value that identifies
1756 the particular scheduled future action. You can use this value to call
1757 @code{cancel-timer} (see below).
1760 A repeating timer nominally ought to run every @var{repeat} seconds,
1761 but remember that any invocation of a timer can be late. Lateness of
1762 one repetition has no effect on the scheduled time of the next
1763 repetition. For instance, if Emacs is busy computing for long enough
1764 to cover three scheduled repetitions of the timer, and then starts to
1765 wait, it will immediately call the timer function three times in
1766 immediate succession (presuming no other timers trigger before or
1767 between them). If you want a timer to run again no less than @var{n}
1768 seconds after the last invocation, don't use the @var{repeat} argument.
1769 Instead, the timer function should explicitly reschedule the timer.
1771 @defopt timer-max-repeats
1772 This variable's value specifies the maximum number of times to repeat
1773 calling a timer function in a row, when many previously scheduled
1774 calls were unavoidably delayed.
1777 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1778 Execute @var{body}, but give up after @var{seconds} seconds. If
1779 @var{body} finishes before the time is up, @code{with-timeout} returns
1780 the value of the last form in @var{body}. If, however, the execution of
1781 @var{body} is cut short by the timeout, then @code{with-timeout}
1782 executes all the @var{timeout-forms} and returns the value of the last
1785 This macro works by setting a timer to run after @var{seconds} seconds. If
1786 @var{body} finishes before that time, it cancels the timer. If the
1787 timer actually runs, it terminates execution of @var{body}, then
1788 executes @var{timeout-forms}.
1790 Since timers can run within a Lisp program only when the program calls a
1791 primitive that can wait, @code{with-timeout} cannot stop executing
1792 @var{body} while it is in the midst of a computation---only when it
1793 calls one of those primitives. So use @code{with-timeout} only with a
1794 @var{body} that waits for input, not one that does a long computation.
1797 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1798 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1801 @defun cancel-timer timer
1802 This cancels the requested action for @var{timer}, which should be a
1803 timer---usually, one previously returned by @code{run-at-time} or
1804 @code{run-with-idle-timer}. This cancels the effect of that call to
1805 one of these functions; the arrival of the specified time will not
1806 cause anything special to happen.
1810 @section Idle Timers
1812 Here is how to set up a timer that runs when Emacs is idle for a
1813 certain length of time. Aside from how to set them up, idle timers
1814 work just like ordinary timers.
1816 @deffn Command run-with-idle-timer secs repeat function &rest args
1817 Set up a timer which runs the next time Emacs is idle for @var{secs}
1818 seconds. The value of @var{secs} may be a number or a value of the type
1819 returned by @code{current-idle-time}.
1821 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1822 Emacs remains idle for a long enough time. More often @var{repeat} is
1823 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1824 remains idle for @var{secs} seconds.
1826 The function @code{run-with-idle-timer} returns a timer value which you
1827 can use in calling @code{cancel-timer} (@pxref{Timers}).
1831 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1832 it remains idle until the user provides some input. If a timer is set
1833 for five seconds of idleness, it runs approximately five seconds after
1834 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1835 this timer will not run again as long as Emacs remains idle, because
1836 the duration of idleness will continue to increase and will not go
1837 down to five seconds again.
1839 Emacs can do various things while idle: garbage collect, autosave or
1840 handle data from a subprocess. But these interludes during idleness do
1841 not interfere with idle timers, because they do not reset the clock of
1842 idleness to zero. An idle timer set for 600 seconds will run when ten
1843 minutes have elapsed since the last user command was finished, even if
1844 subprocess output has been accepted thousands of times within those ten
1845 minutes, and even if there have been garbage collections and autosaves.
1847 When the user supplies input, Emacs becomes non-idle while executing the
1848 input. Then it becomes idle again, and all the idle timers that are
1849 set up to repeat will subsequently run another time, one by one.
1851 Do not write an idle timer function containing a loop which does a
1852 certain amount of processing each time around, and exits when
1853 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1854 natural but has two problems:
1858 It blocks out all process output (since Emacs accepts process output
1859 only while waiting).
1862 It blocks out any idle timers that ought to run during that time.
1866 Similarly, do not write an idle timer function that sets up another
1867 idle timer (including the same idle timer) with @var{secs} argument
1868 less than or equal to the current idleness time. Such a timer will
1869 run almost immediately, and continue running again and again, instead
1870 of waiting for the next time Emacs becomes idle. The correct approach
1871 is to reschedule with an appropriate increment of the current value of
1872 the idleness time, as described below.
1874 @defun current-idle-time
1875 If Emacs is idle, this function returns the length of time Emacs has
1876 been idle, as a list of four integers: @code{(@var{sec-high}
1877 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1878 @code{current-time} (@pxref{Time of Day}).
1880 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1881 This is a convenient way to test whether Emacs is idle.
1884 The main use of @code{current-idle-time} is when an idle timer
1885 function wants to ``take a break'' for a while. It can set up another
1886 idle timer to call the same function again, after a few seconds more
1887 idleness. Here's an example:
1890 (defvar my-resume-timer nil
1891 "Timer for `my-timer-function' to reschedule itself, or nil.")
1893 (defun my-timer-function ()
1894 ;; @r{If the user types a command while @code{my-resume-timer}}
1895 ;; @r{is active, the next time this function is called from}
1896 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1897 (when my-resume-timer
1898 (cancel-timer my-resume-timer))
1899 ...@var{do the work for a while}...
1900 (when @var{taking-a-break}
1901 (setq my-resume-timer
1902 (run-with-idle-timer
1903 ;; Compute an idle time @var{break-length}
1904 ;; more than the current value.
1905 (time-add (current-idle-time)
1906 (seconds-to-time @var{break-length}))
1908 'my-timer-function))))
1911 @node Terminal Input
1912 @section Terminal Input
1913 @cindex terminal input
1915 This section describes functions and variables for recording or
1916 manipulating terminal input. See @ref{Display}, for related
1920 * Input Modes:: Options for how input is processed.
1921 * Recording Input:: Saving histories of recent or all input events.
1925 @subsection Input Modes
1927 @cindex terminal input modes
1929 @defun set-input-mode interrupt flow meta &optional quit-char
1930 This function sets the mode for reading keyboard input. If
1931 @var{interrupt} is non-@code{nil}, then Emacs uses input interrupts.
1932 If it is @code{nil}, then it uses @sc{cbreak} mode. The default
1933 setting is system-dependent. Some systems always use @sc{cbreak} mode
1934 regardless of what is specified.
1936 When Emacs communicates directly with X, it ignores this argument and
1937 uses interrupts if that is the way it knows how to communicate.
1939 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1940 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1941 has no effect except in @sc{cbreak} mode.
1943 The argument @var{meta} controls support for input character codes
1944 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1945 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1946 Emacs disregards the 8th bit; this is necessary when the terminal uses
1947 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1948 Emacs uses all 8 bits of input unchanged. This is good for terminals
1949 that use 8-bit character sets.
1951 If @var{quit-char} is non-@code{nil}, it specifies the character to
1952 use for quitting. Normally this character is @kbd{C-g}.
1956 The @code{current-input-mode} function returns the input mode settings
1957 Emacs is currently using.
1959 @defun current-input-mode
1960 This function returns the current mode for reading keyboard input. It
1961 returns a list, corresponding to the arguments of @code{set-input-mode},
1962 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1966 is non-@code{nil} when Emacs is using interrupt-driven input. If
1967 @code{nil}, Emacs is using @sc{cbreak} mode.
1969 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1970 flow control for output to the terminal. This value is meaningful only
1971 when @var{interrupt} is @code{nil}.
1973 is @code{t} if Emacs treats the eighth bit of input characters as
1974 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1975 input character; any other value means Emacs uses all eight bits as the
1976 basic character code.
1978 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1982 @node Recording Input
1983 @subsection Recording Input
1984 @cindex recording input
1987 This function returns a vector containing the last 300 input events from
1988 the keyboard or mouse. All input events are included, whether or not
1989 they were used as parts of key sequences. Thus, you always get the last
1990 300 input events, not counting events generated by keyboard macros.
1991 (These are excluded because they are less interesting for debugging; it
1992 should be enough to see the events that invoked the macros.)
1994 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1995 causes this function to return an empty vector immediately afterward.
1998 @deffn Command open-dribble-file filename
1999 @cindex dribble file
2000 This function opens a @dfn{dribble file} named @var{filename}. When a
2001 dribble file is open, each input event from the keyboard or mouse (but
2002 not those from keyboard macros) is written in that file. A
2003 non-character event is expressed using its printed representation
2004 surrounded by @samp{<@dots{}>}. Be aware that sensitive information
2005 (such as passwords) may end up recorded in the dribble file.
2007 You close the dribble file by calling this function with an argument
2011 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2013 @node Terminal Output
2014 @section Terminal Output
2015 @cindex terminal output
2017 The terminal output functions send output to a text terminal, or keep
2018 track of output sent to the terminal. The variable @code{baud-rate}
2019 tells you what Emacs thinks is the output speed of the terminal.
2022 This variable's value is the output speed of the terminal, as far as
2023 Emacs knows. Setting this variable does not change the speed of actual
2024 data transmission, but the value is used for calculations such as
2027 It also affects decisions about whether to scroll part of the
2028 screen or repaint on text terminals. @xref{Forcing Redisplay},
2029 for the corresponding functionality on graphical terminals.
2031 The value is measured in baud.
2034 If you are running across a network, and different parts of the
2035 network work at different baud rates, the value returned by Emacs may be
2036 different from the value used by your local terminal. Some network
2037 protocols communicate the local terminal speed to the remote machine, so
2038 that Emacs and other programs can get the proper value, but others do
2039 not. If Emacs has the wrong value, it makes decisions that are less
2040 than optimal. To fix the problem, set @code{baud-rate}.
2042 @defun send-string-to-terminal string &optional terminal
2043 This function sends @var{string} to @var{terminal} without alteration.
2044 Control characters in @var{string} have terminal-dependent effects.
2045 This function operates only on text terminals. @var{terminal} may be
2046 a terminal object, a frame, or @code{nil} for the selected frame's
2047 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2048 @var{terminal} is @code{nil}.
2050 One use of this function is to define function keys on terminals that
2051 have downloadable function key definitions. For example, this is how (on
2052 certain terminals) to define function key 4 to move forward four
2053 characters (by transmitting the characters @kbd{C-u C-f} to the
2058 (send-string-to-terminal "\eF4\^U\^F")
2064 @deffn Command open-termscript filename
2065 @cindex termscript file
2066 This function is used to open a @dfn{termscript file} that will record
2067 all the characters sent by Emacs to the terminal. It returns
2068 @code{nil}. Termscript files are useful for investigating problems
2069 where Emacs garbles the screen, problems that are due to incorrect
2070 Termcap entries or to undesirable settings of terminal options more
2071 often than to actual Emacs bugs. Once you are certain which characters
2072 were actually output, you can determine reliably whether they correspond
2073 to the Termcap specifications in use.
2077 (open-termscript "../junk/termscript")
2082 You close the termscript file by calling this function with an
2083 argument of @code{nil}.
2085 See also @code{open-dribble-file} in @ref{Recording Input}.
2089 @section Sound Output
2092 To play sound using Emacs, use the function @code{play-sound}. Only
2093 certain systems are supported; if you call @code{play-sound} on a
2094 system which cannot really do the job, it gives an error.
2096 @c FIXME: Add indexes for Au and WAV? --xfq
2097 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2098 or Sun Audio format (@samp{.au}).
2100 @defun play-sound sound
2101 This function plays a specified sound. The argument, @var{sound}, has
2102 the form @code{(sound @var{properties}...)}, where the @var{properties}
2103 consist of alternating keywords (particular symbols recognized
2104 specially) and values corresponding to them.
2106 Here is a table of the keywords that are currently meaningful in
2107 @var{sound}, and their meanings:
2110 @item :file @var{file}
2111 This specifies the file containing the sound to play.
2112 If the file name is not absolute, it is expanded against
2113 the directory @code{data-directory}.
2115 @item :data @var{data}
2116 This specifies the sound to play without need to refer to a file. The
2117 value, @var{data}, should be a string containing the same bytes as a
2118 sound file. We recommend using a unibyte string.
2120 @item :volume @var{volume}
2121 This specifies how loud to play the sound. It should be a number in the
2122 range of 0 to 1. The default is to use whatever volume has been
2125 @item :device @var{device}
2126 This specifies the system device on which to play the sound, as a
2127 string. The default device is system-dependent.
2130 Before actually playing the sound, @code{play-sound}
2131 calls the functions in the list @code{play-sound-functions}.
2132 Each function is called with one argument, @var{sound}.
2135 @deffn Command play-sound-file file &optional volume device
2136 This function is an alternative interface to playing a sound @var{file}
2137 specifying an optional @var{volume} and @var{device}.
2140 @defvar play-sound-functions
2141 A list of functions to be called before playing a sound. Each function
2142 is called with one argument, a property list that describes the sound.
2146 @section Operating on X11 Keysyms
2149 To define system-specific X11 keysyms, set the variable
2150 @code{system-key-alist}.
2152 @defvar system-key-alist
2153 This variable's value should be an alist with one element for each
2154 system-specific keysym. Each element has the form @code{(@var{code}
2155 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2156 including the ``vendor specific'' bit,
2163 and @var{symbol} is the name for the function key.
2165 For example @code{(168 . mute-acute)} defines a system-specific key (used
2166 by HP X servers) whose numeric code is
2175 It is not crucial to exclude from the alist the keysyms of other X
2176 servers; those do no harm, as long as they don't conflict with the ones
2177 used by the X server actually in use.
2179 The variable is always local to the current terminal, and cannot be
2180 buffer-local. @xref{Multiple Terminals}.
2183 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2185 @defvar x-alt-keysym
2186 @defvarx x-meta-keysym
2187 @defvarx x-hyper-keysym
2188 @defvarx x-super-keysym
2189 The name of the keysym that should stand for the Alt modifier
2190 (respectively, for Meta, Hyper, and Super). For example, here is
2191 how to swap the Meta and Alt modifiers within Emacs:
2193 (setq x-alt-keysym 'meta)
2194 (setq x-meta-keysym 'alt)
2202 The command-line option @samp{-batch} causes Emacs to run
2203 noninteractively. In this mode, Emacs does not read commands from the
2204 terminal, it does not alter the terminal modes, and it does not expect
2205 to be outputting to an erasable screen. The idea is that you specify
2206 Lisp programs to run; when they are finished, Emacs should exit. The
2207 way to specify the programs to run is with @samp{-l @var{file}}, which
2208 loads the library named @var{file}, or @samp{-f @var{function}}, which
2209 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2211 Any Lisp program output that would normally go to the echo area,
2212 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2213 as the stream, goes instead to Emacs's standard error descriptor when
2214 in batch mode. Similarly, input that would normally come from the
2215 minibuffer is read from the standard input descriptor.
2216 Thus, Emacs behaves much like a noninteractive
2217 application program. (The echo area output that Emacs itself normally
2218 generates, such as command echoing, is suppressed entirely.)
2220 @defvar noninteractive
2221 This variable is non-@code{nil} when Emacs is running in batch mode.
2224 @node Session Management
2225 @section Session Management
2226 @cindex session manager
2228 Emacs supports the X Session Management Protocol, which is used to
2229 suspend and restart applications. In the X Window System, a program
2230 called the @dfn{session manager} is responsible for keeping track of
2231 the applications that are running. When the X server shuts down, the
2232 session manager asks applications to save their state, and delays the
2233 actual shutdown until they respond. An application can also cancel
2236 When the session manager restarts a suspended session, it directs
2237 these applications to individually reload their saved state. It does
2238 this by specifying a special command-line argument that says what
2239 saved session to restore. For Emacs, this argument is @samp{--smid
2242 @defvar emacs-save-session-functions
2243 @cindex session file
2244 Emacs supports saving state via a hook called
2245 @code{emacs-save-session-functions}. Emacs runs this hook when the
2246 session manager tells it that the window system is shutting down. The
2247 functions are called with no arguments, and with the current buffer
2248 set to a temporary buffer. Each function can use @code{insert} to add
2249 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2250 file, called the @dfn{session file}.
2252 @findex emacs-session-restore
2253 Subsequently, when the session manager restarts Emacs, it loads the
2254 session file automatically (@pxref{Loading}). This is performed by a
2255 function named @code{emacs-session-restore}, which is called during
2256 startup. @xref{Startup Summary}.
2258 If a function in @code{emacs-save-session-functions} returns
2259 non-@code{nil}, Emacs tells the session manager to cancel the
2263 Here is an example that just inserts some text into @file{*scratch*} when
2264 Emacs is restarted by the session manager.
2268 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2272 (defun save-yourself-test ()
2273 (insert "(save-current-buffer
2274 (switch-to-buffer \"*scratch*\")
2275 (insert \"I am restored\"))")
2280 @node Desktop Notifications
2281 @section Desktop Notifications
2282 @cindex desktop notifications
2283 @cindex notifications, on desktop
2285 Emacs is able to send @dfn{notifications} on systems that support the
2286 freedesktop.org Desktop Notifications Specification. In order to use
2287 this functionality, Emacs must have been compiled with D-Bus support,
2288 and the @code{notifications} library must be loaded. @xref{Top, ,
2289 D-Bus,dbus,D-Bus integration in Emacs}.
2291 @defun notifications-notify &rest params
2292 This function sends a notification to the desktop via D-Bus,
2293 consisting of the parameters specified by the @var{params} arguments.
2294 These arguments should consist of alternating keyword and value pairs.
2295 The supported keywords and values are as follows:
2298 @item :bus @var{bus}
2299 The D-Bus bus. This argument is needed only if a bus other than
2300 @code{:session} shall be used.
2302 @item :title @var{title}
2303 The notification title.
2305 @item :body @var{text}
2306 The notification body text. Depending on the implementation of the
2307 notification server, the text could contain HTML markups, like
2308 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2309 characters must be encoded, as @samp{"Contact
2310 <postmaster@@localhost>!"}.
2312 @item :app-name @var{name}
2313 The name of the application sending the notification. The default is
2314 @code{notifications-application-name}.
2316 @item :replaces-id @var{id}
2317 The notification @var{id} that this notification replaces. @var{id}
2318 must be the result of a previous @code{notifications-notify} call.
2320 @item :app-icon @var{icon-file}
2321 The file name of the notification icon. If set to @code{nil}, no icon
2322 is displayed. The default is @code{notifications-application-icon}.
2324 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2325 A list of actions to be applied. @var{key} and @var{title} are both
2326 strings. The default action (usually invoked by clicking the
2327 notification) should have a key named @samp{"default"}. The title can
2328 be anything, though implementations are free not to display it.
2330 @item :timeout @var{timeout}
2331 The timeout time in milliseconds since the display of the notification
2332 at which the notification should automatically close. If @minus{}1, the
2333 notification's expiration time is dependent on the notification
2334 server's settings, and may vary for the type of notification. If 0,
2335 the notification never expires. Default value is @minus{}1.
2337 @item :urgency @var{urgency}
2338 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2341 When this keyword is given, the @var{title} string of the actions is
2342 interpreted as icon name.
2344 @item :category @var{category}
2345 The type of notification this is, a string. See the
2346 @uref{http://developer.gnome.org/notification-spec/#categories,
2347 Desktop Notifications Specification} for a list of standard
2350 @item :desktop-entry @var{filename}
2351 This specifies the name of the desktop filename representing the
2352 calling program, like @samp{"emacs"}.
2354 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2355 This is a raw data image format that describes the width, height,
2356 rowstride, whether there is an alpha channel, bits per sample,
2357 channels and image data, respectively.
2359 @item :image-path @var{path}
2360 This is represented either as a URI (@samp{file://} is the only URI
2361 schema supported right now) or a name in a freedesktop.org-compliant
2362 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2364 @item :sound-file @var{filename}
2365 The path to a sound file to play when the notification pops up.
2367 @item :sound-name @var{name}
2368 A themable named sound from the freedesktop.org sound naming
2369 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2370 notification pops up. Similar to the icon name, only for sounds. An
2371 example would be @samp{"message-new-instant"}.
2373 @item :suppress-sound
2374 Causes the server to suppress playing any sounds, if it has that
2378 When set the server will not automatically remove the notification
2379 when an action has been invoked. The notification will remain resident
2380 in the server until it is explicitly removed by the user or by the
2381 sender. This hint is likely only useful when the server has the
2382 @code{:persistence} capability.
2385 When set the server will treat the notification as transient and
2386 by-pass the server's persistence capability, if it should exist.
2388 @item :x @var{position}
2389 @itemx :y @var{position}
2390 Specifies the X, Y location on the screen that the
2391 notification should point to. Both arguments must be used together.
2393 @item :on-action @var{function}
2394 Function to call when an action is invoked. The notification @var{id}
2395 and the @var{key} of the action are passed as arguments to the
2398 @item :on-close @var{function}
2399 Function to call when the notification has been closed by timeout or
2400 by the user. The function receive the notification @var{id} and the closing
2401 @var{reason} as arguments:
2404 @item @code{expired} if the notification has expired
2405 @item @code{dismissed} if the notification was dismissed by the user
2406 @item @code{close-notification} if the notification was closed by a call to
2407 @code{notifications-close-notification}
2408 @item @code{undefined} if the notification server hasn't provided a reason
2412 Which parameters are accepted by the notification server can be
2413 checked via @code{notifications-get-capabilities}.
2415 This function returns a notification id, an integer, which can be used
2416 to manipulate the notification item with
2417 @code{notifications-close-notification} or the @code{:replaces-id}
2418 argument of another @code{notifications-notify} call. For example:
2422 (defun my-on-action-function (id key)
2423 (message "Message %d, key \"%s\" pressed" id key))
2424 @result{} my-on-action-function
2428 (defun my-on-close-function (id reason)
2429 (message "Message %d, closed due to \"%s\"" id reason))
2430 @result{} my-on-close-function
2434 (notifications-notify
2436 :body "This is <b>important</b>."
2437 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2438 :on-action 'my-on-action-function
2439 :on-close 'my-on-close-function)
2444 A message window opens on the desktop. Press "I agree"
2445 @result{} Message 22, key "Confirm" pressed
2446 Message 22, closed due to "dismissed"
2451 @defun notifications-close-notification id &optional bus
2452 This function closes a notification with identifier @var{id}.
2453 @var{bus} can be a string denoting a D-Bus connection, the default is
2457 @defun notifications-get-capabilities &optional bus
2458 Returns the capabilities of the notification server, a list of
2459 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2460 default is @code{:session}. The following capabilities can be
2465 The server will provide the specified actions to the user.
2470 @item :body-hyperlinks
2471 The server supports hyperlinks in the notifications.
2474 The server supports images in the notifications.
2477 Supports markup in the body text.
2480 The server will render an animation of all the frames in a given image
2484 Supports display of exactly 1 frame of any given image array. This
2485 value is mutually exclusive with @code{:icon-multi}.
2488 The server supports persistence of notifications.
2491 The server supports sounds on notifications.
2494 Further vendor-specific caps start with @code{:x-vendor}, like
2495 @code{:x-gnome-foo-cap}.
2498 @defun notifications-get-server-information &optional bus
2499 Return information on the notification server, a list of strings.
2500 @var{bus} can be a string denoting a D-Bus connection, the default is
2501 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2502 @var{version} @var{spec-version})}.
2506 The product name of the server.
2509 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2512 The server's version number.
2515 The specification version the server is compliant with.
2518 If @var{SPEC_VERSION} is @code{nil}, the server supports a
2519 specification prior to @samp{"1.0"}.
2522 @node File Notifications
2523 @section Notifications on File Changes
2524 @cindex file notifications
2525 @cindex watch, for filesystem events
2527 Several operating systems support watching of filesystems for changes
2528 of files. If configured properly, Emacs links a respective library
2529 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2530 statically. These libraries enable watching of filesystems on the
2533 It is also possible to watch filesystems on remote machines,
2534 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2535 This does not depend on one of the libraries linked to Emacs.
2537 Since all these libraries emit different events on notified file
2538 changes, there is the Emacs library @code{filenotify} which provides a
2541 @defun file-notify-add-watch file flags callback
2542 Add a watch for filesystem events pertaining to @var{file}. This
2543 arranges for filesystem events pertaining to @var{file} to be reported
2546 The returned value is a descriptor for the added watch. Its type
2547 depends on the underlying library, it cannot be assumed to be an
2548 integer as in the example below. It should be used for comparison by
2551 If the @var{file} cannot be watched for some reason, this function
2552 signals a @code{file-notify-error} error.
2554 Sometimes, mounted filesystems cannot be watched for file changes.
2555 This is not detected by this function, a non-@code{nil} return value
2556 does not guarantee that changes on @var{file} will be notified.
2558 @var{flags} is a list of conditions to set what will be watched for.
2559 It can include the following symbols:
2563 watch for file changes
2564 @item attribute-change
2565 watch for file attribute changes, like permissions or modification
2569 If @var{file} is a directory, changes for all files in that directory
2570 will be notified. This does not work recursively.
2572 When any event happens, Emacs will call the @var{callback} function
2573 passing it a single argument @var{event}, which is of the form
2576 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2579 @var{descriptor} is the same object as the one returned by this
2580 function. @var{action} is the description of the event. It could be
2581 any one of the following symbols:
2585 @var{file} was created
2587 @var{file} was deleted
2589 @var{file} has changed
2591 @var{file} has been renamed to @var{file1}
2592 @item attribute-changed
2593 a @var{file} attribute was changed
2596 @var{file} and @var{file1} are the name of the file(s) whose event is
2597 being reported. For example:
2601 (require 'filenotify)
2602 @result{} filenotify
2606 (defun my-notify-callback (event)
2607 (message "Event %S" event))
2608 @result{} my-notify-callback
2612 (file-notify-add-watch
2613 "/tmp" '(change attribute-change) 'my-notify-callback)
2618 (write-region "foo" nil "/tmp/foo")
2619 @result{} Event (35025468 created "/tmp/.#foo")
2620 Event (35025468 created "/tmp/foo")
2621 Event (35025468 changed "/tmp/foo")
2622 Event (35025468 deleted "/tmp/.#foo")
2626 (write-region "bla" nil "/tmp/foo")
2627 @result{} Event (35025468 created "/tmp/.#foo")
2628 Event (35025468 changed "/tmp/foo") [2 times]
2629 Event (35025468 deleted "/tmp/.#foo")
2633 (set-file-modes "/tmp/foo" (default-file-modes))
2634 @result{} Event (35025468 attribute-changed "/tmp/foo")
2638 Whether the action @code{renamed} is returned, depends on the used
2639 watch library. It can be expected, when a directory is watched, and
2640 both @var{file} and @var{file1} belong to this directory. Otherwise,
2641 the actions @code{deleted} and @code{created} could be returned in a
2646 (rename-file "/tmp/foo" "/tmp/bla")
2647 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2651 (file-notify-add-watch
2652 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2657 (rename-file "/tmp/bla" "/var/tmp/bla")
2658 @result{} ;; gfilenotify
2659 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2661 @result{} ;; inotify
2662 Event (35025504 created "/var/tmp/bla")
2663 Event (35025468 deleted "/tmp/bla")
2668 @defun file-notify-rm-watch descriptor
2669 Removes an existing file watch specified by its @var{descriptor}.
2670 @var{descriptor} should be an object returned by
2671 @code{file-notify-add-watch}.
2674 @node Dynamic Libraries
2675 @section Dynamically Loaded Libraries
2676 @cindex dynamic libraries
2678 A @dfn{dynamically loaded library} is a library that is loaded on
2679 demand, when its facilities are first needed. Emacs supports such
2680 on-demand loading of support libraries for some of its features.
2682 @defvar dynamic-library-alist
2683 This is an alist of dynamic libraries and external library files
2686 Each element is a list of the form
2687 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2688 a symbol representing a supported external library, and the rest are
2689 strings giving alternate filenames for that library.
2691 Emacs tries to load the library from the files in the order they
2692 appear in the list; if none is found, the Emacs session won't have
2693 access to that library, and the features it provides will be
2696 Image support on some platforms uses this facility. Here's an example
2697 of setting this variable for supporting images on MS-Windows:
2700 (setq dynamic-library-alist
2701 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2702 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2703 "libpng13d.dll" "libpng13.dll")
2704 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2706 (tiff "libtiff3.dll" "libtiff.dll")
2707 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2708 (svg "librsvg-2-2.dll")
2709 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2710 (glib "libglib-2.0-0.dll")
2711 (gobject "libgobject-2.0-0.dll")))
2714 Note that image types @code{pbm} and @code{xbm} do not need entries in
2715 this variable because they do not depend on external libraries and are
2716 always available in Emacs.
2718 Also note that this variable is not meant to be a generic facility for
2719 accessing external libraries; only those already known by Emacs can
2720 be loaded through it.
2722 This variable is ignored if the given @var{library} is statically