2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2015 Free Software
5 @c See the file elisp.texi for copying conditions.
7 @chapter Operating System Interface
9 This chapter is about starting and getting out of Emacs, access to
10 values in the operating system environment, and terminal input, output.
12 @xref{Building Emacs}, for related information. @xref{Display}, for
13 additional operating system status information pertaining to the
14 terminal and the screen.
17 * Starting Up:: Customizing Emacs startup processing.
18 * Getting Out:: How exiting works (permanent or temporary).
19 * System Environment:: Distinguish the name and kind of system.
20 * User Identification:: Finding the name and user id of the user.
21 * Time of Day:: Getting the current time.
22 * Time Conversion:: Converting a time from numeric form to
23 calendrical data and vice versa.
24 * Time Parsing:: Converting a time from numeric form to text
26 * Processor Run Time:: Getting the run time used by Emacs.
27 * Time Calculations:: Adding, subtracting, comparing times, etc.
28 * Timers:: Setting a timer to call a function at a certain time.
29 * Idle Timers:: Setting a timer to call a function when Emacs has
30 been idle for a certain length of time.
31 * Terminal Input:: Accessing and recording terminal input.
32 * Terminal Output:: Controlling and recording terminal output.
33 * Sound Output:: Playing sounds on the computer's speaker.
34 * X11 Keysyms:: Operating on key symbols for X Windows.
35 * Batch Mode:: Running Emacs without terminal interaction.
36 * Session Management:: Saving and restoring state with X Session Management.
37 * Desktop Notifications:: Desktop notifications.
38 * File Notifications:: File notifications.
39 * Dynamic Libraries:: On-demand loading of support libraries.
43 @section Starting Up Emacs
45 This section describes what Emacs does when it is started, and how you
46 can customize these actions.
49 * Startup Summary:: Sequence of actions Emacs performs at startup.
50 * Init File:: Details on reading the init file.
51 * Terminal-Specific:: How the terminal-specific Lisp file is read.
52 * Command-Line Arguments:: How command-line arguments are processed,
53 and how you can customize them.
57 @subsection Summary: Sequence of Actions at Startup
58 @cindex initialization of Emacs
59 @cindex startup of Emacs
60 @cindex @file{startup.el}
62 When Emacs is started up, it performs the following operations
63 (see @code{normal-top-level} in @file{startup.el}):
67 It adds subdirectories to @code{load-path}, by running the file named
68 @file{subdirs.el} in each directory in the list. Normally, this file
69 adds the directory's subdirectories to the list, and those are scanned
70 in their turn. The files @file{subdirs.el} are normally generated
71 automatically when Emacs is installed.
74 It loads any @file{leim-list.el} that it finds in the @code{load-path}
75 directories. This file is intended for registering input methods.
76 The search is only for any personal @file{leim-list.el} files that you
77 may have created; it skips the directories containing the standard Emacs
78 libraries (these should contain only a single @file{leim-list.el} file,
79 which is compiled into the Emacs executable).
81 @vindex before-init-time
83 It sets the variable @code{before-init-time} to the value of
84 @code{current-time} (@pxref{Time of Day}). It also sets
85 @code{after-init-time} to @code{nil}, which signals to Lisp programs
86 that Emacs is being initialized.
88 @c set-locale-environment
90 It sets the language environment and the terminal coding system,
91 if requested by environment variables such as @env{LANG}.
94 It does some basic parsing of the command-line arguments.
96 @vindex initial-window-system@r{, and startup}
97 @vindex window-system-initialization-alist
99 If not running in batch mode, it initializes the window system that
100 the variable @code{initial-window-system} specifies (@pxref{Window
101 Systems, initial-window-system}). The initialization function for
102 each supported window system is specified by
103 @code{window-system-initialization-alist}. If the value
104 of @code{initial-window-system} is @var{windowsystem}, then the
105 appropriate initialization function is defined in the file
106 @file{term/@var{windowsystem}-win.el}. This file should have been
107 compiled into the Emacs executable when it was built.
110 It runs the normal hook @code{before-init-hook}.
113 If appropriate, it creates a graphical frame. This is not done if the
114 options @samp{--batch} or @samp{--daemon} were specified.
117 It initializes the initial frame's faces, and sets up the menu bar
118 and tool bar if needed. If graphical frames are supported, it sets up
119 the tool bar even if the current frame is not a graphical one, since a
120 graphical frame may be created later on.
123 It use @code{custom-reevaluate-setting} to re-initialize the members
124 of the list @code{custom-delayed-init-variables}. These are any
125 pre-loaded user options whose default value depends on the run-time,
126 rather than build-time, context.
127 @xref{Building Emacs, custom-initialize-delay}.
130 @c It registers the colors available for tty frames.
133 It loads the library @file{site-start}, if it exists. This is not
134 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
135 @cindex @file{site-start.el}
138 It loads your init file (@pxref{Init File}). This is not done if the
139 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
140 the @samp{-u} option was specified, Emacs looks for the init file in
141 that user's home directory instead.
144 It loads the library @file{default}, if it exists. This is not done
145 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
146 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
147 @cindex @file{default.el}
150 It loads your abbrevs from the file specified by
151 @code{abbrev-file-name}, if that file exists and can be read
152 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
153 option @samp{--batch} was specified.
156 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
157 function @code{package-initialize} to activate any optional Emacs Lisp
158 package that has been installed. @xref{Packaging Basics}.
160 @vindex after-init-time
162 It sets the variable @code{after-init-time} to the value of
163 @code{current-time}. This variable was set to @code{nil} earlier;
164 setting it to the current time signals that the initialization phase
165 is over, and, together with @code{before-init-time}, provides the
166 measurement of how long it took.
169 It runs the normal hook @code{after-init-hook}.
172 If the buffer @file{*scratch*} exists and is still in Fundamental mode
173 (as it should be by default), it sets its major mode according to
174 @code{initial-major-mode}.
177 If started on a text terminal, it loads the terminal-specific
178 Lisp library (@pxref{Terminal-Specific}), and runs the hook
179 @code{tty-setup-hook}. This is not done
180 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
182 @c Now command-line calls command-line-1.
185 It displays the initial echo area message, unless you have suppressed
186 that with @code{inhibit-startup-echo-area-message}.
189 It processes any command-line options that were not handled earlier.
191 @c This next one is back in command-line, but the remaining bits of
192 @c command-line-1 are not done if noninteractive.
194 It now exits if the option @code{--batch} was specified.
197 If the @file{*scratch*} buffer exists and is empty, it inserts
198 @code{(substitute-command-keys initial-scratch-message)} into that buffer.
201 If @code{initial-buffer-choice} is a string, it visits the file (or
202 directory) with that name. If it is a function, it calls the function
203 with no arguments and selects the buffer that it returns. If one file
204 is given as a command line argument, that file is visited and its
205 buffer displayed alongside @code{initial-buffer-choice}. If more than
206 one file is given, all of the files are visited and the @file{*Buffer
207 List*} buffer is displayed alongside @code{initial-buffer-choice}.
210 @c I do not think this should be mentioned. AFAICS it is just a dodge
211 @c around inhibit-startup-screen not being settable on a site-wide basis.
212 If it is @code{t}, it selects the @file{*scratch*} buffer.
215 @c To make things nice and confusing, the next three items can be
216 @c called from two places. If displaying a startup screen, they are
217 @c called in command-line-1 before the startup screen is shown.
218 @c inhibit-startup-hooks is then set and window-setup-hook set to nil.
219 @c If not displaying a startup screen, they are are called in
221 @c FIXME? So it seems they can be called before or after the
222 @c daemon/session restore step?
225 It runs @code{emacs-startup-hook}.
228 It calls @code{frame-notice-user-settings}, which modifies the
229 parameters of the selected frame according to whatever the init files
233 It runs @code{window-setup-hook}. The only difference between this
234 hook and @code{emacs-startup-hook} is that this one runs after the
235 previously mentioned modifications to the frame parameters.
238 @cindex startup screen
239 It displays the @dfn{startup screen}, which is a special buffer that
240 contains information about copyleft and basic Emacs usage. This is
241 not done if @code{inhibit-startup-screen} or @code{initial-buffer-choice}
242 are non-@code{nil}, or if the @samp{--no-splash} or @samp{-Q} command-line
243 options were specified.
245 @c End of command-line-1.
247 @c Back to command-line from command-line-1.
249 @c This is the point at which we actually exit in batch mode, but the
250 @c last few bits of command-line-1 are not done in batch mode.
253 If the option @code{--daemon} was specified, it calls
254 @code{server-start}, and on Posix systems also detaches from the
255 controlling terminal. @xref{Emacs Server,,, emacs, The GNU Emacs
259 If started by the X session manager, it calls
260 @code{emacs-session-restore} passing it as argument the ID of the
261 previous session. @xref{Session Management}.
263 @c End of command-line.
265 @c Back to normal-top-level from command-line.
270 The following options affect some aspects of the startup sequence.
272 @defopt inhibit-startup-screen
273 This variable, if non-@code{nil}, inhibits the startup screen. In
274 that case, Emacs typically displays the @file{*scratch*} buffer; but
275 see @code{initial-buffer-choice}, below.
277 Do not set this variable in the init file of a new user, or in a way
278 that affects more than one user, as that would prevent new users from
279 receiving information about copyleft and basic Emacs usage.
281 @vindex inhibit-startup-message
282 @vindex inhibit-splash-screen
283 @code{inhibit-startup-message} and @code{inhibit-splash-screen} are
284 aliases for this variable.
287 @defopt initial-buffer-choice
288 If non-@code{nil}, this variable is a string that specifies a file or
289 directory for Emacs to display after starting up, instead of the
291 If its value is a function, Emacs calls that function which must
292 return a buffer which is then displayed.
293 If its value is @code{t}, Emacs displays the @file{*scratch*} buffer.
296 @defopt inhibit-startup-echo-area-message
297 This variable controls the display of the startup echo area message.
298 You can suppress the startup echo area message by adding text with this
299 form to your init file:
302 (setq inhibit-startup-echo-area-message
303 "@var{your-login-name}")
306 Emacs explicitly checks for an expression as shown above in your init
307 file; your login name must appear in the expression as a Lisp string
308 constant. You can also use the Customize interface. Other methods of
309 setting @code{inhibit-startup-echo-area-message} to the same value do
310 not inhibit the startup message. This way, you can easily inhibit the
311 message for yourself if you wish, but thoughtless copying of your init
312 file will not inhibit the message for someone else.
315 @defopt initial-scratch-message
316 This variable, if non-@code{nil}, should be a string, which is
317 treated as documentation to be
318 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
319 is @code{nil}, the @file{*scratch*} buffer is empty.
323 The following command-line options affect some aspects of the startup
324 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
328 Do not display a splash screen.
331 Run without an interactive terminal. @xref{Batch Mode}.
334 Do not initialize any display; just start a server in the background.
338 Do not load either the init file, or the @file{default} library.
341 Do not load the @file{site-start} library.
345 Equivalent to @samp{-q --no-site-file --no-splash}.
346 @c and --no-site-lisp, but let's not mention that here.
351 @subsection The Init File
353 @cindex @file{.emacs}
354 @cindex @file{init.el}
356 When you start Emacs, it normally attempts to load your @dfn{init
357 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
358 in your home directory, or a file named @file{init.el} in a
359 subdirectory named @file{.emacs.d} in your home directory.
361 Whichever place you use, you can also compile the file (@pxref{Byte
362 Compilation}); then the actual file loaded will be @file{.emacs.elc}
366 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
367 control whether and where to find the init file; @samp{-q} (and the
368 stronger @samp{-Q}) says not to load an init file, while @samp{-u
369 @var{user}} says to load @var{user}'s init file instead of yours.
370 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
371 option is specified, Emacs uses the @env{LOGNAME} environment
372 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
373 systems) variable, to find your home directory and thus your init
374 file; this way, even if you have su'd, Emacs still loads your own init
375 file. If those environment variables are absent, though, Emacs uses
376 your user-id to find your home directory.
378 @cindex default init file
379 An Emacs installation may have a @dfn{default init file}, which is a
380 Lisp library named @file{default.el}. Emacs finds this file through
381 the standard search path for libraries (@pxref{How Programs Do
382 Loading}). The Emacs distribution does not come with this file; it is
383 intended for local customizations. If the default init file exists,
384 it is loaded whenever you start Emacs. But your own personal init
385 file, if any, is loaded first; if it sets @code{inhibit-default-init}
386 to a non-@code{nil} value, then Emacs does not subsequently load the
387 @file{default.el} file. In batch mode, or if you specify @samp{-q}
388 (or @samp{-Q}), Emacs loads neither your personal init file nor
389 the default init file.
391 Another file for site-customization is @file{site-start.el}. Emacs
392 loads this @emph{before} the user's init file. You can inhibit the
393 loading of this file with the option @samp{--no-site-file}.
395 @defopt site-run-file
396 This variable specifies the site-customization file to load before the
397 user's init file. Its normal value is @code{"site-start"}. The only
398 way you can change it with real effect is to do so before dumping
400 @c So why even mention it here. I imagine it is almost never changed.
403 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
404 examples of how to make various commonly desired customizations in your
407 @defopt inhibit-default-init
408 If this variable is non-@code{nil}, it prevents Emacs from loading the
409 default initialization library file. The default value is @code{nil}.
412 @defvar before-init-hook
413 This normal hook is run, once, just before loading all the init files
414 (@file{site-start.el}, your init file, and @file{default.el}).
415 (The only way to change it with real effect is before dumping Emacs.)
418 @defvar after-init-hook
419 This normal hook is run, once, just after loading all the init files
420 (@file{site-start.el}, your init file, and @file{default.el}),
421 before loading the terminal-specific library (if started on a text
422 terminal) and processing the command-line action arguments.
425 @defvar emacs-startup-hook
426 This normal hook is run, once, just after handling the command line
427 arguments. In batch mode, Emacs does not run this hook.
430 @defvar window-setup-hook
431 This normal hook is very similar to @code{emacs-startup-hook}.
432 The only difference is that it runs slightly later, after setting
433 of the frame parameters. @xref{Startup Summary, window-setup-hook}.
436 @defvar user-init-file
437 This variable holds the absolute file name of the user's init file. If the
438 actual init file loaded is a compiled file, such as @file{.emacs.elc},
439 the value refers to the corresponding source file.
442 @defvar user-emacs-directory
443 This variable holds the name of the @file{.emacs.d} directory. It is
444 @file{~/.emacs.d} on all platforms but MS-DOS.
447 @node Terminal-Specific
448 @subsection Terminal-Specific Initialization
449 @cindex terminal-specific initialization
451 Each terminal type can have its own Lisp library that Emacs loads when
452 run on that type of terminal. The library's name is constructed by
453 concatenating the value of the variable @code{term-file-prefix} and the
454 terminal type (specified by the environment variable @env{TERM}).
455 Normally, @code{term-file-prefix} has the value @code{"term/"};
456 changing this is not recommended. If there is an entry matching
457 @env{TERM} in the @code{term-file-aliases} association list,
458 Emacs uses the associated value in place of @env{TERM}.
459 Emacs finds the file in the normal manner, by searching the
460 @code{load-path} directories, and trying the @samp{.elc} and
464 The usual role of a terminal-specific library is to enable special
465 keys to send sequences that Emacs can recognize. It may also need to
466 set or add to @code{input-decode-map} if the Termcap or Terminfo entry
467 does not specify all the terminal's function keys. @xref{Terminal Input}.
469 When the name of the terminal type contains a hyphen or underscore,
470 and no library is found whose name is identical to the terminal's
471 name, Emacs strips from the terminal's name the last hyphen or
472 underscore and everything that follows
473 it, and tries again. This process is repeated until Emacs finds a
474 matching library, or until there are no more hyphens or underscores in the name
475 (i.e., there is no terminal-specific library). For example, if the
476 terminal name is @samp{xterm-256color} and there is no
477 @file{term/xterm-256color.el} library, Emacs tries to load
478 @file{term/xterm.el}. If necessary, the terminal library can evaluate
479 @code{(getenv "TERM")} to find the full name of the terminal type.
481 Your init file can prevent the loading of the terminal-specific
482 library by setting the variable @code{term-file-prefix} to @code{nil}.
484 You can also arrange to override some of the actions of the
485 terminal-specific library by using @code{tty-setup-hook}. This is
486 a normal hook that Emacs runs after initializing a new text terminal.
487 You could use this hook to define initializations for terminals that do not
488 have their own libraries. @xref{Hooks}.
490 @defopt term-file-prefix
491 @cindex @env{TERM} environment variable
492 If the value of this variable is non-@code{nil}, Emacs loads a
493 terminal-specific initialization file as follows:
496 (load (concat term-file-prefix (getenv "TERM")))
500 You may set the @code{term-file-prefix} variable to @code{nil} in your
501 init file if you do not wish to load the
502 terminal-initialization file.
504 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
507 @defopt term-file-aliases
508 This variable is an an association list mapping terminal types to
509 their aliases. For example, an element of the form @code{("vt102"
510 . "vt100")} means to treat a terminal of type @samp{vt102} like one of
514 @defvar tty-setup-hook
515 This variable is a normal hook that Emacs runs after initializing a
516 new text terminal. (This applies when Emacs starts up in non-windowed
517 mode, and when making a tty @command{emacsclient} connection.) The
518 hook runs after loading your init file (if applicable) and the
519 terminal-specific Lisp file, so you can use it to adjust the
520 definitions made by that file.
522 For a related feature, @pxref{Init File, window-setup-hook}.
525 @node Command-Line Arguments
526 @subsection Command-Line Arguments
527 @cindex command-line arguments
529 You can use command-line arguments to request various actions when
530 you start Emacs. Note that the recommended way of using Emacs is to
531 start it just once, after logging in, and then do all editing in the same
532 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
533 For this reason, you might not use command-line arguments very often;
534 nonetheless, they can be useful when invoking Emacs from session
535 scripts or debugging Emacs. This section describes how Emacs
536 processes command-line arguments.
539 This function parses the command line that Emacs was called with,
540 processes it, and (amongst other things) loads the user's init file and
541 displays the startup messages.
544 @defvar command-line-processed
545 The value of this variable is @code{t} once the command line has been
548 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
549 Emacs}), you may wish to set this variable to @code{nil} first in
550 order to cause the new dumped Emacs to process its new command-line
554 @defvar command-switch-alist
555 @cindex switches on command line
556 @cindex options on command line
557 @cindex command-line options
558 This variable is an alist of user-defined command-line options and
559 associated handler functions. By default it is empty, but you can
560 add elements if you wish.
562 A @dfn{command-line option} is an argument on the command line, which
569 The elements of the @code{command-switch-alist} look like this:
572 (@var{option} . @var{handler-function})
575 The @sc{car}, @var{option}, is a string, the name of a command-line
576 option (not including the initial hyphen). The @var{handler-function}
577 is called to handle @var{option}, and receives the option name as its
580 In some cases, the option is followed in the command line by an
581 argument. In these cases, the @var{handler-function} can find all the
582 remaining command-line arguments in the variable
583 @code{command-line-args-left} (see below). (The entire list of
584 command-line arguments is in @code{command-line-args}.)
586 The command-line arguments are parsed by the @code{command-line-1}
587 function in the @file{startup.el} file. See also @ref{Emacs
588 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
592 @defvar command-line-args
593 The value of this variable is the list of command-line arguments passed
597 @defvar command-line-args-left
599 The value of this variable is the list of command-line arguments that
600 have not yet been processed.
601 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
602 @c @code{argv} is an alias for this.
605 @defvar command-line-functions
606 This variable's value is a list of functions for handling an
607 unrecognized command-line argument. Each time the next argument to be
608 processed has no special meaning, the functions in this list are called,
609 in order of appearance, until one of them returns a non-@code{nil}
612 These functions are called with no arguments. They can access the
613 command-line argument under consideration through the variable
614 @code{argi}, which is bound temporarily at this point. The remaining
615 arguments (not including the current one) are in the variable
616 @code{command-line-args-left}.
618 When a function recognizes and processes the argument in @code{argi}, it
619 should return a non-@code{nil} value to say it has dealt with that
620 argument. If it has also dealt with some of the following arguments, it
621 can indicate that by deleting them from @code{command-line-args-left}.
623 If all of these functions return @code{nil}, then the argument is treated
624 as a file name to visit.
628 @section Getting Out of Emacs
629 @cindex exiting Emacs
631 There are two ways to get out of Emacs: you can kill the Emacs job,
632 which exits permanently, or you can suspend it, which permits you to
633 reenter the Emacs process later. (In a graphical environment, you can
634 of course simply switch to another application without doing anything
635 special to Emacs, then switch back to Emacs when you want.)
638 * Killing Emacs:: Exiting Emacs irreversibly.
639 * Suspending Emacs:: Exiting Emacs reversibly.
643 @subsection Killing Emacs
644 @cindex killing Emacs
646 Killing Emacs means ending the execution of the Emacs process.
647 If you started Emacs from a terminal, the parent process normally
648 resumes control. The low-level primitive for killing Emacs is
651 @deffn Command kill-emacs &optional exit-data
652 This command calls the hook @code{kill-emacs-hook}, then exits the
653 Emacs process and kills it.
655 If @var{exit-data} is an integer, that is used as the exit status of
656 the Emacs process. (This is useful primarily in batch operation; see
659 If @var{exit-data} is a string, its contents are stuffed into the
660 terminal input buffer so that the shell (or whatever program next reads
661 input) can read them.
667 @cindex operating system signal
668 The @code{kill-emacs} function is normally called via the
669 higher-level command @kbd{C-x C-c}
670 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
671 Emacs Manual}. It is also called automatically if Emacs receives a
672 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
673 controlling terminal is disconnected), or if it receives a
674 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
676 @defvar kill-emacs-hook
677 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
679 Because @code{kill-emacs} can be called in situations where user
680 interaction is impossible (e.g., when the terminal is disconnected),
681 functions on this hook should not attempt to interact with the user.
682 If you want to interact with the user when Emacs is shutting down, use
683 @code{kill-emacs-query-functions}, described below.
686 When Emacs is killed, all the information in the Emacs process,
687 aside from files that have been saved, is lost. Because killing Emacs
688 inadvertently can lose a lot of work, the
689 @code{save-buffers-kill-terminal} command queries for confirmation if
690 you have buffers that need saving or subprocesses that are running.
691 It also runs the abnormal hook @code{kill-emacs-query-functions}:
693 @defvar kill-emacs-query-functions
694 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
695 functions in this hook, after asking the standard questions and before
696 calling @code{kill-emacs}. The functions are called in order of
697 appearance, with no arguments. Each function can ask for additional
698 confirmation from the user. If any of them returns @code{nil},
699 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
700 the remaining functions in this hook. Calling @code{kill-emacs}
701 directly does not run this hook.
704 @node Suspending Emacs
705 @subsection Suspending Emacs
706 @cindex suspending Emacs
708 On text terminals, it is possible to @dfn{suspend Emacs}, which
709 means stopping Emacs temporarily and returning control to its superior
710 process, which is usually the shell. This allows you to resume
711 editing later in the same Emacs process, with the same buffers, the
712 same kill ring, the same undo history, and so on. To resume Emacs,
713 use the appropriate command in the parent shell---most likely
716 @cindex controlling terminal
717 Suspending works only on a terminal device from which the Emacs
718 session was started. We call that device the @dfn{controlling
719 terminal} of the session. Suspending is not allowed if the
720 controlling terminal is a graphical terminal. Suspending is usually
721 not relevant in graphical environments, since you can simply switch to
722 another application without doing anything special to Emacs.
724 @c FIXME? Are there any systems Emacs still supports that do not
727 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
728 not support suspension of jobs; on these systems, suspension
729 actually creates a new shell temporarily as a subprocess of Emacs.
730 Then you would exit the shell to return to Emacs.
732 @deffn Command suspend-emacs &optional string
733 This function stops Emacs and returns control to the superior process.
734 If and when the superior process resumes Emacs, @code{suspend-emacs}
735 returns @code{nil} to its caller in Lisp.
737 This function works only on the controlling terminal of the Emacs
738 session; to relinquish control of other tty devices, use
739 @code{suspend-tty} (see below). If the Emacs session uses more than
740 one terminal, you must delete the frames on all the other terminals
741 before suspending Emacs, or this function signals an error.
742 @xref{Multiple Terminals}.
744 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
745 superior shell, to be read as terminal input.
746 @c FIXME? It seems to me that shell does echo STRING.
747 The characters in @var{string} are not echoed by the superior shell;
748 only the results appear.
750 Before suspending, @code{suspend-emacs} runs the normal hook
751 @code{suspend-hook}. After the user resumes Emacs,
752 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
755 The next redisplay after resumption will redraw the entire screen,
756 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
757 @xref{Refresh Screen}.
759 Here is an example of how you could use these hooks:
763 (add-hook 'suspend-hook
764 (lambda () (or (y-or-n-p "Really suspend? ")
765 (error "Suspend canceled"))))
767 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
770 @c The sit-for prevents the @code{nil} that suspend-emacs returns
771 @c hiding the message.
773 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
777 ---------- Buffer: Minibuffer ----------
778 Really suspend? @kbd{y}
779 ---------- Buffer: Minibuffer ----------
783 ---------- Parent Shell ----------
789 ---------- Echo Area ----------
794 @c FIXME? AFAICS, it is echoed.
795 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
796 is read and executed by the shell.
800 This variable is a normal hook that Emacs runs before suspending.
803 @defvar suspend-resume-hook
804 This variable is a normal hook that Emacs runs on resuming
808 @defun suspend-tty &optional tty
809 If @var{tty} specifies a terminal device used by Emacs, this function
810 relinquishes the device and restores it to its prior state. Frames
811 that used the device continue to exist, but are not updated and Emacs
812 doesn't read input from them. @var{tty} can be a terminal object, a
813 frame (meaning the terminal for that frame), or @code{nil} (meaning
814 the terminal for the selected frame). @xref{Multiple Terminals}.
816 If @var{tty} is already suspended, this function does nothing.
818 @vindex suspend-tty-functions
819 This function runs the hook @code{suspend-tty-functions}, passing the
820 terminal object as an argument to each function.
823 @defun resume-tty &optional tty
824 This function resumes the previously suspended terminal device
825 @var{tty}; where @var{tty} has the same possible values as it does
826 for @code{suspend-tty}.
828 @vindex resume-tty-functions
829 This function reopens the terminal device, re-initializes it, and
830 redraws it with that terminal's selected frame. It then runs the
831 hook @code{resume-tty-functions}, passing the terminal object as an
832 argument to each function.
834 If the same device is already used by another Emacs terminal, this
835 function signals an error. If @var{tty} is not suspended, this
836 function does nothing.
839 @defun controlling-tty-p &optional tty
840 This function returns non-@code{nil} if @var{tty} is the
841 controlling terminal of the Emacs session; @var{tty} can be a
842 terminal object, a frame (meaning the terminal for that frame), or
843 @code{nil} (meaning the terminal for the selected frame).
846 @deffn Command suspend-frame
847 This command @dfn{suspends} a frame. For GUI frames, it calls
848 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
849 text terminals, it calls either @code{suspend-emacs} or
850 @code{suspend-tty}, depending on whether the frame is displayed on the
851 controlling terminal device or not.
854 @node System Environment
855 @section Operating System Environment
856 @cindex operating system environment
858 Emacs provides access to variables in the operating system environment
859 through various functions. These variables include the name of the
860 system, the user's @acronym{UID}, and so on.
862 @defvar system-configuration
863 This variable holds the standard GNU configuration name for the
864 hardware/software configuration of your system, as a string. For
865 example, a typical value for a 64-bit GNU/Linux system is
866 @samp{"x86_64-unknown-linux-gnu"}.
869 @cindex system type and name
871 The value of this variable is a symbol indicating the type of operating
872 system Emacs is running on. The possible values are:
879 Berkeley BSD and its variants.
882 Cygwin, a Posix layer on top of MS-Windows.
888 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
891 A GNU/Linux system---that is, a variant GNU system, using the Linux
892 kernel. (These systems are the ones people often call ``Linux'', but
893 actually Linux is just the kernel, not the whole system.)
896 A GNU (glibc-based) system with a FreeBSD kernel.
899 Hewlett-Packard HPUX operating system.
902 Silicon Graphics Irix system.
905 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
906 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
912 Microsoft Windows NT, 9X and later. The value of @code{system-type}
913 is always @code{windows-nt}, e.g., even on Windows 7.
917 We do not wish to add new symbols to make finer distinctions unless it
918 is absolutely necessary! In fact, we hope to eliminate some of these
919 alternatives in the future. If you need to make a finer distinction
920 than @code{system-type} allows for, you can test
921 @code{system-configuration}, e.g., against a regexp.
925 This function returns the name of the machine you are running on, as a
929 @c FIXME seems like this section is not the best place for this option?
930 @defopt mail-host-address
931 If this variable is non-@code{nil}, it is used instead of
932 @code{system-name} for purposes of generating email addresses. For
933 example, it is used when constructing the default value of
934 @code{user-mail-address}. @xref{User Identification}. (Since this is
935 done when Emacs starts up, the value actually used is the one saved when
936 Emacs was dumped. @xref{Building Emacs}.)
937 @c FIXME sounds like should probably give this a :set-after and some
938 @c custom-initialize-delay voodoo.
941 @deffn Command getenv var &optional frame
942 @cindex environment variable access
943 This function returns the value of the environment variable @var{var},
944 as a string. @var{var} should be a string. If @var{var} is undefined
945 in the environment, @code{getenv} returns @code{nil}. It returns
946 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
947 variables and their values is kept in the variable @code{process-environment}.
956 The shell command @code{printenv} prints all or part of the environment:
961 PATH=/usr/local/bin:/usr/bin:/bin
973 @deffn Command setenv variable &optional value substitute
974 This command sets the value of the environment variable named
975 @var{variable} to @var{value}. @var{variable} should be a string.
976 Internally, Emacs Lisp can handle any string. However, normally
977 @var{variable} should be a valid shell identifier, that is, a sequence
978 of letters, digits and underscores, starting with a letter or
979 underscore. Otherwise, errors may occur if subprocesses of Emacs try
980 to access the value of @var{variable}. If @var{value} is omitted or
981 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
982 removes @var{variable} from the environment. Otherwise, @var{value}
985 @c FIXME: Document 'substitute-env-vars'? --xfq
986 If the optional argument @var{substitute} is non-@code{nil}, Emacs
987 calls the function @code{substitute-env-vars} to expand any
988 environment variables in @var{value}.
990 @code{setenv} works by modifying @code{process-environment}; binding
991 that variable with @code{let} is also reasonable practice.
993 @code{setenv} returns the new value of @var{variable}, or @code{nil}
994 if it removed @var{variable} from the environment.
997 @defvar process-environment
998 This variable is a list of strings, each describing one environment
999 variable. The functions @code{getenv} and @code{setenv} work by means
1005 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
1016 If @code{process-environment} contains multiple elements that
1017 specify the same environment variable, the first of these elements
1018 specifies the variable, and the others are ignored.
1021 @defvar initial-environment
1022 This variable holds the list of environment variables Emacs inherited
1023 from its parent process when Emacs started.
1026 @defvar path-separator
1027 This variable holds a string that says which character separates
1028 directories in a search path (as found in an environment variable). Its
1029 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1032 @defun parse-colon-path path
1033 This function takes a search path string such as the value of
1034 the @env{PATH} environment variable, and splits it at the separators,
1035 returning a list of directory names. @code{nil} in this list means
1036 the current directory. Although the function's name says
1037 ``colon'', it actually uses the value of @code{path-separator}.
1040 (parse-colon-path ":/foo:/bar")
1041 @result{} (nil "/foo/" "/bar/")
1045 @defvar invocation-name
1046 This variable holds the program name under which Emacs was invoked. The
1047 value is a string, and does not include a directory name.
1050 @defvar invocation-directory
1051 This variable holds the directory from which the Emacs executable was
1052 invoked, or @code{nil} if that directory cannot be determined.
1055 @defvar installation-directory
1056 If non-@code{nil}, this is a directory within which to look for the
1057 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1058 it is normally @code{nil}. It is non-@code{nil}
1059 when Emacs can't find those directories in their standard installed
1060 locations, but can find them in a directory related somehow to the one
1061 containing the Emacs executable (i.e., @code{invocation-directory}).
1064 @defun load-average &optional use-float
1065 This function returns the current 1-minute, 5-minute, and 15-minute
1066 system load averages, in a list. The load average indicates the
1067 number of processes trying to run on the system.
1069 By default, the values are integers that are 100 times the system load
1070 averages, but if @var{use-float} is non-@code{nil}, then they are
1071 returned as floating-point numbers without multiplying by 100.
1073 If it is impossible to obtain the load average, this function signals
1074 an error. On some platforms, access to load averages requires
1075 installing Emacs as setuid or setgid so that it can read kernel
1076 information, and that usually isn't advisable.
1077 @c FIXME which platforms are these? Are they still relevant?
1079 If the 1-minute load average is available, but the 5- or 15-minute
1080 averages are not, this function returns a shortened list containing
1081 the available averages.
1086 @result{} (169 48 36)
1090 @result{} (1.69 0.48 0.36)
1094 The shell command @code{uptime} returns similar information.
1098 This function returns the process @acronym{ID} of the Emacs process,
1102 @defvar tty-erase-char
1103 This variable holds the erase character that was selected
1104 in the system's terminal driver, before Emacs was started.
1105 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1106 @c The value is @code{nil} if Emacs is running under a window system.
1109 @node User Identification
1110 @section User Identification
1111 @cindex user identification
1113 @defvar init-file-user
1114 This variable says which user's init files should be used by
1115 Emacs---or @code{nil} if none. @code{""} stands for the user who
1116 originally logged in. The value reflects command-line options such as
1117 @samp{-q} or @samp{-u @var{user}}.
1119 Lisp packages that load files of customizations, or any other sort of
1120 user profile, should obey this variable in deciding where to find it.
1121 They should load the profile of the user name found in this variable.
1122 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q},
1123 @samp{-Q}, or @samp{-batch} option was used, then Lisp packages should
1124 not load any customization files or user profile.
1127 @defopt user-mail-address
1128 This holds the nominal email address of the user who is using Emacs.
1129 Emacs normally sets this variable to a default value after reading your
1130 init files, but not if you have already set it. So you can set the
1131 variable to some other value in your init file if you do not
1132 want to use the default value.
1135 @defun user-login-name &optional uid
1136 This function returns the name under which the user is logged in.
1137 It uses the environment variables @env{LOGNAME} or @env{USER} if
1138 either is set. Otherwise, the value is based on the effective
1139 @acronym{UID}, not the real @acronym{UID}.
1141 If you specify @var{uid} (a number), the result is the user name that
1142 corresponds to @var{uid}, or @code{nil} if there is no such user.
1145 @defun user-real-login-name
1146 This function returns the user name corresponding to Emacs's real
1147 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1148 environment variables @env{LOGNAME} and @env{USER}.
1151 @defun user-full-name &optional uid
1152 This function returns the full name of the logged-in user---or the value
1153 of the environment variable @env{NAME}, if that is set.
1155 If the Emacs process's user-id does not correspond to any known user (and
1156 provided @code{NAME} is not set), the result is @code{"unknown"}.
1158 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1159 or a string (a login name). Then @code{user-full-name} returns the full
1160 name corresponding to that user-id or login name. If you specify a
1161 user-id or login name that isn't defined, it returns @code{nil}.
1164 @vindex user-full-name
1165 @vindex user-real-login-name
1166 @vindex user-login-name
1167 The symbols @code{user-login-name}, @code{user-real-login-name} and
1168 @code{user-full-name} are variables as well as functions. The functions
1169 return the same values that the variables hold. These variables allow
1170 you to fake out Emacs by telling the functions what to return. The
1171 variables are also useful for constructing frame titles (@pxref{Frame
1175 @defun user-real-uid
1176 This function returns the real @acronym{UID} of the user.
1177 The value may be floating point, in the (unlikely) event that
1178 the UID is too large to fit in a Lisp integer.
1182 This function returns the effective @acronym{UID} of the user.
1183 The value may be floating point.
1188 This function returns the effective @acronym{GID} of the Emacs process.
1189 The value may be floating point.
1192 @defun group-real-gid
1193 This function returns the real @acronym{GID} of the Emacs process.
1194 The value may be floating point.
1198 This function returns a list of strings, listing the user names on the
1199 system. If Emacs cannot retrieve this information, the return value
1200 is a list containing just the value of @code{user-real-login-name}.
1204 @defun system-groups
1205 This function returns a list of strings, listing the names of user
1206 groups on the system. If Emacs cannot retrieve this information, the
1207 return value is @code{nil}.
1212 @section Time of Day
1215 This section explains how to determine the current time and time
1219 Most of these functions represent time as a list of four integers
1220 @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1221 This represents the number of seconds from the @dfn{epoch} (January
1222 1, 1970 at 00:00 UTC), using the formula:
1224 @var{high} * 2**16 + @var{low} + @var{micro} * 10**@minus{}6 +
1225 @var{pico} * 10**@minus{}12.
1228 $high*2^{16} + low + micro*10^{-6} + pico*10^{-12}$.
1230 The return value of @code{current-time} represents time using this
1231 form, as do the timestamps in the return values of other functions
1232 such as @code{file-attributes} (@pxref{Definition of
1233 file-attributes}). In some cases, functions may return two- or
1234 three-element lists, with omitted @var{microsec} and @var{picosec}
1235 components defaulting to zero.
1238 Function arguments, e.g., the @var{time} argument to
1239 @code{current-time-string}, accept a more-general @dfn{time value}
1240 format, which can be a list of integers as above, or a single number
1241 for seconds since the epoch, or @code{nil} for the current time. You
1242 can convert a time value into a human-readable string using
1243 @code{current-time-string} and @code{format-time-string}, into a list
1244 of integers using @code{seconds-to-time}, and into other forms using
1245 @code{decode-time} and @code{float-time}. These functions are
1246 described in the following sections.
1248 @defun current-time-string &optional time zone
1249 This function returns the current time and date as a human-readable
1250 string. The format does not vary for the initial part of the string,
1251 which contains the day of week, month, day of month, and time of day
1252 in that order: the number of characters used for these fields is
1253 always the same, so you can reliably
1254 use @code{substring} to extract them. You should count
1255 characters from the beginning of the string rather than from the end,
1256 as the year might not have exactly four digits, and additional
1257 information may some day be added at the end.
1259 The argument @var{time}, if given, specifies a time to format,
1260 instead of the current time. The optional argument @var{zone}
1261 defaults to the current time zone rule.
1265 (current-time-string)
1266 @result{} "Wed Oct 14 22:21:05 1987"
1272 This function returns the current time, represented as a list of four
1273 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1274 These integers have trailing zeros on systems that return time with
1275 lower resolutions. On all current machines @var{picosec} is a
1276 multiple of 1000, but this may change as higher-resolution clocks
1280 @defun float-time &optional time
1281 This function returns the current time as a floating-point number of
1282 seconds since the epoch. The optional argument @var{time}, if
1283 given, specifies a time to convert instead of the current time.
1285 @emph{Warning}: Since the result is floating point, it may not be
1286 exact. Do not use this function if precise time stamps are required.
1288 @code{time-to-seconds} is an alias for this function.
1291 @defun seconds-to-time time
1292 This function converts a time value to list-of-integer form.
1293 For example, if @var{time} is a number, @code{(time-to-seconds
1294 (seconds-to-time @var{time}))} equals the number unless overflow
1295 or rounding errors occur.
1298 @defun current-time-zone &optional time zone
1299 @cindex time zone, current
1300 This function returns a list describing the time zone that the user is
1303 The value has the form @code{(@var{offset} @var{name})}. Here
1304 @var{offset} is an integer giving the number of seconds ahead of UTC
1305 (east of Greenwich). A negative value means west of Greenwich. The
1306 second element, @var{name}, is a string giving the name of the time
1307 zone. Both elements change when daylight saving time begins or ends;
1308 if the user has specified a time zone that does not use a seasonal time
1309 adjustment, then the value is constant through time.
1311 If the operating system doesn't supply all the information necessary to
1312 compute the value, the unknown elements of the list are @code{nil}.
1314 The argument @var{time}, if given, specifies a time value to
1315 analyze instead of the current time. The optional argument @var{zone}
1316 defaults to the current time zone rule.
1319 @vindex TZ, environment variable
1320 The default time zone is determined by the @env{TZ} environment
1321 variable. @xref{System Environment}. For example, you can tell Emacs
1322 to default to universal time with @code{(setenv "TZ" "UTC0")}. If
1323 @env{TZ} is not in the environment, Emacs uses system wall clock time,
1324 which is a platform-dependent default time zone.
1326 @cindex time zone rule
1327 Functions that convert to and from local time accept an optional
1328 @dfn{time zone rule} argument, which specifies the conversion's time
1329 zone and daylight saving time history. If the time zone rule is
1330 omitted or @code{nil}, the conversion uses Emacs's default time zone.
1331 If it is @code{t}, the conversion uses Universal Time. If it is
1332 @code{wall}, the conversion uses the system wall clock time. If it is
1333 a string, the conversion uses the time zone rule equivalent to setting
1334 @env{TZ} to that string.
1336 @node Time Conversion
1337 @section Time Conversion
1338 @cindex calendrical information
1339 @cindex time conversion
1341 These functions convert time values (@pxref{Time of Day}) into
1342 calendrical information and vice versa.
1344 Many 32-bit operating systems are limited to system times containing
1345 32 bits of information in their seconds component; these systems
1346 typically handle only the times from 1901-12-13 20:45:52 UTC through
1347 2038-01-19 03:14:07 UTC@. However, 64-bit and some 32-bit operating
1348 systems have larger seconds components, and can represent times far in
1351 Time conversion functions always use the Gregorian calendar, even
1352 for dates before the Gregorian calendar was introduced. Year numbers
1353 count the number of years since the year 1 B.C., and do not skip zero
1354 as traditional Gregorian years do; for example, the year number
1355 @minus{}37 represents the Gregorian year 38 B.C@.
1357 @defun decode-time &optional time zone
1358 This function converts a time value into calendrical information. If
1359 you don't specify @var{time}, it decodes the current time, and similarly
1360 @var{zone} defaults to the current time zone rule. The return
1361 value is a list of nine elements, as follows:
1364 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{utcoff})
1367 Here is what the elements mean:
1371 The number of seconds past the minute, as an integer between 0 and 59.
1372 On some operating systems, this is 60 for leap seconds.
1374 The number of minutes past the hour, as an integer between 0 and 59.
1376 The hour of the day, as an integer between 0 and 23.
1378 The day of the month, as an integer between 1 and 31.
1380 The month of the year, as an integer between 1 and 12.
1382 The year, an integer typically greater than 1900.
1384 The day of week, as an integer between 0 and 6, where 0 stands for
1387 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1389 An integer indicating the UTC offset in seconds, i.e., the number of
1390 seconds east of Greenwich.
1393 @strong{Common Lisp Note:} Common Lisp has different meanings for
1394 @var{dow} and @var{utcoff}.
1397 @defun encode-time seconds minutes hour day month year &optional zone
1398 This function is the inverse of @code{decode-time}. It converts seven
1399 items of calendrical data into a list-of-integer time value. For the
1400 meanings of the arguments, see the table above under
1403 Year numbers less than 100 are not treated specially. If you want them
1404 to stand for years above 1900, or years above 2000, you must alter them
1405 yourself before you call @code{encode-time}.
1407 The optional argument @var{zone} defaults to the current time zone rule.
1408 In addition to the usual time zone rule values, it can also be a list
1409 (as you would get from @code{current-time-zone}) or an integer (as
1410 from @code{decode-time}), applied without any further alteration for
1411 daylight saving time.
1413 If you pass more than seven arguments to @code{encode-time}, the first
1414 six are used as @var{seconds} through @var{year}, the last argument is
1415 used as @var{zone}, and the arguments in between are ignored. This
1416 feature makes it possible to use the elements of a list returned by
1417 @code{decode-time} as the arguments to @code{encode-time}, like this:
1420 (apply 'encode-time (decode-time @dots{}))
1423 You can perform simple date arithmetic by using out-of-range values for
1424 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1425 arguments; for example, day 0 means the day preceding the given month.
1427 The operating system puts limits on the range of possible time values;
1428 if you try to encode a time that is out of range, an error results.
1429 For instance, years before 1970 do not work on some systems;
1430 on others, years as early as 1901 do work.
1434 @section Parsing and Formatting Times
1435 @cindex time parsing
1436 @cindex time formatting
1437 @cindex formatting time values
1439 These functions convert time values to text in a string, and vice versa.
1440 Time values are lists of two to four integers (@pxref{Time of Day}).
1442 @defun date-to-time string
1443 This function parses the time-string @var{string} and returns the
1444 corresponding time value.
1447 @defun format-time-string format-string &optional time zone
1449 This function converts @var{time} (or the current time, if
1450 @var{time} is omitted) to a string according to
1451 @var{format-string}. The conversion uses the time zone rule @var{zone}
1452 (or the current time zone rule, if omitted). The argument
1453 @var{format-string} may contain @samp{%}-sequences which say to
1454 substitute parts of the time. Here is a table of what the
1455 @samp{%}-sequences mean:
1459 This stands for the abbreviated name of the day of week.
1461 This stands for the full name of the day of week.
1463 This stands for the abbreviated name of the month.
1465 This stands for the full name of the month.
1467 This is a synonym for @samp{%x %X}.
1469 This has a locale-specific meaning. In the default locale (named C), it
1470 is equivalent to @samp{%A, %B %e, %Y}.
1472 This stands for the day of month, zero-padded.
1474 This is a synonym for @samp{%m/%d/%y}.
1476 This stands for the day of month, blank-padded.
1478 This is a synonym for @samp{%b}.
1480 This stands for the hour (00--23).
1482 This stands for the hour (01--12).
1484 This stands for the day of the year (001--366).
1486 This stands for the hour (0--23), blank padded.
1488 This stands for the hour (1--12), blank padded.
1490 This stands for the month (01--12).
1492 This stands for the minute (00--59).
1494 This stands for a newline.
1496 This stands for the nanoseconds (000000000--999999999). To ask for
1497 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1498 microseconds, etc. Any excess digits are discarded, without rounding.
1500 This stands for @samp{AM} or @samp{PM}, as appropriate.
1502 This is a synonym for @samp{%I:%M:%S %p}.
1504 This is a synonym for @samp{%H:%M}.
1506 This stands for the seconds (00--59).
1508 This stands for a tab character.
1510 This is a synonym for @samp{%H:%M:%S}.
1512 This stands for the week of the year (01--52), assuming that weeks
1515 This stands for the numeric day of week (0--6). Sunday is day 0.
1517 This stands for the week of the year (01--52), assuming that weeks
1520 This has a locale-specific meaning. In the default locale (named
1521 @samp{C}), it is equivalent to @samp{%D}.
1523 This has a locale-specific meaning. In the default locale (named
1524 @samp{C}), it is equivalent to @samp{%T}.
1526 This stands for the year without century (00--99).
1528 This stands for the year with century.
1530 This stands for the time zone abbreviation (e.g., @samp{EST}).
1532 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1535 You can also specify the field width and type of padding for any of
1536 these @samp{%}-sequences. This works as in @code{printf}: you write
1537 the field width as digits in the middle of a @samp{%}-sequences. If you
1538 start the field width with @samp{0}, it means to pad with zeros. If you
1539 start the field width with @samp{_}, it means to pad with spaces.
1541 For example, @samp{%S} specifies the number of seconds since the minute;
1542 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1543 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1544 because that is how @samp{%S} normally pads to two positions.
1546 The characters @samp{E} and @samp{O} act as modifiers when used between
1547 @samp{%} and one of the letters in the table above. @samp{E} specifies
1548 using the current locale's alternative version of the date and time.
1549 In a Japanese locale, for example, @code{%Ex} might yield a date format
1550 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1551 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1554 @samp{O} means to use the current locale's alternative
1555 representation of numbers, instead of the ordinary decimal digits. This
1556 is allowed with most letters, all the ones that output numbers.
1558 If @var{universal} is non-@code{nil}, that means to describe the time as
1559 Universal Time; @code{nil} means describe it using what Emacs believes
1560 is the local time zone (see @code{current-time-zone}).
1562 This function uses the C library function @code{strftime}
1563 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1564 Manual}) to do most of the work. In order to communicate with that
1565 function, it first encodes its argument using the coding system
1566 specified by @code{locale-coding-system} (@pxref{Locales}); after
1567 @code{strftime} returns the resulting string,
1568 @code{format-time-string} decodes the string using that same coding
1572 @defun format-seconds format-string seconds
1573 This function converts its argument @var{seconds} into a string of
1574 years, days, hours, etc., according to @var{format-string}. The
1575 argument @var{format-string} may contain @samp{%}-sequences which
1576 control the conversion. Here is a table of what the
1577 @samp{%}-sequences mean:
1582 The integer number of 365-day years.
1585 The integer number of days.
1588 The integer number of hours.
1591 The integer number of minutes.
1594 The integer number of seconds.
1596 Non-printing control flag. When it is used, other specifiers must be
1597 given in the order of decreasing size, i.e., years before days, hours
1598 before minutes, etc. Nothing will be produced in the result string to
1599 the left of @samp{%z} until the first non-zero conversion is
1600 encountered. For example, the default format used by
1601 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1602 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1603 will always be produced, but years, days, hours, and minutes will only
1604 be shown if they are non-zero.
1606 Produces a literal @samp{%}.
1609 Upper-case format sequences produce the units in addition to the
1610 numbers, lower-case formats produce only the numbers.
1612 You can also specify the field width by following the @samp{%} with a
1613 number; shorter numbers will be padded with blanks. An optional
1614 period before the width requests zero-padding instead. For example,
1615 @code{"%.3Y"} might produce @code{"004 years"}.
1617 @emph{Warning:} This function works only with values of @var{seconds}
1618 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1619 most-positive-fixnum}).
1622 @node Processor Run Time
1623 @section Processor Run time
1624 @cindex processor run time
1625 @cindex Emacs process run time
1627 Emacs provides several functions and primitives that return time,
1628 both elapsed and processor time, used by the Emacs process.
1630 @deffn Command emacs-uptime &optional format
1631 @cindex uptime of Emacs
1632 This function returns a string representing the Emacs
1633 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1634 running. The string is formatted by @code{format-seconds} according
1635 to the optional argument @var{format}. For the available format
1636 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1637 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1640 When called interactively, it prints the uptime in the echo area.
1643 @defun get-internal-run-time
1644 This function returns the processor run time used by Emacs as a list
1645 of four integers: @code{(@var{sec-high} @var{sec-low} @var{microsec}
1646 @var{picosec})}, using the same format as @code{current-time}
1647 (@pxref{Time of Day}).
1649 Note that the time returned by this function excludes the time Emacs
1650 was not using the processor, and if the Emacs process has several
1651 threads, the returned value is the sum of the processor times used up
1652 by all Emacs threads.
1654 If the system doesn't provide a way to determine the processor run
1655 time, @code{get-internal-run-time} returns the same time as
1656 @code{current-time}.
1659 @deffn Command emacs-init-time
1660 This function returns the duration of the Emacs initialization
1661 (@pxref{Startup Summary}) in seconds, as a string. When called
1662 interactively, it prints the duration in the echo area.
1665 @node Time Calculations
1666 @section Time Calculations
1667 @cindex time calculations
1668 @cindex comparing time values
1669 @cindex calendrical computations
1671 These functions perform calendrical computations using time values
1672 (@pxref{Time of Day}).
1674 @defun time-less-p t1 t2
1675 This returns @code{t} if time value @var{t1} is less than time value
1679 @defun time-subtract t1 t2
1680 This returns the time difference @var{t1} @minus{} @var{t2} between
1681 two time values, as a time value.
1684 @defun time-add t1 t2
1685 This returns the sum of two time values, as a time value.
1686 One argument should represent a time difference rather than a point in time.
1687 Here is how to add a number of seconds to a time value:
1690 (time-add @var{time} @var{seconds})
1694 @defun time-to-days time-value
1695 This function returns the number of days between the beginning of year
1696 1 and @var{time-value}.
1699 @defun time-to-day-in-year time-value
1700 This returns the day number within the year corresponding to @var{time-value}.
1703 @defun date-leap-year-p year
1704 This function returns @code{t} if @var{year} is a leap year.
1708 @section Timers for Delayed Execution
1711 You can set up a @dfn{timer} to call a function at a specified
1712 future time or after a certain length of idleness.
1714 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1715 can run them only when Emacs could accept output from a subprocess:
1716 namely, while waiting or inside certain primitive functions such as
1717 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1718 timer's execution may be delayed if Emacs is busy. However, the time of
1719 execution is very precise if Emacs is idle.
1721 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1722 function, because quitting out of many timer functions can leave
1723 things in an inconsistent state. This is normally unproblematical
1724 because most timer functions don't do a lot of work. Indeed, for a
1725 timer to call a function that takes substantial time to run is likely
1726 to be annoying. If a timer function needs to allow quitting, it
1727 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1728 a timer function calls @code{accept-process-output} to receive output
1729 from an external process, that call should be wrapped inside
1730 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1733 It is usually a bad idea for timer functions to alter buffer
1734 contents. When they do, they usually should call @code{undo-boundary}
1735 both before and after changing the buffer, to separate the timer's
1736 changes from user commands' changes and prevent a single undo entry
1737 from growing to be quite large.
1739 Timer functions should also avoid calling functions that cause Emacs
1740 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1741 unpredictable effects, since other timers (or even the same timer) can
1742 run while waiting. If a timer function needs to perform an action
1743 after a certain time has elapsed, it can do this by scheduling a new
1746 If a timer function calls functions that can change the match data,
1747 it should save and restore the match data. @xref{Saving Match Data}.
1749 @deffn Command run-at-time time repeat function &rest args
1750 This sets up a timer that calls the function @var{function} with
1751 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1752 (integer or floating point), the timer is scheduled to run again every
1753 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1754 the timer runs only once.
1756 @var{time} may specify an absolute or a relative time.
1758 Absolute times may be specified using a string with a limited variety
1759 of formats, and are taken to be times @emph{today}, even if already in
1760 the past. The recognized forms are @samp{@var{xxxx}},
1761 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1762 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1763 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1764 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1765 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1766 to separate the hour and minute parts.
1768 To specify a relative time as a string, use numbers followed by units.
1773 denotes 1 minute from now.
1775 denotes 65 seconds from now.
1776 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1777 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1780 For relative time values, Emacs considers a month to be exactly thirty
1781 days, and a year to be exactly 365.25 days.
1783 Not all convenient formats are strings. If @var{time} is a number
1784 (integer or floating point), that specifies a relative time measured in
1785 seconds. The result of @code{encode-time} can also be used to specify
1786 an absolute value for @var{time}.
1788 In most cases, @var{repeat} has no effect on when @emph{first} call
1789 takes place---@var{time} alone specifies that. There is one exception:
1790 if @var{time} is @code{t}, then the timer runs whenever the time is a
1791 multiple of @var{repeat} seconds after the epoch. This is useful for
1792 functions like @code{display-time}.
1794 The function @code{run-at-time} returns a timer value that identifies
1795 the particular scheduled future action. You can use this value to call
1796 @code{cancel-timer} (see below).
1799 A repeating timer nominally ought to run every @var{repeat} seconds,
1800 but remember that any invocation of a timer can be late. Lateness of
1801 one repetition has no effect on the scheduled time of the next
1802 repetition. For instance, if Emacs is busy computing for long enough
1803 to cover three scheduled repetitions of the timer, and then starts to
1804 wait, it will immediately call the timer function three times in
1805 immediate succession (presuming no other timers trigger before or
1806 between them). If you want a timer to run again no less than @var{n}
1807 seconds after the last invocation, don't use the @var{repeat} argument.
1808 Instead, the timer function should explicitly reschedule the timer.
1810 @defopt timer-max-repeats
1811 This variable's value specifies the maximum number of times to repeat
1812 calling a timer function in a row, when many previously scheduled
1813 calls were unavoidably delayed.
1816 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1817 Execute @var{body}, but give up after @var{seconds} seconds. If
1818 @var{body} finishes before the time is up, @code{with-timeout} returns
1819 the value of the last form in @var{body}. If, however, the execution of
1820 @var{body} is cut short by the timeout, then @code{with-timeout}
1821 executes all the @var{timeout-forms} and returns the value of the last
1824 This macro works by setting a timer to run after @var{seconds} seconds. If
1825 @var{body} finishes before that time, it cancels the timer. If the
1826 timer actually runs, it terminates execution of @var{body}, then
1827 executes @var{timeout-forms}.
1829 Since timers can run within a Lisp program only when the program calls a
1830 primitive that can wait, @code{with-timeout} cannot stop executing
1831 @var{body} while it is in the midst of a computation---only when it
1832 calls one of those primitives. So use @code{with-timeout} only with a
1833 @var{body} that waits for input, not one that does a long computation.
1836 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1837 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1840 @defun cancel-timer timer
1841 This cancels the requested action for @var{timer}, which should be a
1842 timer---usually, one previously returned by @code{run-at-time} or
1843 @code{run-with-idle-timer}. This cancels the effect of that call to
1844 one of these functions; the arrival of the specified time will not
1845 cause anything special to happen.
1849 @section Idle Timers
1852 Here is how to set up a timer that runs when Emacs is idle for a
1853 certain length of time. Aside from how to set them up, idle timers
1854 work just like ordinary timers.
1856 @deffn Command run-with-idle-timer secs repeat function &rest args
1857 Set up a timer which runs the next time Emacs is idle for @var{secs}
1858 seconds. The value of @var{secs} may be a number or a value of the type
1859 returned by @code{current-idle-time}.
1861 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1862 Emacs remains idle for a long enough time. More often @var{repeat} is
1863 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1864 remains idle for @var{secs} seconds.
1866 The function @code{run-with-idle-timer} returns a timer value which you
1867 can use in calling @code{cancel-timer} (@pxref{Timers}).
1871 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1872 it remains idle until the user provides some input. If a timer is set
1873 for five seconds of idleness, it runs approximately five seconds after
1874 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1875 this timer will not run again as long as Emacs remains idle, because
1876 the duration of idleness will continue to increase and will not go
1877 down to five seconds again.
1879 Emacs can do various things while idle: garbage collect, autosave or
1880 handle data from a subprocess. But these interludes during idleness do
1881 not interfere with idle timers, because they do not reset the clock of
1882 idleness to zero. An idle timer set for 600 seconds will run when ten
1883 minutes have elapsed since the last user command was finished, even if
1884 subprocess output has been accepted thousands of times within those ten
1885 minutes, and even if there have been garbage collections and autosaves.
1887 When the user supplies input, Emacs becomes non-idle while executing the
1888 input. Then it becomes idle again, and all the idle timers that are
1889 set up to repeat will subsequently run another time, one by one.
1891 Do not write an idle timer function containing a loop which does a
1892 certain amount of processing each time around, and exits when
1893 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1894 natural but has two problems:
1898 It blocks out all process output (since Emacs accepts process output
1899 only while waiting).
1902 It blocks out any idle timers that ought to run during that time.
1906 Similarly, do not write an idle timer function that sets up another
1907 idle timer (including the same idle timer) with @var{secs} argument
1908 less than or equal to the current idleness time. Such a timer will
1909 run almost immediately, and continue running again and again, instead
1910 of waiting for the next time Emacs becomes idle. The correct approach
1911 is to reschedule with an appropriate increment of the current value of
1912 the idleness time, as described below.
1914 @defun current-idle-time
1915 If Emacs is idle, this function returns the length of time Emacs has
1916 been idle, as a list of four integers: @code{(@var{sec-high}
1917 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1918 @code{current-time} (@pxref{Time of Day}).
1920 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1921 This is a convenient way to test whether Emacs is idle.
1924 The main use of @code{current-idle-time} is when an idle timer
1925 function wants to take a break for a while. It can set up another
1926 idle timer to call the same function again, after a few seconds more
1927 idleness. Here's an example:
1930 (defvar my-resume-timer nil
1931 "Timer for `my-timer-function' to reschedule itself, or nil.")
1933 (defun my-timer-function ()
1934 ;; @r{If the user types a command while @code{my-resume-timer}}
1935 ;; @r{is active, the next time this function is called from}
1936 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1937 (when my-resume-timer
1938 (cancel-timer my-resume-timer))
1939 ...@var{do the work for a while}...
1940 (when @var{taking-a-break}
1941 (setq my-resume-timer
1942 (run-with-idle-timer
1943 ;; Compute an idle time @var{break-length}
1944 ;; more than the current value.
1945 (time-add (current-idle-time) @var{break-length})
1947 'my-timer-function))))
1950 @node Terminal Input
1951 @section Terminal Input
1952 @cindex terminal input
1954 This section describes functions and variables for recording or
1955 manipulating terminal input. See @ref{Display}, for related
1959 * Input Modes:: Options for how input is processed.
1960 * Recording Input:: Saving histories of recent or all input events.
1964 @subsection Input Modes
1966 @cindex terminal input modes
1968 @defun set-input-mode interrupt flow meta &optional quit-char
1969 This function sets the mode for reading keyboard input. If
1970 @var{interrupt} is non-@code{nil}, then Emacs uses input interrupts.
1971 If it is @code{nil}, then it uses @sc{cbreak} mode. The default
1972 setting is system-dependent. Some systems always use @sc{cbreak} mode
1973 regardless of what is specified.
1975 When Emacs communicates directly with X, it ignores this argument and
1976 uses interrupts if that is the way it knows how to communicate.
1978 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1979 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1980 has no effect except in @sc{cbreak} mode.
1982 The argument @var{meta} controls support for input character codes
1983 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1984 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1985 Emacs disregards the 8th bit; this is necessary when the terminal uses
1986 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1987 Emacs uses all 8 bits of input unchanged. This is good for terminals
1988 that use 8-bit character sets.
1990 If @var{quit-char} is non-@code{nil}, it specifies the character to
1991 use for quitting. Normally this character is @kbd{C-g}.
1995 The @code{current-input-mode} function returns the input mode settings
1996 Emacs is currently using.
1998 @defun current-input-mode
1999 This function returns the current mode for reading keyboard input. It
2000 returns a list, corresponding to the arguments of @code{set-input-mode},
2001 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
2005 is non-@code{nil} when Emacs is using interrupt-driven input. If
2006 @code{nil}, Emacs is using @sc{cbreak} mode.
2008 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
2009 flow control for output to the terminal. This value is meaningful only
2010 when @var{interrupt} is @code{nil}.
2012 is @code{t} if Emacs treats the eighth bit of input characters as
2013 the meta bit; @code{nil} means Emacs clears the eighth bit of every
2014 input character; any other value means Emacs uses all eight bits as the
2015 basic character code.
2017 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
2021 @node Recording Input
2022 @subsection Recording Input
2023 @cindex recording input
2026 This function returns a vector containing the last 300 input events from
2027 the keyboard or mouse. All input events are included, whether or not
2028 they were used as parts of key sequences. Thus, you always get the last
2029 300 input events, not counting events generated by keyboard macros.
2030 (These are excluded because they are less interesting for debugging; it
2031 should be enough to see the events that invoked the macros.)
2033 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
2034 causes this function to return an empty vector immediately afterward.
2037 @deffn Command open-dribble-file filename
2038 @cindex dribble file
2039 This function opens a @dfn{dribble file} named @var{filename}. When a
2040 dribble file is open, each input event from the keyboard or mouse (but
2041 not those from keyboard macros) is written in that file. A
2042 non-character event is expressed using its printed representation
2043 surrounded by @samp{<@dots{}>}. Be aware that sensitive information
2044 (such as passwords) may end up recorded in the dribble file.
2046 You close the dribble file by calling this function with an argument
2050 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2052 @node Terminal Output
2053 @section Terminal Output
2054 @cindex terminal output
2056 The terminal output functions send output to a text terminal, or keep
2057 track of output sent to the terminal. The variable @code{baud-rate}
2058 tells you what Emacs thinks is the output speed of the terminal.
2061 This variable's value is the output speed of the terminal, as far as
2062 Emacs knows. Setting this variable does not change the speed of actual
2063 data transmission, but the value is used for calculations such as
2066 It also affects decisions about whether to scroll part of the
2067 screen or repaint on text terminals. @xref{Forcing Redisplay},
2068 for the corresponding functionality on graphical terminals.
2070 The value is measured in baud.
2073 If you are running across a network, and different parts of the
2074 network work at different baud rates, the value returned by Emacs may be
2075 different from the value used by your local terminal. Some network
2076 protocols communicate the local terminal speed to the remote machine, so
2077 that Emacs and other programs can get the proper value, but others do
2078 not. If Emacs has the wrong value, it makes decisions that are less
2079 than optimal. To fix the problem, set @code{baud-rate}.
2081 @defun send-string-to-terminal string &optional terminal
2082 This function sends @var{string} to @var{terminal} without alteration.
2083 Control characters in @var{string} have terminal-dependent effects.
2084 This function operates only on text terminals. @var{terminal} may be
2085 a terminal object, a frame, or @code{nil} for the selected frame's
2086 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2087 @var{terminal} is @code{nil}.
2089 One use of this function is to define function keys on terminals that
2090 have downloadable function key definitions. For example, this is how (on
2091 certain terminals) to define function key 4 to move forward four
2092 characters (by transmitting the characters @kbd{C-u C-f} to the
2097 (send-string-to-terminal "\eF4\^U\^F")
2103 @deffn Command open-termscript filename
2104 @cindex termscript file
2105 This function is used to open a @dfn{termscript file} that will record
2106 all the characters sent by Emacs to the terminal. It returns
2107 @code{nil}. Termscript files are useful for investigating problems
2108 where Emacs garbles the screen, problems that are due to incorrect
2109 Termcap entries or to undesirable settings of terminal options more
2110 often than to actual Emacs bugs. Once you are certain which characters
2111 were actually output, you can determine reliably whether they correspond
2112 to the Termcap specifications in use.
2116 (open-termscript "../junk/termscript")
2121 You close the termscript file by calling this function with an
2122 argument of @code{nil}.
2124 See also @code{open-dribble-file} in @ref{Recording Input}.
2128 @section Sound Output
2131 To play sound using Emacs, use the function @code{play-sound}. Only
2132 certain systems are supported; if you call @code{play-sound} on a
2133 system which cannot really do the job, it gives an error.
2135 @c FIXME: Add indexes for Au and WAV? --xfq
2136 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2137 or Sun Audio format (@samp{.au}).
2139 @defun play-sound sound
2140 This function plays a specified sound. The argument, @var{sound}, has
2141 the form @code{(sound @var{properties}...)}, where the @var{properties}
2142 consist of alternating keywords (particular symbols recognized
2143 specially) and values corresponding to them.
2145 Here is a table of the keywords that are currently meaningful in
2146 @var{sound}, and their meanings:
2149 @item :file @var{file}
2150 This specifies the file containing the sound to play.
2151 If the file name is not absolute, it is expanded against
2152 the directory @code{data-directory}.
2154 @item :data @var{data}
2155 This specifies the sound to play without need to refer to a file. The
2156 value, @var{data}, should be a string containing the same bytes as a
2157 sound file. We recommend using a unibyte string.
2159 @item :volume @var{volume}
2160 This specifies how loud to play the sound. It should be a number in the
2161 range of 0 to 1. The default is to use whatever volume has been
2164 @item :device @var{device}
2165 This specifies the system device on which to play the sound, as a
2166 string. The default device is system-dependent.
2169 Before actually playing the sound, @code{play-sound}
2170 calls the functions in the list @code{play-sound-functions}.
2171 Each function is called with one argument, @var{sound}.
2174 @deffn Command play-sound-file file &optional volume device
2175 This function is an alternative interface to playing a sound @var{file}
2176 specifying an optional @var{volume} and @var{device}.
2179 @defvar play-sound-functions
2180 A list of functions to be called before playing a sound. Each function
2181 is called with one argument, a property list that describes the sound.
2185 @section Operating on X11 Keysyms
2188 To define system-specific X11 keysyms, set the variable
2189 @code{system-key-alist}.
2191 @defvar system-key-alist
2192 This variable's value should be an alist with one element for each
2193 system-specific keysym. Each element has the form @code{(@var{code}
2194 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2195 including the vendor-specific bit,
2202 and @var{symbol} is the name for the function key.
2204 For example @code{(168 . mute-acute)} defines a system-specific key (used
2205 by HP X servers) whose numeric code is
2214 It is not crucial to exclude from the alist the keysyms of other X
2215 servers; those do no harm, as long as they don't conflict with the ones
2216 used by the X server actually in use.
2218 The variable is always local to the current terminal, and cannot be
2219 buffer-local. @xref{Multiple Terminals}.
2222 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2224 @defvar x-alt-keysym
2225 @defvarx x-meta-keysym
2226 @defvarx x-hyper-keysym
2227 @defvarx x-super-keysym
2228 The name of the keysym that should stand for the Alt modifier
2229 (respectively, for Meta, Hyper, and Super). For example, here is
2230 how to swap the Meta and Alt modifiers within Emacs:
2232 (setq x-alt-keysym 'meta)
2233 (setq x-meta-keysym 'alt)
2241 The command-line option @samp{-batch} causes Emacs to run
2242 noninteractively. In this mode, Emacs does not read commands from the
2243 terminal, it does not alter the terminal modes, and it does not expect
2244 to be outputting to an erasable screen. The idea is that you specify
2245 Lisp programs to run; when they are finished, Emacs should exit. The
2246 way to specify the programs to run is with @samp{-l @var{file}}, which
2247 loads the library named @var{file}, or @samp{-f @var{function}}, which
2248 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2250 Any Lisp program output that would normally go to the echo area,
2251 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2252 as the stream, goes instead to Emacs's standard error descriptor when
2253 in batch mode. Similarly, input that would normally come from the
2254 minibuffer is read from the standard input descriptor.
2255 Thus, Emacs behaves much like a noninteractive
2256 application program. (The echo area output that Emacs itself normally
2257 generates, such as command echoing, is suppressed entirely.)
2259 @defvar noninteractive
2260 This variable is non-@code{nil} when Emacs is running in batch mode.
2263 @node Session Management
2264 @section Session Management
2265 @cindex session manager
2267 Emacs supports the X Session Management Protocol, which is used to
2268 suspend and restart applications. In the X Window System, a program
2269 called the @dfn{session manager} is responsible for keeping track of
2270 the applications that are running. When the X server shuts down, the
2271 session manager asks applications to save their state, and delays the
2272 actual shutdown until they respond. An application can also cancel
2275 When the session manager restarts a suspended session, it directs
2276 these applications to individually reload their saved state. It does
2277 this by specifying a special command-line argument that says what
2278 saved session to restore. For Emacs, this argument is @samp{--smid
2281 @defvar emacs-save-session-functions
2282 @cindex session file
2283 Emacs supports saving state via a hook called
2284 @code{emacs-save-session-functions}. Emacs runs this hook when the
2285 session manager tells it that the window system is shutting down. The
2286 functions are called with no arguments, and with the current buffer
2287 set to a temporary buffer. Each function can use @code{insert} to add
2288 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2289 file, called the @dfn{session file}.
2291 @findex emacs-session-restore
2292 Subsequently, when the session manager restarts Emacs, it loads the
2293 session file automatically (@pxref{Loading}). This is performed by a
2294 function named @code{emacs-session-restore}, which is called during
2295 startup. @xref{Startup Summary}.
2297 If a function in @code{emacs-save-session-functions} returns
2298 non-@code{nil}, Emacs tells the session manager to cancel the
2302 Here is an example that just inserts some text into @file{*scratch*} when
2303 Emacs is restarted by the session manager.
2307 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2311 (defun save-yourself-test ()
2312 (insert "(save-current-buffer
2313 (switch-to-buffer \"*scratch*\")
2314 (insert \"I am restored\"))")
2319 @node Desktop Notifications
2320 @section Desktop Notifications
2321 @cindex desktop notifications
2322 @cindex notifications, on desktop
2324 Emacs is able to send @dfn{notifications} on systems that support the
2325 freedesktop.org Desktop Notifications Specification. In order to use
2326 this functionality, Emacs must have been compiled with D-Bus support,
2327 and the @code{notifications} library must be loaded. @xref{Top, ,
2328 D-Bus,dbus,D-Bus integration in Emacs}.
2330 @defun notifications-notify &rest params
2331 This function sends a notification to the desktop via D-Bus,
2332 consisting of the parameters specified by the @var{params} arguments.
2333 These arguments should consist of alternating keyword and value pairs.
2334 The supported keywords and values are as follows:
2337 @item :bus @var{bus}
2338 The D-Bus bus. This argument is needed only if a bus other than
2339 @code{:session} shall be used.
2341 @item :title @var{title}
2342 The notification title.
2344 @item :body @var{text}
2345 The notification body text. Depending on the implementation of the
2346 notification server, the text could contain HTML markups, like
2347 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2348 characters must be encoded, as @samp{"Contact
2349 <postmaster@@localhost>!"}.
2351 @item :app-name @var{name}
2352 The name of the application sending the notification. The default is
2353 @code{notifications-application-name}.
2355 @item :replaces-id @var{id}
2356 The notification @var{id} that this notification replaces. @var{id}
2357 must be the result of a previous @code{notifications-notify} call.
2359 @item :app-icon @var{icon-file}
2360 The file name of the notification icon. If set to @code{nil}, no icon
2361 is displayed. The default is @code{notifications-application-icon}.
2363 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2364 A list of actions to be applied. @var{key} and @var{title} are both
2365 strings. The default action (usually invoked by clicking the
2366 notification) should have a key named @samp{"default"}. The title can
2367 be anything, though implementations are free not to display it.
2369 @item :timeout @var{timeout}
2370 The timeout time in milliseconds since the display of the notification
2371 at which the notification should automatically close. If @minus{}1, the
2372 notification's expiration time is dependent on the notification
2373 server's settings, and may vary for the type of notification. If 0,
2374 the notification never expires. Default value is @minus{}1.
2376 @item :urgency @var{urgency}
2377 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2380 When this keyword is given, the @var{title} string of the actions is
2381 interpreted as icon name.
2383 @item :category @var{category}
2384 The type of notification this is, a string. See the
2385 @uref{http://developer.gnome.org/notification-spec/#categories,
2386 Desktop Notifications Specification} for a list of standard
2389 @item :desktop-entry @var{filename}
2390 This specifies the name of the desktop filename representing the
2391 calling program, like @samp{"emacs"}.
2393 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2394 This is a raw data image format that describes the width, height,
2395 rowstride, whether there is an alpha channel, bits per sample,
2396 channels and image data, respectively.
2398 @item :image-path @var{path}
2399 This is represented either as a URI (@samp{file://} is the only URI
2400 schema supported right now) or a name in a freedesktop.org-compliant
2401 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2403 @item :sound-file @var{filename}
2404 The path to a sound file to play when the notification pops up.
2406 @item :sound-name @var{name}
2407 A themable named sound from the freedesktop.org sound naming
2408 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2409 notification pops up. Similar to the icon name, only for sounds. An
2410 example would be @samp{"message-new-instant"}.
2412 @item :suppress-sound
2413 Causes the server to suppress playing any sounds, if it has that
2417 When set the server will not automatically remove the notification
2418 when an action has been invoked. The notification will remain resident
2419 in the server until it is explicitly removed by the user or by the
2420 sender. This hint is likely only useful when the server has the
2421 @code{:persistence} capability.
2424 When set the server will treat the notification as transient and
2425 by-pass the server's persistence capability, if it should exist.
2427 @item :x @var{position}
2428 @itemx :y @var{position}
2429 Specifies the X, Y location on the screen that the
2430 notification should point to. Both arguments must be used together.
2432 @item :on-action @var{function}
2433 Function to call when an action is invoked. The notification @var{id}
2434 and the @var{key} of the action are passed as arguments to the
2437 @item :on-close @var{function}
2438 Function to call when the notification has been closed by timeout or
2439 by the user. The function receive the notification @var{id} and the closing
2440 @var{reason} as arguments:
2443 @item @code{expired} if the notification has expired
2444 @item @code{dismissed} if the notification was dismissed by the user
2445 @item @code{close-notification} if the notification was closed by a call to
2446 @code{notifications-close-notification}
2447 @item @code{undefined} if the notification server hasn't provided a reason
2451 Which parameters are accepted by the notification server can be
2452 checked via @code{notifications-get-capabilities}.
2454 This function returns a notification id, an integer, which can be used
2455 to manipulate the notification item with
2456 @code{notifications-close-notification} or the @code{:replaces-id}
2457 argument of another @code{notifications-notify} call. For example:
2461 (defun my-on-action-function (id key)
2462 (message "Message %d, key \"%s\" pressed" id key))
2463 @result{} my-on-action-function
2467 (defun my-on-close-function (id reason)
2468 (message "Message %d, closed due to \"%s\"" id reason))
2469 @result{} my-on-close-function
2473 (notifications-notify
2475 :body "This is <b>important</b>."
2476 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2477 :on-action 'my-on-action-function
2478 :on-close 'my-on-close-function)
2483 A message window opens on the desktop. Press ``I agree''.
2484 @result{} Message 22, key "Confirm" pressed
2485 Message 22, closed due to "dismissed"
2490 @defun notifications-close-notification id &optional bus
2491 This function closes a notification with identifier @var{id}.
2492 @var{bus} can be a string denoting a D-Bus connection, the default is
2496 @defun notifications-get-capabilities &optional bus
2497 Returns the capabilities of the notification server, a list of
2498 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2499 default is @code{:session}. The following capabilities can be
2504 The server will provide the specified actions to the user.
2509 @item :body-hyperlinks
2510 The server supports hyperlinks in the notifications.
2513 The server supports images in the notifications.
2516 Supports markup in the body text.
2519 The server will render an animation of all the frames in a given image
2523 Supports display of exactly 1 frame of any given image array. This
2524 value is mutually exclusive with @code{:icon-multi}.
2527 The server supports persistence of notifications.
2530 The server supports sounds on notifications.
2533 Further vendor-specific caps start with @code{:x-vendor}, like
2534 @code{:x-gnome-foo-cap}.
2537 @defun notifications-get-server-information &optional bus
2538 Return information on the notification server, a list of strings.
2539 @var{bus} can be a string denoting a D-Bus connection, the default is
2540 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2541 @var{version} @var{spec-version})}.
2545 The product name of the server.
2548 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2551 The server's version number.
2554 The specification version the server is compliant with.
2557 If @var{spec_version} is @code{nil}, the server supports a
2558 specification prior to @samp{"1.0"}.
2561 @node File Notifications
2562 @section Notifications on File Changes
2563 @cindex file notifications
2564 @cindex watch, for filesystem events
2566 Several operating systems support watching of filesystems for changes
2567 of files. If configured properly, Emacs links a respective library
2568 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2569 statically. These libraries enable watching of filesystems on the
2572 It is also possible to watch filesystems on remote machines,
2573 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2574 This does not depend on one of the libraries linked to Emacs.
2576 Since all these libraries emit different events on notified file
2577 changes, there is the Emacs library @code{filenotify} which provides a
2580 @defun file-notify-add-watch file flags callback
2581 Add a watch for filesystem events pertaining to @var{file}. This
2582 arranges for filesystem events pertaining to @var{file} to be reported
2585 The returned value is a descriptor for the added watch. Its type
2586 depends on the underlying library, it cannot be assumed to be an
2587 integer as in the example below. It should be used for comparison by
2590 If the @var{file} cannot be watched for some reason, this function
2591 signals a @code{file-notify-error} error.
2593 Sometimes, mounted filesystems cannot be watched for file changes.
2594 This is not detected by this function, a non-@code{nil} return value
2595 does not guarantee that changes on @var{file} will be notified.
2597 @var{flags} is a list of conditions to set what will be watched for.
2598 It can include the following symbols:
2602 watch for file changes
2603 @item attribute-change
2604 watch for file attribute changes, like permissions or modification
2608 If @var{file} is a directory, changes for all files in that directory
2609 will be notified. This does not work recursively.
2611 When any event happens, Emacs will call the @var{callback} function
2612 passing it a single argument @var{event}, which is of the form
2615 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2618 @var{descriptor} is the same object as the one returned by this
2619 function. @var{action} is the description of the event. It could be
2620 any one of the following symbols:
2624 @var{file} was created
2626 @var{file} was deleted
2628 @var{file} has changed
2630 @var{file} has been renamed to @var{file1}
2631 @item attribute-changed
2632 a @var{file} attribute was changed
2635 @var{file} and @var{file1} are the name of the file(s) whose event is
2636 being reported. For example:
2640 (require 'filenotify)
2641 @result{} filenotify
2645 (defun my-notify-callback (event)
2646 (message "Event %S" event))
2647 @result{} my-notify-callback
2651 (file-notify-add-watch
2652 "/tmp" '(change attribute-change) 'my-notify-callback)
2657 (write-region "foo" nil "/tmp/foo")
2658 @result{} Event (35025468 created "/tmp/.#foo")
2659 Event (35025468 created "/tmp/foo")
2660 Event (35025468 changed "/tmp/foo")
2661 Event (35025468 deleted "/tmp/.#foo")
2665 (write-region "bla" nil "/tmp/foo")
2666 @result{} Event (35025468 created "/tmp/.#foo")
2667 Event (35025468 changed "/tmp/foo") [2 times]
2668 Event (35025468 deleted "/tmp/.#foo")
2672 (set-file-modes "/tmp/foo" (default-file-modes))
2673 @result{} Event (35025468 attribute-changed "/tmp/foo")
2677 Whether the action @code{renamed} is returned, depends on the used
2678 watch library. Otherwise, the actions @code{deleted} and
2679 @code{created} could be returned in a random order.
2683 (rename-file "/tmp/foo" "/tmp/bla")
2684 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2689 @defun file-notify-rm-watch descriptor
2690 Removes an existing file watch specified by its @var{descriptor}.
2691 @var{descriptor} should be an object returned by
2692 @code{file-notify-add-watch}.
2695 @node Dynamic Libraries
2696 @section Dynamically Loaded Libraries
2697 @cindex dynamic libraries
2699 A @dfn{dynamically loaded library} is a library that is loaded on
2700 demand, when its facilities are first needed. Emacs supports such
2701 on-demand loading of support libraries for some of its features.
2703 @defvar dynamic-library-alist
2704 This is an alist of dynamic libraries and external library files
2707 Each element is a list of the form
2708 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2709 a symbol representing a supported external library, and the rest are
2710 strings giving alternate filenames for that library.
2712 Emacs tries to load the library from the files in the order they
2713 appear in the list; if none is found, the Emacs session won't have
2714 access to that library, and the features it provides will be
2717 Image support on some platforms uses this facility. Here's an example
2718 of setting this variable for supporting images on MS-Windows:
2721 (setq dynamic-library-alist
2722 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2723 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2724 "libpng13d.dll" "libpng13.dll")
2725 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2727 (tiff "libtiff3.dll" "libtiff.dll")
2728 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2729 (svg "librsvg-2-2.dll")
2730 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2731 (glib "libglib-2.0-0.dll")
2732 (gobject "libgobject-2.0-0.dll")))
2735 Note that image types @code{pbm} and @code{xbm} do not need entries in
2736 this variable because they do not depend on external libraries and are
2737 always available in Emacs.
2739 Also note that this variable is not meant to be a generic facility for
2740 accessing external libraries; only those already known by Emacs can
2741 be loaded through it.
2743 This variable is ignored if the given @var{library} is statically