2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software
5 @c See the file elisp.texi for copying conditions.
7 @chapter Operating System Interface
9 This chapter is about starting and getting out of Emacs, access to
10 values in the operating system environment, and terminal input, output.
12 @xref{Building Emacs}, for related information. @xref{Display}, for
13 additional operating system status information pertaining to the
14 terminal and the screen.
17 * Starting Up:: Customizing Emacs startup processing.
18 * Getting Out:: How exiting works (permanent or temporary).
19 * System Environment:: Distinguish the name and kind of system.
20 * User Identification:: Finding the name and user id of the user.
21 * Time of Day:: Getting the current time.
22 * Time Conversion:: Converting a time from numeric form to
23 calendrical data and vice versa.
24 * Time Parsing:: Converting a time from numeric form to text
26 * Processor Run Time:: Getting the run time used by Emacs.
27 * Time Calculations:: Adding, subtracting, comparing times, etc.
28 * Timers:: Setting a timer to call a function at a certain time.
29 * Idle Timers:: Setting a timer to call a function when Emacs has
30 been idle for a certain length of time.
31 * Terminal Input:: Accessing and recording terminal input.
32 * Terminal Output:: Controlling and recording terminal output.
33 * Sound Output:: Playing sounds on the computer's speaker.
34 * X11 Keysyms:: Operating on key symbols for X Windows.
35 * Batch Mode:: Running Emacs without terminal interaction.
36 * Session Management:: Saving and restoring state with X Session Management.
37 * Desktop Notifications:: Desktop notifications.
38 * File Notifications:: File notifications.
39 * Dynamic Libraries:: On-demand loading of support libraries.
43 @section Starting Up Emacs
45 This section describes what Emacs does when it is started, and how you
46 can customize these actions.
49 * Startup Summary:: Sequence of actions Emacs performs at startup.
50 * Init File:: Details on reading the init file.
51 * Terminal-Specific:: How the terminal-specific Lisp file is read.
52 * Command-Line Arguments:: How command-line arguments are processed,
53 and how you can customize them.
57 @subsection Summary: Sequence of Actions at Startup
58 @cindex initialization of Emacs
59 @cindex startup of Emacs
60 @cindex @file{startup.el}
62 When Emacs is started up, it performs the following operations
63 (see @code{normal-top-level} in @file{startup.el}):
67 It adds subdirectories to @code{load-path}, by running the file named
68 @file{subdirs.el} in each directory in the list. Normally, this file
69 adds the directory's subdirectories to the list, and those are scanned
70 in their turn. The files @file{subdirs.el} are normally generated
71 automatically when Emacs is installed.
74 It loads any @file{leim-list.el} that it finds in the @code{load-path}
75 directories. This file is intended for registering input methods.
76 The search is only for any personal @file{leim-list.el} files that you
77 may have created; it skips the directories containing the standard Emacs
78 libraries (these should contain only a single @file{leim-list.el} file,
79 which is compiled into the Emacs executable).
81 @vindex before-init-time
83 It sets the variable @code{before-init-time} to the value of
84 @code{current-time} (@pxref{Time of Day}). It also sets
85 @code{after-init-time} to @code{nil}, which signals to Lisp programs
86 that Emacs is being initialized.
88 @c set-locale-environment
90 It sets the language environment and the terminal coding system,
91 if requested by environment variables such as @env{LANG}.
94 It does some basic parsing of the command-line arguments.
96 @vindex initial-window-system@r{, and startup}
97 @vindex window-system-initialization-alist
99 If not running in batch mode, it initializes the window system that
100 the variable @code{initial-window-system} specifies (@pxref{Window
101 Systems, initial-window-system}). The initialization function for
102 each supported window system is specified by
103 @code{window-system-initialization-alist}. If the value
104 of @code{initial-window-system} is @var{windowsystem}, then the
105 appropriate initialization function is defined in the file
106 @file{term/@var{windowsystem}-win.el}. This file should have been
107 compiled into the Emacs executable when it was built.
110 It runs the normal hook @code{before-init-hook}.
113 If appropriate, it creates a graphical frame. This is not done if the
114 options @samp{--batch} or @samp{--daemon} were specified.
117 It initializes the initial frame's faces, and sets up the menu bar
118 and tool bar if needed. If graphical frames are supported, it sets up
119 the tool bar even if the current frame is not a graphical one, since a
120 graphical frame may be created later on.
123 It use @code{custom-reevaluate-setting} to re-initialize the members
124 of the list @code{custom-delayed-init-variables}. These are any
125 pre-loaded user options whose default value depends on the run-time,
126 rather than build-time, context.
127 @xref{Building Emacs, custom-initialize-delay}.
130 @c It registers the colors available for tty frames.
133 It loads the library @file{site-start}, if it exists. This is not
134 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
135 @cindex @file{site-start.el}
138 It loads your init file (@pxref{Init File}). This is not done if the
139 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
140 the @samp{-u} option was specified, Emacs looks for the init file in
141 that user's home directory instead.
144 It loads the library @file{default}, if it exists. This is not done
145 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
146 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
147 @cindex @file{default.el}
150 It loads your abbrevs from the file specified by
151 @code{abbrev-file-name}, if that file exists and can be read
152 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
153 option @samp{--batch} was specified.
156 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
157 function @code{package-initialize} to activate any optional Emacs Lisp
158 package that has been installed. @xref{Packaging Basics}.
160 @vindex after-init-time
162 It sets the variable @code{after-init-time} to the value of
163 @code{current-time}. This variable was set to @code{nil} earlier;
164 setting it to the current time signals that the initialization phase
165 is over, and, together with @code{before-init-time}, provides the
166 measurement of how long it took.
169 It runs the normal hook @code{after-init-hook}.
172 If the buffer @file{*scratch*} exists and is still in Fundamental mode
173 (as it should be by default), it sets its major mode according to
174 @code{initial-major-mode}.
177 If started on a text terminal, it loads the terminal-specific
178 Lisp library (@pxref{Terminal-Specific}), and runs the hook
179 @code{tty-setup-hook}. This is not done
180 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
182 @c Now command-line calls command-line-1.
185 It displays the initial echo area message, unless you have suppressed
186 that with @code{inhibit-startup-echo-area-message}.
189 It processes any command-line options that were not handled earlier.
191 @c This next one is back in command-line, but the remaining bits of
192 @c command-line-1 are not done if noninteractive.
194 It now exits if the option @code{--batch} was specified.
197 If @code{initial-buffer-choice} is a string, it visits the file with
198 that name. If it is a function, it calls the function and selects the
199 buffer returned by the function. It it is @code{t}, it selects the
200 @file{*scratch*} buffer. If the @file{*scratch*} buffer exists and is
201 empty, it inserts @code{initial-scratch-message} into that buffer.
203 @c To make things nice and confusing, the next three items can be
204 @c called from two places. If displaying a startup screen, they are
205 @c called in command-line-1 before the startup screen is shown.
206 @c inhibit-startup-hooks is then set and window-setup-hook set to nil.
207 @c If not displaying a startup screen, they are are called in
209 @c FIXME? So it seems they can be called before or after the
210 @c daemon/session restore step?
213 It runs @code{emacs-startup-hook}.
216 It calls @code{frame-notice-user-settings}, which modifies the
217 parameters of the selected frame according to whatever the init files
221 It runs @code{window-setup-hook}. @xref{Window Systems}.
224 @cindex startup screen
225 It displays the @dfn{startup screen}, which is a special buffer that
226 contains information about copyleft and basic Emacs usage. This is
227 not done if @code{inhibit-startup-screen} or @code{initial-buffer-choice}
228 are non-@code{nil}, or if the @samp{--no-splash} or @samp{-Q} command-line
229 options were specified.
231 @c End of command-line-1.
233 @c Back to command-line from command-line-1.
235 @c This is the point at which we actually exit in batch mode, but the
236 @c last few bits of command-line-1 are not done in batch mode.
239 If the option @code{--daemon} was specified, it calls
240 @code{server-start} and detaches from the controlling terminal.
241 @xref{Emacs Server,,, emacs, The GNU Emacs Manual}.
244 If started by the X session manager, it calls
245 @code{emacs-session-restore} passing it as argument the ID of the
246 previous session. @xref{Session Management}.
248 @c End of command-line.
250 @c Back to normal-top-level from command-line.
255 The following options affect some aspects of the startup sequence.
257 @defopt inhibit-startup-screen
258 This variable, if non-@code{nil}, inhibits the startup screen. In
259 that case, Emacs typically displays the @file{*scratch*} buffer; but
260 see @code{initial-buffer-choice}, below.
262 Do not set this variable in the init file of a new user, or in a way
263 that affects more than one user, as that would prevent new users from
264 receiving information about copyleft and basic Emacs usage.
266 @vindex inhibit-startup-message
267 @vindex inhibit-splash-screen
268 @code{inhibit-startup-message} and @code{inhibit-splash-screen} are
269 aliases for this variable.
272 @defopt initial-buffer-choice
273 If non-@code{nil}, this variable is a string that specifies a file or
274 directory for Emacs to display after starting up, instead of the
276 If its value is a function, Emacs calls that function which must
277 return a buffer which is then displayed.
278 If its value is @code{t}, Emacs displays the @file{*scratch*} buffer.
281 @defopt inhibit-startup-echo-area-message
282 This variable controls the display of the startup echo area message.
283 You can suppress the startup echo area message by adding text with this
284 form to your init file:
287 (setq inhibit-startup-echo-area-message
288 "@var{your-login-name}")
291 Emacs explicitly checks for an expression as shown above in your init
292 file; your login name must appear in the expression as a Lisp string
293 constant. You can also use the Customize interface. Other methods of
294 setting @code{inhibit-startup-echo-area-message} to the same value do
295 not inhibit the startup message. This way, you can easily inhibit the
296 message for yourself if you wish, but thoughtless copying of your init
297 file will not inhibit the message for someone else.
300 @defopt initial-scratch-message
301 This variable, if non-@code{nil}, should be a string, which is
302 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
303 is @code{nil}, the @file{*scratch*} buffer is empty.
307 The following command-line options affect some aspects of the startup
308 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
312 Do not display a splash screen.
315 Run without an interactive terminal. @xref{Batch Mode}.
318 Do not initialize any display; just start a server in the background.
322 Do not load either the init file, or the @file{default} library.
325 Do not load the @file{site-start} library.
329 Equivalent to @samp{-q --no-site-file --no-splash}.
330 @c and --no-site-lisp, but let's not mention that here.
335 @subsection The Init File
337 @cindex @file{.emacs}
338 @cindex @file{init.el}
340 When you start Emacs, it normally attempts to load your @dfn{init
341 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
342 in your home directory, or a file named @file{init.el} in a
343 subdirectory named @file{.emacs.d} in your home directory.
345 Whichever place you use, you can also compile the file (@pxref{Byte
346 Compilation}); then the actual file loaded will be @file{.emacs.elc}
350 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
351 control whether and where to find the init file; @samp{-q} (and the
352 stronger @samp{-Q}) says not to load an init file, while @samp{-u
353 @var{user}} says to load @var{user}'s init file instead of yours.
354 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
355 option is specified, Emacs uses the @env{LOGNAME} environment
356 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
357 systems) variable, to find your home directory and thus your init
358 file; this way, even if you have su'd, Emacs still loads your own init
359 file. If those environment variables are absent, though, Emacs uses
360 your user-id to find your home directory.
362 @cindex default init file
363 An Emacs installation may have a @dfn{default init file}, which is a
364 Lisp library named @file{default.el}. Emacs finds this file through
365 the standard search path for libraries (@pxref{How Programs Do
366 Loading}). The Emacs distribution does not come with this file; it is
367 intended for local customizations. If the default init file exists,
368 it is loaded whenever you start Emacs. But your own personal init
369 file, if any, is loaded first; if it sets @code{inhibit-default-init}
370 to a non-@code{nil} value, then Emacs does not subsequently load the
371 @file{default.el} file. In batch mode, or if you specify @samp{-q}
372 (or @samp{-Q}), Emacs loads neither your personal init file nor
373 the default init file.
375 Another file for site-customization is @file{site-start.el}. Emacs
376 loads this @emph{before} the user's init file. You can inhibit the
377 loading of this file with the option @samp{--no-site-file}.
379 @defopt site-run-file
380 This variable specifies the site-customization file to load before the
381 user's init file. Its normal value is @code{"site-start"}. The only
382 way you can change it with real effect is to do so before dumping
384 @c So why even mention it here. I imagine it is almost never changed.
387 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
388 examples of how to make various commonly desired customizations in your
391 @defopt inhibit-default-init
392 If this variable is non-@code{nil}, it prevents Emacs from loading the
393 default initialization library file. The default value is @code{nil}.
396 @defvar before-init-hook
397 This normal hook is run, once, just before loading all the init files
398 (@file{site-start.el}, your init file, and @file{default.el}).
399 (The only way to change it with real effect is before dumping Emacs.)
402 @defvar after-init-hook
403 This normal hook is run, once, just after loading all the init files
404 (@file{site-start.el}, your init file, and @file{default.el}),
405 before loading the terminal-specific library (if started on a text
406 terminal) and processing the command-line action arguments.
409 @defvar emacs-startup-hook
410 This normal hook is run, once, just after handling the command line
411 arguments. In batch mode, Emacs does not run this hook.
414 @defvar user-init-file
415 This variable holds the absolute file name of the user's init file. If the
416 actual init file loaded is a compiled file, such as @file{.emacs.elc},
417 the value refers to the corresponding source file.
420 @defvar user-emacs-directory
421 This variable holds the name of the @file{.emacs.d} directory. It is
422 @file{~/.emacs.d} on all platforms but MS-DOS.
425 @node Terminal-Specific
426 @subsection Terminal-Specific Initialization
427 @cindex terminal-specific initialization
429 Each terminal type can have its own Lisp library that Emacs loads when
430 run on that type of terminal. The library's name is constructed by
431 concatenating the value of the variable @code{term-file-prefix} and the
432 terminal type (specified by the environment variable @env{TERM}).
433 Normally, @code{term-file-prefix} has the value
434 @code{"term/"}; changing this is not recommended. Emacs finds the file
435 in the normal manner, by searching the @code{load-path} directories, and
436 trying the @samp{.elc} and @samp{.el} suffixes.
439 The usual role of a terminal-specific library is to enable special
440 keys to send sequences that Emacs can recognize. It may also need to
441 set or add to @code{input-decode-map} if the Termcap or Terminfo entry
442 does not specify all the terminal's function keys. @xref{Terminal Input}.
444 When the name of the terminal type contains a hyphen or underscore,
445 and no library is found whose name is identical to the terminal's
446 name, Emacs strips from the terminal's name the last hyphen or
447 underscore and everything that follows
448 it, and tries again. This process is repeated until Emacs finds a
449 matching library, or until there are no more hyphens or underscores in the name
450 (i.e., there is no terminal-specific library). For example, if the
451 terminal name is @samp{xterm-256color} and there is no
452 @file{term/xterm-256color.el} library, Emacs tries to load
453 @file{term/xterm.el}. If necessary, the terminal library can evaluate
454 @code{(getenv "TERM")} to find the full name of the terminal type.
456 Your init file can prevent the loading of the terminal-specific
457 library by setting the variable @code{term-file-prefix} to @code{nil}.
459 You can also arrange to override some of the actions of the
460 terminal-specific library by using @code{tty-setup-hook}. This is
461 a normal hook that Emacs runs after initializing a new text terminal.
462 You could use this hook to define initializations for terminals that do not
463 have their own libraries. @xref{Hooks}.
465 @defvar term-file-prefix
466 @cindex @env{TERM} environment variable
467 If the value of this variable is non-@code{nil}, Emacs loads a
468 terminal-specific initialization file as follows:
471 (load (concat term-file-prefix (getenv "TERM")))
475 You may set the @code{term-file-prefix} variable to @code{nil} in your
476 init file if you do not wish to load the
477 terminal-initialization file.
479 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
482 @defvar tty-setup-hook
483 This variable is a normal hook that Emacs runs after initializing a
484 new text terminal. (This applies when Emacs starts up in non-windowed
485 mode, and when making a tty @command{emacsclient} connection.) The
486 hook runs after loading your init file (if applicable) and the
487 terminal-specific Lisp file, so you can use it to adjust the
488 definitions made by that file.
490 For a related feature, @pxref{Window Systems, window-setup-hook}.
493 @node Command-Line Arguments
494 @subsection Command-Line Arguments
495 @cindex command-line arguments
497 You can use command-line arguments to request various actions when
498 you start Emacs. Note that the recommended way of using Emacs is to
499 start it just once, after logging in, and then do all editing in the same
500 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
501 For this reason, you might not use command-line arguments very often;
502 nonetheless, they can be useful when invoking Emacs from session
503 scripts or debugging Emacs. This section describes how Emacs
504 processes command-line arguments.
507 This function parses the command line that Emacs was called with,
508 processes it, and (amongst other things) loads the user's init file and
509 displays the startup messages.
512 @defvar command-line-processed
513 The value of this variable is @code{t} once the command line has been
516 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
517 Emacs}), you may wish to set this variable to @code{nil} first in
518 order to cause the new dumped Emacs to process its new command-line
522 @defvar command-switch-alist
523 @cindex switches on command line
524 @cindex options on command line
525 @cindex command-line options
526 This variable is an alist of user-defined command-line options and
527 associated handler functions. By default it is empty, but you can
528 add elements if you wish.
530 A @dfn{command-line option} is an argument on the command line, which
537 The elements of the @code{command-switch-alist} look like this:
540 (@var{option} . @var{handler-function})
543 The @sc{car}, @var{option}, is a string, the name of a command-line
544 option (not including the initial hyphen). The @var{handler-function}
545 is called to handle @var{option}, and receives the option name as its
548 In some cases, the option is followed in the command line by an
549 argument. In these cases, the @var{handler-function} can find all the
550 remaining command-line arguments in the variable
551 @code{command-line-args-left} (see below). (The entire list of
552 command-line arguments is in @code{command-line-args}.)
554 The command-line arguments are parsed by the @code{command-line-1}
555 function in the @file{startup.el} file. See also @ref{Emacs
556 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
560 @defvar command-line-args
561 The value of this variable is the list of command-line arguments passed
565 @defvar command-line-args-left
567 The value of this variable is the list of command-line arguments that
568 have not yet been processed.
569 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
570 @c @code{argv} is an alias for this.
573 @defvar command-line-functions
574 This variable's value is a list of functions for handling an
575 unrecognized command-line argument. Each time the next argument to be
576 processed has no special meaning, the functions in this list are called,
577 in order of appearance, until one of them returns a non-@code{nil}
580 These functions are called with no arguments. They can access the
581 command-line argument under consideration through the variable
582 @code{argi}, which is bound temporarily at this point. The remaining
583 arguments (not including the current one) are in the variable
584 @code{command-line-args-left}.
586 When a function recognizes and processes the argument in @code{argi}, it
587 should return a non-@code{nil} value to say it has dealt with that
588 argument. If it has also dealt with some of the following arguments, it
589 can indicate that by deleting them from @code{command-line-args-left}.
591 If all of these functions return @code{nil}, then the argument is treated
592 as a file name to visit.
596 @section Getting Out of Emacs
597 @cindex exiting Emacs
599 There are two ways to get out of Emacs: you can kill the Emacs job,
600 which exits permanently, or you can suspend it, which permits you to
601 reenter the Emacs process later. (In a graphical environment, you can
602 of course simply switch to another application without doing anything
603 special to Emacs, then switch back to Emacs when you want.)
606 * Killing Emacs:: Exiting Emacs irreversibly.
607 * Suspending Emacs:: Exiting Emacs reversibly.
611 @subsection Killing Emacs
612 @cindex killing Emacs
614 Killing Emacs means ending the execution of the Emacs process.
615 If you started Emacs from a terminal, the parent process normally
616 resumes control. The low-level primitive for killing Emacs is
619 @deffn Command kill-emacs &optional exit-data
620 This command calls the hook @code{kill-emacs-hook}, then exits the
621 Emacs process and kills it.
623 If @var{exit-data} is an integer, that is used as the exit status of
624 the Emacs process. (This is useful primarily in batch operation; see
627 If @var{exit-data} is a string, its contents are stuffed into the
628 terminal input buffer so that the shell (or whatever program next reads
629 input) can read them.
635 @cindex operating system signal
636 The @code{kill-emacs} function is normally called via the
637 higher-level command @kbd{C-x C-c}
638 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
639 Emacs Manual}. It is also called automatically if Emacs receives a
640 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
641 controlling terminal is disconnected), or if it receives a
642 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
644 @defvar kill-emacs-hook
645 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
647 Because @code{kill-emacs} can be called in situations where user
648 interaction is impossible (e.g., when the terminal is disconnected),
649 functions on this hook should not attempt to interact with the user.
650 If you want to interact with the user when Emacs is shutting down, use
651 @code{kill-emacs-query-functions}, described below.
654 When Emacs is killed, all the information in the Emacs process,
655 aside from files that have been saved, is lost. Because killing Emacs
656 inadvertently can lose a lot of work, the
657 @code{save-buffers-kill-terminal} command queries for confirmation if
658 you have buffers that need saving or subprocesses that are running.
659 It also runs the abnormal hook @code{kill-emacs-query-functions}:
661 @defvar kill-emacs-query-functions
662 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
663 functions in this hook, after asking the standard questions and before
664 calling @code{kill-emacs}. The functions are called in order of
665 appearance, with no arguments. Each function can ask for additional
666 confirmation from the user. If any of them returns @code{nil},
667 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
668 the remaining functions in this hook. Calling @code{kill-emacs}
669 directly does not run this hook.
672 @node Suspending Emacs
673 @subsection Suspending Emacs
674 @cindex suspending Emacs
676 On text terminals, it is possible to @dfn{suspend Emacs}, which
677 means stopping Emacs temporarily and returning control to its superior
678 process, which is usually the shell. This allows you to resume
679 editing later in the same Emacs process, with the same buffers, the
680 same kill ring, the same undo history, and so on. To resume Emacs,
681 use the appropriate command in the parent shell---most likely
684 @cindex controlling terminal
685 Suspending works only on a terminal device from which the Emacs
686 session was started. We call that device the @dfn{controlling
687 terminal} of the session. Suspending is not allowed if the
688 controlling terminal is a graphical terminal. Suspending is usually
689 not relevant in graphical environments, since you can simply switch to
690 another application without doing anything special to Emacs.
692 @c FIXME? Are there any systems Emacs still supports that do not
695 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
696 not support suspension of jobs; on these systems, ``suspension''
697 actually creates a new shell temporarily as a subprocess of Emacs.
698 Then you would exit the shell to return to Emacs.
700 @deffn Command suspend-emacs &optional string
701 This function stops Emacs and returns control to the superior process.
702 If and when the superior process resumes Emacs, @code{suspend-emacs}
703 returns @code{nil} to its caller in Lisp.
705 This function works only on the controlling terminal of the Emacs
706 session; to relinquish control of other tty devices, use
707 @code{suspend-tty} (see below). If the Emacs session uses more than
708 one terminal, you must delete the frames on all the other terminals
709 before suspending Emacs, or this function signals an error.
710 @xref{Multiple Terminals}.
712 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
713 superior shell, to be read as terminal input.
714 @c FIXME? It seems to me that shell does echo STRING.
715 The characters in @var{string} are not echoed by the superior shell;
716 only the results appear.
718 Before suspending, @code{suspend-emacs} runs the normal hook
719 @code{suspend-hook}. After the user resumes Emacs,
720 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
723 The next redisplay after resumption will redraw the entire screen,
724 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
725 @xref{Refresh Screen}.
727 Here is an example of how you could use these hooks:
731 (add-hook 'suspend-hook
732 (lambda () (or (y-or-n-p "Really suspend? ")
733 (error "Suspend canceled"))))
735 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
738 @c The sit-for prevents the ``nil'' that suspend-emacs returns
739 @c hiding the message.
741 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
745 ---------- Buffer: Minibuffer ----------
746 Really suspend? @kbd{y}
747 ---------- Buffer: Minibuffer ----------
751 ---------- Parent Shell ----------
757 ---------- Echo Area ----------
762 @c FIXME? AFAICS, it is echoed.
763 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
764 is read and executed by the shell.
768 This variable is a normal hook that Emacs runs before suspending.
771 @defvar suspend-resume-hook
772 This variable is a normal hook that Emacs runs on resuming
776 @defun suspend-tty &optional tty
777 If @var{tty} specifies a terminal device used by Emacs, this function
778 relinquishes the device and restores it to its prior state. Frames
779 that used the device continue to exist, but are not updated and Emacs
780 doesn't read input from them. @var{tty} can be a terminal object, a
781 frame (meaning the terminal for that frame), or @code{nil} (meaning
782 the terminal for the selected frame). @xref{Multiple Terminals}.
784 If @var{tty} is already suspended, this function does nothing.
786 @vindex suspend-tty-functions
787 This function runs the hook @code{suspend-tty-functions}, passing the
788 terminal object as an argument to each function.
791 @defun resume-tty &optional tty
792 This function resumes the previously suspended terminal device
793 @var{tty}; where @var{tty} has the same possible values as it does
794 for @code{suspend-tty}.
796 @vindex resume-tty-functions
797 This function reopens the terminal device, re-initializes it, and
798 redraws it with that terminal's selected frame. It then runs the
799 hook @code{resume-tty-functions}, passing the terminal object as an
800 argument to each function.
802 If the same device is already used by another Emacs terminal, this
803 function signals an error. If @var{tty} is not suspended, this
804 function does nothing.
807 @defun controlling-tty-p &optional tty
808 This function returns non-@code{nil} if @var{tty} is the
809 controlling terminal of the Emacs session; @var{tty} can be a
810 terminal object, a frame (meaning the terminal for that frame), or
811 @code{nil} (meaning the terminal for the selected frame).
814 @deffn Command suspend-frame
815 This command @dfn{suspends} a frame. For GUI frames, it calls
816 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
817 text terminals, it calls either @code{suspend-emacs} or
818 @code{suspend-tty}, depending on whether the frame is displayed on the
819 controlling terminal device or not.
822 @node System Environment
823 @section Operating System Environment
824 @cindex operating system environment
826 Emacs provides access to variables in the operating system environment
827 through various functions. These variables include the name of the
828 system, the user's @acronym{UID}, and so on.
830 @defvar system-configuration
831 This variable holds the standard GNU configuration name for the
832 hardware/software configuration of your system, as a string. For
833 example, a typical value for a 64-bit GNU/Linux system is
834 @samp{"x86_64-unknown-linux-gnu"}.
837 @cindex system type and name
839 The value of this variable is a symbol indicating the type of operating
840 system Emacs is running on. The possible values are:
847 Berkeley BSD and its variants.
850 Cygwin, a Posix layer on top of MS-Windows.
856 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
859 A GNU/Linux system---that is, a variant GNU system, using the Linux
860 kernel. (These systems are the ones people often call ``Linux'', but
861 actually Linux is just the kernel, not the whole system.)
864 A GNU (glibc-based) system with a FreeBSD kernel.
867 Hewlett-Packard HPUX operating system.
870 Silicon Graphics Irix system.
873 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
874 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
880 Microsoft Windows NT, 9X and later. The value of @code{system-type}
881 is always @code{windows-nt}, e.g., even on Windows 7.
885 We do not wish to add new symbols to make finer distinctions unless it
886 is absolutely necessary! In fact, we hope to eliminate some of these
887 alternatives in the future. If you need to make a finer distinction
888 than @code{system-type} allows for, you can test
889 @code{system-configuration}, e.g., against a regexp.
893 This function returns the name of the machine you are running on, as a
897 The symbol @code{system-name} is a variable as well as a function. In
898 fact, the function returns whatever value the variable
899 @code{system-name} currently holds. Thus, you can set the variable
900 @code{system-name} in case Emacs is confused about the name of your
901 system. The variable is also useful for constructing frame titles
902 (@pxref{Frame Titles}).
904 @c FIXME seems like this section is not the best place for this option?
905 @defopt mail-host-address
906 If this variable is non-@code{nil}, it is used instead of
907 @code{system-name} for purposes of generating email addresses. For
908 example, it is used when constructing the default value of
909 @code{user-mail-address}. @xref{User Identification}. (Since this is
910 done when Emacs starts up, the value actually used is the one saved when
911 Emacs was dumped. @xref{Building Emacs}.)
912 @c FIXME sounds like should probably give this a :set-after and some
913 @c custom-initialize-delay voodoo.
916 @deffn Command getenv var &optional frame
917 @cindex environment variable access
918 This function returns the value of the environment variable @var{var},
919 as a string. @var{var} should be a string. If @var{var} is undefined
920 in the environment, @code{getenv} returns @code{nil}. It returns
921 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
922 variables and their values is kept in the variable @code{process-environment}.
931 The shell command @code{printenv} prints all or part of the environment:
936 PATH=/usr/local/bin:/usr/bin:/bin
948 @deffn Command setenv variable &optional value substitute
949 This command sets the value of the environment variable named
950 @var{variable} to @var{value}. @var{variable} should be a string.
951 Internally, Emacs Lisp can handle any string. However, normally
952 @var{variable} should be a valid shell identifier, that is, a sequence
953 of letters, digits and underscores, starting with a letter or
954 underscore. Otherwise, errors may occur if subprocesses of Emacs try
955 to access the value of @var{variable}. If @var{value} is omitted or
956 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
957 removes @var{variable} from the environment. Otherwise, @var{value}
960 @c FIXME: Document `substitute-env-vars'? --xfq
961 If the optional argument @var{substitute} is non-@code{nil}, Emacs
962 calls the function @code{substitute-env-vars} to expand any
963 environment variables in @var{value}.
965 @code{setenv} works by modifying @code{process-environment}; binding
966 that variable with @code{let} is also reasonable practice.
968 @code{setenv} returns the new value of @var{variable}, or @code{nil}
969 if it removed @var{variable} from the environment.
972 @defvar process-environment
973 This variable is a list of strings, each describing one environment
974 variable. The functions @code{getenv} and @code{setenv} work by means
980 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
991 If @code{process-environment} contains ``duplicate'' elements that
992 specify the same environment variable, the first of these elements
993 specifies the variable, and the other ``duplicates'' are ignored.
996 @defvar initial-environment
997 This variable holds the list of environment variables Emacs inherited
998 from its parent process when Emacs started.
1001 @defvar path-separator
1002 This variable holds a string that says which character separates
1003 directories in a search path (as found in an environment variable). Its
1004 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1007 @defun parse-colon-path path
1008 This function takes a search path string such as the value of
1009 the @env{PATH} environment variable, and splits it at the separators,
1010 returning a list of directory names. @code{nil} in this list means
1011 the current directory. Although the function's name says
1012 ``colon'', it actually uses the value of @code{path-separator}.
1015 (parse-colon-path ":/foo:/bar")
1016 @result{} (nil "/foo/" "/bar/")
1020 @defvar invocation-name
1021 This variable holds the program name under which Emacs was invoked. The
1022 value is a string, and does not include a directory name.
1025 @defvar invocation-directory
1026 This variable holds the directory from which the Emacs executable was
1027 invoked, or @code{nil} if that directory cannot be determined.
1030 @defvar installation-directory
1031 If non-@code{nil}, this is a directory within which to look for the
1032 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1033 it is normally @code{nil}. It is non-@code{nil}
1034 when Emacs can't find those directories in their standard installed
1035 locations, but can find them in a directory related somehow to the one
1036 containing the Emacs executable (i.e., @code{invocation-directory}).
1039 @defun load-average &optional use-float
1040 This function returns the current 1-minute, 5-minute, and 15-minute
1041 system load averages, in a list. The load average indicates the
1042 number of processes trying to run on the system.
1044 By default, the values are integers that are 100 times the system load
1045 averages, but if @var{use-float} is non-@code{nil}, then they are
1046 returned as floating point numbers without multiplying by 100.
1048 If it is impossible to obtain the load average, this function signals
1049 an error. On some platforms, access to load averages requires
1050 installing Emacs as setuid or setgid so that it can read kernel
1051 information, and that usually isn't advisable.
1052 @c FIXME which platforms are these? Are they still relevant?
1054 If the 1-minute load average is available, but the 5- or 15-minute
1055 averages are not, this function returns a shortened list containing
1056 the available averages.
1061 @result{} (169 48 36)
1065 @result{} (1.69 0.48 0.36)
1069 The shell command @code{uptime} returns similar information.
1073 This function returns the process @acronym{ID} of the Emacs process,
1077 @defvar tty-erase-char
1078 This variable holds the erase character that was selected
1079 in the system's terminal driver, before Emacs was started.
1080 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1081 @c The value is @code{nil} if Emacs is running under a window system.
1084 @node User Identification
1085 @section User Identification
1086 @cindex user identification
1088 @defvar init-file-user
1089 This variable says which user's init files should be used by
1090 Emacs---or @code{nil} if none. @code{""} stands for the user who
1091 originally logged in. The value reflects command-line options such as
1092 @samp{-q} or @samp{-u @var{user}}.
1094 Lisp packages that load files of customizations, or any other sort of
1095 user profile, should obey this variable in deciding where to find it.
1096 They should load the profile of the user name found in this variable.
1097 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q},
1098 @samp{-Q}, or @samp{-batch} option was used, then Lisp packages should
1099 not load any customization files or user profile.
1102 @defopt user-mail-address
1103 This holds the nominal email address of the user who is using Emacs.
1104 Emacs normally sets this variable to a default value after reading your
1105 init files, but not if you have already set it. So you can set the
1106 variable to some other value in your init file if you do not
1107 want to use the default value.
1110 @defun user-login-name &optional uid
1111 This function returns the name under which the user is logged in.
1112 It uses the environment variables @env{LOGNAME} or @env{USER} if
1113 either is set. Otherwise, the value is based on the effective
1114 @acronym{UID}, not the real @acronym{UID}.
1116 If you specify @var{uid} (a number), the result is the user name that
1117 corresponds to @var{uid}, or @code{nil} if there is no such user.
1120 @defun user-real-login-name
1121 This function returns the user name corresponding to Emacs's real
1122 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1123 environment variables @env{LOGNAME} and @env{USER}.
1126 @defun user-full-name &optional uid
1127 This function returns the full name of the logged-in user---or the value
1128 of the environment variable @env{NAME}, if that is set.
1130 If the Emacs process's user-id does not correspond to any known user (and
1131 provided @code{NAME} is not set), the result is @code{"unknown"}.
1133 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1134 or a string (a login name). Then @code{user-full-name} returns the full
1135 name corresponding to that user-id or login name. If you specify a
1136 user-id or login name that isn't defined, it returns @code{nil}.
1139 @vindex user-full-name
1140 @vindex user-real-login-name
1141 @vindex user-login-name
1142 The symbols @code{user-login-name}, @code{user-real-login-name} and
1143 @code{user-full-name} are variables as well as functions. The functions
1144 return the same values that the variables hold. These variables allow
1145 you to ``fake out'' Emacs by telling the functions what to return. The
1146 variables are also useful for constructing frame titles (@pxref{Frame
1150 @defun user-real-uid
1151 This function returns the real @acronym{UID} of the user.
1152 The value may be a floating point number, in the (unlikely) event that
1153 the UID is too large to fit in a Lisp integer.
1157 This function returns the effective @acronym{UID} of the user.
1158 The value may be a floating point number.
1163 This function returns the effective @acronym{GID} of the Emacs process.
1164 The value may be a floating point number.
1167 @defun group-real-gid
1168 This function returns the real @acronym{GID} of the Emacs process.
1169 The value may be a floating point number.
1173 This function returns a list of strings, listing the user names on the
1174 system. If Emacs cannot retrieve this information, the return value
1175 is a list containing just the value of @code{user-real-login-name}.
1179 @defun system-groups
1180 This function returns a list of strings, listing the names of user
1181 groups on the system. If Emacs cannot retrieve this information, the
1182 return value is @code{nil}.
1187 @section Time of Day
1189 This section explains how to determine the current time and time
1193 Most of these functions represent time as a list of either four
1194 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
1195 @var{picosec})}, or of three
1196 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1197 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1198 @var{sec-high} and @var{sec-low} give the high and low bits of an
1199 integer number of seconds. This integer number,
1201 @var{high} * 2**16 + @var{low},
1206 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1207 UTC) to the specified time. The third list element @var{microsec}, if
1208 present, gives the number of microseconds from the start of that
1209 second to the specified time.
1210 Similarly, the fourth list element @var{picosec}, if present, gives
1211 the number of picoseconds from the start of that microsecond to the
1214 The return value of @code{current-time} represents time using four
1215 integers, as do the timestamps in the return value of
1216 @code{file-attributes} (@pxref{Definition of
1217 file-attributes}). In function arguments, e.g., the @var{time-value}
1218 argument to @code{current-time-string}, two-, three-, and four-integer
1219 lists are accepted. You can convert times from the list
1220 representation into standard human-readable strings using
1221 @code{current-time-string}, or to other forms using the
1222 @code{decode-time} and @code{format-time-string} functions documented
1223 in the following sections.
1225 @defun current-time-string &optional time-value
1226 This function returns the current time and date as a human-readable
1227 string. The format does not vary for the initial part of the string,
1228 which contains the day of week, month, day of month, and time of day
1229 in that order: the number of characters used for these fields is
1230 always the same, so you can reliably
1231 use @code{substring} to extract them. You should count
1232 characters from the beginning of the string rather than from the end,
1233 as the year might not have exactly four digits, and additional
1234 information may some day be added at the end.
1236 The argument @var{time-value}, if given, specifies a time to format
1237 (represented as a list of integers), instead of the current time.
1241 (current-time-string)
1242 @result{} "Wed Oct 14 22:21:05 1987"
1248 This function returns the current time, represented as a list of four
1249 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1250 These integers have trailing zeros on systems that return time with
1251 lower resolutions. On all current machines @var{picosec} is a
1252 multiple of 1000, but this may change as higher-resolution clocks
1256 @defun float-time &optional time-value
1257 This function returns the current time as a floating-point number of
1258 seconds since the epoch. The optional argument @var{time-value}, if
1259 given, specifies a time (represented as a list of integers) to convert
1260 instead of the current time.
1262 @emph{Warning}: Since the result is floating point, it may not be
1263 exact. Do not use this function if precise time stamps are required.
1266 @defun current-time-zone &optional time-value
1267 @cindex time zone, current
1268 This function returns a list describing the time zone that the user is
1271 The value has the form @code{(@var{offset} @var{name})}. Here
1272 @var{offset} is an integer giving the number of seconds ahead of UTC
1273 (east of Greenwich). A negative value means west of Greenwich. The
1274 second element, @var{name}, is a string giving the name of the time
1275 zone. Both elements change when daylight saving time begins or ends;
1276 if the user has specified a time zone that does not use a seasonal time
1277 adjustment, then the value is constant through time.
1279 If the operating system doesn't supply all the information necessary to
1280 compute the value, the unknown elements of the list are @code{nil}.
1282 The argument @var{time-value}, if given, specifies a time (represented
1283 as a list of integers) to analyze instead of the current time.
1286 The current time zone is determined by the @env{TZ} environment
1287 variable. @xref{System Environment}. For example, you can tell Emacs
1288 to use universal time with @code{(setenv "TZ" "UTC0")}. If @env{TZ}
1289 is not in the environment, Emacs uses a platform-dependent default
1292 @node Time Conversion
1293 @section Time Conversion
1294 @cindex calendrical information
1296 These functions convert time values (lists of two to four integers,
1297 as explained in the previous section) into calendrical information and
1300 Many 32-bit operating systems are limited to time values containing
1301 32 bits of information; these systems typically handle only the times
1302 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
1303 However, 64-bit and some 32-bit operating systems have larger time
1304 values, and can represent times far in the past or future.
1306 Time conversion functions always use the Gregorian calendar, even
1307 for dates before the Gregorian calendar was introduced. Year numbers
1308 count the number of years since the year 1 B.C., and do not skip zero
1309 as traditional Gregorian years do; for example, the year number
1310 @minus{}37 represents the Gregorian year 38 B.C@.
1312 @defun decode-time &optional time
1313 This function converts a time value into calendrical information. If
1314 you don't specify @var{time}, it decodes the current time. The return
1315 value is a list of nine elements, as follows:
1318 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1321 Here is what the elements mean:
1325 The number of seconds past the minute, as an integer between 0 and 59.
1326 On some operating systems, this is 60 for leap seconds.
1328 The number of minutes past the hour, as an integer between 0 and 59.
1330 The hour of the day, as an integer between 0 and 23.
1332 The day of the month, as an integer between 1 and 31.
1334 The month of the year, as an integer between 1 and 12.
1336 The year, an integer typically greater than 1900.
1338 The day of week, as an integer between 0 and 6, where 0 stands for
1341 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1343 An integer indicating the time zone, as the number of seconds east of
1347 @strong{Common Lisp Note:} Common Lisp has different meanings for
1348 @var{dow} and @var{zone}.
1351 @defun encode-time seconds minutes hour day month year &optional zone
1352 This function is the inverse of @code{decode-time}. It converts seven
1353 items of calendrical data into a time value. For the meanings of the
1354 arguments, see the table above under @code{decode-time}.
1356 Year numbers less than 100 are not treated specially. If you want them
1357 to stand for years above 1900, or years above 2000, you must alter them
1358 yourself before you call @code{encode-time}.
1360 The optional argument @var{zone} defaults to the current time zone and
1361 its daylight saving time rules. If specified, it can be either a list
1362 (as you would get from @code{current-time-zone}), a string as in the
1363 @env{TZ} environment variable, @code{t} for Universal Time, or an
1364 integer (as you would get from @code{decode-time}). The specified
1365 zone is used without any further alteration for daylight saving time.
1367 If you pass more than seven arguments to @code{encode-time}, the first
1368 six are used as @var{seconds} through @var{year}, the last argument is
1369 used as @var{zone}, and the arguments in between are ignored. This
1370 feature makes it possible to use the elements of a list returned by
1371 @code{decode-time} as the arguments to @code{encode-time}, like this:
1374 (apply 'encode-time (decode-time @dots{}))
1377 You can perform simple date arithmetic by using out-of-range values for
1378 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1379 arguments; for example, day 0 means the day preceding the given month.
1381 The operating system puts limits on the range of possible time values;
1382 if you try to encode a time that is out of range, an error results.
1383 For instance, years before 1970 do not work on some systems;
1384 on others, years as early as 1901 do work.
1388 @section Parsing and Formatting Times
1390 These functions convert time values to text in a string, and vice versa.
1391 Time values are lists of two to four integers (@pxref{Time of Day}).
1393 @defun date-to-time string
1394 This function parses the time-string @var{string} and returns the
1395 corresponding time value.
1398 @defun format-time-string format-string &optional time universal
1399 This function converts @var{time} (or the current time, if @var{time} is
1400 omitted) to a string according to @var{format-string}. The argument
1401 @var{format-string} may contain @samp{%}-sequences which say to
1402 substitute parts of the time. Here is a table of what the
1403 @samp{%}-sequences mean:
1407 This stands for the abbreviated name of the day of week.
1409 This stands for the full name of the day of week.
1411 This stands for the abbreviated name of the month.
1413 This stands for the full name of the month.
1415 This is a synonym for @samp{%x %X}.
1417 This has a locale-specific meaning. In the default locale (named C), it
1418 is equivalent to @samp{%A, %B %e, %Y}.
1420 This stands for the day of month, zero-padded.
1422 This is a synonym for @samp{%m/%d/%y}.
1424 This stands for the day of month, blank-padded.
1426 This is a synonym for @samp{%b}.
1428 This stands for the hour (00--23).
1430 This stands for the hour (01--12).
1432 This stands for the day of the year (001--366).
1434 This stands for the hour (0--23), blank padded.
1436 This stands for the hour (1--12), blank padded.
1438 This stands for the month (01--12).
1440 This stands for the minute (00--59).
1442 This stands for a newline.
1444 This stands for the nanoseconds (000000000--999999999). To ask for
1445 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1446 microseconds, etc. Any excess digits are discarded, without rounding.
1448 This stands for @samp{AM} or @samp{PM}, as appropriate.
1450 This is a synonym for @samp{%I:%M:%S %p}.
1452 This is a synonym for @samp{%H:%M}.
1454 This stands for the seconds (00--59).
1456 This stands for a tab character.
1458 This is a synonym for @samp{%H:%M:%S}.
1460 This stands for the week of the year (01--52), assuming that weeks
1463 This stands for the numeric day of week (0--6). Sunday is day 0.
1465 This stands for the week of the year (01--52), assuming that weeks
1468 This has a locale-specific meaning. In the default locale (named
1469 @samp{C}), it is equivalent to @samp{%D}.
1471 This has a locale-specific meaning. In the default locale (named
1472 @samp{C}), it is equivalent to @samp{%T}.
1474 This stands for the year without century (00--99).
1476 This stands for the year with century.
1478 This stands for the time zone abbreviation (e.g., @samp{EST}).
1480 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1483 You can also specify the field width and type of padding for any of
1484 these @samp{%}-sequences. This works as in @code{printf}: you write
1485 the field width as digits in the middle of a @samp{%}-sequences. If you
1486 start the field width with @samp{0}, it means to pad with zeros. If you
1487 start the field width with @samp{_}, it means to pad with spaces.
1489 For example, @samp{%S} specifies the number of seconds since the minute;
1490 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1491 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1492 because that is how @samp{%S} normally pads to two positions.
1494 The characters @samp{E} and @samp{O} act as modifiers when used between
1495 @samp{%} and one of the letters in the table above. @samp{E} specifies
1496 using the current locale's ``alternative'' version of the date and time.
1497 In a Japanese locale, for example, @code{%Ex} might yield a date format
1498 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1499 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1502 @samp{O} means to use the current locale's ``alternative''
1503 representation of numbers, instead of the ordinary decimal digits. This
1504 is allowed with most letters, all the ones that output numbers.
1506 If @var{universal} is non-@code{nil}, that means to describe the time as
1507 Universal Time; @code{nil} means describe it using what Emacs believes
1508 is the local time zone (see @code{current-time-zone}).
1510 This function uses the C library function @code{strftime}
1511 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1512 Manual}) to do most of the work. In order to communicate with that
1513 function, it first encodes its argument using the coding system
1514 specified by @code{locale-coding-system} (@pxref{Locales}); after
1515 @code{strftime} returns the resulting string,
1516 @code{format-time-string} decodes the string using that same coding
1520 @defun seconds-to-time seconds
1521 This function converts @var{seconds}, a floating point number of
1522 seconds since the epoch, to a time value and returns that. To perform
1523 the inverse conversion, use @code{float-time} (@pxref{Time of Day}).
1526 @defun format-seconds format-string seconds
1527 This function converts its argument @var{seconds} into a string of
1528 years, days, hours, etc., according to @var{format-string}. The
1529 argument @var{format-string} may contain @samp{%}-sequences which
1530 control the conversion. Here is a table of what the
1531 @samp{%}-sequences mean:
1536 The integer number of 365-day years.
1539 The integer number of days.
1542 The integer number of hours.
1545 The integer number of minutes.
1548 The integer number of seconds.
1550 Non-printing control flag. When it is used, other specifiers must be
1551 given in the order of decreasing size, i.e., years before days, hours
1552 before minutes, etc. Nothing will be produced in the result string to
1553 the left of @samp{%z} until the first non-zero conversion is
1554 encountered. For example, the default format used by
1555 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1556 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1557 will always be produced, but years, days, hours, and minutes will only
1558 be shown if they are non-zero.
1560 Produces a literal @samp{%}.
1563 Upper-case format sequences produce the units in addition to the
1564 numbers, lower-case formats produce only the numbers.
1566 You can also specify the field width by following the @samp{%} with a
1567 number; shorter numbers will be padded with blanks. An optional
1568 period before the width requests zero-padding instead. For example,
1569 @code{"%.3Y"} might produce @code{"004 years"}.
1571 @emph{Warning:} This function works only with values of @var{seconds}
1572 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1573 most-positive-fixnum}).
1576 @node Processor Run Time
1577 @section Processor Run time
1578 @cindex processor run time
1579 @cindex Emacs process run time
1581 Emacs provides several functions and primitives that return time,
1582 both elapsed and processor time, used by the Emacs process.
1584 @deffn Command emacs-uptime &optional format
1585 @cindex uptime of Emacs
1586 This function returns a string representing the Emacs
1587 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1588 running. The string is formatted by @code{format-seconds} according
1589 to the optional argument @var{format}. For the available format
1590 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1591 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1594 When called interactively, it prints the uptime in the echo area.
1597 @defun get-internal-run-time
1598 This function returns the processor run time used by Emacs as a list
1599 of four integers: @code{(@var{high} @var{low} @var{microsec}
1600 @var{picosec})}, using the same format as @code{current-time}
1601 (@pxref{Time of Day}).
1603 Note that the time returned by this function excludes the time Emacs
1604 was not using the processor, and if the Emacs process has several
1605 threads, the returned value is the sum of the processor times used up
1606 by all Emacs threads.
1608 If the system doesn't provide a way to determine the processor run
1609 time, @code{get-internal-run-time} returns the same time as
1610 @code{current-time}.
1613 @deffn Command emacs-init-time
1614 This function returns the duration of the Emacs initialization
1615 (@pxref{Startup Summary}) in seconds, as a string. When called
1616 interactively, it prints the duration in the echo area.
1619 @node Time Calculations
1620 @section Time Calculations
1622 These functions perform calendrical computations using time values
1623 (the kind of list that @code{current-time} returns).
1625 @defun time-less-p t1 t2
1626 This returns @code{t} if time value @var{t1} is less than time value
1630 @defun time-subtract t1 t2
1631 This returns the time difference @var{t1} @minus{} @var{t2} between
1632 two time values, in the same format as a time value.
1635 @defun time-add t1 t2
1636 This returns the sum of two time values, one of which ought to
1637 represent a time difference rather than a point in time.
1638 Here is how to add a number of seconds to a time value:
1641 (time-add @var{time} (seconds-to-time @var{seconds}))
1645 @defun time-to-days time
1646 This function returns the number of days between the beginning of year
1650 @defun time-to-day-in-year time
1651 This returns the day number within the year corresponding to @var{time}.
1654 @defun date-leap-year-p year
1655 This function returns @code{t} if @var{year} is a leap year.
1659 @section Timers for Delayed Execution
1662 You can set up a @dfn{timer} to call a function at a specified
1663 future time or after a certain length of idleness.
1665 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1666 can run them only when Emacs could accept output from a subprocess:
1667 namely, while waiting or inside certain primitive functions such as
1668 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1669 timer's execution may be delayed if Emacs is busy. However, the time of
1670 execution is very precise if Emacs is idle.
1672 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1673 function, because quitting out of many timer functions can leave
1674 things in an inconsistent state. This is normally unproblematical
1675 because most timer functions don't do a lot of work. Indeed, for a
1676 timer to call a function that takes substantial time to run is likely
1677 to be annoying. If a timer function needs to allow quitting, it
1678 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1679 a timer function calls @code{accept-process-output} to receive output
1680 from an external process, that call should be wrapped inside
1681 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1684 It is usually a bad idea for timer functions to alter buffer
1685 contents. When they do, they usually should call @code{undo-boundary}
1686 both before and after changing the buffer, to separate the timer's
1687 changes from user commands' changes and prevent a single undo entry
1688 from growing to be quite large.
1690 Timer functions should also avoid calling functions that cause Emacs
1691 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1692 unpredictable effects, since other timers (or even the same timer) can
1693 run while waiting. If a timer function needs to perform an action
1694 after a certain time has elapsed, it can do this by scheduling a new
1697 If a timer function calls functions that can change the match data,
1698 it should save and restore the match data. @xref{Saving Match Data}.
1700 @deffn Command run-at-time time repeat function &rest args
1701 This sets up a timer that calls the function @var{function} with
1702 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1703 (integer or floating point), the timer is scheduled to run again every
1704 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1705 the timer runs only once.
1707 @var{time} may specify an absolute or a relative time.
1709 Absolute times may be specified using a string with a limited variety
1710 of formats, and are taken to be times @emph{today}, even if already in
1711 the past. The recognized forms are @samp{@var{xxxx}},
1712 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1713 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1714 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1715 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1716 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1717 to separate the hour and minute parts.
1719 To specify a relative time as a string, use numbers followed by units.
1724 denotes 1 minute from now.
1726 denotes 65 seconds from now.
1727 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1728 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1731 For relative time values, Emacs considers a month to be exactly thirty
1732 days, and a year to be exactly 365.25 days.
1734 Not all convenient formats are strings. If @var{time} is a number
1735 (integer or floating point), that specifies a relative time measured in
1736 seconds. The result of @code{encode-time} can also be used to specify
1737 an absolute value for @var{time}.
1739 In most cases, @var{repeat} has no effect on when @emph{first} call
1740 takes place---@var{time} alone specifies that. There is one exception:
1741 if @var{time} is @code{t}, then the timer runs whenever the time is a
1742 multiple of @var{repeat} seconds after the epoch. This is useful for
1743 functions like @code{display-time}.
1745 The function @code{run-at-time} returns a timer value that identifies
1746 the particular scheduled future action. You can use this value to call
1747 @code{cancel-timer} (see below).
1750 A repeating timer nominally ought to run every @var{repeat} seconds,
1751 but remember that any invocation of a timer can be late. Lateness of
1752 one repetition has no effect on the scheduled time of the next
1753 repetition. For instance, if Emacs is busy computing for long enough
1754 to cover three scheduled repetitions of the timer, and then starts to
1755 wait, it will immediately call the timer function three times in
1756 immediate succession (presuming no other timers trigger before or
1757 between them). If you want a timer to run again no less than @var{n}
1758 seconds after the last invocation, don't use the @var{repeat} argument.
1759 Instead, the timer function should explicitly reschedule the timer.
1761 @defopt timer-max-repeats
1762 This variable's value specifies the maximum number of times to repeat
1763 calling a timer function in a row, when many previously scheduled
1764 calls were unavoidably delayed.
1767 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1768 Execute @var{body}, but give up after @var{seconds} seconds. If
1769 @var{body} finishes before the time is up, @code{with-timeout} returns
1770 the value of the last form in @var{body}. If, however, the execution of
1771 @var{body} is cut short by the timeout, then @code{with-timeout}
1772 executes all the @var{timeout-forms} and returns the value of the last
1775 This macro works by setting a timer to run after @var{seconds} seconds. If
1776 @var{body} finishes before that time, it cancels the timer. If the
1777 timer actually runs, it terminates execution of @var{body}, then
1778 executes @var{timeout-forms}.
1780 Since timers can run within a Lisp program only when the program calls a
1781 primitive that can wait, @code{with-timeout} cannot stop executing
1782 @var{body} while it is in the midst of a computation---only when it
1783 calls one of those primitives. So use @code{with-timeout} only with a
1784 @var{body} that waits for input, not one that does a long computation.
1787 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1788 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1791 @defun cancel-timer timer
1792 This cancels the requested action for @var{timer}, which should be a
1793 timer---usually, one previously returned by @code{run-at-time} or
1794 @code{run-with-idle-timer}. This cancels the effect of that call to
1795 one of these functions; the arrival of the specified time will not
1796 cause anything special to happen.
1800 @section Idle Timers
1802 Here is how to set up a timer that runs when Emacs is idle for a
1803 certain length of time. Aside from how to set them up, idle timers
1804 work just like ordinary timers.
1806 @deffn Command run-with-idle-timer secs repeat function &rest args
1807 Set up a timer which runs the next time Emacs is idle for @var{secs}
1808 seconds. The value of @var{secs} may be an integer or a floating
1809 point number; a value of the type returned by @code{current-idle-time}
1812 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1813 Emacs remains idle for a long enough time. More often @var{repeat} is
1814 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1815 remains idle for @var{secs} seconds.
1817 The function @code{run-with-idle-timer} returns a timer value which you
1818 can use in calling @code{cancel-timer} (@pxref{Timers}).
1822 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1823 it remains idle until the user provides some input. If a timer is set
1824 for five seconds of idleness, it runs approximately five seconds after
1825 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1826 this timer will not run again as long as Emacs remains idle, because
1827 the duration of idleness will continue to increase and will not go
1828 down to five seconds again.
1830 Emacs can do various things while idle: garbage collect, autosave or
1831 handle data from a subprocess. But these interludes during idleness do
1832 not interfere with idle timers, because they do not reset the clock of
1833 idleness to zero. An idle timer set for 600 seconds will run when ten
1834 minutes have elapsed since the last user command was finished, even if
1835 subprocess output has been accepted thousands of times within those ten
1836 minutes, and even if there have been garbage collections and autosaves.
1838 When the user supplies input, Emacs becomes non-idle while executing the
1839 input. Then it becomes idle again, and all the idle timers that are
1840 set up to repeat will subsequently run another time, one by one.
1842 Do not write an idle timer function containing a loop which does a
1843 certain amount of processing each time around, and exits when
1844 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1845 natural but has two problems:
1849 It blocks out all process output (since Emacs accepts process output
1850 only while waiting).
1853 It blocks out any idle timers that ought to run during that time.
1857 Similarly, do not write an idle timer function that sets up another
1858 idle timer (including the same idle timer) with @var{secs} argument
1859 less than or equal to the current idleness time. Such a timer will
1860 run almost immediately, and continue running again and again, instead
1861 of waiting for the next time Emacs becomes idle. The correct approach
1862 is to reschedule with an appropriate increment of the current value of
1863 the idleness time, as described below.
1865 @defun current-idle-time
1866 If Emacs is idle, this function returns the length of time Emacs has
1867 been idle, as a list of four integers: @code{(@var{sec-high}
1868 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1869 @code{current-time} (@pxref{Time of Day}).
1871 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1872 This is a convenient way to test whether Emacs is idle.
1875 The main use of @code{current-idle-time} is when an idle timer
1876 function wants to ``take a break'' for a while. It can set up another
1877 idle timer to call the same function again, after a few seconds more
1878 idleness. Here's an example:
1881 (defvar my-resume-timer nil
1882 "Timer for `my-timer-function' to reschedule itself, or nil.")
1884 (defun my-timer-function ()
1885 ;; @r{If the user types a command while @code{my-resume-timer}}
1886 ;; @r{is active, the next time this function is called from}
1887 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1888 (when my-resume-timer
1889 (cancel-timer my-resume-timer))
1890 ...@var{do the work for a while}...
1891 (when @var{taking-a-break}
1892 (setq my-resume-timer
1893 (run-with-idle-timer
1894 ;; Compute an idle time @var{break-length}
1895 ;; more than the current value.
1896 (time-add (current-idle-time)
1897 (seconds-to-time @var{break-length}))
1899 'my-timer-function))))
1902 @node Terminal Input
1903 @section Terminal Input
1904 @cindex terminal input
1906 This section describes functions and variables for recording or
1907 manipulating terminal input. See @ref{Display}, for related
1911 * Input Modes:: Options for how input is processed.
1912 * Recording Input:: Saving histories of recent or all input events.
1916 @subsection Input Modes
1918 @cindex terminal input modes
1920 @defun set-input-mode interrupt flow meta &optional quit-char
1921 This function sets the mode for reading keyboard input. If
1922 @var{interrupt} is non-@code{nil}, then Emacs uses input interrupts.
1923 If it is @code{nil}, then it uses @sc{cbreak} mode. The default
1924 setting is system-dependent. Some systems always use @sc{cbreak} mode
1925 regardless of what is specified.
1927 When Emacs communicates directly with X, it ignores this argument and
1928 uses interrupts if that is the way it knows how to communicate.
1930 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1931 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1932 has no effect except in @sc{cbreak} mode.
1934 The argument @var{meta} controls support for input character codes
1935 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1936 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1937 Emacs disregards the 8th bit; this is necessary when the terminal uses
1938 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1939 Emacs uses all 8 bits of input unchanged. This is good for terminals
1940 that use 8-bit character sets.
1942 If @var{quit-char} is non-@code{nil}, it specifies the character to
1943 use for quitting. Normally this character is @kbd{C-g}.
1947 The @code{current-input-mode} function returns the input mode settings
1948 Emacs is currently using.
1950 @defun current-input-mode
1951 This function returns the current mode for reading keyboard input. It
1952 returns a list, corresponding to the arguments of @code{set-input-mode},
1953 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1957 is non-@code{nil} when Emacs is using interrupt-driven input. If
1958 @code{nil}, Emacs is using @sc{cbreak} mode.
1960 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1961 flow control for output to the terminal. This value is meaningful only
1962 when @var{interrupt} is @code{nil}.
1964 is @code{t} if Emacs treats the eighth bit of input characters as
1965 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1966 input character; any other value means Emacs uses all eight bits as the
1967 basic character code.
1969 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1973 @node Recording Input
1974 @subsection Recording Input
1975 @cindex recording input
1978 This function returns a vector containing the last 300 input events from
1979 the keyboard or mouse. All input events are included, whether or not
1980 they were used as parts of key sequences. Thus, you always get the last
1981 300 input events, not counting events generated by keyboard macros.
1982 (These are excluded because they are less interesting for debugging; it
1983 should be enough to see the events that invoked the macros.)
1985 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1986 causes this function to return an empty vector immediately afterward.
1989 @deffn Command open-dribble-file filename
1990 @cindex dribble file
1991 This function opens a @dfn{dribble file} named @var{filename}. When a
1992 dribble file is open, each input event from the keyboard or mouse (but
1993 not those from keyboard macros) is written in that file. A
1994 non-character event is expressed using its printed representation
1995 surrounded by @samp{<@dots{}>}.
1997 You close the dribble file by calling this function with an argument
2000 This function is normally used to record the input necessary to
2001 trigger an Emacs bug, for the sake of a bug report.
2005 (open-dribble-file "~/dribble")
2011 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2013 @node Terminal Output
2014 @section Terminal Output
2015 @cindex terminal output
2017 The terminal output functions send output to a text terminal, or keep
2018 track of output sent to the terminal. The variable @code{baud-rate}
2019 tells you what Emacs thinks is the output speed of the terminal.
2022 This variable's value is the output speed of the terminal, as far as
2023 Emacs knows. Setting this variable does not change the speed of actual
2024 data transmission, but the value is used for calculations such as
2027 It also affects decisions about whether to scroll part of the
2028 screen or repaint on text terminals. @xref{Forcing Redisplay},
2029 for the corresponding functionality on graphical terminals.
2031 The value is measured in baud.
2034 If you are running across a network, and different parts of the
2035 network work at different baud rates, the value returned by Emacs may be
2036 different from the value used by your local terminal. Some network
2037 protocols communicate the local terminal speed to the remote machine, so
2038 that Emacs and other programs can get the proper value, but others do
2039 not. If Emacs has the wrong value, it makes decisions that are less
2040 than optimal. To fix the problem, set @code{baud-rate}.
2042 @defun send-string-to-terminal string &optional terminal
2043 This function sends @var{string} to @var{terminal} without alteration.
2044 Control characters in @var{string} have terminal-dependent effects.
2045 This function operates only on text terminals. @var{terminal} may be
2046 a terminal object, a frame, or @code{nil} for the selected frame's
2047 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2048 @var{terminal} is @code{nil}.
2050 One use of this function is to define function keys on terminals that
2051 have downloadable function key definitions. For example, this is how (on
2052 certain terminals) to define function key 4 to move forward four
2053 characters (by transmitting the characters @kbd{C-u C-f} to the
2058 (send-string-to-terminal "\eF4\^U\^F")
2064 @deffn Command open-termscript filename
2065 @cindex termscript file
2066 This function is used to open a @dfn{termscript file} that will record
2067 all the characters sent by Emacs to the terminal. It returns
2068 @code{nil}. Termscript files are useful for investigating problems
2069 where Emacs garbles the screen, problems that are due to incorrect
2070 Termcap entries or to undesirable settings of terminal options more
2071 often than to actual Emacs bugs. Once you are certain which characters
2072 were actually output, you can determine reliably whether they correspond
2073 to the Termcap specifications in use.
2077 (open-termscript "../junk/termscript")
2082 You close the termscript file by calling this function with an
2083 argument of @code{nil}.
2085 See also @code{open-dribble-file} in @ref{Recording Input}.
2089 @section Sound Output
2092 To play sound using Emacs, use the function @code{play-sound}. Only
2093 certain systems are supported; if you call @code{play-sound} on a
2094 system which cannot really do the job, it gives an error.
2096 @c FIXME: Add indexes for Au and WAV? --xfq
2097 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2098 or Sun Audio format (@samp{.au}).
2100 @defun play-sound sound
2101 This function plays a specified sound. The argument, @var{sound}, has
2102 the form @code{(sound @var{properties}...)}, where the @var{properties}
2103 consist of alternating keywords (particular symbols recognized
2104 specially) and values corresponding to them.
2106 Here is a table of the keywords that are currently meaningful in
2107 @var{sound}, and their meanings:
2110 @item :file @var{file}
2111 This specifies the file containing the sound to play.
2112 If the file name is not absolute, it is expanded against
2113 the directory @code{data-directory}.
2115 @item :data @var{data}
2116 This specifies the sound to play without need to refer to a file. The
2117 value, @var{data}, should be a string containing the same bytes as a
2118 sound file. We recommend using a unibyte string.
2120 @item :volume @var{volume}
2121 This specifies how loud to play the sound. It should be a number in the
2122 range of 0 to 1. The default is to use whatever volume has been
2125 @item :device @var{device}
2126 This specifies the system device on which to play the sound, as a
2127 string. The default device is system-dependent.
2130 Before actually playing the sound, @code{play-sound}
2131 calls the functions in the list @code{play-sound-functions}.
2132 Each function is called with one argument, @var{sound}.
2135 @deffn Command play-sound-file file &optional volume device
2136 This function is an alternative interface to playing a sound @var{file}
2137 specifying an optional @var{volume} and @var{device}.
2140 @defvar play-sound-functions
2141 A list of functions to be called before playing a sound. Each function
2142 is called with one argument, a property list that describes the sound.
2146 @section Operating on X11 Keysyms
2149 To define system-specific X11 keysyms, set the variable
2150 @code{system-key-alist}.
2152 @defvar system-key-alist
2153 This variable's value should be an alist with one element for each
2154 system-specific keysym. Each element has the form @code{(@var{code}
2155 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2156 including the ``vendor specific'' bit,
2163 and @var{symbol} is the name for the function key.
2165 For example @code{(168 . mute-acute)} defines a system-specific key (used
2166 by HP X servers) whose numeric code is
2175 It is not crucial to exclude from the alist the keysyms of other X
2176 servers; those do no harm, as long as they don't conflict with the ones
2177 used by the X server actually in use.
2179 The variable is always local to the current terminal, and cannot be
2180 buffer-local. @xref{Multiple Terminals}.
2183 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2185 @defvar x-alt-keysym
2186 @defvarx x-meta-keysym
2187 @defvarx x-hyper-keysym
2188 @defvarx x-super-keysym
2189 The name of the keysym that should stand for the Alt modifier
2190 (respectively, for Meta, Hyper, and Super). For example, here is
2191 how to swap the Meta and Alt modifiers within Emacs:
2193 (setq x-alt-keysym 'meta)
2194 (setq x-meta-keysym 'alt)
2202 The command-line option @samp{-batch} causes Emacs to run
2203 noninteractively. In this mode, Emacs does not read commands from the
2204 terminal, it does not alter the terminal modes, and it does not expect
2205 to be outputting to an erasable screen. The idea is that you specify
2206 Lisp programs to run; when they are finished, Emacs should exit. The
2207 way to specify the programs to run is with @samp{-l @var{file}}, which
2208 loads the library named @var{file}, or @samp{-f @var{function}}, which
2209 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2211 Any Lisp program output that would normally go to the echo area,
2212 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2213 as the stream, goes instead to Emacs's standard error descriptor when
2214 in batch mode. Similarly, input that would normally come from the
2215 minibuffer is read from the standard input descriptor.
2216 Thus, Emacs behaves much like a noninteractive
2217 application program. (The echo area output that Emacs itself normally
2218 generates, such as command echoing, is suppressed entirely.)
2220 @defvar noninteractive
2221 This variable is non-@code{nil} when Emacs is running in batch mode.
2224 @node Session Management
2225 @section Session Management
2226 @cindex session manager
2228 Emacs supports the X Session Management Protocol, which is used to
2229 suspend and restart applications. In the X Window System, a program
2230 called the @dfn{session manager} is responsible for keeping track of
2231 the applications that are running. When the X server shuts down, the
2232 session manager asks applications to save their state, and delays the
2233 actual shutdown until they respond. An application can also cancel
2236 When the session manager restarts a suspended session, it directs
2237 these applications to individually reload their saved state. It does
2238 this by specifying a special command-line argument that says what
2239 saved session to restore. For Emacs, this argument is @samp{--smid
2242 @defvar emacs-save-session-functions
2243 @cindex session file
2244 Emacs supports saving state via a hook called
2245 @code{emacs-save-session-functions}. Emacs runs this hook when the
2246 session manager tells it that the window system is shutting down. The
2247 functions are called with no arguments, and with the current buffer
2248 set to a temporary buffer. Each function can use @code{insert} to add
2249 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2250 file, called the @dfn{session file}.
2252 @findex emacs-session-restore
2253 Subsequently, when the session manager restarts Emacs, it loads the
2254 session file automatically (@pxref{Loading}). This is performed by a
2255 function named @code{emacs-session-restore}, which is called during
2256 startup. @xref{Startup Summary}.
2258 If a function in @code{emacs-save-session-functions} returns
2259 non-@code{nil}, Emacs tells the session manager to cancel the
2263 Here is an example that just inserts some text into @file{*scratch*} when
2264 Emacs is restarted by the session manager.
2268 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2272 (defun save-yourself-test ()
2273 (insert "(save-current-buffer
2274 (switch-to-buffer \"*scratch*\")
2275 (insert \"I am restored\"))")
2280 @node Desktop Notifications
2281 @section Desktop Notifications
2282 @cindex desktop notifications
2283 @cindex notifications, on desktop
2285 Emacs is able to send @dfn{notifications} on systems that support the
2286 freedesktop.org Desktop Notifications Specification. In order to use
2287 this functionality, Emacs must have been compiled with D-Bus support,
2288 and the @code{notifications} library must be loaded. @xref{Top, ,
2289 D-Bus,dbus,D-Bus integration in Emacs}.
2291 @defun notifications-notify &rest params
2292 This function sends a notification to the desktop via D-Bus,
2293 consisting of the parameters specified by the @var{params} arguments.
2294 These arguments should consist of alternating keyword and value pairs.
2295 The supported keywords and values are as follows:
2298 @item :bus @var{bus}
2299 The D-Bus bus. This argument is needed only if a bus other than
2300 @code{:session} shall be used.
2302 @item :title @var{title}
2303 The notification title.
2305 @item :body @var{text}
2306 The notification body text. Depending on the implementation of the
2307 notification server, the text could contain HTML markups, like
2308 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2309 characters must be encoded, as @samp{"Contact
2310 <postmaster@@localhost>!"}.
2312 @item :app-name @var{name}
2313 The name of the application sending the notification. The default is
2314 @code{notifications-application-name}.
2316 @item :replaces-id @var{id}
2317 The notification @var{id} that this notification replaces. @var{id}
2318 must be the result of a previous @code{notifications-notify} call.
2320 @item :app-icon @var{icon-file}
2321 The file name of the notification icon. If set to @code{nil}, no icon
2322 is displayed. The default is @code{notifications-application-icon}.
2324 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2325 A list of actions to be applied. @var{key} and @var{title} are both
2326 strings. The default action (usually invoked by clicking the
2327 notification) should have a key named @samp{"default"}. The title can
2328 be anything, though implementations are free not to display it.
2330 @item :timeout @var{timeout}
2331 The timeout time in milliseconds since the display of the notification
2332 at which the notification should automatically close. If -1, the
2333 notification's expiration time is dependent on the notification
2334 server's settings, and may vary for the type of notification. If 0,
2335 the notification never expires. Default value is -1.
2337 @item :urgency @var{urgency}
2338 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2341 When this keyword is given, the @var{title} string of the actions is
2342 interpreted as icon name.
2344 @item :category @var{category}
2345 The type of notification this is, a string. See the
2346 @uref{http://developer.gnome.org/notification-spec/#categories,
2347 Desktop Notifications Specification} for a list of standard
2350 @item :desktop-entry @var{filename}
2351 This specifies the name of the desktop filename representing the
2352 calling program, like @samp{"emacs"}.
2354 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2355 This is a raw data image format that describes the width, height,
2356 rowstride, whether there is an alpha channel, bits per sample,
2357 channels and image data, respectively.
2359 @item :image-path @var{path}
2360 This is represented either as a URI (@samp{file://} is the only URI
2361 schema supported right now) or a name in a freedesktop.org-compliant
2362 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2364 @item :sound-file @var{filename}
2365 The path to a sound file to play when the notification pops up.
2367 @item :sound-name @var{name}
2368 A themable named sound from the freedesktop.org sound naming
2369 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2370 notification pops up. Similar to the icon name, only for sounds. An
2371 example would be @samp{"message-new-instant"}.
2373 @item :suppress-sound
2374 Causes the server to suppress playing any sounds, if it has that
2378 When set the server will not automatically remove the notification
2379 when an action has been invoked. The notification will remain resident
2380 in the server until it is explicitly removed by the user or by the
2381 sender. This hint is likely only useful when the server has the
2382 @code{:persistence} capability.
2385 When set the server will treat the notification as transient and
2386 by-pass the server's persistence capability, if it should exist.
2388 @item :x @var{position}
2389 @itemx :y @var{position}
2390 Specifies the X, Y location on the screen that the
2391 notification should point to. Both arguments must be used together.
2393 @item :on-action @var{function}
2394 Function to call when an action is invoked. The notification @var{id}
2395 and the @var{key} of the action are passed as arguments to the
2398 @item :on-close @var{function}
2399 Function to call when the notification has been closed by timeout or
2400 by the user. The function receive the notification @var{id} and the closing
2401 @var{reason} as arguments:
2404 @item @code{expired} if the notification has expired
2405 @item @code{dismissed} if the notification was dismissed by the user
2406 @item @code{close-notification} if the notification was closed by a call to
2407 @code{notifications-close-notification}
2408 @item @code{undefined} if the notification server hasn't provided a reason
2412 Which parameters are accepted by the notification server can be
2413 checked via @code{notifications-get-capabilities}.
2415 This function returns a notification id, an integer, which can be used
2416 to manipulate the notification item with
2417 @code{notifications-close-notification} or the @code{:replaces-id}
2418 argument of another @code{notifications-notify} call. For example:
2422 (defun my-on-action-function (id key)
2423 (message "Message %d, key \"%s\" pressed" id key))
2424 @result{} my-on-action-function
2428 (defun my-on-close-function (id reason)
2429 (message "Message %d, closed due to \"%s\"" id reason))
2430 @result{} my-on-close-function
2434 (notifications-notify
2436 :body "This is <b>important</b>."
2437 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2438 :on-action 'my-on-action-function
2439 :on-close 'my-on-close-function)
2444 A message window opens on the desktop. Press "I agree"
2445 @result{} Message 22, key "Confirm" pressed
2446 Message 22, closed due to "dismissed"
2451 @defun notifications-close-notification id &optional bus
2452 This function closes a notification with identifier @var{id}.
2453 @var{bus} can be a string denoting a D-Bus connection, the default is
2457 @defun notifications-get-capabilities &optional bus
2458 Returns the capabilities of the notification server, a list of
2459 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2460 default is @code{:session}. The following capabilities can be
2465 The server will provide the specified actions to the user.
2470 @item :body-hyperlinks
2471 The server supports hyperlinks in the notifications.
2474 The server supports images in the notifications.
2477 Supports markup in the body text.
2480 The server will render an animation of all the frames in a given image
2484 Supports display of exactly 1 frame of any given image array. This
2485 value is mutually exclusive with @code{:icon-multi}.
2488 The server supports persistence of notifications.
2491 The server supports sounds on notifications.
2494 Further vendor-specific caps start with @code{:x-vendor}, like
2495 @code{:x-gnome-foo-cap}.
2498 @defun notifications-get-server-information &optional bus
2499 Return information on the notification server, a list of strings.
2500 @var{bus} can be a string denoting a D-Bus connection, the default is
2501 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2502 @var{version} @var{spec-version})}.
2506 The product name of the server.
2509 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2512 The server's version number.
2515 The specification version the server is compliant with.
2518 If @var{SPEC_VERSION} is @code{nil}, the server supports a
2519 specification prior to @samp{"1.0"}.
2522 @node File Notifications
2523 @section Notifications on File Changes
2524 @cindex file notifications
2525 @cindex watch, for filesystem events
2527 Several operating systems support watching of filesystems for changes
2528 of files. If configured properly, Emacs links a respective library
2529 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2530 statically. These libraries enable watching of filesystems on the
2533 It is also possible to watch filesystems on remote machines,
2534 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2535 This does not depend on one of the libraries linked to Emacs.
2537 Since all these libraries emit different events on notified file
2538 changes, there is the Emacs library @code{filenotify} which provides a
2541 @defun file-notify-add-watch file flags callback
2542 Add a watch for filesystem events pertaining to @var{file}. This
2543 arranges for filesystem events pertaining to @var{file} to be reported
2546 The returned value is a descriptor for the added watch. Its type
2547 depends on the underlying library, it cannot be assumed to be an
2548 integer as in the example below. It should be used for comparison by
2551 If the @var{file} cannot be watched for some reason, this function
2552 signals a @code{file-notify-error} error.
2554 Sometimes, mounted filesystems cannot be watched for file changes.
2555 This is not detected by this function, a non-@code{nil} return value
2556 does not guarantee that changes on @var{file} will be notified.
2558 @var{flags} is a list of conditions to set what will be watched for.
2559 It can include the following symbols:
2563 watch for file changes
2564 @item attribute-change
2565 watch for file attribute changes, like permissions or modification
2569 If @var{file} is a directory, changes for all files in that directory
2570 will be notified. This does not work recursively.
2572 When any event happens, Emacs will call the @var{callback} function
2573 passing it a single argument @var{event}, which is of the form
2576 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2579 @var{descriptor} is the same object as the one returned by this
2580 function. @var{action} is the description of the event. It could be
2581 any one of the following symbols:
2585 @var{file} was created
2587 @var{file} was deleted
2589 @var{file} has changed
2591 @var{file} has been renamed to @var{file1}
2592 @item attribute-changed
2593 a @var{file} attribute was changed
2596 @var{file} and @var{file1} are the name of the file(s) whose event is
2597 being reported. For example:
2601 (require 'filenotify)
2602 @result{} filenotify
2606 (defun my-notify-callback (event)
2607 (message "Event %S" event))
2608 @result{} my-notify-callback
2612 (file-notify-add-watch
2613 "/tmp" '(change attribute-change) 'my-notify-callback)
2618 (write-region "foo" nil "/tmp/foo")
2619 @result{} Event (35025468 created "/tmp/.#foo")
2620 Event (35025468 created "/tmp/foo")
2621 Event (35025468 changed "/tmp/foo")
2622 Event (35025468 deleted "/tmp/.#foo")
2626 (write-region "bla" nil "/tmp/foo")
2627 @result{} Event (35025468 created "/tmp/.#foo")
2628 Event (35025468 changed "/tmp/foo") [2 times]
2629 Event (35025468 deleted "/tmp/.#foo")
2633 (set-file-modes "/tmp/foo" (default-file-modes))
2634 @result{} Event (35025468 attribute-changed "/tmp/foo")
2638 Whether the action @code{renamed} is returned, depends on the used
2639 watch library. It can be expected, when a directory is watched, and
2640 both @var{file} and @var{file1} belong to this directory. Otherwise,
2641 the actions @code{deleted} and @code{created} could be returned in a
2646 (rename-file "/tmp/foo" "/tmp/bla")
2647 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2651 (file-notify-add-watch
2652 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2657 (rename-file "/tmp/bla" "/var/tmp/bla")
2658 @result{} ;; gfilenotify
2659 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2661 @result{} ;; inotify
2662 Event (35025504 created "/var/tmp/bla")
2663 Event (35025468 deleted "/tmp/bla")
2668 @defun file-notify-rm-watch descriptor
2669 Removes an existing file watch specified by its @var{descriptor}.
2670 @var{descriptor} should be an object returned by
2671 @code{file-notify-add-watch}.
2674 @node Dynamic Libraries
2675 @section Dynamically Loaded Libraries
2676 @cindex dynamic libraries
2678 A @dfn{dynamically loaded library} is a library that is loaded on
2679 demand, when its facilities are first needed. Emacs supports such
2680 on-demand loading of support libraries for some of its features.
2682 @defvar dynamic-library-alist
2683 This is an alist of dynamic libraries and external library files
2686 Each element is a list of the form
2687 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2688 a symbol representing a supported external library, and the rest are
2689 strings giving alternate filenames for that library.
2691 Emacs tries to load the library from the files in the order they
2692 appear in the list; if none is found, the Emacs session won't have
2693 access to that library, and the features it provides will be
2696 Image support on some platforms uses this facility. Here's an example
2697 of setting this variable for supporting images on MS-Windows:
2700 (setq dynamic-library-alist
2701 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2702 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2703 "libpng13d.dll" "libpng13.dll")
2704 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2706 (tiff "libtiff3.dll" "libtiff.dll")
2707 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2708 (svg "librsvg-2-2.dll")
2709 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2710 (glib "libglib-2.0-0.dll")
2711 (gobject "libgobject-2.0-0.dll")))
2714 Note that image types @code{pbm} and @code{xbm} do not need entries in
2715 this variable because they do not depend on external libraries and are
2716 always available in Emacs.
2718 Also note that this variable is not meant to be a generic facility for
2719 accessing external libraries; only those already known by Emacs can
2720 be loaded through it.
2722 This variable is ignored if the given @var{library} is statically