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{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 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
318 is @code{nil}, the @file{*scratch*} buffer is empty.
322 The following command-line options affect some aspects of the startup
323 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
327 Do not display a splash screen.
330 Run without an interactive terminal. @xref{Batch Mode}.
333 Do not initialize any display; just start a server in the background.
337 Do not load either the init file, or the @file{default} library.
340 Do not load the @file{site-start} library.
344 Equivalent to @samp{-q --no-site-file --no-splash}.
345 @c and --no-site-lisp, but let's not mention that here.
350 @subsection The Init File
352 @cindex @file{.emacs}
353 @cindex @file{init.el}
355 When you start Emacs, it normally attempts to load your @dfn{init
356 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
357 in your home directory, or a file named @file{init.el} in a
358 subdirectory named @file{.emacs.d} in your home directory.
360 Whichever place you use, you can also compile the file (@pxref{Byte
361 Compilation}); then the actual file loaded will be @file{.emacs.elc}
365 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
366 control whether and where to find the init file; @samp{-q} (and the
367 stronger @samp{-Q}) says not to load an init file, while @samp{-u
368 @var{user}} says to load @var{user}'s init file instead of yours.
369 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
370 option is specified, Emacs uses the @env{LOGNAME} environment
371 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
372 systems) variable, to find your home directory and thus your init
373 file; this way, even if you have su'd, Emacs still loads your own init
374 file. If those environment variables are absent, though, Emacs uses
375 your user-id to find your home directory.
377 @cindex default init file
378 An Emacs installation may have a @dfn{default init file}, which is a
379 Lisp library named @file{default.el}. Emacs finds this file through
380 the standard search path for libraries (@pxref{How Programs Do
381 Loading}). The Emacs distribution does not come with this file; it is
382 intended for local customizations. If the default init file exists,
383 it is loaded whenever you start Emacs. But your own personal init
384 file, if any, is loaded first; if it sets @code{inhibit-default-init}
385 to a non-@code{nil} value, then Emacs does not subsequently load the
386 @file{default.el} file. In batch mode, or if you specify @samp{-q}
387 (or @samp{-Q}), Emacs loads neither your personal init file nor
388 the default init file.
390 Another file for site-customization is @file{site-start.el}. Emacs
391 loads this @emph{before} the user's init file. You can inhibit the
392 loading of this file with the option @samp{--no-site-file}.
394 @defopt site-run-file
395 This variable specifies the site-customization file to load before the
396 user's init file. Its normal value is @code{"site-start"}. The only
397 way you can change it with real effect is to do so before dumping
399 @c So why even mention it here. I imagine it is almost never changed.
402 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
403 examples of how to make various commonly desired customizations in your
406 @defopt inhibit-default-init
407 If this variable is non-@code{nil}, it prevents Emacs from loading the
408 default initialization library file. The default value is @code{nil}.
411 @defvar before-init-hook
412 This normal hook is run, once, just before loading all the init files
413 (@file{site-start.el}, your init file, and @file{default.el}).
414 (The only way to change it with real effect is before dumping Emacs.)
417 @defvar after-init-hook
418 This normal hook is run, once, just after loading all the init files
419 (@file{site-start.el}, your init file, and @file{default.el}),
420 before loading the terminal-specific library (if started on a text
421 terminal) and processing the command-line action arguments.
424 @defvar emacs-startup-hook
425 This normal hook is run, once, just after handling the command line
426 arguments. In batch mode, Emacs does not run this hook.
429 @defvar window-setup-hook
430 This normal hook is very similar to @code{emacs-startup-hook}.
431 The only difference is that it runs slightly later, after setting
432 of the frame parameters. @xref{Startup Summary, window-setup-hook}.
435 @defvar user-init-file
436 This variable holds the absolute file name of the user's init file. If the
437 actual init file loaded is a compiled file, such as @file{.emacs.elc},
438 the value refers to the corresponding source file.
441 @defvar user-emacs-directory
442 This variable holds the name of the @file{.emacs.d} directory. It is
443 @file{~/.emacs.d} on all platforms but MS-DOS.
446 @node Terminal-Specific
447 @subsection Terminal-Specific Initialization
448 @cindex terminal-specific initialization
450 Each terminal type can have its own Lisp library that Emacs loads when
451 run on that type of terminal. The library's name is constructed by
452 concatenating the value of the variable @code{term-file-prefix} and the
453 terminal type (specified by the environment variable @env{TERM}).
454 Normally, @code{term-file-prefix} has the value @code{"term/"};
455 changing this is not recommended. If there is an entry matching
456 @env{TERM} in the @code{term-file-aliases} association list,
457 Emacs uses the associated value in place of @env{TERM}.
458 Emacs finds the file in the normal manner, by searching the
459 @code{load-path} directories, and trying the @samp{.elc} and
463 The usual role of a terminal-specific library is to enable special
464 keys to send sequences that Emacs can recognize. It may also need to
465 set or add to @code{input-decode-map} if the Termcap or Terminfo entry
466 does not specify all the terminal's function keys. @xref{Terminal Input}.
468 When the name of the terminal type contains a hyphen or underscore,
469 and no library is found whose name is identical to the terminal's
470 name, Emacs strips from the terminal's name the last hyphen or
471 underscore and everything that follows
472 it, and tries again. This process is repeated until Emacs finds a
473 matching library, or until there are no more hyphens or underscores in the name
474 (i.e., there is no terminal-specific library). For example, if the
475 terminal name is @samp{xterm-256color} and there is no
476 @file{term/xterm-256color.el} library, Emacs tries to load
477 @file{term/xterm.el}. If necessary, the terminal library can evaluate
478 @code{(getenv "TERM")} to find the full name of the terminal type.
480 Your init file can prevent the loading of the terminal-specific
481 library by setting the variable @code{term-file-prefix} to @code{nil}.
483 You can also arrange to override some of the actions of the
484 terminal-specific library by using @code{tty-setup-hook}. This is
485 a normal hook that Emacs runs after initializing a new text terminal.
486 You could use this hook to define initializations for terminals that do not
487 have their own libraries. @xref{Hooks}.
489 @defopt term-file-prefix
490 @cindex @env{TERM} environment variable
491 If the value of this variable is non-@code{nil}, Emacs loads a
492 terminal-specific initialization file as follows:
495 (load (concat term-file-prefix (getenv "TERM")))
499 You may set the @code{term-file-prefix} variable to @code{nil} in your
500 init file if you do not wish to load the
501 terminal-initialization file.
503 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
506 @defopt term-file-aliases
507 This variable is an an association list mapping terminal types to
508 their aliases. For example, an element of the form @code{("vt102"
509 . "vt100")} means to treat a terminal of type @samp{vt102} like one of
513 @defvar tty-setup-hook
514 This variable is a normal hook that Emacs runs after initializing a
515 new text terminal. (This applies when Emacs starts up in non-windowed
516 mode, and when making a tty @command{emacsclient} connection.) The
517 hook runs after loading your init file (if applicable) and the
518 terminal-specific Lisp file, so you can use it to adjust the
519 definitions made by that file.
521 For a related feature, @pxref{Init File, window-setup-hook}.
524 @node Command-Line Arguments
525 @subsection Command-Line Arguments
526 @cindex command-line arguments
528 You can use command-line arguments to request various actions when
529 you start Emacs. Note that the recommended way of using Emacs is to
530 start it just once, after logging in, and then do all editing in the same
531 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
532 For this reason, you might not use command-line arguments very often;
533 nonetheless, they can be useful when invoking Emacs from session
534 scripts or debugging Emacs. This section describes how Emacs
535 processes command-line arguments.
538 This function parses the command line that Emacs was called with,
539 processes it, and (amongst other things) loads the user's init file and
540 displays the startup messages.
543 @defvar command-line-processed
544 The value of this variable is @code{t} once the command line has been
547 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
548 Emacs}), you may wish to set this variable to @code{nil} first in
549 order to cause the new dumped Emacs to process its new command-line
553 @defvar command-switch-alist
554 @cindex switches on command line
555 @cindex options on command line
556 @cindex command-line options
557 This variable is an alist of user-defined command-line options and
558 associated handler functions. By default it is empty, but you can
559 add elements if you wish.
561 A @dfn{command-line option} is an argument on the command line, which
568 The elements of the @code{command-switch-alist} look like this:
571 (@var{option} . @var{handler-function})
574 The @sc{car}, @var{option}, is a string, the name of a command-line
575 option (not including the initial hyphen). The @var{handler-function}
576 is called to handle @var{option}, and receives the option name as its
579 In some cases, the option is followed in the command line by an
580 argument. In these cases, the @var{handler-function} can find all the
581 remaining command-line arguments in the variable
582 @code{command-line-args-left} (see below). (The entire list of
583 command-line arguments is in @code{command-line-args}.)
585 The command-line arguments are parsed by the @code{command-line-1}
586 function in the @file{startup.el} file. See also @ref{Emacs
587 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
591 @defvar command-line-args
592 The value of this variable is the list of command-line arguments passed
596 @defvar command-line-args-left
598 The value of this variable is the list of command-line arguments that
599 have not yet been processed.
600 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
601 @c @code{argv} is an alias for this.
604 @defvar command-line-functions
605 This variable's value is a list of functions for handling an
606 unrecognized command-line argument. Each time the next argument to be
607 processed has no special meaning, the functions in this list are called,
608 in order of appearance, until one of them returns a non-@code{nil}
611 These functions are called with no arguments. They can access the
612 command-line argument under consideration through the variable
613 @code{argi}, which is bound temporarily at this point. The remaining
614 arguments (not including the current one) are in the variable
615 @code{command-line-args-left}.
617 When a function recognizes and processes the argument in @code{argi}, it
618 should return a non-@code{nil} value to say it has dealt with that
619 argument. If it has also dealt with some of the following arguments, it
620 can indicate that by deleting them from @code{command-line-args-left}.
622 If all of these functions return @code{nil}, then the argument is treated
623 as a file name to visit.
627 @section Getting Out of Emacs
628 @cindex exiting Emacs
630 There are two ways to get out of Emacs: you can kill the Emacs job,
631 which exits permanently, or you can suspend it, which permits you to
632 reenter the Emacs process later. (In a graphical environment, you can
633 of course simply switch to another application without doing anything
634 special to Emacs, then switch back to Emacs when you want.)
637 * Killing Emacs:: Exiting Emacs irreversibly.
638 * Suspending Emacs:: Exiting Emacs reversibly.
642 @subsection Killing Emacs
643 @cindex killing Emacs
645 Killing Emacs means ending the execution of the Emacs process.
646 If you started Emacs from a terminal, the parent process normally
647 resumes control. The low-level primitive for killing Emacs is
650 @deffn Command kill-emacs &optional exit-data
651 This command calls the hook @code{kill-emacs-hook}, then exits the
652 Emacs process and kills it.
654 If @var{exit-data} is an integer, that is used as the exit status of
655 the Emacs process. (This is useful primarily in batch operation; see
658 If @var{exit-data} is a string, its contents are stuffed into the
659 terminal input buffer so that the shell (or whatever program next reads
660 input) can read them.
666 @cindex operating system signal
667 The @code{kill-emacs} function is normally called via the
668 higher-level command @kbd{C-x C-c}
669 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
670 Emacs Manual}. It is also called automatically if Emacs receives a
671 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
672 controlling terminal is disconnected), or if it receives a
673 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
675 @defvar kill-emacs-hook
676 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
678 Because @code{kill-emacs} can be called in situations where user
679 interaction is impossible (e.g., when the terminal is disconnected),
680 functions on this hook should not attempt to interact with the user.
681 If you want to interact with the user when Emacs is shutting down, use
682 @code{kill-emacs-query-functions}, described below.
685 When Emacs is killed, all the information in the Emacs process,
686 aside from files that have been saved, is lost. Because killing Emacs
687 inadvertently can lose a lot of work, the
688 @code{save-buffers-kill-terminal} command queries for confirmation if
689 you have buffers that need saving or subprocesses that are running.
690 It also runs the abnormal hook @code{kill-emacs-query-functions}:
692 @defvar kill-emacs-query-functions
693 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
694 functions in this hook, after asking the standard questions and before
695 calling @code{kill-emacs}. The functions are called in order of
696 appearance, with no arguments. Each function can ask for additional
697 confirmation from the user. If any of them returns @code{nil},
698 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
699 the remaining functions in this hook. Calling @code{kill-emacs}
700 directly does not run this hook.
703 @node Suspending Emacs
704 @subsection Suspending Emacs
705 @cindex suspending Emacs
707 On text terminals, it is possible to @dfn{suspend Emacs}, which
708 means stopping Emacs temporarily and returning control to its superior
709 process, which is usually the shell. This allows you to resume
710 editing later in the same Emacs process, with the same buffers, the
711 same kill ring, the same undo history, and so on. To resume Emacs,
712 use the appropriate command in the parent shell---most likely
715 @cindex controlling terminal
716 Suspending works only on a terminal device from which the Emacs
717 session was started. We call that device the @dfn{controlling
718 terminal} of the session. Suspending is not allowed if the
719 controlling terminal is a graphical terminal. Suspending is usually
720 not relevant in graphical environments, since you can simply switch to
721 another application without doing anything special to Emacs.
723 @c FIXME? Are there any systems Emacs still supports that do not
726 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
727 not support suspension of jobs; on these systems, ``suspension''
728 actually creates a new shell temporarily as a subprocess of Emacs.
729 Then you would exit the shell to return to Emacs.
731 @deffn Command suspend-emacs &optional string
732 This function stops Emacs and returns control to the superior process.
733 If and when the superior process resumes Emacs, @code{suspend-emacs}
734 returns @code{nil} to its caller in Lisp.
736 This function works only on the controlling terminal of the Emacs
737 session; to relinquish control of other tty devices, use
738 @code{suspend-tty} (see below). If the Emacs session uses more than
739 one terminal, you must delete the frames on all the other terminals
740 before suspending Emacs, or this function signals an error.
741 @xref{Multiple Terminals}.
743 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
744 superior shell, to be read as terminal input.
745 @c FIXME? It seems to me that shell does echo STRING.
746 The characters in @var{string} are not echoed by the superior shell;
747 only the results appear.
749 Before suspending, @code{suspend-emacs} runs the normal hook
750 @code{suspend-hook}. After the user resumes Emacs,
751 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
754 The next redisplay after resumption will redraw the entire screen,
755 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
756 @xref{Refresh Screen}.
758 Here is an example of how you could use these hooks:
762 (add-hook 'suspend-hook
763 (lambda () (or (y-or-n-p "Really suspend? ")
764 (error "Suspend canceled"))))
766 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
769 @c The sit-for prevents the @code{nil} that suspend-emacs returns
770 @c hiding the message.
772 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
776 ---------- Buffer: Minibuffer ----------
777 Really suspend? @kbd{y}
778 ---------- Buffer: Minibuffer ----------
782 ---------- Parent Shell ----------
788 ---------- Echo Area ----------
793 @c FIXME? AFAICS, it is echoed.
794 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
795 is read and executed by the shell.
799 This variable is a normal hook that Emacs runs before suspending.
802 @defvar suspend-resume-hook
803 This variable is a normal hook that Emacs runs on resuming
807 @defun suspend-tty &optional tty
808 If @var{tty} specifies a terminal device used by Emacs, this function
809 relinquishes the device and restores it to its prior state. Frames
810 that used the device continue to exist, but are not updated and Emacs
811 doesn't read input from them. @var{tty} can be a terminal object, a
812 frame (meaning the terminal for that frame), or @code{nil} (meaning
813 the terminal for the selected frame). @xref{Multiple Terminals}.
815 If @var{tty} is already suspended, this function does nothing.
817 @vindex suspend-tty-functions
818 This function runs the hook @code{suspend-tty-functions}, passing the
819 terminal object as an argument to each function.
822 @defun resume-tty &optional tty
823 This function resumes the previously suspended terminal device
824 @var{tty}; where @var{tty} has the same possible values as it does
825 for @code{suspend-tty}.
827 @vindex resume-tty-functions
828 This function reopens the terminal device, re-initializes it, and
829 redraws it with that terminal's selected frame. It then runs the
830 hook @code{resume-tty-functions}, passing the terminal object as an
831 argument to each function.
833 If the same device is already used by another Emacs terminal, this
834 function signals an error. If @var{tty} is not suspended, this
835 function does nothing.
838 @defun controlling-tty-p &optional tty
839 This function returns non-@code{nil} if @var{tty} is the
840 controlling terminal of the Emacs session; @var{tty} can be a
841 terminal object, a frame (meaning the terminal for that frame), or
842 @code{nil} (meaning the terminal for the selected frame).
845 @deffn Command suspend-frame
846 This command @dfn{suspends} a frame. For GUI frames, it calls
847 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
848 text terminals, it calls either @code{suspend-emacs} or
849 @code{suspend-tty}, depending on whether the frame is displayed on the
850 controlling terminal device or not.
853 @node System Environment
854 @section Operating System Environment
855 @cindex operating system environment
857 Emacs provides access to variables in the operating system environment
858 through various functions. These variables include the name of the
859 system, the user's @acronym{UID}, and so on.
861 @defvar system-configuration
862 This variable holds the standard GNU configuration name for the
863 hardware/software configuration of your system, as a string. For
864 example, a typical value for a 64-bit GNU/Linux system is
865 @samp{"x86_64-unknown-linux-gnu"}.
868 @cindex system type and name
870 The value of this variable is a symbol indicating the type of operating
871 system Emacs is running on. The possible values are:
878 Berkeley BSD and its variants.
881 Cygwin, a Posix layer on top of MS-Windows.
887 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
890 A GNU/Linux system---that is, a variant GNU system, using the Linux
891 kernel. (These systems are the ones people often call ``Linux'', but
892 actually Linux is just the kernel, not the whole system.)
895 A GNU (glibc-based) system with a FreeBSD kernel.
898 Hewlett-Packard HPUX operating system.
901 Silicon Graphics Irix system.
904 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
905 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
911 Microsoft Windows NT, 9X and later. The value of @code{system-type}
912 is always @code{windows-nt}, e.g., even on Windows 7.
916 We do not wish to add new symbols to make finer distinctions unless it
917 is absolutely necessary! In fact, we hope to eliminate some of these
918 alternatives in the future. If you need to make a finer distinction
919 than @code{system-type} allows for, you can test
920 @code{system-configuration}, e.g., against a regexp.
924 This function returns the name of the machine you are running on, as a
928 @c FIXME seems like this section is not the best place for this option?
929 @defopt mail-host-address
930 If this variable is non-@code{nil}, it is used instead of
931 @code{system-name} for purposes of generating email addresses. For
932 example, it is used when constructing the default value of
933 @code{user-mail-address}. @xref{User Identification}. (Since this is
934 done when Emacs starts up, the value actually used is the one saved when
935 Emacs was dumped. @xref{Building Emacs}.)
936 @c FIXME sounds like should probably give this a :set-after and some
937 @c custom-initialize-delay voodoo.
940 @deffn Command getenv var &optional frame
941 @cindex environment variable access
942 This function returns the value of the environment variable @var{var},
943 as a string. @var{var} should be a string. If @var{var} is undefined
944 in the environment, @code{getenv} returns @code{nil}. It returns
945 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
946 variables and their values is kept in the variable @code{process-environment}.
955 The shell command @code{printenv} prints all or part of the environment:
960 PATH=/usr/local/bin:/usr/bin:/bin
972 @deffn Command setenv variable &optional value substitute
973 This command sets the value of the environment variable named
974 @var{variable} to @var{value}. @var{variable} should be a string.
975 Internally, Emacs Lisp can handle any string. However, normally
976 @var{variable} should be a valid shell identifier, that is, a sequence
977 of letters, digits and underscores, starting with a letter or
978 underscore. Otherwise, errors may occur if subprocesses of Emacs try
979 to access the value of @var{variable}. If @var{value} is omitted or
980 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
981 removes @var{variable} from the environment. Otherwise, @var{value}
984 @c FIXME: Document 'substitute-env-vars'? --xfq
985 If the optional argument @var{substitute} is non-@code{nil}, Emacs
986 calls the function @code{substitute-env-vars} to expand any
987 environment variables in @var{value}.
989 @code{setenv} works by modifying @code{process-environment}; binding
990 that variable with @code{let} is also reasonable practice.
992 @code{setenv} returns the new value of @var{variable}, or @code{nil}
993 if it removed @var{variable} from the environment.
996 @defvar process-environment
997 This variable is a list of strings, each describing one environment
998 variable. The functions @code{getenv} and @code{setenv} work by means
1004 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
1015 If @code{process-environment} contains ``duplicate'' elements that
1016 specify the same environment variable, the first of these elements
1017 specifies the variable, and the other ``duplicates'' are ignored.
1020 @defvar initial-environment
1021 This variable holds the list of environment variables Emacs inherited
1022 from its parent process when Emacs started.
1025 @defvar path-separator
1026 This variable holds a string that says which character separates
1027 directories in a search path (as found in an environment variable). Its
1028 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1031 @defun parse-colon-path path
1032 This function takes a search path string such as the value of
1033 the @env{PATH} environment variable, and splits it at the separators,
1034 returning a list of directory names. @code{nil} in this list means
1035 the current directory. Although the function's name says
1036 ``colon'', it actually uses the value of @code{path-separator}.
1039 (parse-colon-path ":/foo:/bar")
1040 @result{} (nil "/foo/" "/bar/")
1044 @defvar invocation-name
1045 This variable holds the program name under which Emacs was invoked. The
1046 value is a string, and does not include a directory name.
1049 @defvar invocation-directory
1050 This variable holds the directory from which the Emacs executable was
1051 invoked, or @code{nil} if that directory cannot be determined.
1054 @defvar installation-directory
1055 If non-@code{nil}, this is a directory within which to look for the
1056 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1057 it is normally @code{nil}. It is non-@code{nil}
1058 when Emacs can't find those directories in their standard installed
1059 locations, but can find them in a directory related somehow to the one
1060 containing the Emacs executable (i.e., @code{invocation-directory}).
1063 @defun load-average &optional use-float
1064 This function returns the current 1-minute, 5-minute, and 15-minute
1065 system load averages, in a list. The load average indicates the
1066 number of processes trying to run on the system.
1068 By default, the values are integers that are 100 times the system load
1069 averages, but if @var{use-float} is non-@code{nil}, then they are
1070 returned as floating-point numbers without multiplying by 100.
1072 If it is impossible to obtain the load average, this function signals
1073 an error. On some platforms, access to load averages requires
1074 installing Emacs as setuid or setgid so that it can read kernel
1075 information, and that usually isn't advisable.
1076 @c FIXME which platforms are these? Are they still relevant?
1078 If the 1-minute load average is available, but the 5- or 15-minute
1079 averages are not, this function returns a shortened list containing
1080 the available averages.
1085 @result{} (169 48 36)
1089 @result{} (1.69 0.48 0.36)
1093 The shell command @code{uptime} returns similar information.
1097 This function returns the process @acronym{ID} of the Emacs process,
1101 @defvar tty-erase-char
1102 This variable holds the erase character that was selected
1103 in the system's terminal driver, before Emacs was started.
1104 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1105 @c The value is @code{nil} if Emacs is running under a window system.
1108 @node User Identification
1109 @section User Identification
1110 @cindex user identification
1112 @defvar init-file-user
1113 This variable says which user's init files should be used by
1114 Emacs---or @code{nil} if none. @code{""} stands for the user who
1115 originally logged in. The value reflects command-line options such as
1116 @samp{-q} or @samp{-u @var{user}}.
1118 Lisp packages that load files of customizations, or any other sort of
1119 user profile, should obey this variable in deciding where to find it.
1120 They should load the profile of the user name found in this variable.
1121 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q},
1122 @samp{-Q}, or @samp{-batch} option was used, then Lisp packages should
1123 not load any customization files or user profile.
1126 @defopt user-mail-address
1127 This holds the nominal email address of the user who is using Emacs.
1128 Emacs normally sets this variable to a default value after reading your
1129 init files, but not if you have already set it. So you can set the
1130 variable to some other value in your init file if you do not
1131 want to use the default value.
1134 @defun user-login-name &optional uid
1135 This function returns the name under which the user is logged in.
1136 It uses the environment variables @env{LOGNAME} or @env{USER} if
1137 either is set. Otherwise, the value is based on the effective
1138 @acronym{UID}, not the real @acronym{UID}.
1140 If you specify @var{uid} (a number), the result is the user name that
1141 corresponds to @var{uid}, or @code{nil} if there is no such user.
1144 @defun user-real-login-name
1145 This function returns the user name corresponding to Emacs's real
1146 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1147 environment variables @env{LOGNAME} and @env{USER}.
1150 @defun user-full-name &optional uid
1151 This function returns the full name of the logged-in user---or the value
1152 of the environment variable @env{NAME}, if that is set.
1154 If the Emacs process's user-id does not correspond to any known user (and
1155 provided @code{NAME} is not set), the result is @code{"unknown"}.
1157 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1158 or a string (a login name). Then @code{user-full-name} returns the full
1159 name corresponding to that user-id or login name. If you specify a
1160 user-id or login name that isn't defined, it returns @code{nil}.
1163 @vindex user-full-name
1164 @vindex user-real-login-name
1165 @vindex user-login-name
1166 The symbols @code{user-login-name}, @code{user-real-login-name} and
1167 @code{user-full-name} are variables as well as functions. The functions
1168 return the same values that the variables hold. These variables allow
1169 you to ``fake out'' Emacs by telling the functions what to return. The
1170 variables are also useful for constructing frame titles (@pxref{Frame
1174 @defun user-real-uid
1175 This function returns the real @acronym{UID} of the user.
1176 The value may be floating point, in the (unlikely) event that
1177 the UID is too large to fit in a Lisp integer.
1181 This function returns the effective @acronym{UID} of the user.
1182 The value may be floating point.
1187 This function returns the effective @acronym{GID} of the Emacs process.
1188 The value may be floating point.
1191 @defun group-real-gid
1192 This function returns the real @acronym{GID} of the Emacs process.
1193 The value may be floating point.
1197 This function returns a list of strings, listing the user names on the
1198 system. If Emacs cannot retrieve this information, the return value
1199 is a list containing just the value of @code{user-real-login-name}.
1203 @defun system-groups
1204 This function returns a list of strings, listing the names of user
1205 groups on the system. If Emacs cannot retrieve this information, the
1206 return value is @code{nil}.
1211 @section Time of Day
1214 This section explains how to determine the current time and time
1218 Most of these functions represent time as a list of four integers
1219 @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1220 This represents the number of seconds from the @dfn{epoch} (January
1221 1, 1970 at 00:00 UTC), using the formula:
1223 @var{high} * 2**16 + @var{low} + @var{micro} * 10**@minus{}6 +
1224 @var{pico} * 10**@minus{}12.
1227 $high*2^{16} + low + micro*10^{-6} + pico*10^{-12}$.
1229 The return value of @code{current-time} represents time using this
1230 form, as do the timestamps in the return values of other functions
1231 such as @code{file-attributes} (@pxref{Definition of
1232 file-attributes}). In some cases, functions may return two- or
1233 three-element lists, with omitted @var{microsec} and @var{picosec}
1234 components defaulting to zero.
1237 Function arguments, e.g., the @var{time-value} argument to
1238 @code{current-time-string}, accept a more-general @dfn{time value}
1239 format, which can be a list of integers as above, or a single number
1240 for seconds since the epoch, or @code{nil} for the current time. You
1241 can convert a time value into a human-readable string using
1242 @code{current-time-string} and @code{format-time-string}, into a list
1243 of integers using @code{seconds-to-time}, and into other forms using
1244 @code{decode-time} and @code{float-time}. These functions are
1245 described in the following sections.
1247 @defun current-time-string &optional time-value
1248 This function returns the current time and date as a human-readable
1249 string. The format does not vary for the initial part of the string,
1250 which contains the day of week, month, day of month, and time of day
1251 in that order: the number of characters used for these fields is
1252 always the same, so you can reliably
1253 use @code{substring} to extract them. You should count
1254 characters from the beginning of the string rather than from the end,
1255 as the year might not have exactly four digits, and additional
1256 information may some day be added at the end.
1258 The argument @var{time-value}, if given, specifies a time to format,
1259 instead of the current time.
1263 (current-time-string)
1264 @result{} "Wed Oct 14 22:21:05 1987"
1270 This function returns the current time, represented as a list of four
1271 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1272 These integers have trailing zeros on systems that return time with
1273 lower resolutions. On all current machines @var{picosec} is a
1274 multiple of 1000, but this may change as higher-resolution clocks
1278 @defun float-time &optional time-value
1279 This function returns the current time as a floating-point number of
1280 seconds since the epoch. The optional argument @var{time-value}, if
1281 given, specifies a time to convert instead of the current time.
1283 @emph{Warning}: Since the result is floating point, it may not be
1284 exact. Do not use this function if precise time stamps are required.
1286 @code{time-to-seconds} is an alias for this function.
1289 @defun seconds-to-time time-value
1290 This function converts a time value to list-of-integer form.
1291 For example, if @var{time-value} is a number, @code{(time-to-seconds
1292 (seconds-to-time @var{time-value}))} equals the number unless overflow
1293 or rounding errors occur.
1296 @defun current-time-zone &optional time-value
1297 @cindex time zone, current
1298 This function returns a list describing the time zone that the user is
1301 The value has the form @code{(@var{offset} @var{name})}. Here
1302 @var{offset} is an integer giving the number of seconds ahead of UTC
1303 (east of Greenwich). A negative value means west of Greenwich. The
1304 second element, @var{name}, is a string giving the name of the time
1305 zone. Both elements change when daylight saving time begins or ends;
1306 if the user has specified a time zone that does not use a seasonal time
1307 adjustment, then the value is constant through time.
1309 If the operating system doesn't supply all the information necessary to
1310 compute the value, the unknown elements of the list are @code{nil}.
1312 The argument @var{time-value}, if given, specifies a time value to
1313 analyze instead of the current time.
1316 The current time zone is determined by the @env{TZ} environment
1317 variable. @xref{System Environment}. For example, you can tell Emacs
1318 to use universal time with @code{(setenv "TZ" "UTC0")}. If @env{TZ}
1319 is not in the environment, Emacs uses a platform-dependent default
1322 @node Time Conversion
1323 @section Time Conversion
1324 @cindex calendrical information
1325 @cindex time conversion
1327 These functions convert time values (@pxref{Time of Day}) into
1328 calendrical information and vice versa.
1330 Many 32-bit operating systems are limited to system times containing
1331 32 bits of information in their seconds component; these systems
1332 typically handle only the times from 1901-12-13 20:45:52 UTC through
1333 2038-01-19 03:14:07 UTC@. However, 64-bit and some 32-bit operating
1334 systems have larger seconds components, and can represent times far in
1337 Time conversion functions always use the Gregorian calendar, even
1338 for dates before the Gregorian calendar was introduced. Year numbers
1339 count the number of years since the year 1 B.C., and do not skip zero
1340 as traditional Gregorian years do; for example, the year number
1341 @minus{}37 represents the Gregorian year 38 B.C@.
1343 @defun decode-time &optional time-value
1344 This function converts a time value into calendrical information. If
1345 you don't specify @var{time-value}, it decodes the current time. The return
1346 value is a list of nine elements, as follows:
1349 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1352 Here is what the elements mean:
1356 The number of seconds past the minute, as an integer between 0 and 59.
1357 On some operating systems, this is 60 for leap seconds.
1359 The number of minutes past the hour, as an integer between 0 and 59.
1361 The hour of the day, as an integer between 0 and 23.
1363 The day of the month, as an integer between 1 and 31.
1365 The month of the year, as an integer between 1 and 12.
1367 The year, an integer typically greater than 1900.
1369 The day of week, as an integer between 0 and 6, where 0 stands for
1372 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1374 An integer indicating the time zone, as the number of seconds east of
1378 @strong{Common Lisp Note:} Common Lisp has different meanings for
1379 @var{dow} and @var{zone}.
1382 @defun encode-time seconds minutes hour day month year &optional zone
1383 This function is the inverse of @code{decode-time}. It converts seven
1384 items of calendrical data into a list-of-integer time value. For the
1385 meanings of the arguments, see the table above under
1388 Year numbers less than 100 are not treated specially. If you want them
1389 to stand for years above 1900, or years above 2000, you must alter them
1390 yourself before you call @code{encode-time}.
1392 The optional argument @var{zone} defaults to the current time zone and
1393 its daylight saving time rules. If specified, it can be either a list
1394 (as you would get from @code{current-time-zone}), a string as in the
1395 @env{TZ} environment variable, @code{t} for Universal Time, or an
1396 integer (as you would get from @code{decode-time}). The specified
1397 zone is used without any further alteration for daylight saving time.
1399 If you pass more than seven arguments to @code{encode-time}, the first
1400 six are used as @var{seconds} through @var{year}, the last argument is
1401 used as @var{zone}, and the arguments in between are ignored. This
1402 feature makes it possible to use the elements of a list returned by
1403 @code{decode-time} as the arguments to @code{encode-time}, like this:
1406 (apply 'encode-time (decode-time @dots{}))
1409 You can perform simple date arithmetic by using out-of-range values for
1410 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1411 arguments; for example, day 0 means the day preceding the given month.
1413 The operating system puts limits on the range of possible time values;
1414 if you try to encode a time that is out of range, an error results.
1415 For instance, years before 1970 do not work on some systems;
1416 on others, years as early as 1901 do work.
1420 @section Parsing and Formatting Times
1421 @cindex time parsing
1422 @cindex time formatting
1423 @cindex formatting time values
1425 These functions convert time values to text in a string, and vice versa.
1426 Time values are lists of two to four integers (@pxref{Time of Day}).
1428 @defun date-to-time string
1429 This function parses the time-string @var{string} and returns the
1430 corresponding time value.
1433 @defun format-time-string format-string &optional time-value universal
1435 This function converts @var{time-value} (or the current time, if
1436 @var{time-value} is omitted) to a string according to
1437 @var{format-string}. The argument
1438 @var{format-string} may contain @samp{%}-sequences which say to
1439 substitute parts of the time. Here is a table of what the
1440 @samp{%}-sequences mean:
1444 This stands for the abbreviated name of the day of week.
1446 This stands for the full name of the day of week.
1448 This stands for the abbreviated name of the month.
1450 This stands for the full name of the month.
1452 This is a synonym for @samp{%x %X}.
1454 This has a locale-specific meaning. In the default locale (named C), it
1455 is equivalent to @samp{%A, %B %e, %Y}.
1457 This stands for the day of month, zero-padded.
1459 This is a synonym for @samp{%m/%d/%y}.
1461 This stands for the day of month, blank-padded.
1463 This is a synonym for @samp{%b}.
1465 This stands for the hour (00--23).
1467 This stands for the hour (01--12).
1469 This stands for the day of the year (001--366).
1471 This stands for the hour (0--23), blank padded.
1473 This stands for the hour (1--12), blank padded.
1475 This stands for the month (01--12).
1477 This stands for the minute (00--59).
1479 This stands for a newline.
1481 This stands for the nanoseconds (000000000--999999999). To ask for
1482 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1483 microseconds, etc. Any excess digits are discarded, without rounding.
1485 This stands for @samp{AM} or @samp{PM}, as appropriate.
1487 This is a synonym for @samp{%I:%M:%S %p}.
1489 This is a synonym for @samp{%H:%M}.
1491 This stands for the seconds (00--59).
1493 This stands for a tab character.
1495 This is a synonym for @samp{%H:%M:%S}.
1497 This stands for the week of the year (01--52), assuming that weeks
1500 This stands for the numeric day of week (0--6). Sunday is day 0.
1502 This stands for the week of the year (01--52), assuming that weeks
1505 This has a locale-specific meaning. In the default locale (named
1506 @samp{C}), it is equivalent to @samp{%D}.
1508 This has a locale-specific meaning. In the default locale (named
1509 @samp{C}), it is equivalent to @samp{%T}.
1511 This stands for the year without century (00--99).
1513 This stands for the year with century.
1515 This stands for the time zone abbreviation (e.g., @samp{EST}).
1517 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1520 You can also specify the field width and type of padding for any of
1521 these @samp{%}-sequences. This works as in @code{printf}: you write
1522 the field width as digits in the middle of a @samp{%}-sequences. If you
1523 start the field width with @samp{0}, it means to pad with zeros. If you
1524 start the field width with @samp{_}, it means to pad with spaces.
1526 For example, @samp{%S} specifies the number of seconds since the minute;
1527 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1528 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1529 because that is how @samp{%S} normally pads to two positions.
1531 The characters @samp{E} and @samp{O} act as modifiers when used between
1532 @samp{%} and one of the letters in the table above. @samp{E} specifies
1533 using the current locale's ``alternative'' version of the date and time.
1534 In a Japanese locale, for example, @code{%Ex} might yield a date format
1535 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1536 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1539 @samp{O} means to use the current locale's ``alternative''
1540 representation of numbers, instead of the ordinary decimal digits. This
1541 is allowed with most letters, all the ones that output numbers.
1543 If @var{universal} is non-@code{nil}, that means to describe the time as
1544 Universal Time; @code{nil} means describe it using what Emacs believes
1545 is the local time zone (see @code{current-time-zone}).
1547 This function uses the C library function @code{strftime}
1548 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1549 Manual}) to do most of the work. In order to communicate with that
1550 function, it first encodes its argument using the coding system
1551 specified by @code{locale-coding-system} (@pxref{Locales}); after
1552 @code{strftime} returns the resulting string,
1553 @code{format-time-string} decodes the string using that same coding
1557 @defun format-seconds format-string seconds
1558 This function converts its argument @var{seconds} into a string of
1559 years, days, hours, etc., according to @var{format-string}. The
1560 argument @var{format-string} may contain @samp{%}-sequences which
1561 control the conversion. Here is a table of what the
1562 @samp{%}-sequences mean:
1567 The integer number of 365-day years.
1570 The integer number of days.
1573 The integer number of hours.
1576 The integer number of minutes.
1579 The integer number of seconds.
1581 Non-printing control flag. When it is used, other specifiers must be
1582 given in the order of decreasing size, i.e., years before days, hours
1583 before minutes, etc. Nothing will be produced in the result string to
1584 the left of @samp{%z} until the first non-zero conversion is
1585 encountered. For example, the default format used by
1586 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1587 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1588 will always be produced, but years, days, hours, and minutes will only
1589 be shown if they are non-zero.
1591 Produces a literal @samp{%}.
1594 Upper-case format sequences produce the units in addition to the
1595 numbers, lower-case formats produce only the numbers.
1597 You can also specify the field width by following the @samp{%} with a
1598 number; shorter numbers will be padded with blanks. An optional
1599 period before the width requests zero-padding instead. For example,
1600 @code{"%.3Y"} might produce @code{"004 years"}.
1602 @emph{Warning:} This function works only with values of @var{seconds}
1603 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1604 most-positive-fixnum}).
1607 @node Processor Run Time
1608 @section Processor Run time
1609 @cindex processor run time
1610 @cindex Emacs process run time
1612 Emacs provides several functions and primitives that return time,
1613 both elapsed and processor time, used by the Emacs process.
1615 @deffn Command emacs-uptime &optional format
1616 @cindex uptime of Emacs
1617 This function returns a string representing the Emacs
1618 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1619 running. The string is formatted by @code{format-seconds} according
1620 to the optional argument @var{format}. For the available format
1621 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1622 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1625 When called interactively, it prints the uptime in the echo area.
1628 @defun get-internal-run-time
1629 This function returns the processor run time used by Emacs as a list
1630 of four integers: @code{(@var{sec-high} @var{sec-low} @var{microsec}
1631 @var{picosec})}, using the same format as @code{current-time}
1632 (@pxref{Time of Day}).
1634 Note that the time returned by this function excludes the time Emacs
1635 was not using the processor, and if the Emacs process has several
1636 threads, the returned value is the sum of the processor times used up
1637 by all Emacs threads.
1639 If the system doesn't provide a way to determine the processor run
1640 time, @code{get-internal-run-time} returns the same time as
1641 @code{current-time}.
1644 @deffn Command emacs-init-time
1645 This function returns the duration of the Emacs initialization
1646 (@pxref{Startup Summary}) in seconds, as a string. When called
1647 interactively, it prints the duration in the echo area.
1650 @node Time Calculations
1651 @section Time Calculations
1652 @cindex time calculations
1653 @cindex comparing time values
1654 @cindex calendrical computations
1656 These functions perform calendrical computations using time values
1657 (@pxref{Time of Day}).
1659 @defun time-less-p t1 t2
1660 This returns @code{t} if time value @var{t1} is less than time value
1664 @defun time-subtract t1 t2
1665 This returns the time difference @var{t1} @minus{} @var{t2} between
1666 two time values, as a time value.
1669 @defun time-add t1 t2
1670 This returns the sum of two time values, as a time value.
1671 One argument should represent a time difference rather than a point in time.
1672 Here is how to add a number of seconds to a time value:
1675 (time-add @var{time} @var{seconds})
1679 @defun time-to-days time-value
1680 This function returns the number of days between the beginning of year
1681 1 and @var{time-value}.
1684 @defun time-to-day-in-year time-value
1685 This returns the day number within the year corresponding to @var{time-value}.
1688 @defun date-leap-year-p year
1689 This function returns @code{t} if @var{year} is a leap year.
1693 @section Timers for Delayed Execution
1696 You can set up a @dfn{timer} to call a function at a specified
1697 future time or after a certain length of idleness.
1699 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1700 can run them only when Emacs could accept output from a subprocess:
1701 namely, while waiting or inside certain primitive functions such as
1702 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1703 timer's execution may be delayed if Emacs is busy. However, the time of
1704 execution is very precise if Emacs is idle.
1706 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1707 function, because quitting out of many timer functions can leave
1708 things in an inconsistent state. This is normally unproblematical
1709 because most timer functions don't do a lot of work. Indeed, for a
1710 timer to call a function that takes substantial time to run is likely
1711 to be annoying. If a timer function needs to allow quitting, it
1712 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1713 a timer function calls @code{accept-process-output} to receive output
1714 from an external process, that call should be wrapped inside
1715 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1718 It is usually a bad idea for timer functions to alter buffer
1719 contents. When they do, they usually should call @code{undo-boundary}
1720 both before and after changing the buffer, to separate the timer's
1721 changes from user commands' changes and prevent a single undo entry
1722 from growing to be quite large.
1724 Timer functions should also avoid calling functions that cause Emacs
1725 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1726 unpredictable effects, since other timers (or even the same timer) can
1727 run while waiting. If a timer function needs to perform an action
1728 after a certain time has elapsed, it can do this by scheduling a new
1731 If a timer function calls functions that can change the match data,
1732 it should save and restore the match data. @xref{Saving Match Data}.
1734 @deffn Command run-at-time time repeat function &rest args
1735 This sets up a timer that calls the function @var{function} with
1736 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1737 (integer or floating point), the timer is scheduled to run again every
1738 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1739 the timer runs only once.
1741 @var{time} may specify an absolute or a relative time.
1743 Absolute times may be specified using a string with a limited variety
1744 of formats, and are taken to be times @emph{today}, even if already in
1745 the past. The recognized forms are @samp{@var{xxxx}},
1746 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1747 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1748 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1749 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1750 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1751 to separate the hour and minute parts.
1753 To specify a relative time as a string, use numbers followed by units.
1758 denotes 1 minute from now.
1760 denotes 65 seconds from now.
1761 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1762 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1765 For relative time values, Emacs considers a month to be exactly thirty
1766 days, and a year to be exactly 365.25 days.
1768 Not all convenient formats are strings. If @var{time} is a number
1769 (integer or floating point), that specifies a relative time measured in
1770 seconds. The result of @code{encode-time} can also be used to specify
1771 an absolute value for @var{time}.
1773 In most cases, @var{repeat} has no effect on when @emph{first} call
1774 takes place---@var{time} alone specifies that. There is one exception:
1775 if @var{time} is @code{t}, then the timer runs whenever the time is a
1776 multiple of @var{repeat} seconds after the epoch. This is useful for
1777 functions like @code{display-time}.
1779 The function @code{run-at-time} returns a timer value that identifies
1780 the particular scheduled future action. You can use this value to call
1781 @code{cancel-timer} (see below).
1784 A repeating timer nominally ought to run every @var{repeat} seconds,
1785 but remember that any invocation of a timer can be late. Lateness of
1786 one repetition has no effect on the scheduled time of the next
1787 repetition. For instance, if Emacs is busy computing for long enough
1788 to cover three scheduled repetitions of the timer, and then starts to
1789 wait, it will immediately call the timer function three times in
1790 immediate succession (presuming no other timers trigger before or
1791 between them). If you want a timer to run again no less than @var{n}
1792 seconds after the last invocation, don't use the @var{repeat} argument.
1793 Instead, the timer function should explicitly reschedule the timer.
1795 @defopt timer-max-repeats
1796 This variable's value specifies the maximum number of times to repeat
1797 calling a timer function in a row, when many previously scheduled
1798 calls were unavoidably delayed.
1801 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1802 Execute @var{body}, but give up after @var{seconds} seconds. If
1803 @var{body} finishes before the time is up, @code{with-timeout} returns
1804 the value of the last form in @var{body}. If, however, the execution of
1805 @var{body} is cut short by the timeout, then @code{with-timeout}
1806 executes all the @var{timeout-forms} and returns the value of the last
1809 This macro works by setting a timer to run after @var{seconds} seconds. If
1810 @var{body} finishes before that time, it cancels the timer. If the
1811 timer actually runs, it terminates execution of @var{body}, then
1812 executes @var{timeout-forms}.
1814 Since timers can run within a Lisp program only when the program calls a
1815 primitive that can wait, @code{with-timeout} cannot stop executing
1816 @var{body} while it is in the midst of a computation---only when it
1817 calls one of those primitives. So use @code{with-timeout} only with a
1818 @var{body} that waits for input, not one that does a long computation.
1821 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1822 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1825 @defun cancel-timer timer
1826 This cancels the requested action for @var{timer}, which should be a
1827 timer---usually, one previously returned by @code{run-at-time} or
1828 @code{run-with-idle-timer}. This cancels the effect of that call to
1829 one of these functions; the arrival of the specified time will not
1830 cause anything special to happen.
1834 @section Idle Timers
1837 Here is how to set up a timer that runs when Emacs is idle for a
1838 certain length of time. Aside from how to set them up, idle timers
1839 work just like ordinary timers.
1841 @deffn Command run-with-idle-timer secs repeat function &rest args
1842 Set up a timer which runs the next time Emacs is idle for @var{secs}
1843 seconds. The value of @var{secs} may be a number or a value of the type
1844 returned by @code{current-idle-time}.
1846 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1847 Emacs remains idle for a long enough time. More often @var{repeat} is
1848 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1849 remains idle for @var{secs} seconds.
1851 The function @code{run-with-idle-timer} returns a timer value which you
1852 can use in calling @code{cancel-timer} (@pxref{Timers}).
1856 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1857 it remains idle until the user provides some input. If a timer is set
1858 for five seconds of idleness, it runs approximately five seconds after
1859 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1860 this timer will not run again as long as Emacs remains idle, because
1861 the duration of idleness will continue to increase and will not go
1862 down to five seconds again.
1864 Emacs can do various things while idle: garbage collect, autosave or
1865 handle data from a subprocess. But these interludes during idleness do
1866 not interfere with idle timers, because they do not reset the clock of
1867 idleness to zero. An idle timer set for 600 seconds will run when ten
1868 minutes have elapsed since the last user command was finished, even if
1869 subprocess output has been accepted thousands of times within those ten
1870 minutes, and even if there have been garbage collections and autosaves.
1872 When the user supplies input, Emacs becomes non-idle while executing the
1873 input. Then it becomes idle again, and all the idle timers that are
1874 set up to repeat will subsequently run another time, one by one.
1876 Do not write an idle timer function containing a loop which does a
1877 certain amount of processing each time around, and exits when
1878 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1879 natural but has two problems:
1883 It blocks out all process output (since Emacs accepts process output
1884 only while waiting).
1887 It blocks out any idle timers that ought to run during that time.
1891 Similarly, do not write an idle timer function that sets up another
1892 idle timer (including the same idle timer) with @var{secs} argument
1893 less than or equal to the current idleness time. Such a timer will
1894 run almost immediately, and continue running again and again, instead
1895 of waiting for the next time Emacs becomes idle. The correct approach
1896 is to reschedule with an appropriate increment of the current value of
1897 the idleness time, as described below.
1899 @defun current-idle-time
1900 If Emacs is idle, this function returns the length of time Emacs has
1901 been idle, as a list of four integers: @code{(@var{sec-high}
1902 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1903 @code{current-time} (@pxref{Time of Day}).
1905 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1906 This is a convenient way to test whether Emacs is idle.
1909 The main use of @code{current-idle-time} is when an idle timer
1910 function wants to ``take a break'' for a while. It can set up another
1911 idle timer to call the same function again, after a few seconds more
1912 idleness. Here's an example:
1915 (defvar my-resume-timer nil
1916 "Timer for `my-timer-function' to reschedule itself, or nil.")
1918 (defun my-timer-function ()
1919 ;; @r{If the user types a command while @code{my-resume-timer}}
1920 ;; @r{is active, the next time this function is called from}
1921 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1922 (when my-resume-timer
1923 (cancel-timer my-resume-timer))
1924 ...@var{do the work for a while}...
1925 (when @var{taking-a-break}
1926 (setq my-resume-timer
1927 (run-with-idle-timer
1928 ;; Compute an idle time @var{break-length}
1929 ;; more than the current value.
1930 (time-add (current-idle-time) @var{break-length})
1932 'my-timer-function))))
1935 @node Terminal Input
1936 @section Terminal Input
1937 @cindex terminal input
1939 This section describes functions and variables for recording or
1940 manipulating terminal input. See @ref{Display}, for related
1944 * Input Modes:: Options for how input is processed.
1945 * Recording Input:: Saving histories of recent or all input events.
1949 @subsection Input Modes
1951 @cindex terminal input modes
1953 @defun set-input-mode interrupt flow meta &optional quit-char
1954 This function sets the mode for reading keyboard input. If
1955 @var{interrupt} is non-@code{nil}, then Emacs uses input interrupts.
1956 If it is @code{nil}, then it uses @sc{cbreak} mode. The default
1957 setting is system-dependent. Some systems always use @sc{cbreak} mode
1958 regardless of what is specified.
1960 When Emacs communicates directly with X, it ignores this argument and
1961 uses interrupts if that is the way it knows how to communicate.
1963 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1964 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1965 has no effect except in @sc{cbreak} mode.
1967 The argument @var{meta} controls support for input character codes
1968 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1969 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1970 Emacs disregards the 8th bit; this is necessary when the terminal uses
1971 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1972 Emacs uses all 8 bits of input unchanged. This is good for terminals
1973 that use 8-bit character sets.
1975 If @var{quit-char} is non-@code{nil}, it specifies the character to
1976 use for quitting. Normally this character is @kbd{C-g}.
1980 The @code{current-input-mode} function returns the input mode settings
1981 Emacs is currently using.
1983 @defun current-input-mode
1984 This function returns the current mode for reading keyboard input. It
1985 returns a list, corresponding to the arguments of @code{set-input-mode},
1986 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1990 is non-@code{nil} when Emacs is using interrupt-driven input. If
1991 @code{nil}, Emacs is using @sc{cbreak} mode.
1993 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1994 flow control for output to the terminal. This value is meaningful only
1995 when @var{interrupt} is @code{nil}.
1997 is @code{t} if Emacs treats the eighth bit of input characters as
1998 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1999 input character; any other value means Emacs uses all eight bits as the
2000 basic character code.
2002 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
2006 @node Recording Input
2007 @subsection Recording Input
2008 @cindex recording input
2011 This function returns a vector containing the last 300 input events from
2012 the keyboard or mouse. All input events are included, whether or not
2013 they were used as parts of key sequences. Thus, you always get the last
2014 300 input events, not counting events generated by keyboard macros.
2015 (These are excluded because they are less interesting for debugging; it
2016 should be enough to see the events that invoked the macros.)
2018 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
2019 causes this function to return an empty vector immediately afterward.
2022 @deffn Command open-dribble-file filename
2023 @cindex dribble file
2024 This function opens a @dfn{dribble file} named @var{filename}. When a
2025 dribble file is open, each input event from the keyboard or mouse (but
2026 not those from keyboard macros) is written in that file. A
2027 non-character event is expressed using its printed representation
2028 surrounded by @samp{<@dots{}>}. Be aware that sensitive information
2029 (such as passwords) may end up recorded in the dribble file.
2031 You close the dribble file by calling this function with an argument
2035 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2037 @node Terminal Output
2038 @section Terminal Output
2039 @cindex terminal output
2041 The terminal output functions send output to a text terminal, or keep
2042 track of output sent to the terminal. The variable @code{baud-rate}
2043 tells you what Emacs thinks is the output speed of the terminal.
2046 This variable's value is the output speed of the terminal, as far as
2047 Emacs knows. Setting this variable does not change the speed of actual
2048 data transmission, but the value is used for calculations such as
2051 It also affects decisions about whether to scroll part of the
2052 screen or repaint on text terminals. @xref{Forcing Redisplay},
2053 for the corresponding functionality on graphical terminals.
2055 The value is measured in baud.
2058 If you are running across a network, and different parts of the
2059 network work at different baud rates, the value returned by Emacs may be
2060 different from the value used by your local terminal. Some network
2061 protocols communicate the local terminal speed to the remote machine, so
2062 that Emacs and other programs can get the proper value, but others do
2063 not. If Emacs has the wrong value, it makes decisions that are less
2064 than optimal. To fix the problem, set @code{baud-rate}.
2066 @defun send-string-to-terminal string &optional terminal
2067 This function sends @var{string} to @var{terminal} without alteration.
2068 Control characters in @var{string} have terminal-dependent effects.
2069 This function operates only on text terminals. @var{terminal} may be
2070 a terminal object, a frame, or @code{nil} for the selected frame's
2071 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2072 @var{terminal} is @code{nil}.
2074 One use of this function is to define function keys on terminals that
2075 have downloadable function key definitions. For example, this is how (on
2076 certain terminals) to define function key 4 to move forward four
2077 characters (by transmitting the characters @kbd{C-u C-f} to the
2082 (send-string-to-terminal "\eF4\^U\^F")
2088 @deffn Command open-termscript filename
2089 @cindex termscript file
2090 This function is used to open a @dfn{termscript file} that will record
2091 all the characters sent by Emacs to the terminal. It returns
2092 @code{nil}. Termscript files are useful for investigating problems
2093 where Emacs garbles the screen, problems that are due to incorrect
2094 Termcap entries or to undesirable settings of terminal options more
2095 often than to actual Emacs bugs. Once you are certain which characters
2096 were actually output, you can determine reliably whether they correspond
2097 to the Termcap specifications in use.
2101 (open-termscript "../junk/termscript")
2106 You close the termscript file by calling this function with an
2107 argument of @code{nil}.
2109 See also @code{open-dribble-file} in @ref{Recording Input}.
2113 @section Sound Output
2116 To play sound using Emacs, use the function @code{play-sound}. Only
2117 certain systems are supported; if you call @code{play-sound} on a
2118 system which cannot really do the job, it gives an error.
2120 @c FIXME: Add indexes for Au and WAV? --xfq
2121 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2122 or Sun Audio format (@samp{.au}).
2124 @defun play-sound sound
2125 This function plays a specified sound. The argument, @var{sound}, has
2126 the form @code{(sound @var{properties}...)}, where the @var{properties}
2127 consist of alternating keywords (particular symbols recognized
2128 specially) and values corresponding to them.
2130 Here is a table of the keywords that are currently meaningful in
2131 @var{sound}, and their meanings:
2134 @item :file @var{file}
2135 This specifies the file containing the sound to play.
2136 If the file name is not absolute, it is expanded against
2137 the directory @code{data-directory}.
2139 @item :data @var{data}
2140 This specifies the sound to play without need to refer to a file. The
2141 value, @var{data}, should be a string containing the same bytes as a
2142 sound file. We recommend using a unibyte string.
2144 @item :volume @var{volume}
2145 This specifies how loud to play the sound. It should be a number in the
2146 range of 0 to 1. The default is to use whatever volume has been
2149 @item :device @var{device}
2150 This specifies the system device on which to play the sound, as a
2151 string. The default device is system-dependent.
2154 Before actually playing the sound, @code{play-sound}
2155 calls the functions in the list @code{play-sound-functions}.
2156 Each function is called with one argument, @var{sound}.
2159 @deffn Command play-sound-file file &optional volume device
2160 This function is an alternative interface to playing a sound @var{file}
2161 specifying an optional @var{volume} and @var{device}.
2164 @defvar play-sound-functions
2165 A list of functions to be called before playing a sound. Each function
2166 is called with one argument, a property list that describes the sound.
2170 @section Operating on X11 Keysyms
2173 To define system-specific X11 keysyms, set the variable
2174 @code{system-key-alist}.
2176 @defvar system-key-alist
2177 This variable's value should be an alist with one element for each
2178 system-specific keysym. Each element has the form @code{(@var{code}
2179 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2180 including the ``vendor specific'' bit,
2187 and @var{symbol} is the name for the function key.
2189 For example @code{(168 . mute-acute)} defines a system-specific key (used
2190 by HP X servers) whose numeric code is
2199 It is not crucial to exclude from the alist the keysyms of other X
2200 servers; those do no harm, as long as they don't conflict with the ones
2201 used by the X server actually in use.
2203 The variable is always local to the current terminal, and cannot be
2204 buffer-local. @xref{Multiple Terminals}.
2207 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2209 @defvar x-alt-keysym
2210 @defvarx x-meta-keysym
2211 @defvarx x-hyper-keysym
2212 @defvarx x-super-keysym
2213 The name of the keysym that should stand for the Alt modifier
2214 (respectively, for Meta, Hyper, and Super). For example, here is
2215 how to swap the Meta and Alt modifiers within Emacs:
2217 (setq x-alt-keysym 'meta)
2218 (setq x-meta-keysym 'alt)
2226 The command-line option @samp{-batch} causes Emacs to run
2227 noninteractively. In this mode, Emacs does not read commands from the
2228 terminal, it does not alter the terminal modes, and it does not expect
2229 to be outputting to an erasable screen. The idea is that you specify
2230 Lisp programs to run; when they are finished, Emacs should exit. The
2231 way to specify the programs to run is with @samp{-l @var{file}}, which
2232 loads the library named @var{file}, or @samp{-f @var{function}}, which
2233 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2235 Any Lisp program output that would normally go to the echo area,
2236 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2237 as the stream, goes instead to Emacs's standard error descriptor when
2238 in batch mode. Similarly, input that would normally come from the
2239 minibuffer is read from the standard input descriptor.
2240 Thus, Emacs behaves much like a noninteractive
2241 application program. (The echo area output that Emacs itself normally
2242 generates, such as command echoing, is suppressed entirely.)
2244 @defvar noninteractive
2245 This variable is non-@code{nil} when Emacs is running in batch mode.
2248 @node Session Management
2249 @section Session Management
2250 @cindex session manager
2252 Emacs supports the X Session Management Protocol, which is used to
2253 suspend and restart applications. In the X Window System, a program
2254 called the @dfn{session manager} is responsible for keeping track of
2255 the applications that are running. When the X server shuts down, the
2256 session manager asks applications to save their state, and delays the
2257 actual shutdown until they respond. An application can also cancel
2260 When the session manager restarts a suspended session, it directs
2261 these applications to individually reload their saved state. It does
2262 this by specifying a special command-line argument that says what
2263 saved session to restore. For Emacs, this argument is @samp{--smid
2266 @defvar emacs-save-session-functions
2267 @cindex session file
2268 Emacs supports saving state via a hook called
2269 @code{emacs-save-session-functions}. Emacs runs this hook when the
2270 session manager tells it that the window system is shutting down. The
2271 functions are called with no arguments, and with the current buffer
2272 set to a temporary buffer. Each function can use @code{insert} to add
2273 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2274 file, called the @dfn{session file}.
2276 @findex emacs-session-restore
2277 Subsequently, when the session manager restarts Emacs, it loads the
2278 session file automatically (@pxref{Loading}). This is performed by a
2279 function named @code{emacs-session-restore}, which is called during
2280 startup. @xref{Startup Summary}.
2282 If a function in @code{emacs-save-session-functions} returns
2283 non-@code{nil}, Emacs tells the session manager to cancel the
2287 Here is an example that just inserts some text into @file{*scratch*} when
2288 Emacs is restarted by the session manager.
2292 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2296 (defun save-yourself-test ()
2297 (insert "(save-current-buffer
2298 (switch-to-buffer \"*scratch*\")
2299 (insert \"I am restored\"))")
2304 @node Desktop Notifications
2305 @section Desktop Notifications
2306 @cindex desktop notifications
2307 @cindex notifications, on desktop
2309 Emacs is able to send @dfn{notifications} on systems that support the
2310 freedesktop.org Desktop Notifications Specification. In order to use
2311 this functionality, Emacs must have been compiled with D-Bus support,
2312 and the @code{notifications} library must be loaded. @xref{Top, ,
2313 D-Bus,dbus,D-Bus integration in Emacs}.
2315 @defun notifications-notify &rest params
2316 This function sends a notification to the desktop via D-Bus,
2317 consisting of the parameters specified by the @var{params} arguments.
2318 These arguments should consist of alternating keyword and value pairs.
2319 The supported keywords and values are as follows:
2322 @item :bus @var{bus}
2323 The D-Bus bus. This argument is needed only if a bus other than
2324 @code{:session} shall be used.
2326 @item :title @var{title}
2327 The notification title.
2329 @item :body @var{text}
2330 The notification body text. Depending on the implementation of the
2331 notification server, the text could contain HTML markups, like
2332 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2333 characters must be encoded, as @samp{"Contact
2334 <postmaster@@localhost>!"}.
2336 @item :app-name @var{name}
2337 The name of the application sending the notification. The default is
2338 @code{notifications-application-name}.
2340 @item :replaces-id @var{id}
2341 The notification @var{id} that this notification replaces. @var{id}
2342 must be the result of a previous @code{notifications-notify} call.
2344 @item :app-icon @var{icon-file}
2345 The file name of the notification icon. If set to @code{nil}, no icon
2346 is displayed. The default is @code{notifications-application-icon}.
2348 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2349 A list of actions to be applied. @var{key} and @var{title} are both
2350 strings. The default action (usually invoked by clicking the
2351 notification) should have a key named @samp{"default"}. The title can
2352 be anything, though implementations are free not to display it.
2354 @item :timeout @var{timeout}
2355 The timeout time in milliseconds since the display of the notification
2356 at which the notification should automatically close. If @minus{}1, the
2357 notification's expiration time is dependent on the notification
2358 server's settings, and may vary for the type of notification. If 0,
2359 the notification never expires. Default value is @minus{}1.
2361 @item :urgency @var{urgency}
2362 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2365 When this keyword is given, the @var{title} string of the actions is
2366 interpreted as icon name.
2368 @item :category @var{category}
2369 The type of notification this is, a string. See the
2370 @uref{http://developer.gnome.org/notification-spec/#categories,
2371 Desktop Notifications Specification} for a list of standard
2374 @item :desktop-entry @var{filename}
2375 This specifies the name of the desktop filename representing the
2376 calling program, like @samp{"emacs"}.
2378 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2379 This is a raw data image format that describes the width, height,
2380 rowstride, whether there is an alpha channel, bits per sample,
2381 channels and image data, respectively.
2383 @item :image-path @var{path}
2384 This is represented either as a URI (@samp{file://} is the only URI
2385 schema supported right now) or a name in a freedesktop.org-compliant
2386 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2388 @item :sound-file @var{filename}
2389 The path to a sound file to play when the notification pops up.
2391 @item :sound-name @var{name}
2392 A themable named sound from the freedesktop.org sound naming
2393 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2394 notification pops up. Similar to the icon name, only for sounds. An
2395 example would be @samp{"message-new-instant"}.
2397 @item :suppress-sound
2398 Causes the server to suppress playing any sounds, if it has that
2402 When set the server will not automatically remove the notification
2403 when an action has been invoked. The notification will remain resident
2404 in the server until it is explicitly removed by the user or by the
2405 sender. This hint is likely only useful when the server has the
2406 @code{:persistence} capability.
2409 When set the server will treat the notification as transient and
2410 by-pass the server's persistence capability, if it should exist.
2412 @item :x @var{position}
2413 @itemx :y @var{position}
2414 Specifies the X, Y location on the screen that the
2415 notification should point to. Both arguments must be used together.
2417 @item :on-action @var{function}
2418 Function to call when an action is invoked. The notification @var{id}
2419 and the @var{key} of the action are passed as arguments to the
2422 @item :on-close @var{function}
2423 Function to call when the notification has been closed by timeout or
2424 by the user. The function receive the notification @var{id} and the closing
2425 @var{reason} as arguments:
2428 @item @code{expired} if the notification has expired
2429 @item @code{dismissed} if the notification was dismissed by the user
2430 @item @code{close-notification} if the notification was closed by a call to
2431 @code{notifications-close-notification}
2432 @item @code{undefined} if the notification server hasn't provided a reason
2436 Which parameters are accepted by the notification server can be
2437 checked via @code{notifications-get-capabilities}.
2439 This function returns a notification id, an integer, which can be used
2440 to manipulate the notification item with
2441 @code{notifications-close-notification} or the @code{:replaces-id}
2442 argument of another @code{notifications-notify} call. For example:
2446 (defun my-on-action-function (id key)
2447 (message "Message %d, key \"%s\" pressed" id key))
2448 @result{} my-on-action-function
2452 (defun my-on-close-function (id reason)
2453 (message "Message %d, closed due to \"%s\"" id reason))
2454 @result{} my-on-close-function
2458 (notifications-notify
2460 :body "This is <b>important</b>."
2461 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2462 :on-action 'my-on-action-function
2463 :on-close 'my-on-close-function)
2468 A message window opens on the desktop. Press "I agree"
2469 @result{} Message 22, key "Confirm" pressed
2470 Message 22, closed due to "dismissed"
2475 @defun notifications-close-notification id &optional bus
2476 This function closes a notification with identifier @var{id}.
2477 @var{bus} can be a string denoting a D-Bus connection, the default is
2481 @defun notifications-get-capabilities &optional bus
2482 Returns the capabilities of the notification server, a list of
2483 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2484 default is @code{:session}. The following capabilities can be
2489 The server will provide the specified actions to the user.
2494 @item :body-hyperlinks
2495 The server supports hyperlinks in the notifications.
2498 The server supports images in the notifications.
2501 Supports markup in the body text.
2504 The server will render an animation of all the frames in a given image
2508 Supports display of exactly 1 frame of any given image array. This
2509 value is mutually exclusive with @code{:icon-multi}.
2512 The server supports persistence of notifications.
2515 The server supports sounds on notifications.
2518 Further vendor-specific caps start with @code{:x-vendor}, like
2519 @code{:x-gnome-foo-cap}.
2522 @defun notifications-get-server-information &optional bus
2523 Return information on the notification server, a list of strings.
2524 @var{bus} can be a string denoting a D-Bus connection, the default is
2525 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2526 @var{version} @var{spec-version})}.
2530 The product name of the server.
2533 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2536 The server's version number.
2539 The specification version the server is compliant with.
2542 If @var{spec_version} is @code{nil}, the server supports a
2543 specification prior to @samp{"1.0"}.
2546 @node File Notifications
2547 @section Notifications on File Changes
2548 @cindex file notifications
2549 @cindex watch, for filesystem events
2551 Several operating systems support watching of filesystems for changes
2552 of files. If configured properly, Emacs links a respective library
2553 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2554 statically. These libraries enable watching of filesystems on the
2557 It is also possible to watch filesystems on remote machines,
2558 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2559 This does not depend on one of the libraries linked to Emacs.
2561 Since all these libraries emit different events on notified file
2562 changes, there is the Emacs library @code{filenotify} which provides a
2565 @defun file-notify-add-watch file flags callback
2566 Add a watch for filesystem events pertaining to @var{file}. This
2567 arranges for filesystem events pertaining to @var{file} to be reported
2570 The returned value is a descriptor for the added watch. Its type
2571 depends on the underlying library, it cannot be assumed to be an
2572 integer as in the example below. It should be used for comparison by
2575 If the @var{file} cannot be watched for some reason, this function
2576 signals a @code{file-notify-error} error.
2578 Sometimes, mounted filesystems cannot be watched for file changes.
2579 This is not detected by this function, a non-@code{nil} return value
2580 does not guarantee that changes on @var{file} will be notified.
2582 @var{flags} is a list of conditions to set what will be watched for.
2583 It can include the following symbols:
2587 watch for file changes
2588 @item attribute-change
2589 watch for file attribute changes, like permissions or modification
2593 If @var{file} is a directory, changes for all files in that directory
2594 will be notified. This does not work recursively.
2596 When any event happens, Emacs will call the @var{callback} function
2597 passing it a single argument @var{event}, which is of the form
2600 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2603 @var{descriptor} is the same object as the one returned by this
2604 function. @var{action} is the description of the event. It could be
2605 any one of the following symbols:
2609 @var{file} was created
2611 @var{file} was deleted
2613 @var{file} has changed
2615 @var{file} has been renamed to @var{file1}
2616 @item attribute-changed
2617 a @var{file} attribute was changed
2620 @var{file} and @var{file1} are the name of the file(s) whose event is
2621 being reported. For example:
2625 (require 'filenotify)
2626 @result{} filenotify
2630 (defun my-notify-callback (event)
2631 (message "Event %S" event))
2632 @result{} my-notify-callback
2636 (file-notify-add-watch
2637 "/tmp" '(change attribute-change) 'my-notify-callback)
2642 (write-region "foo" nil "/tmp/foo")
2643 @result{} Event (35025468 created "/tmp/.#foo")
2644 Event (35025468 created "/tmp/foo")
2645 Event (35025468 changed "/tmp/foo")
2646 Event (35025468 deleted "/tmp/.#foo")
2650 (write-region "bla" nil "/tmp/foo")
2651 @result{} Event (35025468 created "/tmp/.#foo")
2652 Event (35025468 changed "/tmp/foo") [2 times]
2653 Event (35025468 deleted "/tmp/.#foo")
2657 (set-file-modes "/tmp/foo" (default-file-modes))
2658 @result{} Event (35025468 attribute-changed "/tmp/foo")
2662 Whether the action @code{renamed} is returned, depends on the used
2663 watch library. It can be expected, when a directory is watched, and
2664 both @var{file} and @var{file1} belong to this directory. Otherwise,
2665 the actions @code{deleted} and @code{created} could be returned in a
2670 (rename-file "/tmp/foo" "/tmp/bla")
2671 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2675 (file-notify-add-watch
2676 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2681 (rename-file "/tmp/bla" "/var/tmp/bla")
2682 @result{} ;; gfilenotify
2683 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2685 @result{} ;; inotify
2686 Event (35025504 created "/var/tmp/bla")
2687 Event (35025468 deleted "/tmp/bla")
2692 @defun file-notify-rm-watch descriptor
2693 Removes an existing file watch specified by its @var{descriptor}.
2694 @var{descriptor} should be an object returned by
2695 @code{file-notify-add-watch}.
2698 @node Dynamic Libraries
2699 @section Dynamically Loaded Libraries
2700 @cindex dynamic libraries
2702 A @dfn{dynamically loaded library} is a library that is loaded on
2703 demand, when its facilities are first needed. Emacs supports such
2704 on-demand loading of support libraries for some of its features.
2706 @defvar dynamic-library-alist
2707 This is an alist of dynamic libraries and external library files
2710 Each element is a list of the form
2711 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2712 a symbol representing a supported external library, and the rest are
2713 strings giving alternate filenames for that library.
2715 Emacs tries to load the library from the files in the order they
2716 appear in the list; if none is found, the Emacs session won't have
2717 access to that library, and the features it provides will be
2720 Image support on some platforms uses this facility. Here's an example
2721 of setting this variable for supporting images on MS-Windows:
2724 (setq dynamic-library-alist
2725 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2726 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2727 "libpng13d.dll" "libpng13.dll")
2728 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2730 (tiff "libtiff3.dll" "libtiff.dll")
2731 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2732 (svg "librsvg-2-2.dll")
2733 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2734 (glib "libglib-2.0-0.dll")
2735 (gobject "libgobject-2.0-0.dll")))
2738 Note that image types @code{pbm} and @code{xbm} do not need entries in
2739 this variable because they do not depend on external libraries and are
2740 always available in Emacs.
2742 Also note that this variable is not meant to be a generic facility for
2743 accessing external libraries; only those already known by Emacs can
2744 be loaded through it.
2746 This variable is ignored if the given @var{library} is statically