2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2013 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; so it skips the directories containing the standard Emacs
78 libraries (for efficiency, since @file{leim-list.el} should not exist
79 in those directories), as well as the @file{leim} directory that is
80 part of the distribution (since the @file{leim-list.el} file in this
81 directory is compiled into the Emacs executable).
83 @vindex before-init-time
85 It sets the variable @code{before-init-time} to the value of
86 @code{current-time} (@pxref{Time of Day}). It also sets
87 @code{after-init-time} to @code{nil}, which signals to Lisp programs
88 that Emacs is being initialized.
90 @c set-locale-environment
92 It sets the language environment and the terminal coding system,
93 if requested by environment variables such as @env{LANG}.
96 It does some basic parsing of the command-line arguments.
98 @vindex initial-window-system@r{, and startup}
99 @vindex window-system-initialization-alist
101 If not running in batch mode, it initializes the window system that
102 the variable @code{initial-window-system} specifies (@pxref{Window
103 Systems, initial-window-system}). The initialization function for
104 each supported window system is specified by
105 @code{window-system-initialization-alist}. If the value
106 of @code{initial-window-system} is @var{windowsystem}, then the
107 appropriate initialization function is defined in the file
108 @file{term/@var{windowsystem}-win.el}. This file should have been
109 compiled into the Emacs executable when it was built.
112 It runs the normal hook @code{before-init-hook}.
115 If appropriate, it creates a graphical frame. This is not done if the
116 options @samp{--batch} or @samp{--daemon} were specified.
119 It initializes the initial frame's faces, and sets up the menu bar
120 and tool bar if needed. If graphical frames are supported, it sets up
121 the tool bar even if the current frame is not a graphical one, since a
122 graphical frame may be created later on.
125 It use @code{custom-reevaluate-setting} to re-initialize the members
126 of the list @code{custom-delayed-init-variables}. These are any
127 pre-loaded user options whose default value depends on the run-time,
128 rather than build-time, context.
129 @xref{Building Emacs, custom-initialize-delay}.
132 @c It registers the colors available for tty frames.
135 It loads the library @file{site-start}, if it exists. This is not
136 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
137 @cindex @file{site-start.el}
140 It loads your init file (@pxref{Init File}). This is not done if the
141 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
142 the @samp{-u} option was specified, Emacs looks for the init file in
143 that user's home directory instead.
146 It loads the library @file{default}, if it exists. This is not done
147 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
148 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
149 @cindex @file{default.el}
152 It loads your abbrevs from the file specified by
153 @code{abbrev-file-name}, if that file exists and can be read
154 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
155 option @samp{--batch} was specified.
158 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
159 function @code{package-initialize} to activate any optional Emacs Lisp
160 package that has been installed. @xref{Packaging Basics}.
162 @vindex after-init-time
164 It sets the variable @code{after-init-time} to the value of
165 @code{current-time}. This variable was set to @code{nil} earlier;
166 setting it to the current time signals that the initialization phase
167 is over, and, together with @code{before-init-time}, provides the
168 measurement of how long it took.
171 It runs the normal hook @code{after-init-hook}.
174 If the buffer @file{*scratch*} exists and is still in Fundamental mode
175 (as it should be by default), it sets its major mode according to
176 @code{initial-major-mode}.
179 If started on a text terminal, it loads the terminal-specific
180 Lisp library, which is specified by the variable
181 @code{term-file-prefix} (@pxref{Terminal-Specific}). This is not done
182 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
184 @c Now command-line calls command-line-1.
187 It displays the initial echo area message, unless you have suppressed
188 that with @code{inhibit-startup-echo-area-message}.
191 It processes any command-line options that were not handled earlier.
193 @c This next one is back in command-line, but the remaining bits of
194 @c command-line-1 are not done if noninteractive.
196 It now exits if the option @code{--batch} was specified.
199 If @code{initial-buffer-choice} is a string, it visits the file with
200 that name. 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} and then @code{term-setup-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
277 @c I do not think this should be mentioned. AFAICS it is just a dodge
278 @c around inhibit-startup-screen not being settable on a site-wide basis.
279 If its value is @code{t}, Emacs displays the @file{*scratch*} buffer.
283 @defopt inhibit-startup-echo-area-message
284 This variable controls the display of the startup echo area message.
285 You can suppress the startup echo area message by adding text with this
286 form to your init file:
289 (setq inhibit-startup-echo-area-message
290 "@var{your-login-name}")
293 Emacs explicitly checks for an expression as shown above in your init
294 file; your login name must appear in the expression as a Lisp string
295 constant. You can also use the Customize interface. Other methods of
296 setting @code{inhibit-startup-echo-area-message} to the same value do
297 not inhibit the startup message. This way, you can easily inhibit the
298 message for yourself if you wish, but thoughtless copying of your init
299 file will not inhibit the message for someone else.
302 @defopt initial-scratch-message
303 This variable, if non-@code{nil}, should be a string, which is
304 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
305 is @code{nil}, the @file{*scratch*} buffer is empty.
309 The following command-line options affect some aspects of the startup
310 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
314 Do not display a splash screen.
317 Run without an interactive terminal. @xref{Batch Mode}.
320 Do not initialize any display; just start a server in the background.
324 Do not load either the init file, or the @file{default} library.
327 Do not load the @file{site-start} library.
331 Equivalent to @samp{-q --no-site-file --no-splash}.
332 @c and --no-site-lisp, but let's not mention that here.
337 @subsection The Init File
339 @cindex @file{.emacs}
340 @cindex @file{init.el}
342 When you start Emacs, it normally attempts to load your @dfn{init
343 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
344 in your home directory, or a file named @file{init.el} in a
345 subdirectory named @file{.emacs.d} in your home directory.
347 Whichever place you use, you can also compile the file (@pxref{Byte
348 Compilation}); then the actual file loaded will be @file{.emacs.elc}
352 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
353 control whether and where to find the init file; @samp{-q} (and the
354 stronger @samp{-Q}) says not to load an init file, while @samp{-u
355 @var{user}} says to load @var{user}'s init file instead of yours.
356 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
357 option is specified, Emacs uses the @env{LOGNAME} environment
358 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
359 systems) variable, to find your home directory and thus your init
360 file; this way, even if you have su'd, Emacs still loads your own init
361 file. If those environment variables are absent, though, Emacs uses
362 your user-id to find your home directory.
364 @cindex default init file
365 An Emacs installation may have a @dfn{default init file}, which is a
366 Lisp library named @file{default.el}. Emacs finds this file through
367 the standard search path for libraries (@pxref{How Programs Do
368 Loading}). The Emacs distribution does not come with this file; it is
369 intended for local customizations. If the default init file exists,
370 it is loaded whenever you start Emacs. But your own personal init
371 file, if any, is loaded first; if it sets @code{inhibit-default-init}
372 to a non-@code{nil} value, then Emacs does not subsequently load the
373 @file{default.el} file. In batch mode, or if you specify @samp{-q}
374 (or @samp{-Q}), Emacs loads neither your personal init file nor
375 the default init file.
377 Another file for site-customization is @file{site-start.el}. Emacs
378 loads this @emph{before} the user's init file. You can inhibit the
379 loading of this file with the option @samp{--no-site-file}.
381 @defopt site-run-file
382 This variable specifies the site-customization file to load before the
383 user's init file. Its normal value is @code{"site-start"}. The only
384 way you can change it with real effect is to do so before dumping
386 @c So why even mention it here. I imagine it is almost never changed.
389 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
390 examples of how to make various commonly desired customizations in your
393 @defopt inhibit-default-init
394 If this variable is non-@code{nil}, it prevents Emacs from loading the
395 default initialization library file. The default value is @code{nil}.
398 @defvar before-init-hook
399 This normal hook is run, once, just before loading all the init files
400 (@file{site-start.el}, your init file, and @file{default.el}).
401 (The only way to change it with real effect is before dumping Emacs.)
404 @defvar after-init-hook
405 This normal hook is run, once, just after loading all the init files
406 (@file{site-start.el}, your init file, and @file{default.el}),
407 before loading the terminal-specific library (if started on a text
408 terminal) and processing the command-line action arguments.
411 @defvar emacs-startup-hook
412 This normal hook is run, once, just after handling the command line
413 arguments, just before @code{term-setup-hook}. In batch mode, Emacs
414 does not run either of these hooks.
417 @defvar user-init-file
418 This variable holds the absolute file name of the user's init file. If the
419 actual init file loaded is a compiled file, such as @file{.emacs.elc},
420 the value refers to the corresponding source file.
423 @defvar user-emacs-directory
424 This variable holds the name of the @file{.emacs.d} directory. It is
425 @file{~/.emacs.d} on all platforms but MS-DOS.
428 @node Terminal-Specific
429 @subsection Terminal-Specific Initialization
430 @cindex terminal-specific initialization
432 Each terminal type can have its own Lisp library that Emacs loads when
433 run on that type of terminal. The library's name is constructed by
434 concatenating the value of the variable @code{term-file-prefix} and the
435 terminal type (specified by the environment variable @env{TERM}).
436 Normally, @code{term-file-prefix} has the value
437 @code{"term/"}; changing this is not recommended. Emacs finds the file
438 in the normal manner, by searching the @code{load-path} directories, and
439 trying the @samp{.elc} and @samp{.el} suffixes.
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
448 When the name of the terminal type contains a hyphen or underscore, and no library
449 is found whose name is identical to the terminal's name, Emacs strips
450 from the terminal's name the last hyphen or 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
460 terminal-specific library by setting the variable
461 @code{term-file-prefix} to @code{nil}. This feature is useful when
462 experimenting with your own peculiar customizations.
464 You can also arrange to override some of the actions of the
465 terminal-specific library by setting the variable
466 @code{term-setup-hook}. This is a normal hook that Emacs runs
467 at the end of its initialization, after loading both
468 your init file and any terminal-specific libraries. You could
469 use this hook to define initializations for terminals that do not
470 have their own libraries. @xref{Hooks}.
472 @defvar term-file-prefix
473 @cindex @env{TERM} environment variable
474 If the value of this variable is non-@code{nil}, Emacs loads a
475 terminal-specific initialization file as follows:
478 (load (concat term-file-prefix (getenv "TERM")))
482 You may set the @code{term-file-prefix} variable to @code{nil} in your
483 init file if you do not wish to load the
484 terminal-initialization file.
486 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
489 @defvar term-setup-hook
490 This variable is a normal hook that Emacs runs after loading your
491 init file, the default initialization file (if any) and the
492 terminal-specific Lisp file.
494 You can use @code{term-setup-hook} to override the definitions made by a
495 terminal-specific file.
497 For a related feature, @pxref{Window Systems, window-setup-hook}.
500 @node Command-Line Arguments
501 @subsection Command-Line Arguments
502 @cindex command-line arguments
504 You can use command-line arguments to request various actions when
505 you start Emacs. Note that the recommended way of using Emacs is to
506 start it just once, after logging in, and then do all editing in the same
507 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
508 For this reason, you might not use command-line arguments very often;
509 nonetheless, they can be useful when invoking Emacs from session
510 scripts or debugging Emacs. This section describes how Emacs
511 processes command-line arguments.
514 This function parses the command line that Emacs was called with,
515 processes it, and (amongst other things) loads the user's init file and
516 displays the startup messages.
519 @defvar command-line-processed
520 The value of this variable is @code{t} once the command line has been
523 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
524 Emacs}), you may wish to set this variable to @code{nil} first in
525 order to cause the new dumped Emacs to process its new command-line
529 @defvar command-switch-alist
530 @cindex switches on command line
531 @cindex options on command line
532 @cindex command-line options
533 This variable is an alist of user-defined command-line options and
534 associated handler functions. By default it is empty, but you can
535 add elements if you wish.
537 A @dfn{command-line option} is an argument on the command line, which
544 The elements of the @code{command-switch-alist} look like this:
547 (@var{option} . @var{handler-function})
550 The @sc{car}, @var{option}, is a string, the name of a command-line
551 option (not including the initial hyphen). The @var{handler-function}
552 is called to handle @var{option}, and receives the option name as its
555 In some cases, the option is followed in the command line by an
556 argument. In these cases, the @var{handler-function} can find all the
557 remaining command-line arguments in the variable
558 @code{command-line-args-left} (see below). (The entire list of
559 command-line arguments is in @code{command-line-args}.)
561 The command-line arguments are parsed by the @code{command-line-1}
562 function in the @file{startup.el} file. See also @ref{Emacs
563 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
567 @defvar command-line-args
568 The value of this variable is the list of command-line arguments passed
572 @defvar command-line-args-left
574 The value of this variable is the list of command-line arguments that
575 have not yet been processed.
576 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
577 @c @code{argv} is an alias for this.
580 @defvar command-line-functions
581 This variable's value is a list of functions for handling an
582 unrecognized command-line argument. Each time the next argument to be
583 processed has no special meaning, the functions in this list are called,
584 in order of appearance, until one of them returns a non-@code{nil}
587 These functions are called with no arguments. They can access the
588 command-line argument under consideration through the variable
589 @code{argi}, which is bound temporarily at this point. The remaining
590 arguments (not including the current one) are in the variable
591 @code{command-line-args-left}.
593 When a function recognizes and processes the argument in @code{argi}, it
594 should return a non-@code{nil} value to say it has dealt with that
595 argument. If it has also dealt with some of the following arguments, it
596 can indicate that by deleting them from @code{command-line-args-left}.
598 If all of these functions return @code{nil}, then the argument is treated
599 as a file name to visit.
603 @section Getting Out of Emacs
604 @cindex exiting Emacs
606 There are two ways to get out of Emacs: you can kill the Emacs job,
607 which exits permanently, or you can suspend it, which permits you to
608 reenter the Emacs process later. (In a graphical environment, you can
609 of course simply switch to another application without doing anything
610 special to Emacs, then switch back to Emacs when you want.)
613 * Killing Emacs:: Exiting Emacs irreversibly.
614 * Suspending Emacs:: Exiting Emacs reversibly.
618 @subsection Killing Emacs
619 @cindex killing Emacs
621 Killing Emacs means ending the execution of the Emacs process.
622 If you started Emacs from a terminal, the parent process normally
623 resumes control. The low-level primitive for killing Emacs is
626 @deffn Command kill-emacs &optional exit-data
627 This command calls the hook @code{kill-emacs-hook}, then exits the
628 Emacs process and kills it.
630 If @var{exit-data} is an integer, that is used as the exit status of
631 the Emacs process. (This is useful primarily in batch operation; see
634 If @var{exit-data} is a string, its contents are stuffed into the
635 terminal input buffer so that the shell (or whatever program next reads
636 input) can read them.
642 @cindex operating system signal
643 The @code{kill-emacs} function is normally called via the
644 higher-level command @kbd{C-x C-c}
645 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
646 Emacs Manual}. It is also called automatically if Emacs receives a
647 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
648 controlling terminal is disconnected), or if it receives a
649 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
651 @defvar kill-emacs-hook
652 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
654 Because @code{kill-emacs} can be called in situations where user
655 interaction is impossible (e.g., when the terminal is disconnected),
656 functions on this hook should not attempt to interact with the user.
657 If you want to interact with the user when Emacs is shutting down, use
658 @code{kill-emacs-query-functions}, described below.
661 When Emacs is killed, all the information in the Emacs process,
662 aside from files that have been saved, is lost. Because killing Emacs
663 inadvertently can lose a lot of work, the
664 @code{save-buffers-kill-terminal} command queries for confirmation if
665 you have buffers that need saving or subprocesses that are running.
666 It also runs the abnormal hook @code{kill-emacs-query-functions}:
668 @defvar kill-emacs-query-functions
669 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
670 functions in this hook, after asking the standard questions and before
671 calling @code{kill-emacs}. The functions are called in order of
672 appearance, with no arguments. Each function can ask for additional
673 confirmation from the user. If any of them returns @code{nil},
674 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
675 the remaining functions in this hook. Calling @code{kill-emacs}
676 directly does not run this hook.
679 @node Suspending Emacs
680 @subsection Suspending Emacs
681 @cindex suspending Emacs
683 On text terminals, it is possible to @dfn{suspend Emacs}, which
684 means stopping Emacs temporarily and returning control to its superior
685 process, which is usually the shell. This allows you to resume
686 editing later in the same Emacs process, with the same buffers, the
687 same kill ring, the same undo history, and so on. To resume Emacs,
688 use the appropriate command in the parent shell---most likely
691 @cindex controlling terminal
692 Suspending works only on a terminal device from which the Emacs
693 session was started. We call that device the @dfn{controlling
694 terminal} of the session. Suspending is not allowed if the
695 controlling terminal is a graphical terminal. Suspending is usually
696 not relevant in graphical environments, since you can simply switch to
697 another application without doing anything special to Emacs.
699 @c FIXME? Are there any systems Emacs still supports that do not
702 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
703 not support suspension of jobs; on these systems, ``suspension''
704 actually creates a new shell temporarily as a subprocess of Emacs.
705 Then you would exit the shell to return to Emacs.
707 @deffn Command suspend-emacs &optional string
708 This function stops Emacs and returns control to the superior process.
709 If and when the superior process resumes Emacs, @code{suspend-emacs}
710 returns @code{nil} to its caller in Lisp.
712 This function works only on the controlling terminal of the Emacs
713 session; to relinquish control of other tty devices, use
714 @code{suspend-tty} (see below). If the Emacs session uses more than
715 one terminal, you must delete the frames on all the other terminals
716 before suspending Emacs, or this function signals an error.
717 @xref{Multiple Terminals}.
719 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
720 superior shell, to be read as terminal input.
721 @c FIXME? It seems to me that shell does echo STRING.
722 The characters in @var{string} are not echoed by the superior shell;
723 only the results appear.
725 Before suspending, @code{suspend-emacs} runs the normal hook
726 @code{suspend-hook}. After the user resumes Emacs,
727 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
730 The next redisplay after resumption will redraw the entire screen,
731 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
732 @xref{Refresh Screen}.
734 Here is an example of how you could use these hooks:
738 (add-hook 'suspend-hook
739 (lambda () (or (y-or-n-p "Really suspend? ")
740 (error "Suspend canceled"))))
742 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
745 @c The sit-for prevents the ``nil'' that suspend-emacs returns
746 @c hiding the message.
748 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
752 ---------- Buffer: Minibuffer ----------
753 Really suspend? @kbd{y}
754 ---------- Buffer: Minibuffer ----------
758 ---------- Parent Shell ----------
764 ---------- Echo Area ----------
769 @c FIXME? AFAICS, it is echoed.
770 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
771 is read and executed by the shell.
775 This variable is a normal hook that Emacs runs before suspending.
778 @defvar suspend-resume-hook
779 This variable is a normal hook that Emacs runs on resuming
783 @defun suspend-tty &optional tty
784 If @var{tty} specifies a terminal device used by Emacs, this function
785 relinquishes the device and restores it to its prior state. Frames
786 that used the device continue to exist, but are not updated and Emacs
787 doesn't read input from them. @var{tty} can be a terminal object, a
788 frame (meaning the terminal for that frame), or @code{nil} (meaning
789 the terminal for the selected frame). @xref{Multiple Terminals}.
791 If @var{tty} is already suspended, this function does nothing.
793 @vindex suspend-tty-functions
794 This function runs the hook @code{suspend-tty-functions}, passing the
795 terminal object as an argument to each function.
798 @defun resume-tty &optional tty
799 This function resumes the previously suspended terminal device
800 @var{tty}; where @var{tty} has the same possible values as it does
801 for @code{suspend-tty}.
803 @vindex resume-tty-functions
804 This function reopens the terminal device, re-initializes it, and
805 redraws it with that terminal's selected frame. It then runs the
806 hook @code{resume-tty-functions}, passing the terminal object as an
807 argument to each function.
809 If the same device is already used by another Emacs terminal, this
810 function signals an error. If @var{tty} is not suspended, this
811 function does nothing.
814 @defun controlling-tty-p &optional tty
815 This function returns non-@code{nil} if @var{tty} is the
816 controlling terminal of the Emacs session; @var{tty} can be a
817 terminal object, a frame (meaning the terminal for that frame), or
818 @code{nil} (meaning the terminal for the selected frame).
821 @deffn Command suspend-frame
822 This command @dfn{suspends} a frame. For GUI frames, it calls
823 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
824 text terminals, it calls either @code{suspend-emacs} or
825 @code{suspend-tty}, depending on whether the frame is displayed on the
826 controlling terminal device or not.
829 @node System Environment
830 @section Operating System Environment
831 @cindex operating system environment
833 Emacs provides access to variables in the operating system environment
834 through various functions. These variables include the name of the
835 system, the user's @acronym{UID}, and so on.
837 @defvar system-configuration
838 This variable holds the standard GNU configuration name for the
839 hardware/software configuration of your system, as a string. For
840 example, a typical value for a 64-bit GNU/Linux system is
841 @samp{"x86_64-unknown-linux-gnu"}.
844 @cindex system type and name
846 The value of this variable is a symbol indicating the type of operating
847 system Emacs is running on. The possible values are:
854 Berkeley BSD and its variants.
857 Cygwin, a Posix layer on top of MS-Windows.
863 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
866 A GNU/Linux system---that is, a variant GNU system, using the Linux
867 kernel. (These systems are the ones people often call ``Linux'', but
868 actually Linux is just the kernel, not the whole system.)
871 A GNU (glibc-based) system with a FreeBSD kernel.
874 Hewlett-Packard HPUX operating system.
877 Silicon Graphics Irix system.
880 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
881 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
887 Microsoft Windows NT, 9X and later. The value of @code{system-type}
888 is always @code{windows-nt}, e.g., even on Windows 7.
892 We do not wish to add new symbols to make finer distinctions unless it
893 is absolutely necessary! In fact, we hope to eliminate some of these
894 alternatives in the future. If you need to make a finer distinction
895 than @code{system-type} allows for, you can test
896 @code{system-configuration}, e.g., against a regexp.
900 This function returns the name of the machine you are running on, as a
904 The symbol @code{system-name} is a variable as well as a function. In
905 fact, the function returns whatever value the variable
906 @code{system-name} currently holds. Thus, you can set the variable
907 @code{system-name} in case Emacs is confused about the name of your
908 system. The variable is also useful for constructing frame titles
909 (@pxref{Frame Titles}).
911 @c FIXME seems like this section is not the best place for this option?
912 @defopt mail-host-address
913 If this variable is non-@code{nil}, it is used instead of
914 @code{system-name} for purposes of generating email addresses. For
915 example, it is used when constructing the default value of
916 @code{user-mail-address}. @xref{User Identification}. (Since this is
917 done when Emacs starts up, the value actually used is the one saved when
918 Emacs was dumped. @xref{Building Emacs}.)
919 @c FIXME sounds like should probably give this a :set-after and some
920 @c custom-initialize-delay voodoo.
923 @deffn Command getenv var &optional frame
924 @cindex environment variable access
925 This function returns the value of the environment variable @var{var},
926 as a string. @var{var} should be a string. If @var{var} is undefined
927 in the environment, @code{getenv} returns @code{nil}. It returns
928 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
929 variables and their values is kept in the variable @code{process-environment}.
938 The shell command @code{printenv} prints all or part of the environment:
943 PATH=/usr/local/bin:/usr/bin:/bin
955 @deffn Command setenv variable &optional value substitute
956 This command sets the value of the environment variable named
957 @var{variable} to @var{value}. @var{variable} should be a string.
958 Internally, Emacs Lisp can handle any string. However, normally
959 @var{variable} should be a valid shell identifier, that is, a sequence
960 of letters, digits and underscores, starting with a letter or
961 underscore. Otherwise, errors may occur if subprocesses of Emacs try
962 to access the value of @var{variable}. If @var{value} is omitted or
963 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
964 removes @var{variable} from the environment. Otherwise, @var{value}
967 @c FIXME: Document `substitute-env-vars'? --xfq
968 If the optional argument @var{substitute} is non-@code{nil}, Emacs
969 calls the function @code{substitute-env-vars} to expand any
970 environment variables in @var{value}.
972 @code{setenv} works by modifying @code{process-environment}; binding
973 that variable with @code{let} is also reasonable practice.
975 @code{setenv} returns the new value of @var{variable}, or @code{nil}
976 if it removed @var{variable} from the environment.
979 @defvar process-environment
980 This variable is a list of strings, each describing one environment
981 variable. The functions @code{getenv} and @code{setenv} work by means
987 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
998 If @code{process-environment} contains ``duplicate'' elements that
999 specify the same environment variable, the first of these elements
1000 specifies the variable, and the other ``duplicates'' are ignored.
1003 @defvar initial-environment
1004 This variable holds the list of environment variables Emacs inherited
1005 from its parent process when Emacs started.
1008 @defvar path-separator
1009 This variable holds a string that says which character separates
1010 directories in a search path (as found in an environment variable). Its
1011 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1014 @defun parse-colon-path path
1015 This function takes a search path string such as the value of
1016 the @env{PATH} environment variable, and splits it at the separators,
1017 returning a list of directory names. @code{nil} in this list means
1018 the current directory. Although the function's name says
1019 ``colon'', it actually uses the value of @code{path-separator}.
1022 (parse-colon-path ":/foo:/bar")
1023 @result{} (nil "/foo/" "/bar/")
1027 @defvar invocation-name
1028 This variable holds the program name under which Emacs was invoked. The
1029 value is a string, and does not include a directory name.
1032 @defvar invocation-directory
1033 This variable holds the directory from which the Emacs executable was
1034 invoked, or @code{nil} if that directory cannot be determined.
1037 @defvar installation-directory
1038 If non-@code{nil}, this is a directory within which to look for the
1039 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1040 it is normally @code{nil}. It is non-@code{nil}
1041 when Emacs can't find those directories in their standard installed
1042 locations, but can find them in a directory related somehow to the one
1043 containing the Emacs executable (i.e., @code{invocation-directory}).
1046 @defun load-average &optional use-float
1047 This function returns the current 1-minute, 5-minute, and 15-minute
1048 system load averages, in a list. The load average indicates the
1049 number of processes trying to run on the system.
1051 By default, the values are integers that are 100 times the system load
1052 averages, but if @var{use-float} is non-@code{nil}, then they are
1053 returned as floating point numbers without multiplying by 100.
1055 If it is impossible to obtain the load average, this function signals
1056 an error. On some platforms, access to load averages requires
1057 installing Emacs as setuid or setgid so that it can read kernel
1058 information, and that usually isn't advisable.
1059 @c FIXME which platforms are these? Are they still relevant?
1061 If the 1-minute load average is available, but the 5- or 15-minute
1062 averages are not, this function returns a shortened list containing
1063 the available averages.
1068 @result{} (169 48 36)
1072 @result{} (1.69 0.48 0.36)
1076 The shell command @code{uptime} returns similar information.
1080 This function returns the process @acronym{ID} of the Emacs process,
1084 @defvar tty-erase-char
1085 This variable holds the erase character that was selected
1086 in the system's terminal driver, before Emacs was started.
1087 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1088 @c The value is @code{nil} if Emacs is running under a window system.
1091 @node User Identification
1092 @section User Identification
1093 @cindex user identification
1095 @defvar init-file-user
1096 This variable says which user's init files should be used by
1097 Emacs---or @code{nil} if none. @code{""} stands for the user who
1098 originally logged in. The value reflects command-line options such as
1099 @samp{-q} or @samp{-u @var{user}}.
1101 Lisp packages that load files of customizations, or any other sort of
1102 user profile, should obey this variable in deciding where to find it.
1103 They should load the profile of the user name found in this variable.
1104 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q},
1105 @samp{-Q}, or @samp{-batch} option was used, then Lisp packages should
1106 not load any customization files or user profile.
1109 @defopt user-mail-address
1110 This holds the nominal email address of the user who is using Emacs.
1111 Emacs normally sets this variable to a default value after reading your
1112 init files, but not if you have already set it. So you can set the
1113 variable to some other value in your init file if you do not
1114 want to use the default value.
1117 @defun user-login-name &optional uid
1118 This function returns the name under which the user is logged in.
1119 It uses the environment variables @env{LOGNAME} or @env{USER} if
1120 either is set. Otherwise, the value is based on the effective
1121 @acronym{UID}, not the real @acronym{UID}.
1123 If you specify @var{uid} (a number), the result is the user name that
1124 corresponds to @var{uid}, or @code{nil} if there is no such user.
1127 @defun user-real-login-name
1128 This function returns the user name corresponding to Emacs's real
1129 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1130 environment variables @env{LOGNAME} and @env{USER}.
1133 @defun user-full-name &optional uid
1134 This function returns the full name of the logged-in user---or the value
1135 of the environment variable @env{NAME}, if that is set.
1137 If the Emacs process's user-id does not correspond to any known user (and
1138 provided @code{NAME} is not set), the result is @code{"unknown"}.
1140 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1141 or a string (a login name). Then @code{user-full-name} returns the full
1142 name corresponding to that user-id or login name. If you specify a
1143 user-id or login name that isn't defined, it returns @code{nil}.
1146 @vindex user-full-name
1147 @vindex user-real-login-name
1148 @vindex user-login-name
1149 The symbols @code{user-login-name}, @code{user-real-login-name} and
1150 @code{user-full-name} are variables as well as functions. The functions
1151 return the same values that the variables hold. These variables allow
1152 you to ``fake out'' Emacs by telling the functions what to return. The
1153 variables are also useful for constructing frame titles (@pxref{Frame
1157 @defun user-real-uid
1158 This function returns the real @acronym{UID} of the user.
1159 The value may be a floating point number, in the (unlikely) event that
1160 the UID is too large to fit in a Lisp integer.
1164 This function returns the effective @acronym{UID} of the user.
1165 The value may be a floating point number.
1170 This function returns the effective @acronym{GID} of the Emacs process.
1171 The value may be a floating point number.
1174 @defun group-real-gid
1175 This function returns the real @acronym{GID} of the Emacs process.
1176 The value may be a floating point number.
1180 This function returns a list of strings, listing the user names on the
1181 system. If Emacs cannot retrieve this information, the return value
1182 is a list containing just the value of @code{user-real-login-name}.
1186 @defun system-groups
1187 This function returns a list of strings, listing the names of user
1188 groups on the system. If Emacs cannot retrieve this information, the
1189 return value is @code{nil}.
1194 @section Time of Day
1196 This section explains how to determine the current time and time
1200 Most of these functions represent time as a list of either four
1201 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
1202 @var{picosec})}, or of three
1203 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1204 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1205 @var{sec-high} and @var{sec-low} give the high and low bits of an
1206 integer number of seconds. This integer number,
1208 @var{high} * 2**16 + @var{low},
1213 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1214 UTC) to the specified time. The third list element @var{microsec}, if
1215 present, gives the number of microseconds from the start of that
1216 second to the specified time.
1217 Similarly, the fourth list element @var{picosec}, if present, gives
1218 the number of picoseconds from the start of that microsecond to the
1221 The return value of @code{current-time} represents time using four
1222 integers, as do the timestamps in the return value of
1223 @code{file-attributes} (@pxref{Definition of
1224 file-attributes}). In function arguments, e.g., the @var{time-value}
1225 argument to @code{current-time-string}, two-, three-, and four-integer
1226 lists are accepted. You can convert times from the list
1227 representation into standard human-readable strings using
1228 @code{current-time-string}, or to other forms using the
1229 @code{decode-time} and @code{format-time-string} functions documented
1230 in the following sections.
1232 @defun current-time-string &optional time-value
1233 This function returns the current time and date as a human-readable
1234 string. The format does not vary for the initial part of the string,
1235 which contains the day of week, month, day of month, and time of day
1236 in that order: the number of characters used for these fields is
1237 always the same, so you can reliably
1238 use @code{substring} to extract them. You should count
1239 characters from the beginning of the string rather than from the end,
1240 as the year might not have exactly four digits, and additional
1241 information may some day be added at the end.
1243 The argument @var{time-value}, if given, specifies a time to format
1244 (represented as a list of integers), instead of the current time.
1248 (current-time-string)
1249 @result{} "Wed Oct 14 22:21:05 1987"
1255 This function returns the current time, represented as a list of four
1256 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1257 These integers have trailing zeros on systems that return time with
1258 lower resolutions. On all current machines @var{picosec} is a
1259 multiple of 1000, but this may change as higher-resolution clocks
1263 @defun float-time &optional time-value
1264 This function returns the current time as a floating-point number of
1265 seconds since the epoch. The optional argument @var{time-value}, if
1266 given, specifies a time (represented as a list of integers) to convert
1267 instead of the current time.
1269 @emph{Warning}: Since the result is floating point, it may not be
1270 exact. Do not use this function if precise time stamps are required.
1273 @defun current-time-zone &optional time-value
1274 @cindex time zone, current
1275 This function returns a list describing the time zone that the user is
1278 The value has the form @code{(@var{offset} @var{name})}. Here
1279 @var{offset} is an integer giving the number of seconds ahead of UTC
1280 (east of Greenwich). A negative value means west of Greenwich. The
1281 second element, @var{name}, is a string giving the name of the time
1282 zone. Both elements change when daylight saving time begins or ends;
1283 if the user has specified a time zone that does not use a seasonal time
1284 adjustment, then the value is constant through time.
1286 If the operating system doesn't supply all the information necessary to
1287 compute the value, the unknown elements of the list are @code{nil}.
1289 The argument @var{time-value}, if given, specifies a time (represented
1290 as a list of integers) to analyze instead of the current time.
1293 The current time zone is determined by the @env{TZ} environment
1294 variable. @xref{System Environment}. For example, you can tell Emacs
1295 to use universal time with @code{(setenv "TZ" "UTC0")}. If @env{TZ}
1296 is not in the environment, Emacs uses a platform-dependent default
1299 @node Time Conversion
1300 @section Time Conversion
1301 @cindex calendrical information
1303 These functions convert time values (lists of two to four integers,
1304 as explained in the previous section) into calendrical information and
1307 Many 32-bit operating systems are limited to time values containing
1308 32 bits of information; these systems typically handle only the times
1309 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
1310 However, 64-bit and some 32-bit operating systems have larger time
1311 values, and can represent times far in the past or future.
1313 Time conversion functions always use the Gregorian calendar, even
1314 for dates before the Gregorian calendar was introduced. Year numbers
1315 count the number of years since the year 1 B.C., and do not skip zero
1316 as traditional Gregorian years do; for example, the year number
1317 @minus{}37 represents the Gregorian year 38 B.C@.
1319 @defun decode-time &optional time
1320 This function converts a time value into calendrical information. If
1321 you don't specify @var{time}, it decodes the current time. The return
1322 value is a list of nine elements, as follows:
1325 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1328 Here is what the elements mean:
1332 The number of seconds past the minute, as an integer between 0 and 59.
1333 On some operating systems, this is 60 for leap seconds.
1335 The number of minutes past the hour, as an integer between 0 and 59.
1337 The hour of the day, as an integer between 0 and 23.
1339 The day of the month, as an integer between 1 and 31.
1341 The month of the year, as an integer between 1 and 12.
1343 The year, an integer typically greater than 1900.
1345 The day of week, as an integer between 0 and 6, where 0 stands for
1348 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1350 An integer indicating the time zone, as the number of seconds east of
1354 @strong{Common Lisp Note:} Common Lisp has different meanings for
1355 @var{dow} and @var{zone}.
1358 @defun encode-time seconds minutes hour day month year &optional zone
1359 This function is the inverse of @code{decode-time}. It converts seven
1360 items of calendrical data into a time value. For the meanings of the
1361 arguments, see the table above under @code{decode-time}.
1363 Year numbers less than 100 are not treated specially. If you want them
1364 to stand for years above 1900, or years above 2000, you must alter them
1365 yourself before you call @code{encode-time}.
1367 The optional argument @var{zone} defaults to the current time zone and
1368 its daylight saving time rules. If specified, it can be either a list
1369 (as you would get from @code{current-time-zone}), a string as in the
1370 @env{TZ} environment variable, @code{t} for Universal Time, or an
1371 integer (as you would get from @code{decode-time}). The specified
1372 zone is used without any further alteration for daylight saving time.
1374 If you pass more than seven arguments to @code{encode-time}, the first
1375 six are used as @var{seconds} through @var{year}, the last argument is
1376 used as @var{zone}, and the arguments in between are ignored. This
1377 feature makes it possible to use the elements of a list returned by
1378 @code{decode-time} as the arguments to @code{encode-time}, like this:
1381 (apply 'encode-time (decode-time @dots{}))
1384 You can perform simple date arithmetic by using out-of-range values for
1385 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1386 arguments; for example, day 0 means the day preceding the given month.
1388 The operating system puts limits on the range of possible time values;
1389 if you try to encode a time that is out of range, an error results.
1390 For instance, years before 1970 do not work on some systems;
1391 on others, years as early as 1901 do work.
1395 @section Parsing and Formatting Times
1397 These functions convert time values to text in a string, and vice versa.
1398 Time values are lists of two to four integers (@pxref{Time of Day}).
1400 @defun date-to-time string
1401 This function parses the time-string @var{string} and returns the
1402 corresponding time value.
1405 @defun format-time-string format-string &optional time universal
1406 This function converts @var{time} (or the current time, if @var{time} is
1407 omitted) to a string according to @var{format-string}. The argument
1408 @var{format-string} may contain @samp{%}-sequences which say to
1409 substitute parts of the time. Here is a table of what the
1410 @samp{%}-sequences mean:
1414 This stands for the abbreviated name of the day of week.
1416 This stands for the full name of the day of week.
1418 This stands for the abbreviated name of the month.
1420 This stands for the full name of the month.
1422 This is a synonym for @samp{%x %X}.
1424 This has a locale-specific meaning. In the default locale (named C), it
1425 is equivalent to @samp{%A, %B %e, %Y}.
1427 This stands for the day of month, zero-padded.
1429 This is a synonym for @samp{%m/%d/%y}.
1431 This stands for the day of month, blank-padded.
1433 This is a synonym for @samp{%b}.
1435 This stands for the hour (00--23).
1437 This stands for the hour (01--12).
1439 This stands for the day of the year (001--366).
1441 This stands for the hour (0--23), blank padded.
1443 This stands for the hour (1--12), blank padded.
1445 This stands for the month (01--12).
1447 This stands for the minute (00--59).
1449 This stands for a newline.
1451 This stands for the nanoseconds (000000000--999999999). To ask for
1452 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1453 microseconds, etc. Any excess digits are discarded, without rounding.
1455 This stands for @samp{AM} or @samp{PM}, as appropriate.
1457 This is a synonym for @samp{%I:%M:%S %p}.
1459 This is a synonym for @samp{%H:%M}.
1461 This stands for the seconds (00--59).
1463 This stands for a tab character.
1465 This is a synonym for @samp{%H:%M:%S}.
1467 This stands for the week of the year (01--52), assuming that weeks
1470 This stands for the numeric day of week (0--6). Sunday is day 0.
1472 This stands for the week of the year (01--52), assuming that weeks
1475 This has a locale-specific meaning. In the default locale (named
1476 @samp{C}), it is equivalent to @samp{%D}.
1478 This has a locale-specific meaning. In the default locale (named
1479 @samp{C}), it is equivalent to @samp{%T}.
1481 This stands for the year without century (00--99).
1483 This stands for the year with century.
1485 This stands for the time zone abbreviation (e.g., @samp{EST}).
1487 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1490 You can also specify the field width and type of padding for any of
1491 these @samp{%}-sequences. This works as in @code{printf}: you write
1492 the field width as digits in the middle of a @samp{%}-sequences. If you
1493 start the field width with @samp{0}, it means to pad with zeros. If you
1494 start the field width with @samp{_}, it means to pad with spaces.
1496 For example, @samp{%S} specifies the number of seconds since the minute;
1497 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1498 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1499 because that is how @samp{%S} normally pads to two positions.
1501 The characters @samp{E} and @samp{O} act as modifiers when used between
1502 @samp{%} and one of the letters in the table above. @samp{E} specifies
1503 using the current locale's ``alternative'' version of the date and time.
1504 In a Japanese locale, for example, @code{%Ex} might yield a date format
1505 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1506 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1509 @samp{O} means to use the current locale's ``alternative''
1510 representation of numbers, instead of the ordinary decimal digits. This
1511 is allowed with most letters, all the ones that output numbers.
1513 If @var{universal} is non-@code{nil}, that means to describe the time as
1514 Universal Time; @code{nil} means describe it using what Emacs believes
1515 is the local time zone (see @code{current-time-zone}).
1517 This function uses the C library function @code{strftime}
1518 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1519 Manual}) to do most of the work. In order to communicate with that
1520 function, it first encodes its argument using the coding system
1521 specified by @code{locale-coding-system} (@pxref{Locales}); after
1522 @code{strftime} returns the resulting string,
1523 @code{format-time-string} decodes the string using that same coding
1527 @defun seconds-to-time seconds
1528 This function converts @var{seconds}, a floating point number of
1529 seconds since the epoch, to a time value and returns that. To perform
1530 the inverse conversion, use @code{float-time} (@pxref{Time of Day}).
1533 @defun format-seconds format-string seconds
1534 This function converts its argument @var{seconds} into a string of
1535 years, days, hours, etc., according to @var{format-string}. The
1536 argument @var{format-string} may contain @samp{%}-sequences which
1537 control the conversion. Here is a table of what the
1538 @samp{%}-sequences mean:
1543 The integer number of 365-day years.
1546 The integer number of days.
1549 The integer number of hours.
1552 The integer number of minutes.
1555 The integer number of seconds.
1557 Non-printing control flag. When it is used, other specifiers must be
1558 given in the order of decreasing size, i.e., years before days, hours
1559 before minutes, etc. Nothing will be produced in the result string to
1560 the left of @samp{%z} until the first non-zero conversion is
1561 encountered. For example, the default format used by
1562 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1563 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1564 will always be produced, but years, days, hours, and minutes will only
1565 be shown if they are non-zero.
1567 Produces a literal @samp{%}.
1570 Upper-case format sequences produce the units in addition to the
1571 numbers, lower-case formats produce only the numbers.
1573 You can also specify the field width by following the @samp{%} with a
1574 number; shorter numbers will be padded with blanks. An optional
1575 period before the width requests zero-padding instead. For example,
1576 @code{"%.3Y"} might produce @code{"004 years"}.
1578 @emph{Warning:} This function works only with values of @var{seconds}
1579 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1580 most-positive-fixnum}).
1583 @node Processor Run Time
1584 @section Processor Run time
1585 @cindex processor run time
1586 @cindex Emacs process run time
1588 Emacs provides several functions and primitives that return time,
1589 both elapsed and processor time, used by the Emacs process.
1591 @deffn Command emacs-uptime &optional format
1592 @cindex uptime of Emacs
1593 This function returns a string representing the Emacs
1594 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1595 running. The string is formatted by @code{format-seconds} according
1596 to the optional argument @var{format}. For the available format
1597 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1598 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1601 When called interactively, it prints the uptime in the echo area.
1604 @defun get-internal-run-time
1605 This function returns the processor run time used by Emacs as a list
1606 of four integers: @code{(@var{high} @var{low} @var{microsec}
1607 @var{picosec})}, using the same format as @code{current-time}
1608 (@pxref{Time of Day}).
1610 Note that the time returned by this function excludes the time Emacs
1611 was not using the processor, and if the Emacs process has several
1612 threads, the returned value is the sum of the processor times used up
1613 by all Emacs threads.
1615 If the system doesn't provide a way to determine the processor run
1616 time, @code{get-internal-run-time} returns the same time as
1617 @code{current-time}.
1620 @deffn Command emacs-init-time
1621 This function returns the duration of the Emacs initialization
1622 (@pxref{Startup Summary}) in seconds, as a string. When called
1623 interactively, it prints the duration in the echo area.
1626 @node Time Calculations
1627 @section Time Calculations
1629 These functions perform calendrical computations using time values
1630 (the kind of list that @code{current-time} returns).
1632 @defun time-less-p t1 t2
1633 This returns @code{t} if time value @var{t1} is less than time value
1637 @defun time-subtract t1 t2
1638 This returns the time difference @var{t1} @minus{} @var{t2} between
1639 two time values, in the same format as a time value.
1642 @defun time-add t1 t2
1643 This returns the sum of two time values, one of which ought to
1644 represent a time difference rather than a point in time.
1645 Here is how to add a number of seconds to a time value:
1648 (time-add @var{time} (seconds-to-time @var{seconds}))
1652 @defun time-to-days time
1653 This function returns the number of days between the beginning of year
1657 @defun time-to-day-in-year time
1658 This returns the day number within the year corresponding to @var{time}.
1661 @defun date-leap-year-p year
1662 This function returns @code{t} if @var{year} is a leap year.
1666 @section Timers for Delayed Execution
1669 You can set up a @dfn{timer} to call a function at a specified
1670 future time or after a certain length of idleness.
1672 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1673 can run them only when Emacs could accept output from a subprocess:
1674 namely, while waiting or inside certain primitive functions such as
1675 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1676 timer's execution may be delayed if Emacs is busy. However, the time of
1677 execution is very precise if Emacs is idle.
1679 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1680 function, because quitting out of many timer functions can leave
1681 things in an inconsistent state. This is normally unproblematical
1682 because most timer functions don't do a lot of work. Indeed, for a
1683 timer to call a function that takes substantial time to run is likely
1684 to be annoying. If a timer function needs to allow quitting, it
1685 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1686 a timer function calls @code{accept-process-output} to receive output
1687 from an external process, that call should be wrapped inside
1688 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1691 It is usually a bad idea for timer functions to alter buffer
1692 contents. When they do, they usually should call @code{undo-boundary}
1693 both before and after changing the buffer, to separate the timer's
1694 changes from user commands' changes and prevent a single undo entry
1695 from growing to be quite large.
1697 Timer functions should also avoid calling functions that cause Emacs
1698 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1699 unpredictable effects, since other timers (or even the same timer) can
1700 run while waiting. If a timer function needs to perform an action
1701 after a certain time has elapsed, it can do this by scheduling a new
1704 If a timer function calls functions that can change the match data,
1705 it should save and restore the match data. @xref{Saving Match Data}.
1707 @deffn Command run-at-time time repeat function &rest args
1708 This sets up a timer that calls the function @var{function} with
1709 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1710 (integer or floating point), the timer is scheduled to run again every
1711 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1712 the timer runs only once.
1714 @var{time} may specify an absolute or a relative time.
1716 Absolute times may be specified using a string with a limited variety
1717 of formats, and are taken to be times @emph{today}, even if already in
1718 the past. The recognized forms are @samp{@var{xxxx}},
1719 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1720 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1721 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1722 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1723 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1724 to separate the hour and minute parts.
1726 To specify a relative time as a string, use numbers followed by units.
1731 denotes 1 minute from now.
1733 denotes 65 seconds from now.
1734 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1735 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1738 For relative time values, Emacs considers a month to be exactly thirty
1739 days, and a year to be exactly 365.25 days.
1741 Not all convenient formats are strings. If @var{time} is a number
1742 (integer or floating point), that specifies a relative time measured in
1743 seconds. The result of @code{encode-time} can also be used to specify
1744 an absolute value for @var{time}.
1746 In most cases, @var{repeat} has no effect on when @emph{first} call
1747 takes place---@var{time} alone specifies that. There is one exception:
1748 if @var{time} is @code{t}, then the timer runs whenever the time is a
1749 multiple of @var{repeat} seconds after the epoch. This is useful for
1750 functions like @code{display-time}.
1752 The function @code{run-at-time} returns a timer value that identifies
1753 the particular scheduled future action. You can use this value to call
1754 @code{cancel-timer} (see below).
1757 A repeating timer nominally ought to run every @var{repeat} seconds,
1758 but remember that any invocation of a timer can be late. Lateness of
1759 one repetition has no effect on the scheduled time of the next
1760 repetition. For instance, if Emacs is busy computing for long enough
1761 to cover three scheduled repetitions of the timer, and then starts to
1762 wait, it will immediately call the timer function three times in
1763 immediate succession (presuming no other timers trigger before or
1764 between them). If you want a timer to run again no less than @var{n}
1765 seconds after the last invocation, don't use the @var{repeat} argument.
1766 Instead, the timer function should explicitly reschedule the timer.
1768 @defopt timer-max-repeats
1769 This variable's value specifies the maximum number of times to repeat
1770 calling a timer function in a row, when many previously scheduled
1771 calls were unavoidably delayed.
1774 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1775 Execute @var{body}, but give up after @var{seconds} seconds. If
1776 @var{body} finishes before the time is up, @code{with-timeout} returns
1777 the value of the last form in @var{body}. If, however, the execution of
1778 @var{body} is cut short by the timeout, then @code{with-timeout}
1779 executes all the @var{timeout-forms} and returns the value of the last
1782 This macro works by setting a timer to run after @var{seconds} seconds. If
1783 @var{body} finishes before that time, it cancels the timer. If the
1784 timer actually runs, it terminates execution of @var{body}, then
1785 executes @var{timeout-forms}.
1787 Since timers can run within a Lisp program only when the program calls a
1788 primitive that can wait, @code{with-timeout} cannot stop executing
1789 @var{body} while it is in the midst of a computation---only when it
1790 calls one of those primitives. So use @code{with-timeout} only with a
1791 @var{body} that waits for input, not one that does a long computation.
1794 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1795 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1798 @defun cancel-timer timer
1799 This cancels the requested action for @var{timer}, which should be a
1800 timer---usually, one previously returned by @code{run-at-time} or
1801 @code{run-with-idle-timer}. This cancels the effect of that call to
1802 one of these functions; the arrival of the specified time will not
1803 cause anything special to happen.
1807 @section Idle Timers
1809 Here is how to set up a timer that runs when Emacs is idle for a
1810 certain length of time. Aside from how to set them up, idle timers
1811 work just like ordinary timers.
1813 @deffn Command run-with-idle-timer secs repeat function &rest args
1814 Set up a timer which runs the next time Emacs is idle for @var{secs}
1815 seconds. The value of @var{secs} may be an integer or a floating
1816 point number; a value of the type returned by @code{current-idle-time}
1819 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1820 Emacs remains idle for a long enough time. More often @var{repeat} is
1821 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1822 remains idle for @var{secs} seconds.
1824 The function @code{run-with-idle-timer} returns a timer value which you
1825 can use in calling @code{cancel-timer} (@pxref{Timers}).
1829 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1830 it remains idle until the user provides some input. If a timer is set
1831 for five seconds of idleness, it runs approximately five seconds after
1832 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1833 this timer will not run again as long as Emacs remains idle, because
1834 the duration of idleness will continue to increase and will not go
1835 down to five seconds again.
1837 Emacs can do various things while idle: garbage collect, autosave or
1838 handle data from a subprocess. But these interludes during idleness do
1839 not interfere with idle timers, because they do not reset the clock of
1840 idleness to zero. An idle timer set for 600 seconds will run when ten
1841 minutes have elapsed since the last user command was finished, even if
1842 subprocess output has been accepted thousands of times within those ten
1843 minutes, and even if there have been garbage collections and autosaves.
1845 When the user supplies input, Emacs becomes non-idle while executing the
1846 input. Then it becomes idle again, and all the idle timers that are
1847 set up to repeat will subsequently run another time, one by one.
1849 Do not write an idle timer function containing a loop which does a
1850 certain amount of processing each time around, and exits when
1851 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1852 natural but has two problems:
1856 It blocks out all process output (since Emacs accepts process output
1857 only while waiting).
1860 It blocks out any idle timers that ought to run during that time.
1864 Similarly, do not write an idle timer function that sets up another
1865 idle timer (including the same idle timer) with @var{secs} argument
1866 less than or equal to the current idleness time. Such a timer will
1867 run almost immediately, and continue running again and again, instead
1868 of waiting for the next time Emacs becomes idle. The correct approach
1869 is to reschedule with an appropriate increment of the current value of
1870 the idleness time, as described below.
1872 @defun current-idle-time
1873 If Emacs is idle, this function returns the length of time Emacs has
1874 been idle, as a list of four integers: @code{(@var{sec-high}
1875 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1876 @code{current-time} (@pxref{Time of Day}).
1878 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1879 This is a convenient way to test whether Emacs is idle.
1882 The main use of @code{current-idle-time} is when an idle timer
1883 function wants to ``take a break'' for a while. It can set up another
1884 idle timer to call the same function again, after a few seconds more
1885 idleness. Here's an example:
1888 (defvar my-resume-timer nil
1889 "Timer for `my-timer-function' to reschedule itself, or nil.")
1891 (defun my-timer-function ()
1892 ;; @r{If the user types a command while @code{my-resume-timer}}
1893 ;; @r{is active, the next time this function is called from}
1894 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1895 (when my-resume-timer
1896 (cancel-timer my-resume-timer))
1897 ...@var{do the work for a while}...
1898 (when @var{taking-a-break}
1899 (setq my-resume-timer
1900 (run-with-idle-timer
1901 ;; Compute an idle time @var{break-length}
1902 ;; more than the current value.
1903 (time-add (current-idle-time)
1904 (seconds-to-time @var{break-length}))
1906 'my-timer-function))))
1909 @node Terminal Input
1910 @section Terminal Input
1911 @cindex terminal input
1913 This section describes functions and variables for recording or
1914 manipulating terminal input. See @ref{Display}, for related
1918 * Input Modes:: Options for how input is processed.
1919 * Recording Input:: Saving histories of recent or all input events.
1923 @subsection Input Modes
1925 @cindex terminal input modes
1927 @defun set-input-mode interrupt flow meta &optional quit-char
1928 This function sets the mode for reading keyboard input. If
1929 @var{interrupt} is non-@code{nil}, then Emacs uses input interrupts.
1930 If it is @code{nil}, then it uses @sc{cbreak} mode. The default
1931 setting is system-dependent. Some systems always use @sc{cbreak} mode
1932 regardless of what is specified.
1934 When Emacs communicates directly with X, it ignores this argument and
1935 uses interrupts if that is the way it knows how to communicate.
1937 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1938 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1939 has no effect except in @sc{cbreak} mode.
1941 The argument @var{meta} controls support for input character codes
1942 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1943 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1944 Emacs disregards the 8th bit; this is necessary when the terminal uses
1945 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1946 Emacs uses all 8 bits of input unchanged. This is good for terminals
1947 that use 8-bit character sets.
1949 If @var{quit-char} is non-@code{nil}, it specifies the character to
1950 use for quitting. Normally this character is @kbd{C-g}.
1954 The @code{current-input-mode} function returns the input mode settings
1955 Emacs is currently using.
1957 @defun current-input-mode
1958 This function returns the current mode for reading keyboard input. It
1959 returns a list, corresponding to the arguments of @code{set-input-mode},
1960 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1964 is non-@code{nil} when Emacs is using interrupt-driven input. If
1965 @code{nil}, Emacs is using @sc{cbreak} mode.
1967 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1968 flow control for output to the terminal. This value is meaningful only
1969 when @var{interrupt} is @code{nil}.
1971 is @code{t} if Emacs treats the eighth bit of input characters as
1972 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1973 input character; any other value means Emacs uses all eight bits as the
1974 basic character code.
1976 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1980 @node Recording Input
1981 @subsection Recording Input
1982 @cindex recording input
1985 This function returns a vector containing the last 300 input events from
1986 the keyboard or mouse. All input events are included, whether or not
1987 they were used as parts of key sequences. Thus, you always get the last
1988 300 input events, not counting events generated by keyboard macros.
1989 (These are excluded because they are less interesting for debugging; it
1990 should be enough to see the events that invoked the macros.)
1992 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1993 causes this function to return an empty vector immediately afterward.
1996 @deffn Command open-dribble-file filename
1997 @cindex dribble file
1998 This function opens a @dfn{dribble file} named @var{filename}. When a
1999 dribble file is open, each input event from the keyboard or mouse (but
2000 not those from keyboard macros) is written in that file. A
2001 non-character event is expressed using its printed representation
2002 surrounded by @samp{<@dots{}>}.
2004 You close the dribble file by calling this function with an argument
2007 This function is normally used to record the input necessary to
2008 trigger an Emacs bug, for the sake of a bug report.
2012 (open-dribble-file "~/dribble")
2018 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2020 @node Terminal Output
2021 @section Terminal Output
2022 @cindex terminal output
2024 The terminal output functions send output to a text terminal, or keep
2025 track of output sent to the terminal. The variable @code{baud-rate}
2026 tells you what Emacs thinks is the output speed of the terminal.
2029 This variable's value is the output speed of the terminal, as far as
2030 Emacs knows. Setting this variable does not change the speed of actual
2031 data transmission, but the value is used for calculations such as
2034 It also affects decisions about whether to scroll part of the
2035 screen or repaint on text terminals. @xref{Forcing Redisplay},
2036 for the corresponding functionality on graphical terminals.
2038 The value is measured in baud.
2041 If you are running across a network, and different parts of the
2042 network work at different baud rates, the value returned by Emacs may be
2043 different from the value used by your local terminal. Some network
2044 protocols communicate the local terminal speed to the remote machine, so
2045 that Emacs and other programs can get the proper value, but others do
2046 not. If Emacs has the wrong value, it makes decisions that are less
2047 than optimal. To fix the problem, set @code{baud-rate}.
2049 @defun send-string-to-terminal string &optional terminal
2050 This function sends @var{string} to @var{terminal} without alteration.
2051 Control characters in @var{string} have terminal-dependent effects.
2052 This function operates only on text terminals. @var{terminal} may be
2053 a terminal object, a frame, or @code{nil} for the selected frame's
2054 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2055 @var{terminal} is @code{nil}.
2057 One use of this function is to define function keys on terminals that
2058 have downloadable function key definitions. For example, this is how (on
2059 certain terminals) to define function key 4 to move forward four
2060 characters (by transmitting the characters @kbd{C-u C-f} to the
2065 (send-string-to-terminal "\eF4\^U\^F")
2071 @deffn Command open-termscript filename
2072 @cindex termscript file
2073 This function is used to open a @dfn{termscript file} that will record
2074 all the characters sent by Emacs to the terminal. It returns
2075 @code{nil}. Termscript files are useful for investigating problems
2076 where Emacs garbles the screen, problems that are due to incorrect
2077 Termcap entries or to undesirable settings of terminal options more
2078 often than to actual Emacs bugs. Once you are certain which characters
2079 were actually output, you can determine reliably whether they correspond
2080 to the Termcap specifications in use.
2084 (open-termscript "../junk/termscript")
2089 You close the termscript file by calling this function with an
2090 argument of @code{nil}.
2092 See also @code{open-dribble-file} in @ref{Recording Input}.
2096 @section Sound Output
2099 To play sound using Emacs, use the function @code{play-sound}. Only
2100 certain systems are supported; if you call @code{play-sound} on a
2101 system which cannot really do the job, it gives an error.
2103 @c FIXME: Add indexes for Au and WAV? --xfq
2104 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2105 or Sun Audio format (@samp{.au}).
2107 @defun play-sound sound
2108 This function plays a specified sound. The argument, @var{sound}, has
2109 the form @code{(sound @var{properties}...)}, where the @var{properties}
2110 consist of alternating keywords (particular symbols recognized
2111 specially) and values corresponding to them.
2113 Here is a table of the keywords that are currently meaningful in
2114 @var{sound}, and their meanings:
2117 @item :file @var{file}
2118 This specifies the file containing the sound to play.
2119 If the file name is not absolute, it is expanded against
2120 the directory @code{data-directory}.
2122 @item :data @var{data}
2123 This specifies the sound to play without need to refer to a file. The
2124 value, @var{data}, should be a string containing the same bytes as a
2125 sound file. We recommend using a unibyte string.
2127 @item :volume @var{volume}
2128 This specifies how loud to play the sound. It should be a number in the
2129 range of 0 to 1. The default is to use whatever volume has been
2132 @item :device @var{device}
2133 This specifies the system device on which to play the sound, as a
2134 string. The default device is system-dependent.
2137 Before actually playing the sound, @code{play-sound}
2138 calls the functions in the list @code{play-sound-functions}.
2139 Each function is called with one argument, @var{sound}.
2142 @deffn Command play-sound-file file &optional volume device
2143 This function is an alternative interface to playing a sound @var{file}
2144 specifying an optional @var{volume} and @var{device}.
2147 @defvar play-sound-functions
2148 A list of functions to be called before playing a sound. Each function
2149 is called with one argument, a property list that describes the sound.
2153 @section Operating on X11 Keysyms
2156 To define system-specific X11 keysyms, set the variable
2157 @code{system-key-alist}.
2159 @defvar system-key-alist
2160 This variable's value should be an alist with one element for each
2161 system-specific keysym. Each element has the form @code{(@var{code}
2162 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2163 including the ``vendor specific'' bit,
2170 and @var{symbol} is the name for the function key.
2172 For example @code{(168 . mute-acute)} defines a system-specific key (used
2173 by HP X servers) whose numeric code is
2182 It is not crucial to exclude from the alist the keysyms of other X
2183 servers; those do no harm, as long as they don't conflict with the ones
2184 used by the X server actually in use.
2186 The variable is always local to the current terminal, and cannot be
2187 buffer-local. @xref{Multiple Terminals}.
2190 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2192 @defvar x-alt-keysym
2193 @defvarx x-meta-keysym
2194 @defvarx x-hyper-keysym
2195 @defvarx x-super-keysym
2196 The name of the keysym that should stand for the Alt modifier
2197 (respectively, for Meta, Hyper, and Super). For example, here is
2198 how to swap the Meta and Alt modifiers within Emacs:
2200 (setq x-alt-keysym 'meta)
2201 (setq x-meta-keysym 'alt)
2209 The command-line option @samp{-batch} causes Emacs to run
2210 noninteractively. In this mode, Emacs does not read commands from the
2211 terminal, it does not alter the terminal modes, and it does not expect
2212 to be outputting to an erasable screen. The idea is that you specify
2213 Lisp programs to run; when they are finished, Emacs should exit. The
2214 way to specify the programs to run is with @samp{-l @var{file}}, which
2215 loads the library named @var{file}, or @samp{-f @var{function}}, which
2216 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2218 Any Lisp program output that would normally go to the echo area,
2219 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2220 as the stream, goes instead to Emacs's standard error descriptor when
2221 in batch mode. Similarly, input that would normally come from the
2222 minibuffer is read from the standard input descriptor.
2223 Thus, Emacs behaves much like a noninteractive
2224 application program. (The echo area output that Emacs itself normally
2225 generates, such as command echoing, is suppressed entirely.)
2227 @defvar noninteractive
2228 This variable is non-@code{nil} when Emacs is running in batch mode.
2231 @node Session Management
2232 @section Session Management
2233 @cindex session manager
2235 Emacs supports the X Session Management Protocol, which is used to
2236 suspend and restart applications. In the X Window System, a program
2237 called the @dfn{session manager} is responsible for keeping track of
2238 the applications that are running. When the X server shuts down, the
2239 session manager asks applications to save their state, and delays the
2240 actual shutdown until they respond. An application can also cancel
2243 When the session manager restarts a suspended session, it directs
2244 these applications to individually reload their saved state. It does
2245 this by specifying a special command-line argument that says what
2246 saved session to restore. For Emacs, this argument is @samp{--smid
2249 @defvar emacs-save-session-functions
2250 @cindex session file
2251 Emacs supports saving state via a hook called
2252 @code{emacs-save-session-functions}. Emacs runs this hook when the
2253 session manager tells it that the window system is shutting down. The
2254 functions are called with no arguments, and with the current buffer
2255 set to a temporary buffer. Each function can use @code{insert} to add
2256 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2257 file, called the @dfn{session file}.
2259 @findex emacs-session-restore
2260 Subsequently, when the session manager restarts Emacs, it loads the
2261 session file automatically (@pxref{Loading}). This is performed by a
2262 function named @code{emacs-session-restore}, which is called during
2263 startup. @xref{Startup Summary}.
2265 If a function in @code{emacs-save-session-functions} returns
2266 non-@code{nil}, Emacs tells the session manager to cancel the
2270 Here is an example that just inserts some text into @file{*scratch*} when
2271 Emacs is restarted by the session manager.
2275 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2279 (defun save-yourself-test ()
2280 (insert "(save-current-buffer
2281 (switch-to-buffer \"*scratch*\")
2282 (insert \"I am restored\"))")
2287 @node Desktop Notifications
2288 @section Desktop Notifications
2289 @cindex desktop notifications
2290 @cindex notifications, on desktop
2292 Emacs is able to send @dfn{notifications} on systems that support the
2293 freedesktop.org Desktop Notifications Specification. In order to use
2294 this functionality, Emacs must have been compiled with D-Bus support,
2295 and the @code{notifications} library must be loaded. @xref{Top, ,
2296 D-Bus,dbus,D-Bus integration in Emacs}.
2298 @defun notifications-notify &rest params
2299 This function sends a notification to the desktop via D-Bus,
2300 consisting of the parameters specified by the @var{params} arguments.
2301 These arguments should consist of alternating keyword and value pairs.
2302 The supported keywords and values are as follows:
2305 @item :bus @var{bus}
2306 The D-Bus bus. This argument is needed only if a bus other than
2307 @code{:session} shall be used.
2309 @item :title @var{title}
2310 The notification title.
2312 @item :body @var{text}
2313 The notification body text. Depending on the implementation of the
2314 notification server, the text could contain HTML markups, like
2315 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2316 characters must be encoded, as @samp{"Contact
2317 <postmaster@@localhost>!"}.
2319 @item :app-name @var{name}
2320 The name of the application sending the notification. The default is
2321 @code{notifications-application-name}.
2323 @item :replaces-id @var{id}
2324 The notification @var{id} that this notification replaces. @var{id}
2325 must be the result of a previous @code{notifications-notify} call.
2327 @item :app-icon @var{icon-file}
2328 The file name of the notification icon. If set to @code{nil}, no icon
2329 is displayed. The default is @code{notifications-application-icon}.
2331 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2332 A list of actions to be applied. @var{key} and @var{title} are both
2333 strings. The default action (usually invoked by clicking the
2334 notification) should have a key named @samp{"default"}. The title can
2335 be anything, though implementations are free not to display it.
2337 @item :timeout @var{timeout}
2338 The timeout time in milliseconds since the display of the notification
2339 at which the notification should automatically close. If -1, the
2340 notification's expiration time is dependent on the notification
2341 server's settings, and may vary for the type of notification. If 0,
2342 the notification never expires. Default value is -1.
2344 @item :urgency @var{urgency}
2345 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2348 When this keyword is given, the @var{title} string of the actions is
2349 interpreted as icon name.
2351 @item :category @var{category}
2352 The type of notification this is, a string. See the
2353 @uref{http://developer.gnome.org/notification-spec/#categories,
2354 Desktop Notifications Specification} for a list of standard
2357 @item :desktop-entry @var{filename}
2358 This specifies the name of the desktop filename representing the
2359 calling program, like @samp{"emacs"}.
2361 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2362 This is a raw data image format that describes the width, height,
2363 rowstride, whether there is an alpha channel, bits per sample,
2364 channels and image data, respectively.
2366 @item :image-path @var{path}
2367 This is represented either as a URI (@samp{file://} is the only URI
2368 schema supported right now) or a name in a freedesktop.org-compliant
2369 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2371 @item :sound-file @var{filename}
2372 The path to a sound file to play when the notification pops up.
2374 @item :sound-name @var{name}
2375 A themable named sound from the freedesktop.org sound naming
2376 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2377 notification pops up. Similar to the icon name, only for sounds. An
2378 example would be @samp{"message-new-instant"}.
2380 @item :suppress-sound
2381 Causes the server to suppress playing any sounds, if it has that
2385 When set the server will not automatically remove the notification
2386 when an action has been invoked. The notification will remain resident
2387 in the server until it is explicitly removed by the user or by the
2388 sender. This hint is likely only useful when the server has the
2389 @code{:persistence} capability.
2392 When set the server will treat the notification as transient and
2393 by-pass the server's persistence capability, if it should exist.
2395 @item :x @var{position}
2396 @itemx :y @var{position}
2397 Specifies the X, Y location on the screen that the
2398 notification should point to. Both arguments must be used together.
2400 @item :on-action @var{function}
2401 Function to call when an action is invoked. The notification @var{id}
2402 and the @var{key} of the action are passed as arguments to the
2405 @item :on-close @var{function}
2406 Function to call when the notification has been closed by timeout or
2407 by the user. The function receive the notification @var{id} and the closing
2408 @var{reason} as arguments:
2411 @item @code{expired} if the notification has expired
2412 @item @code{dismissed} if the notification was dismissed by the user
2413 @item @code{close-notification} if the notification was closed by a call to
2414 @code{notifications-close-notification}
2415 @item @code{undefined} if the notification server hasn't provided a reason
2419 Which parameters are accepted by the notification server can be
2420 checked via @code{notifications-get-capabilities}.
2422 This function returns a notification id, an integer, which can be used
2423 to manipulate the notification item with
2424 @code{notifications-close-notification} or the @code{:replaces-id}
2425 argument of another @code{notifications-notify} call. For example:
2429 (defun my-on-action-function (id key)
2430 (message "Message %d, key \"%s\" pressed" id key))
2431 @result{} my-on-action-function
2435 (defun my-on-close-function (id reason)
2436 (message "Message %d, closed due to \"%s\"" id reason))
2437 @result{} my-on-close-function
2441 (notifications-notify
2443 :body "This is <b>important</b>."
2444 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2445 :on-action 'my-on-action-function
2446 :on-close 'my-on-close-function)
2451 A message window opens on the desktop. Press "I agree"
2452 @result{} Message 22, key "Confirm" pressed
2453 Message 22, closed due to "dismissed"
2458 @defun notifications-close-notification id &optional bus
2459 This function closes a notification with identifier @var{id}.
2460 @var{bus} can be a string denoting a D-Bus connection, the default is
2464 @defun notifications-get-capabilities &optional bus
2465 Returns the capabilities of the notification server, a list of
2466 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2467 default is @code{:session}. The following capabilities can be
2472 The server will provide the specified actions to the user.
2477 @item :body-hyperlinks
2478 The server supports hyperlinks in the notifications.
2481 The server supports images in the notifications.
2484 Supports markup in the body text.
2487 The server will render an animation of all the frames in a given image
2491 Supports display of exactly 1 frame of any given image array. This
2492 value is mutually exclusive with @code{:icon-multi}.
2495 The server supports persistence of notifications.
2498 The server supports sounds on notifications.
2501 Further vendor-specific caps start with @code{:x-vendor}, like
2502 @code{:x-gnome-foo-cap}.
2505 @defun notifications-get-server-information &optional bus
2506 Return information on the notification server, a list of strings.
2507 @var{bus} can be a string denoting a D-Bus connection, the default is
2508 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2509 @var{version} @var{spec-version})}.
2513 The product name of the server.
2516 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2519 The server's version number.
2522 The specification version the server is compliant with.
2525 If @var{SPEC_VERSION} is @code{nil}, the server supports a
2526 specification prior to @samp{"1.0"}.
2529 @node File Notifications
2530 @section Notifications on File Changes
2531 @cindex file notifications
2532 @cindex watch, for filesystem events
2534 Several operating systems support watching of filesystems for changes
2535 of files. If configured properly, Emacs links a respective library
2536 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2537 statically. These libraries enable watching of filesystems on the
2540 It is also possible to watch filesystems on remote machines,
2541 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2542 This does not depend on one of the libraries linked to Emacs.
2544 Since all these libraries emit different events on notified file
2545 changes, there is the Emacs library @code{filenotify} which provides a
2548 @defun file-notify-add-watch file flags callback
2549 Add a watch for filesystem events pertaining to @var{file}. This
2550 arranges for filesystem events pertaining to @var{file} to be reported
2553 The returned value is a descriptor for the added watch. Its type
2554 depends on the underlying library, it cannot be assumed to be an
2555 integer as in the example below. It should be used for comparison by
2558 If the @var{file} cannot be watched for some reason, this function
2559 signals a @code{file-notify-error} error.
2561 Sometimes, mounted filesystems cannot be watched for file changes.
2562 This is not detected by this function, a non-@code{nil} return value
2563 does not guarantee that changes on @var{file} will be notified.
2565 @var{flags} is a list of conditions to set what will be watched for.
2566 It can include the following symbols:
2570 watch for file changes
2571 @item attribute-change
2572 watch for file attribute changes, like permissions or modification
2576 If @var{file} is a directory, changes for all files in that directory
2577 will be notified. This does not work recursively.
2579 When any event happens, Emacs will call the @var{callback} function
2580 passing it a single argument @var{event}, which is of the form
2583 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2586 @var{descriptor} is the same object as the one returned by this
2587 function. @var{action} is the description of the event. It could be
2588 any one of the following symbols:
2592 @var{file} was created
2594 @var{file} was deleted
2596 @var{file} has changed
2598 @var{file} has been renamed to @var{file1}
2599 @item attribute-changed
2600 a @var{file} attribute was changed
2603 @var{file} and @var{file1} are the name of the file(s) whose event is
2604 being reported. For example:
2608 (require 'filenotify)
2609 @result{} filenotify
2613 (defun my-notify-callback (event)
2614 (message "Event %S" event))
2615 @result{} my-notify-callback
2619 (file-notify-add-watch
2620 "/tmp" '(change attribute-change) 'my-notify-callback)
2625 (write-region "foo" nil "/tmp/foo")
2626 @result{} Event (35025468 created "/tmp/.#foo")
2627 Event (35025468 created "/tmp/foo")
2628 Event (35025468 changed "/tmp/foo")
2629 Event (35025468 deleted "/tmp/.#foo")
2633 (write-region "bla" nil "/tmp/foo")
2634 @result{} Event (35025468 created "/tmp/.#foo")
2635 Event (35025468 changed "/tmp/foo") [2 times]
2636 Event (35025468 deleted "/tmp/.#foo")
2640 (set-file-modes "/tmp/foo" (default-file-modes))
2641 @result{} Event (35025468 attribute-changed "/tmp/foo")
2645 Whether the action @code{renamed} is returned, depends on the used
2646 watch library. It can be expected, when a directory is watched, and
2647 both @var{file} and @var{file1} belong to this directory. Otherwise,
2648 the actions @code{deleted} and @code{created} could be returned in a
2653 (rename-file "/tmp/foo" "/tmp/bla")
2654 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2658 (file-notify-add-watch
2659 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2664 (rename-file "/tmp/bla" "/var/tmp/bla")
2665 @result{} ;; gfilenotify
2666 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2668 @result{} ;; inotify
2669 Event (35025504 created "/var/tmp/bla")
2670 Event (35025468 deleted "/tmp/bla")
2675 @defun file-notify-rm-watch descriptor
2676 Removes an existing file watch specified by its @var{descriptor}.
2677 @var{descriptor} should be an object returned by
2678 @code{file-notify-add-watch}.
2681 @node Dynamic Libraries
2682 @section Dynamically Loaded Libraries
2683 @cindex dynamic libraries
2685 A @dfn{dynamically loaded library} is a library that is loaded on
2686 demand, when its facilities are first needed. Emacs supports such
2687 on-demand loading of support libraries for some of its features.
2689 @defvar dynamic-library-alist
2690 This is an alist of dynamic libraries and external library files
2693 Each element is a list of the form
2694 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2695 a symbol representing a supported external library, and the rest are
2696 strings giving alternate filenames for that library.
2698 Emacs tries to load the library from the files in the order they
2699 appear in the list; if none is found, the Emacs session won't have
2700 access to that library, and the features it provides will be
2703 Image support on some platforms uses this facility. Here's an example
2704 of setting this variable for supporting images on MS-Windows:
2707 (setq dynamic-library-alist
2708 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2709 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2710 "libpng13d.dll" "libpng13.dll")
2711 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2713 (tiff "libtiff3.dll" "libtiff.dll")
2714 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2715 (svg "librsvg-2-2.dll")
2716 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2717 (glib "libglib-2.0-0.dll")
2718 (gobject "libgobject-2.0-0.dll")))
2721 Note that image types @code{pbm} and @code{xbm} do not need entries in
2722 this variable because they do not depend on external libraries and are
2723 always available in Emacs.
2725 Also note that this variable is not meant to be a generic facility for
2726 accessing external libraries; only those already known by Emacs can
2727 be loaded through it.
2729 This variable is ignored if the given @var{library} is statically