2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2013 Free Software
5 @c See the file elisp.texi for copying conditions.
7 @chapter Operating System Interface
9 This chapter is about starting and getting out of Emacs, access to
10 values in the operating system environment, and terminal input, output.
12 @xref{Building Emacs}, for related information. @xref{Display}, for
13 additional operating system status information pertaining to the
14 terminal and the screen.
17 * Starting Up:: Customizing Emacs startup processing.
18 * Getting Out:: How exiting works (permanent or temporary).
19 * System Environment:: Distinguish the name and kind of system.
20 * User Identification:: Finding the name and user id of the user.
21 * Time of Day:: Getting the current time.
22 * Time Conversion:: Converting a time from numeric form to
23 calendrical data and vice versa.
24 * Time Parsing:: Converting a time from numeric form to text
26 * Processor Run Time:: Getting the run time used by Emacs.
27 * Time Calculations:: Adding, subtracting, comparing times, etc.
28 * Timers:: Setting a timer to call a function at a certain time.
29 * Idle Timers:: Setting a timer to call a function when Emacs has
30 been idle for a certain length of time.
31 * Terminal Input:: Accessing and recording terminal input.
32 * Terminal Output:: Controlling and recording terminal output.
33 * Sound Output:: Playing sounds on the computer's speaker.
34 * X11 Keysyms:: Operating on key symbols for X Windows.
35 * Batch Mode:: Running Emacs without terminal interaction.
36 * Session Management:: Saving and restoring state with X Session Management.
37 * Desktop Notifications:: Desktop notifications.
38 * File Notifications:: File notifications.
39 * Dynamic Libraries:: On-demand loading of support libraries.
43 @section Starting Up Emacs
45 This section describes what Emacs does when it is started, and how you
46 can customize these actions.
49 * Startup Summary:: Sequence of actions Emacs performs at startup.
50 * Init File:: Details on reading the init file.
51 * Terminal-Specific:: How the terminal-specific Lisp file is read.
52 * Command-Line Arguments:: How command-line arguments are processed,
53 and how you can customize them.
57 @subsection Summary: Sequence of Actions at Startup
58 @cindex initialization of Emacs
59 @cindex startup of Emacs
60 @cindex @file{startup.el}
62 When Emacs is started up, it performs the following operations
63 (see @code{normal-top-level} in @file{startup.el}):
67 It adds subdirectories to @code{load-path}, by running the file named
68 @file{subdirs.el} in each directory in the list. Normally, this file
69 adds the directory's subdirectories to the list, and those are scanned
70 in their turn. The files @file{subdirs.el} are normally generated
71 automatically when Emacs is installed.
74 If the library @file{leim-list.el} exists, Emacs loads it. This
75 optional library is intended for registering input methods; Emacs
76 looks for it in @code{load-path} (@pxref{Library Search}), skipping
77 those directories containing the standard Emacs libraries (since
78 @file{leim-list.el} should not exist in those directories).
80 @vindex before-init-time
82 It sets the variable @code{before-init-time} to the value of
83 @code{current-time} (@pxref{Time of Day}). It also sets
84 @code{after-init-time} to @code{nil}, which signals to Lisp programs
85 that Emacs is being initialized.
87 @c set-locale-environment
89 It sets the language environment and the terminal coding system,
90 if requested by environment variables such as @env{LANG}.
93 It does some basic parsing of the command-line arguments.
95 @vindex initial-window-system@r{, and startup}
96 @vindex window-system-initialization-alist
98 If not running in batch mode, it initializes the window system that
99 the variable @code{initial-window-system} specifies (@pxref{Window
100 Systems, initial-window-system}). The initialization function for
101 each supported window system is specified by
102 @code{window-system-initialization-alist}. If the value
103 of @code{initial-window-system} is @var{windowsystem}, then the
104 appropriate initialization function is defined in the file
105 @file{term/@var{windowsystem}-win.el}. This file should have been
106 compiled into the Emacs executable when it was built.
109 It runs the normal hook @code{before-init-hook}.
112 If appropriate, it creates a graphical frame. This is not done if the
113 options @samp{--batch} or @samp{--daemon} were specified.
116 It initializes the initial frame's faces, and sets up the menu bar
117 and tool bar if needed. If graphical frames are supported, it sets up
118 the tool bar even if the current frame is not a graphical one, since a
119 graphical frame may be created later on.
122 It use @code{custom-reevaluate-setting} to re-initialize the members
123 of the list @code{custom-delayed-init-variables}. These are any
124 pre-loaded user options whose default value depends on the run-time,
125 rather than build-time, context.
126 @xref{Building Emacs, custom-initialize-delay}.
129 @c It registers the colors available for tty frames.
132 It loads the library @file{site-start}, if it exists. This is not
133 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
134 @cindex @file{site-start.el}
137 It loads your init file (@pxref{Init File}). This is not done if the
138 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
139 the @samp{-u} option was specified, Emacs looks for the init file in
140 that user's home directory instead.
143 It loads the library @file{default}, if it exists. This is not done
144 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
145 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
146 @cindex @file{default.el}
149 It loads your abbrevs from the file specified by
150 @code{abbrev-file-name}, if that file exists and can be read
151 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
152 option @samp{--batch} was specified.
155 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
156 function @code{package-initialize} to activate any optional Emacs Lisp
157 package that has been installed. @xref{Packaging Basics}.
159 @vindex after-init-time
161 It sets the variable @code{after-init-time} to the value of
162 @code{current-time}. This variable was set to @code{nil} earlier;
163 setting it to the current time signals that the initialization phase
164 is over, and, together with @code{before-init-time}, provides the
165 measurement of how long it took.
168 It runs the normal hook @code{after-init-hook}.
171 If the buffer @file{*scratch*} exists and is still in Fundamental mode
172 (as it should be by default), it sets its major mode according to
173 @code{initial-major-mode}.
176 If started on a text terminal, it loads the terminal-specific
177 Lisp library, which is specified by the variable
178 @code{term-file-prefix} (@pxref{Terminal-Specific}). This is not done
179 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
181 @c Now command-line calls command-line-1.
184 It displays the initial echo area message, unless you have suppressed
185 that with @code{inhibit-startup-echo-area-message}.
188 It processes any command-line options that were not handled earlier.
190 @c This next one is back in command-line, but the remaining bits of
191 @c command-line-1 are not done if noninteractive.
193 It now exits if the option @code{--batch} was specified.
196 If @code{initial-buffer-choice} is a string, it visits the file with
197 that name. If the @file{*scratch*} buffer exists and is
198 empty, it inserts @code{initial-scratch-message} into that buffer.
200 @c To make things nice and confusing, the next three items can be
201 @c called from two places. If displaying a startup screen, they are
202 @c called in command-line-1 before the startup screen is shown.
203 @c inhibit-startup-hooks is then set and window-setup-hook set to nil.
204 @c If not displaying a startup screen, they are are called in
206 @c FIXME? So it seems they can be called before or after the
207 @c daemon/session restore step?
210 It runs @code{emacs-startup-hook} and then @code{term-setup-hook}.
213 It calls @code{frame-notice-user-settings}, which modifies the
214 parameters of the selected frame according to whatever the init files
218 It runs @code{window-setup-hook}. @xref{Window Systems}.
221 @cindex startup screen
222 It displays the @dfn{startup screen}, which is a special buffer that
223 contains information about copyleft and basic Emacs usage. This is
224 not done if @code{inhibit-startup-screen} or @code{initial-buffer-choice}
225 are non-@code{nil}, or if the @samp{--no-splash} or @samp{-Q} command-line
226 options were specified.
228 @c End of command-line-1.
230 @c Back to command-line from command-line-1.
232 @c This is the point at which we actually exit in batch mode, but the
233 @c last few bits of command-line-1 are not done in batch mode.
236 If the option @code{--daemon} was specified, it calls
237 @code{server-start} and detaches from the controlling terminal.
238 @xref{Emacs Server,,, emacs, The GNU Emacs Manual}.
241 If started by the X session manager, it calls
242 @code{emacs-session-restore} passing it as argument the ID of the
243 previous session. @xref{Session Management}.
245 @c End of command-line.
247 @c Back to normal-top-level from command-line.
252 The following options affect some aspects of the startup sequence.
254 @defopt inhibit-startup-screen
255 This variable, if non-@code{nil}, inhibits the startup screen. In
256 that case, Emacs typically displays the @file{*scratch*} buffer; but
257 see @code{initial-buffer-choice}, below.
259 Do not set this variable in the init file of a new user, or in a way
260 that affects more than one user, as that would prevent new users from
261 receiving information about copyleft and basic Emacs usage.
263 @vindex inhibit-startup-message
264 @vindex inhibit-splash-screen
265 @code{inhibit-startup-message} and @code{inhibit-splash-screen} are
266 aliases for this variable.
269 @defopt initial-buffer-choice
270 If non-@code{nil}, this variable is a string that specifies a file or
271 directory for Emacs to display after starting up, instead of the
274 @c I do not think this should be mentioned. AFAICS it is just a dodge
275 @c around inhibit-startup-screen not being settable on a site-wide basis.
276 If its value is @code{t}, Emacs displays the @file{*scratch*} buffer.
280 @defopt inhibit-startup-echo-area-message
281 This variable controls the display of the startup echo area message.
282 You can suppress the startup echo area message by adding text with this
283 form to your init file:
286 (setq inhibit-startup-echo-area-message
287 "@var{your-login-name}")
290 Emacs explicitly checks for an expression as shown above in your init
291 file; your login name must appear in the expression as a Lisp string
292 constant. You can also use the Customize interface. Other methods of
293 setting @code{inhibit-startup-echo-area-message} to the same value do
294 not inhibit the startup message. This way, you can easily inhibit the
295 message for yourself if you wish, but thoughtless copying of your init
296 file will not inhibit the message for someone else.
299 @defopt initial-scratch-message
300 This variable, if non-@code{nil}, should be a string, which is
301 inserted into the @file{*scratch*} buffer when Emacs starts up. If it
302 is @code{nil}, the @file{*scratch*} buffer is empty.
306 The following command-line options affect some aspects of the startup
307 sequence. @xref{Initial Options,,, emacs, The GNU Emacs Manual}.
311 Do not display a splash screen.
314 Run without an interactive terminal. @xref{Batch Mode}.
317 Do not initialize any display; just start a server in the background.
321 Do not load either the init file, or the @file{default} library.
324 Do not load the @file{site-start} library.
328 Equivalent to @samp{-q --no-site-file --no-splash}.
329 @c and --no-site-lisp, but let's not mention that here.
334 @subsection The Init File
336 @cindex @file{.emacs}
337 @cindex @file{init.el}
339 When you start Emacs, it normally attempts to load your @dfn{init
340 file}. This is either a file named @file{.emacs} or @file{.emacs.el}
341 in your home directory, or a file named @file{init.el} in a
342 subdirectory named @file{.emacs.d} in your home directory.
344 Whichever place you use, you can also compile the file (@pxref{Byte
345 Compilation}); then the actual file loaded will be @file{.emacs.elc}
349 The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
350 control whether and where to find the init file; @samp{-q} (and the
351 stronger @samp{-Q}) says not to load an init file, while @samp{-u
352 @var{user}} says to load @var{user}'s init file instead of yours.
353 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
354 option is specified, Emacs uses the @env{LOGNAME} environment
355 variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
356 systems) variable, to find your home directory and thus your init
357 file; this way, even if you have su'd, Emacs still loads your own init
358 file. If those environment variables are absent, though, Emacs uses
359 your user-id to find your home directory.
361 @cindex default init file
362 An Emacs installation may have a @dfn{default init file}, which is a
363 Lisp library named @file{default.el}. Emacs finds this file through
364 the standard search path for libraries (@pxref{How Programs Do
365 Loading}). The Emacs distribution does not come with this file; it is
366 intended for local customizations. If the default init file exists,
367 it is loaded whenever you start Emacs. But your own personal init
368 file, if any, is loaded first; if it sets @code{inhibit-default-init}
369 to a non-@code{nil} value, then Emacs does not subsequently load the
370 @file{default.el} file. In batch mode, or if you specify @samp{-q}
371 (or @samp{-Q}), Emacs loads neither your personal init file nor
372 the default init file.
374 Another file for site-customization is @file{site-start.el}. Emacs
375 loads this @emph{before} the user's init file. You can inhibit the
376 loading of this file with the option @samp{--no-site-file}.
378 @defopt site-run-file
379 This variable specifies the site-customization file to load before the
380 user's init file. Its normal value is @code{"site-start"}. The only
381 way you can change it with real effect is to do so before dumping
383 @c So why even mention it here. I imagine it is almost never changed.
386 @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
387 examples of how to make various commonly desired customizations in your
390 @defopt inhibit-default-init
391 If this variable is non-@code{nil}, it prevents Emacs from loading the
392 default initialization library file. The default value is @code{nil}.
395 @defvar before-init-hook
396 This normal hook is run, once, just before loading all the init files
397 (@file{site-start.el}, your init file, and @file{default.el}).
398 (The only way to change it with real effect is before dumping Emacs.)
401 @defvar after-init-hook
402 This normal hook is run, once, just after loading all the init files
403 (@file{site-start.el}, your init file, and @file{default.el}),
404 before loading the terminal-specific library (if started on a text
405 terminal) and processing the command-line action arguments.
408 @defvar emacs-startup-hook
409 This normal hook is run, once, just after handling the command line
410 arguments, just before @code{term-setup-hook}. In batch mode, Emacs
411 does not run either of these hooks.
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
445 When the name of the terminal type contains a hyphen or underscore, and no library
446 is found whose name is identical to the terminal's name, Emacs strips
447 from the terminal's name the last hyphen or 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
457 terminal-specific library by setting the variable
458 @code{term-file-prefix} to @code{nil}. This feature is useful when
459 experimenting with your own peculiar customizations.
461 You can also arrange to override some of the actions of the
462 terminal-specific library by setting the variable
463 @code{term-setup-hook}. This is a normal hook that Emacs runs
464 at the end of its initialization, after loading both
465 your init file and any terminal-specific libraries. You could
466 use this hook to define initializations for terminals that do not
467 have their own libraries. @xref{Hooks}.
469 @defvar term-file-prefix
470 @cindex @env{TERM} environment variable
471 If the value of this variable is non-@code{nil}, Emacs loads a
472 terminal-specific initialization file as follows:
475 (load (concat term-file-prefix (getenv "TERM")))
479 You may set the @code{term-file-prefix} variable to @code{nil} in your
480 init file if you do not wish to load the
481 terminal-initialization file.
483 On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
486 @defvar term-setup-hook
487 This variable is a normal hook that Emacs runs after loading your
488 init file, the default initialization file (if any) and the
489 terminal-specific Lisp file.
491 You can use @code{term-setup-hook} to override the definitions made by a
492 terminal-specific file.
494 For a related feature, @pxref{Window Systems, window-setup-hook}.
497 @node Command-Line Arguments
498 @subsection Command-Line Arguments
499 @cindex command-line arguments
501 You can use command-line arguments to request various actions when
502 you start Emacs. Note that the recommended way of using Emacs is to
503 start it just once, after logging in, and then do all editing in the same
504 Emacs session (@pxref{Entering Emacs,,, emacs, The GNU Emacs Manual}).
505 For this reason, you might not use command-line arguments very often;
506 nonetheless, they can be useful when invoking Emacs from session
507 scripts or debugging Emacs. This section describes how Emacs
508 processes command-line arguments.
511 This function parses the command line that Emacs was called with,
512 processes it, and (amongst other things) loads the user's init file and
513 displays the startup messages.
516 @defvar command-line-processed
517 The value of this variable is @code{t} once the command line has been
520 If you redump Emacs by calling @code{dump-emacs} (@pxref{Building
521 Emacs}), you may wish to set this variable to @code{nil} first in
522 order to cause the new dumped Emacs to process its new command-line
526 @defvar command-switch-alist
527 @cindex switches on command line
528 @cindex options on command line
529 @cindex command-line options
530 This variable is an alist of user-defined command-line options and
531 associated handler functions. By default it is empty, but you can
532 add elements if you wish.
534 A @dfn{command-line option} is an argument on the command line, which
541 The elements of the @code{command-switch-alist} look like this:
544 (@var{option} . @var{handler-function})
547 The @sc{car}, @var{option}, is a string, the name of a command-line
548 option (not including the initial hyphen). The @var{handler-function}
549 is called to handle @var{option}, and receives the option name as its
552 In some cases, the option is followed in the command line by an
553 argument. In these cases, the @var{handler-function} can find all the
554 remaining command-line arguments in the variable
555 @code{command-line-args-left}. (The entire list of command-line
556 arguments is in @code{command-line-args}.)
558 The command-line arguments are parsed by the @code{command-line-1}
559 function in the @file{startup.el} file. See also @ref{Emacs
560 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
564 @defvar command-line-args
565 The value of this variable is the list of command-line arguments passed
569 @defvar command-line-args-left
571 The value of this variable is the list of command-line arguments that
572 have not yet been processed.
573 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
574 @c @code{argv} is an alias for this.
577 @defvar command-line-functions
578 This variable's value is a list of functions for handling an
579 unrecognized command-line argument. Each time the next argument to be
580 processed has no special meaning, the functions in this list are called,
581 in order of appearance, until one of them returns a non-@code{nil}
584 These functions are called with no arguments. They can access the
585 command-line argument under consideration through the variable
586 @code{argi}, which is bound temporarily at this point. The remaining
587 arguments (not including the current one) are in the variable
588 @code{command-line-args-left}.
590 When a function recognizes and processes the argument in @code{argi}, it
591 should return a non-@code{nil} value to say it has dealt with that
592 argument. If it has also dealt with some of the following arguments, it
593 can indicate that by deleting them from @code{command-line-args-left}.
595 If all of these functions return @code{nil}, then the argument is treated
596 as a file name to visit.
600 @section Getting Out of Emacs
601 @cindex exiting Emacs
603 There are two ways to get out of Emacs: you can kill the Emacs job,
604 which exits permanently, or you can suspend it, which permits you to
605 reenter the Emacs process later. (In a graphical environment, you can
606 of course simply switch to another application without doing anything
607 special to Emacs, then switch back to Emacs when you want.)
610 * Killing Emacs:: Exiting Emacs irreversibly.
611 * Suspending Emacs:: Exiting Emacs reversibly.
615 @subsection Killing Emacs
616 @cindex killing Emacs
618 Killing Emacs means ending the execution of the Emacs process.
619 If you started Emacs from a terminal, the parent process normally
620 resumes control. The low-level primitive for killing Emacs is
623 @deffn Command kill-emacs &optional exit-data
624 This command calls the hook @code{kill-emacs-hook}, then exits the
625 Emacs process and kills it.
627 If @var{exit-data} is an integer, that is used as the exit status of
628 the Emacs process. (This is useful primarily in batch operation; see
631 If @var{exit-data} is a string, its contents are stuffed into the
632 terminal input buffer so that the shell (or whatever program next reads
633 input) can read them.
639 @cindex operating system signal
640 The @code{kill-emacs} function is normally called via the
641 higher-level command @kbd{C-x C-c}
642 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
643 Emacs Manual}. It is also called automatically if Emacs receives a
644 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
645 controlling terminal is disconnected), or if it receives a
646 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
648 @defvar kill-emacs-hook
649 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
651 Because @code{kill-emacs} can be called in situations where user
652 interaction is impossible (e.g., when the terminal is disconnected),
653 functions on this hook should not attempt to interact with the user.
654 If you want to interact with the user when Emacs is shutting down, use
655 @code{kill-emacs-query-functions}, described below.
658 When Emacs is killed, all the information in the Emacs process,
659 aside from files that have been saved, is lost. Because killing Emacs
660 inadvertently can lose a lot of work, the
661 @code{save-buffers-kill-terminal} command queries for confirmation if
662 you have buffers that need saving or subprocesses that are running.
663 It also runs the abnormal hook @code{kill-emacs-query-functions}:
665 @defvar kill-emacs-query-functions
666 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
667 functions in this hook, after asking the standard questions and before
668 calling @code{kill-emacs}. The functions are called in order of
669 appearance, with no arguments. Each function can ask for additional
670 confirmation from the user. If any of them returns @code{nil},
671 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
672 the remaining functions in this hook. Calling @code{kill-emacs}
673 directly does not run this hook.
676 @node Suspending Emacs
677 @subsection Suspending Emacs
678 @cindex suspending Emacs
680 On text terminals, it is possible to @dfn{suspend Emacs}, which
681 means stopping Emacs temporarily and returning control to its superior
682 process, which is usually the shell. This allows you to resume
683 editing later in the same Emacs process, with the same buffers, the
684 same kill ring, the same undo history, and so on. To resume Emacs,
685 use the appropriate command in the parent shell---most likely
688 @cindex controlling terminal
689 Suspending works only on a terminal device from which the Emacs
690 session was started. We call that device the @dfn{controlling
691 terminal} of the session. Suspending is not allowed if the
692 controlling terminal is a graphical terminal. Suspending is usually
693 not relevant in graphical environments, since you can simply switch to
694 another application without doing anything special to Emacs.
696 @c FIXME? Are there any systems Emacs still supports that do not
699 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
700 not support suspension of jobs; on these systems, ``suspension''
701 actually creates a new shell temporarily as a subprocess of Emacs.
702 Then you would exit the shell to return to Emacs.
704 @deffn Command suspend-emacs &optional string
705 This function stops Emacs and returns control to the superior process.
706 If and when the superior process resumes Emacs, @code{suspend-emacs}
707 returns @code{nil} to its caller in Lisp.
709 This function works only on the controlling terminal of the Emacs
710 session; to relinquish control of other tty devices, use
711 @code{suspend-tty} (see below). If the Emacs session uses more than
712 one terminal, you must delete the frames on all the other terminals
713 before suspending Emacs, or this function signals an error.
714 @xref{Multiple Terminals}.
716 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
717 superior shell, to be read as terminal input.
718 @c FIXME? It seems to me that shell does echo STRING.
719 The characters in @var{string} are not echoed by the superior shell;
720 only the results appear.
722 Before suspending, @code{suspend-emacs} runs the normal hook
723 @code{suspend-hook}. After the user resumes Emacs,
724 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
727 The next redisplay after resumption will redraw the entire screen,
728 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
729 @xref{Refresh Screen}.
731 Here is an example of how you could use these hooks:
735 (add-hook 'suspend-hook
736 (lambda () (or (y-or-n-p "Really suspend? ")
737 (error "Suspend canceled"))))
739 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
742 @c The sit-for prevents the ``nil'' that suspend-emacs returns
743 @c hiding the message.
745 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
749 ---------- Buffer: Minibuffer ----------
750 Really suspend? @kbd{y}
751 ---------- Buffer: Minibuffer ----------
755 ---------- Parent Shell ----------
761 ---------- Echo Area ----------
766 @c FIXME? AFAICS, it is echoed.
767 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
768 is read and executed by the shell.
772 This variable is a normal hook that Emacs runs before suspending.
775 @defvar suspend-resume-hook
776 This variable is a normal hook that Emacs runs on resuming
780 @defun suspend-tty &optional tty
781 If @var{tty} specifies a terminal device used by Emacs, this function
782 relinquishes the device and restores it to its prior state. Frames
783 that used the device continue to exist, but are not updated and Emacs
784 doesn't read input from them. @var{tty} can be a terminal object, a
785 frame (meaning the terminal for that frame), or @code{nil} (meaning
786 the terminal for the selected frame). @xref{Multiple Terminals}.
788 If @var{tty} is already suspended, this function does nothing.
790 @vindex suspend-tty-functions
791 This function runs the hook @code{suspend-tty-functions}, passing the
792 terminal object as an argument to each function.
795 @defun resume-tty &optional tty
796 This function resumes the previously suspended terminal device
797 @var{tty}; where @var{tty} has the same possible values as it does
798 for @code{suspend-tty}.
800 @vindex resume-tty-functions
801 This function reopens the terminal device, re-initializes it, and
802 redraws it with that terminal's selected frame. It then runs the
803 hook @code{resume-tty-functions}, passing the terminal object as an
804 argument to each function.
806 If the same device is already used by another Emacs terminal, this
807 function signals an error. If @var{tty} is not suspended, this
808 function does nothing.
811 @defun controlling-tty-p &optional tty
812 This function returns non-@code{nil} if @var{tty} is the
813 controlling terminal of the Emacs session; @var{tty} can be a
814 terminal object, a frame (meaning the terminal for that frame), or
815 @code{nil} (meaning the terminal for the selected frame).
818 @deffn Command suspend-frame
819 This command @dfn{suspends} a frame. For GUI frames, it calls
820 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
821 text terminals, it calls either @code{suspend-emacs} or
822 @code{suspend-tty}, depending on whether the frame is displayed on the
823 controlling terminal device or not.
826 @node System Environment
827 @section Operating System Environment
828 @cindex operating system environment
830 Emacs provides access to variables in the operating system environment
831 through various functions. These variables include the name of the
832 system, the user's @acronym{UID}, and so on.
834 @defvar system-configuration
835 This variable holds the standard GNU configuration name for the
836 hardware/software configuration of your system, as a string. For
837 example, a typical value for a 64-bit GNU/Linux system is
838 @samp{"x86_64-unknown-linux-gnu"}.
841 @cindex system type and name
843 The value of this variable is a symbol indicating the type of operating
844 system Emacs is running on. The possible values are:
851 Berkeley BSD and its variants.
854 Cygwin, a Posix layer on top of MS-Windows.
860 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
863 A GNU/Linux system---that is, a variant GNU system, using the Linux
864 kernel. (These systems are the ones people often call ``Linux'', but
865 actually Linux is just the kernel, not the whole system.)
868 A GNU (glibc-based) system with a FreeBSD kernel.
871 Hewlett-Packard HPUX operating system.
874 Silicon Graphics Irix system.
877 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
878 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
884 Microsoft Windows NT, 9X and later. The value of @code{system-type}
885 is always @code{windows-nt}, e.g., even on Windows 7.
889 We do not wish to add new symbols to make finer distinctions unless it
890 is absolutely necessary! In fact, we hope to eliminate some of these
891 alternatives in the future. If you need to make a finer distinction
892 than @code{system-type} allows for, you can test
893 @code{system-configuration}, e.g., against a regexp.
897 This function returns the name of the machine you are running on, as a
901 The symbol @code{system-name} is a variable as well as a function. In
902 fact, the function returns whatever value the variable
903 @code{system-name} currently holds. Thus, you can set the variable
904 @code{system-name} in case Emacs is confused about the name of your
905 system. The variable is also useful for constructing frame titles
906 (@pxref{Frame Titles}).
908 @c FIXME seems like this section is not the best place for this option?
909 @defopt mail-host-address
910 If this variable is non-@code{nil}, it is used instead of
911 @code{system-name} for purposes of generating email addresses. For
912 example, it is used when constructing the default value of
913 @code{user-mail-address}. @xref{User Identification}. (Since this is
914 done when Emacs starts up, the value actually used is the one saved when
915 Emacs was dumped. @xref{Building Emacs}.)
916 @c FIXME sounds like should probably give this a :set-after and some
917 @c custom-initialize-delay voodoo.
920 @deffn Command getenv var &optional frame
921 @cindex environment variable access
922 This function returns the value of the environment variable @var{var},
923 as a string. @var{var} should be a string. If @var{var} is undefined
924 in the environment, @code{getenv} returns @code{nil}. It returns
925 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
926 variables and their values is kept in the variable @code{process-environment}.
935 The shell command @code{printenv} prints all or part of the environment:
940 PATH=/usr/local/bin:/usr/bin:/bin
952 @deffn Command setenv variable &optional value substitute
953 This command sets the value of the environment variable named
954 @var{variable} to @var{value}. @var{variable} should be a string.
955 Internally, Emacs Lisp can handle any string. However, normally
956 @var{variable} should be a valid shell identifier, that is, a sequence
957 of letters, digits and underscores, starting with a letter or
958 underscore. Otherwise, errors may occur if subprocesses of Emacs try
959 to access the value of @var{variable}. If @var{value} is omitted or
960 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
961 removes @var{variable} from the environment. Otherwise, @var{value}
964 If the optional argument @var{substitute} is non-@code{nil}, Emacs
965 calls the function @code{substitute-env-vars} to expand any
966 environment variables in @var{value}.
968 @code{setenv} works by modifying @code{process-environment}; binding
969 that variable with @code{let} is also reasonable practice.
971 @code{setenv} returns the new value of @var{variable}, or @code{nil}
972 if it removed @var{variable} from the environment.
975 @defvar process-environment
976 This variable is a list of strings, each describing one environment
977 variable. The functions @code{getenv} and @code{setenv} work by means
983 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
994 If @code{process-environment} contains ``duplicate'' elements that
995 specify the same environment variable, the first of these elements
996 specifies the variable, and the other ``duplicates'' are ignored.
999 @defvar initial-environment
1000 This variable holds the list of environment variables Emacs inherited
1001 from its parent process when Emacs started.
1004 @defvar path-separator
1005 This variable holds a string that says which character separates
1006 directories in a search path (as found in an environment variable). Its
1007 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1010 @defun parse-colon-path path
1011 This function takes a search path string such as the value of
1012 the @env{PATH} environment variable, and splits it at the separators,
1013 returning a list of directory names. @code{nil} in this list means
1014 the current directory. Although the function's name says
1015 ``colon'', it actually uses the value of @code{path-separator}.
1018 (parse-colon-path ":/foo:/bar")
1019 @result{} (nil "/foo/" "/bar/")
1023 @defvar invocation-name
1024 This variable holds the program name under which Emacs was invoked. The
1025 value is a string, and does not include a directory name.
1028 @defvar invocation-directory
1029 This variable holds the directory from which the Emacs executable was
1030 invoked, or @code{nil} if that directory cannot be determined.
1033 @defvar installation-directory
1034 If non-@code{nil}, this is a directory within which to look for the
1035 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1036 it is normally @code{nil}. It is non-@code{nil}
1037 when Emacs can't find those directories in their standard installed
1038 locations, but can find them in a directory related somehow to the one
1039 containing the Emacs executable (i.e., @code{invocation-directory}).
1042 @defun load-average &optional use-float
1043 This function returns the current 1-minute, 5-minute, and 15-minute
1044 system load averages, in a list. The load average indicates the
1045 number of processes trying to run on the system.
1047 By default, the values are integers that are 100 times the system load
1048 averages, but if @var{use-float} is non-@code{nil}, then they are
1049 returned as floating point numbers without multiplying by 100.
1051 If it is impossible to obtain the load average, this function signals
1052 an error. On some platforms, access to load averages requires
1053 installing Emacs as setuid or setgid so that it can read kernel
1054 information, and that usually isn't advisable.
1055 @c FIXME which platforms are these? Are they still relevant?
1057 If the 1-minute load average is available, but the 5- or 15-minute
1058 averages are not, this function returns a shortened list containing
1059 the available averages.
1064 @result{} (169 48 36)
1068 @result{} (1.69 0.48 0.36)
1072 The shell command @code{uptime} returns similar information.
1076 This function returns the process @acronym{ID} of the Emacs process,
1080 @defvar tty-erase-char
1081 This variable holds the erase character that was selected
1082 in the system's terminal driver, before Emacs was started.
1083 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1084 @c The value is @code{nil} if Emacs is running under a window system.
1087 @node User Identification
1088 @section User Identification
1089 @cindex user identification
1091 @defvar init-file-user
1092 This variable says which user's init files should be used by
1093 Emacs---or @code{nil} if none. @code{""} stands for the user who
1094 originally logged in. The value reflects command-line options such as
1095 @samp{-q} or @samp{-u @var{user}}.
1097 Lisp packages that load files of customizations, or any other sort of
1098 user profile, should obey this variable in deciding where to find it.
1099 They should load the profile of the user name found in this variable.
1100 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q}
1101 option was used, then Lisp packages should not load any customization
1102 files or user profile.
1105 @defopt user-mail-address
1106 This holds the nominal email address of the user who is using Emacs.
1107 Emacs normally sets this variable to a default value after reading your
1108 init files, but not if you have already set it. So you can set the
1109 variable to some other value in your init file if you do not
1110 want to use the default value.
1113 @defun user-login-name &optional uid
1114 This function returns the name under which the user is logged in.
1115 It uses the environment variables @env{LOGNAME} or @env{USER} if
1116 either is set. Otherwise, the value is based on the effective
1117 @acronym{UID}, not the real @acronym{UID}.
1119 If you specify @var{uid} (a number), the result is the user name that
1120 corresponds to @var{uid}, or @code{nil} if there is no such user.
1123 @defun user-real-login-name
1124 This function returns the user name corresponding to Emacs's real
1125 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1126 environment variables @env{LOGNAME} and @env{USER}.
1129 @defun user-full-name &optional uid
1130 This function returns the full name of the logged-in user---or the value
1131 of the environment variable @env{NAME}, if that is set.
1133 If the Emacs process's user-id does not correspond to any known user (and
1134 provided @code{NAME} is not set), the result is @code{"unknown"}.
1136 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1137 or a string (a login name). Then @code{user-full-name} returns the full
1138 name corresponding to that user-id or login name. If you specify a
1139 user-id or login name that isn't defined, it returns @code{nil}.
1142 @vindex user-full-name
1143 @vindex user-real-login-name
1144 @vindex user-login-name
1145 The symbols @code{user-login-name}, @code{user-real-login-name} and
1146 @code{user-full-name} are variables as well as functions. The functions
1147 return the same values that the variables hold. These variables allow
1148 you to ``fake out'' Emacs by telling the functions what to return. The
1149 variables are also useful for constructing frame titles (@pxref{Frame
1152 @defun user-real-uid
1153 This function returns the real @acronym{UID} of the user.
1154 The value may be a floating point number, in the (unlikely) event that
1155 the UID is too large to fit in a Lisp integer.
1159 This function returns the effective @acronym{UID} of the user.
1160 The value may be a floating point number.
1164 This function returns the effective @acronym{GID} of the Emacs process.
1165 The value may be a floating point number.
1168 @defun group-real-gid
1169 This function returns the real @acronym{GID} of the Emacs process.
1170 The value may be a floating point number.
1174 This function returns a list of strings, listing the user names on the
1175 system. If Emacs cannot retrieve this information, the return value
1176 is a list containing just the value of @code{user-real-login-name}.
1180 @defun system-groups
1181 This function returns a list of strings, listing the names of user
1182 groups on the system. If Emacs cannot retrieve this information, the
1183 return value is @code{nil}.
1188 @section Time of Day
1190 This section explains how to determine the current time and time
1194 Most of these functions represent time as a list of either four
1195 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
1196 @var{picosec})}, or of three
1197 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1198 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1199 @var{sec-high} and @var{sec-low} give the high and low bits of an
1200 integer number of seconds. This integer number,
1202 @var{high} * 2**16 + @var{low},
1207 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1208 UTC) to the specified time. The third list element @var{microsec}, if
1209 present, gives the number of microseconds from the start of that
1210 second to the specified time.
1211 Similarly, the fourth list element @var{picosec}, if present, gives
1212 the number of picoseconds from the start of that microsecond to the
1215 The return value of @code{current-time} represents time using four
1216 integers, as do the timestamps in the return value of
1217 @code{file-attributes} (@pxref{Definition of
1218 file-attributes}). In function arguments, e.g., the @var{time-value}
1219 argument to @code{current-time-string}, two-, three-, and four-integer
1220 lists are accepted. You can convert times from the list
1221 representation into standard human-readable strings using
1222 @code{current-time}, or to other forms using the @code{decode-time}
1223 and @code{format-time-string} functions documented in the following
1226 @defun current-time-string &optional time-value
1227 This function returns the current time and date as a human-readable
1228 string. The format does not vary for the initial part of the string,
1229 which contains the day of week, month, day of month, and time of day
1230 in that order: the number of characters used for these fields is
1231 always the same, so you can reliably
1232 use @code{substring} to extract them. You should count
1233 characters from the beginning of the string rather than from the end,
1234 as the year might not have exactly four digits, and additional
1235 information may some day be added at the end.
1237 The argument @var{time-value}, if given, specifies a time to format
1238 (represented as a list of integers), instead of the current time.
1242 (current-time-string)
1243 @result{} "Wed Oct 14 22:21:05 1987"
1249 This function returns the current time, represented as a list of four
1250 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1251 These integers have trailing zeros on systems that return time with
1252 lower resolutions. On all current machines @var{picosec} is a
1253 multiple of 1000, but this may change as higher-resolution clocks
1257 @defun float-time &optional time-value
1258 This function returns the current time as a floating-point number of
1259 seconds since the epoch. The optional argument @var{time-value}, if
1260 given, specifies a time (represented as a list of integers) to convert
1261 instead of the current time.
1263 @emph{Warning}: Since the result is floating point, it may not be
1264 exact. Do not use this function if precise time stamps are required.
1267 @defun current-time-zone &optional time-value
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
1295 These functions convert time values (lists of two to four integers,
1296 as explained in the previous section) into calendrical information and
1299 Many 32-bit operating systems are limited to time values containing
1300 32 bits of information; these systems typically handle only the times
1301 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
1302 However, 64-bit and some 32-bit operating systems have larger time
1303 values, and can represent times far in the past or future.
1305 Time conversion functions always use the Gregorian calendar, even
1306 for dates before the Gregorian calendar was introduced. Year numbers
1307 count the number of years since the year 1 B.C., and do not skip zero
1308 as traditional Gregorian years do; for example, the year number
1309 @minus{}37 represents the Gregorian year 38 B.C@.
1311 @defun decode-time &optional time
1312 This function converts a time value into calendrical information. If
1313 you don't specify @var{time}, it decodes the current time. The return
1314 value is a list of nine elements, as follows:
1317 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1320 Here is what the elements mean:
1324 The number of seconds past the minute, as an integer between 0 and 59.
1325 On some operating systems, this is 60 for leap seconds.
1327 The number of minutes past the hour, as an integer between 0 and 59.
1329 The hour of the day, as an integer between 0 and 23.
1331 The day of the month, as an integer between 1 and 31.
1333 The month of the year, as an integer between 1 and 12.
1335 The year, an integer typically greater than 1900.
1337 The day of week, as an integer between 0 and 6, where 0 stands for
1340 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1342 An integer indicating the time zone, as the number of seconds east of
1346 @strong{Common Lisp Note:} Common Lisp has different meanings for
1347 @var{dow} and @var{zone}.
1350 @defun encode-time seconds minutes hour day month year &optional zone
1351 This function is the inverse of @code{decode-time}. It converts seven
1352 items of calendrical data into a time value. For the meanings of the
1353 arguments, see the table above under @code{decode-time}.
1355 Year numbers less than 100 are not treated specially. If you want them
1356 to stand for years above 1900, or years above 2000, you must alter them
1357 yourself before you call @code{encode-time}.
1359 The optional argument @var{zone} defaults to the current time zone and
1360 its daylight saving time rules. If specified, it can be either a list
1361 (as you would get from @code{current-time-zone}), a string as in the
1362 @env{TZ} environment variable, @code{t} for Universal Time, or an
1363 integer (as you would get from @code{decode-time}). The specified
1364 zone is used without any further alteration for daylight saving time.
1366 If you pass more than seven arguments to @code{encode-time}, the first
1367 six are used as @var{seconds} through @var{year}, the last argument is
1368 used as @var{zone}, and the arguments in between are ignored. This
1369 feature makes it possible to use the elements of a list returned by
1370 @code{decode-time} as the arguments to @code{encode-time}, like this:
1373 (apply 'encode-time (decode-time @dots{}))
1376 You can perform simple date arithmetic by using out-of-range values for
1377 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1378 arguments; for example, day 0 means the day preceding the given month.
1380 The operating system puts limits on the range of possible time values;
1381 if you try to encode a time that is out of range, an error results.
1382 For instance, years before 1970 do not work on some systems;
1383 on others, years as early as 1901 do work.
1387 @section Parsing and Formatting Times
1389 These functions convert time values to text in a string, and vice versa.
1390 Time values are lists of two to four integers (@pxref{Time of Day}).
1392 @defun date-to-time string
1393 This function parses the time-string @var{string} and returns the
1394 corresponding time value.
1397 @defun format-time-string format-string &optional time universal
1398 This function converts @var{time} (or the current time, if @var{time} is
1399 omitted) to a string according to @var{format-string}. The argument
1400 @var{format-string} may contain @samp{%}-sequences which say to
1401 substitute parts of the time. Here is a table of what the
1402 @samp{%}-sequences mean:
1406 This stands for the abbreviated name of the day of week.
1408 This stands for the full name of the day of week.
1410 This stands for the abbreviated name of the month.
1412 This stands for the full name of the month.
1414 This is a synonym for @samp{%x %X}.
1416 This has a locale-specific meaning. In the default locale (named C), it
1417 is equivalent to @samp{%A, %B %e, %Y}.
1419 This stands for the day of month, zero-padded.
1421 This is a synonym for @samp{%m/%d/%y}.
1423 This stands for the day of month, blank-padded.
1425 This is a synonym for @samp{%b}.
1427 This stands for the hour (00--23).
1429 This stands for the hour (01--12).
1431 This stands for the day of the year (001--366).
1433 This stands for the hour (0--23), blank padded.
1435 This stands for the hour (1--12), blank padded.
1437 This stands for the month (01--12).
1439 This stands for the minute (00--59).
1441 This stands for a newline.
1443 This stands for the nanoseconds (000000000--999999999). To ask for
1444 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1445 microseconds, etc. Any excess digits are discarded, without rounding.
1447 This stands for @samp{AM} or @samp{PM}, as appropriate.
1449 This is a synonym for @samp{%I:%M:%S %p}.
1451 This is a synonym for @samp{%H:%M}.
1453 This stands for the seconds (00--59).
1455 This stands for a tab character.
1457 This is a synonym for @samp{%H:%M:%S}.
1459 This stands for the week of the year (01--52), assuming that weeks
1462 This stands for the numeric day of week (0--6). Sunday is day 0.
1464 This stands for the week of the year (01--52), assuming that weeks
1467 This has a locale-specific meaning. In the default locale (named
1468 @samp{C}), it is equivalent to @samp{%D}.
1470 This has a locale-specific meaning. In the default locale (named
1471 @samp{C}), it is equivalent to @samp{%T}.
1473 This stands for the year without century (00--99).
1475 This stands for the year with century.
1477 This stands for the time zone abbreviation (e.g., @samp{EST}).
1479 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1482 You can also specify the field width and type of padding for any of
1483 these @samp{%}-sequences. This works as in @code{printf}: you write
1484 the field width as digits in the middle of a @samp{%}-sequences. If you
1485 start the field width with @samp{0}, it means to pad with zeros. If you
1486 start the field width with @samp{_}, it means to pad with spaces.
1488 For example, @samp{%S} specifies the number of seconds since the minute;
1489 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1490 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1491 because that is how @samp{%S} normally pads to two positions.
1493 The characters @samp{E} and @samp{O} act as modifiers when used between
1494 @samp{%} and one of the letters in the table above. @samp{E} specifies
1495 using the current locale's ``alternative'' version of the date and time.
1496 In a Japanese locale, for example, @code{%Ex} might yield a date format
1497 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1498 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1501 @samp{O} means to use the current locale's ``alternative''
1502 representation of numbers, instead of the ordinary decimal digits. This
1503 is allowed with most letters, all the ones that output numbers.
1505 If @var{universal} is non-@code{nil}, that means to describe the time as
1506 Universal Time; @code{nil} means describe it using what Emacs believes
1507 is the local time zone (see @code{current-time-zone}).
1509 This function uses the C library function @code{strftime}
1510 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1511 Manual}) to do most of the work. In order to communicate with that
1512 function, it first encodes its argument using the coding system
1513 specified by @code{locale-coding-system} (@pxref{Locales}); after
1514 @code{strftime} returns the resulting string,
1515 @code{format-time-string} decodes the string using that same coding
1519 @defun seconds-to-time seconds
1520 This function converts @var{seconds}, a floating point number of
1521 seconds since the epoch, to a time value and returns that. To perform
1522 the inverse conversion, use @code{float-time}.
1525 @defun format-seconds format-string seconds
1526 This function converts its argument @var{seconds} into a string of
1527 years, days, hours, etc., according to @var{format-string}. The
1528 argument @var{format-string} may contain @samp{%}-sequences which
1529 control the conversion. Here is a table of what the
1530 @samp{%}-sequences mean:
1535 The integer number of 365-day years.
1538 The integer number of days.
1541 The integer number of hours.
1544 The integer number of minutes.
1547 The integer number of seconds.
1549 Non-printing control flag. When it is used, other specifiers must be
1550 given in the order of decreasing size, i.e., years before days, hours
1551 before minutes, etc. Nothing will be produced in the result string to
1552 the left of @samp{%z} until the first non-zero conversion is
1553 encountered. For example, the default format used by
1554 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1555 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1556 will always be produced, but years, days, hours, and minutes will only
1557 be shown if they are non-zero.
1559 Produces a literal @samp{%}.
1562 Upper-case format sequences produce the units in addition to the
1563 numbers, lower-case formats produce only the numbers.
1565 You can also specify the field width by following the @samp{%} with a
1566 number; shorter numbers will be padded with blanks. An optional
1567 period before the width requests zero-padding instead. For example,
1568 @code{"%.3Y"} might produce @code{"004 years"}.
1570 @emph{Warning:} This function works only with values of @var{seconds}
1571 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1572 most-positive-fixnum}).
1575 @node Processor Run Time
1576 @section Processor Run time
1577 @cindex processor run time
1578 @cindex Emacs process run time
1580 Emacs provides several functions and primitives that return time,
1581 both elapsed and processor time, used by the Emacs process.
1583 @deffn Command emacs-uptime &optional format
1584 This function returns a string representing the Emacs
1585 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1586 running. The string is formatted by @code{format-seconds} according
1587 to the optional argument @var{format}. For the available format
1588 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1589 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1592 When called interactively, it prints the uptime in the echo area.
1595 @defun get-internal-run-time
1596 This function returns the processor run time used by Emacs as a list
1597 of four integers: @code{(@var{high} @var{low} @var{microsec}
1598 @var{picosec})}, using the same format as @code{current-time}
1599 (@pxref{Time of Day}).
1601 Note that the time returned by this function excludes the time Emacs
1602 was not using the processor, and if the Emacs process has several
1603 threads, the returned value is the sum of the processor times used up
1604 by all Emacs threads.
1606 If the system doesn't provide a way to determine the processor run
1607 time, @code{get-internal-run-time} returns the same time as
1608 @code{current-time}.
1611 @deffn Command emacs-init-time
1612 This function returns the duration of the Emacs initialization
1613 (@pxref{Startup Summary}) in seconds, as a string. When called
1614 interactively, it prints the duration in the echo area.
1617 @node Time Calculations
1618 @section Time Calculations
1620 These functions perform calendrical computations using time values
1621 (the kind of list that @code{current-time} returns).
1623 @defun time-less-p t1 t2
1624 This returns @code{t} if time value @var{t1} is less than time value
1628 @defun time-subtract t1 t2
1629 This returns the time difference @var{t1} @minus{} @var{t2} between
1630 two time values, in the same format as a time value.
1633 @defun time-add t1 t2
1634 This returns the sum of two time values, one of which ought to
1635 represent a time difference rather than a point in time.
1636 Here is how to add a number of seconds to a time value:
1639 (time-add @var{time} (seconds-to-time @var{seconds}))
1643 @defun time-to-days time
1644 This function returns the number of days between the beginning of year
1648 @defun time-to-day-in-year time
1649 This returns the day number within the year corresponding to @var{time}.
1652 @defun date-leap-year-p year
1653 This function returns @code{t} if @var{year} is a leap year.
1657 @section Timers for Delayed Execution
1660 You can set up a @dfn{timer} to call a function at a specified
1661 future time or after a certain length of idleness.
1663 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1664 can run them only when Emacs could accept output from a subprocess:
1665 namely, while waiting or inside certain primitive functions such as
1666 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1667 timer's execution may be delayed if Emacs is busy. However, the time of
1668 execution is very precise if Emacs is idle.
1670 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1671 function, because quitting out of many timer functions can leave
1672 things in an inconsistent state. This is normally unproblematical
1673 because most timer functions don't do a lot of work. Indeed, for a
1674 timer to call a function that takes substantial time to run is likely
1675 to be annoying. If a timer function needs to allow quitting, it
1676 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1677 a timer function calls @code{accept-process-output} to receive output
1678 from an external process, that call should be wrapped inside
1679 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1682 It is usually a bad idea for timer functions to alter buffer
1683 contents. When they do, they usually should call @code{undo-boundary}
1684 both before and after changing the buffer, to separate the timer's
1685 changes from user commands' changes and prevent a single undo entry
1686 from growing to be quite large.
1688 Timer functions should also avoid calling functions that cause Emacs
1689 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1690 unpredictable effects, since other timers (or even the same timer) can
1691 run while waiting. If a timer function needs to perform an action
1692 after a certain time has elapsed, it can do this by scheduling a new
1695 If a timer function calls functions that can change the match data,
1696 it should save and restore the match data. @xref{Saving Match Data}.
1698 @deffn Command run-at-time time repeat function &rest args
1699 This sets up a timer that calls the function @var{function} with
1700 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1701 (integer or floating point), the timer is scheduled to run again every
1702 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1703 the timer runs only once.
1705 @var{time} may specify an absolute or a relative time.
1707 Absolute times may be specified using a string with a limited variety
1708 of formats, and are taken to be times @emph{today}, even if already in
1709 the past. The recognized forms are @samp{@var{xxxx}},
1710 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1711 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1712 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1713 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1714 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1715 to separate the hour and minute parts.
1717 To specify a relative time as a string, use numbers followed by units.
1722 denotes 1 minute from now.
1724 denotes 65 seconds from now.
1725 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1726 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1729 For relative time values, Emacs considers a month to be exactly thirty
1730 days, and a year to be exactly 365.25 days.
1732 Not all convenient formats are strings. If @var{time} is a number
1733 (integer or floating point), that specifies a relative time measured in
1734 seconds. The result of @code{encode-time} can also be used to specify
1735 an absolute value for @var{time}.
1737 In most cases, @var{repeat} has no effect on when @emph{first} call
1738 takes place---@var{time} alone specifies that. There is one exception:
1739 if @var{time} is @code{t}, then the timer runs whenever the time is a
1740 multiple of @var{repeat} seconds after the epoch. This is useful for
1741 functions like @code{display-time}.
1743 The function @code{run-at-time} returns a timer value that identifies
1744 the particular scheduled future action. You can use this value to call
1745 @code{cancel-timer} (see below).
1748 A repeating timer nominally ought to run every @var{repeat} seconds,
1749 but remember that any invocation of a timer can be late. Lateness of
1750 one repetition has no effect on the scheduled time of the next
1751 repetition. For instance, if Emacs is busy computing for long enough
1752 to cover three scheduled repetitions of the timer, and then starts to
1753 wait, it will immediately call the timer function three times in
1754 immediate succession (presuming no other timers trigger before or
1755 between them). If you want a timer to run again no less than @var{n}
1756 seconds after the last invocation, don't use the @var{repeat} argument.
1757 Instead, the timer function should explicitly reschedule the timer.
1759 @defopt timer-max-repeats
1760 This variable's value specifies the maximum number of times to repeat
1761 calling a timer function in a row, when many previously scheduled
1762 calls were unavoidably delayed.
1765 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1766 Execute @var{body}, but give up after @var{seconds} seconds. If
1767 @var{body} finishes before the time is up, @code{with-timeout} returns
1768 the value of the last form in @var{body}. If, however, the execution of
1769 @var{body} is cut short by the timeout, then @code{with-timeout}
1770 executes all the @var{timeout-forms} and returns the value of the last
1773 This macro works by setting a timer to run after @var{seconds} seconds. If
1774 @var{body} finishes before that time, it cancels the timer. If the
1775 timer actually runs, it terminates execution of @var{body}, then
1776 executes @var{timeout-forms}.
1778 Since timers can run within a Lisp program only when the program calls a
1779 primitive that can wait, @code{with-timeout} cannot stop executing
1780 @var{body} while it is in the midst of a computation---only when it
1781 calls one of those primitives. So use @code{with-timeout} only with a
1782 @var{body} that waits for input, not one that does a long computation.
1785 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1786 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1789 @defun cancel-timer timer
1790 This cancels the requested action for @var{timer}, which should be a
1791 timer---usually, one previously returned by @code{run-at-time} or
1792 @code{run-with-idle-timer}. This cancels the effect of that call to
1793 one of these functions; the arrival of the specified time will not
1794 cause anything special to happen.
1798 @section Idle Timers
1800 Here is how to set up a timer that runs when Emacs is idle for a
1801 certain length of time. Aside from how to set them up, idle timers
1802 work just like ordinary timers.
1804 @deffn Command run-with-idle-timer secs repeat function &rest args
1805 Set up a timer which runs the next time Emacs is idle for @var{secs}
1806 seconds. The value of @var{secs} may be an integer or a floating
1807 point number; a value of the type returned by @code{current-idle-time}
1810 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1811 Emacs remains idle for a long enough time. More often @var{repeat} is
1812 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1813 remains idle for @var{secs} seconds.
1815 The function @code{run-with-idle-timer} returns a timer value which you
1816 can use in calling @code{cancel-timer} (@pxref{Timers}).
1820 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1821 it remains idle until the user provides some input. If a timer is set
1822 for five seconds of idleness, it runs approximately five seconds after
1823 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1824 this timer will not run again as long as Emacs remains idle, because
1825 the duration of idleness will continue to increase and will not go
1826 down to five seconds again.
1828 Emacs can do various things while idle: garbage collect, autosave or
1829 handle data from a subprocess. But these interludes during idleness do
1830 not interfere with idle timers, because they do not reset the clock of
1831 idleness to zero. An idle timer set for 600 seconds will run when ten
1832 minutes have elapsed since the last user command was finished, even if
1833 subprocess output has been accepted thousands of times within those ten
1834 minutes, and even if there have been garbage collections and autosaves.
1836 When the user supplies input, Emacs becomes non-idle while executing the
1837 input. Then it becomes idle again, and all the idle timers that are
1838 set up to repeat will subsequently run another time, one by one.
1840 Do not write an idle timer function containing a loop which does a
1841 certain amount of processing each time around, and exits when
1842 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1843 natural but has two problems:
1847 It blocks out all process output (since Emacs accepts process output
1848 only while waiting).
1851 It blocks out any idle timers that ought to run during that time.
1855 Similarly, do not write an idle timer function that sets up another
1856 idle timer (including the same idle timer) with @var{secs} argument
1857 less than or equal to the current idleness time. Such a timer will
1858 run almost immediately, and continue running again and again, instead
1859 of waiting for the next time Emacs becomes idle. The correct approach
1860 is to reschedule with an appropriate increment of the current value of
1861 the idleness time, as described below.
1863 @defun current-idle-time
1864 If Emacs is idle, this function returns the length of time Emacs has
1865 been idle, as a list of four integers: @code{(@var{sec-high}
1866 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1867 @code{current-time} (@pxref{Time of Day}).
1869 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1870 This is a convenient way to test whether Emacs is idle.
1873 The main use of @code{current-idle-time} is when an idle timer
1874 function wants to ``take a break'' for a while. It can set up another
1875 idle timer to call the same function again, after a few seconds more
1876 idleness. Here's an example:
1879 (defvar my-resume-timer nil
1880 "Timer for `my-timer-function' to reschedule itself, or nil.")
1882 (defun my-timer-function ()
1883 ;; @r{If the user types a command while @code{my-resume-timer}}
1884 ;; @r{is active, the next time this function is called from}
1885 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1886 (when my-resume-timer
1887 (cancel-timer my-resume-timer))
1888 ...@var{do the work for a while}...
1889 (when @var{taking-a-break}
1890 (setq my-resume-timer
1891 (run-with-idle-timer
1892 ;; Compute an idle time @var{break-length}
1893 ;; more than the current value.
1894 (time-add (current-idle-time)
1895 (seconds-to-time @var{break-length}))
1897 'my-timer-function))))
1900 @node Terminal Input
1901 @section Terminal Input
1902 @cindex terminal input
1904 This section describes functions and variables for recording or
1905 manipulating terminal input. See @ref{Display}, for related
1909 * Input Modes:: Options for how input is processed.
1910 * Recording Input:: Saving histories of recent or all input events.
1914 @subsection Input Modes
1916 @cindex terminal input modes
1918 @defun set-input-mode interrupt flow meta &optional quit-char
1919 This function sets the mode for reading keyboard input. If
1920 @var{interrupt} is non-null, then Emacs uses input interrupts. If it is
1921 @code{nil}, then it uses @sc{cbreak} mode. The default setting is
1922 system-dependent. Some systems always use @sc{cbreak} mode regardless
1923 of what is specified.
1925 When Emacs communicates directly with X, it ignores this argument and
1926 uses interrupts if that is the way it knows how to communicate.
1928 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1929 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1930 has no effect except in @sc{cbreak} mode.
1932 The argument @var{meta} controls support for input character codes
1933 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1934 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1935 Emacs disregards the 8th bit; this is necessary when the terminal uses
1936 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1937 Emacs uses all 8 bits of input unchanged. This is good for terminals
1938 that use 8-bit character sets.
1940 If @var{quit-char} is non-@code{nil}, it specifies the character to
1941 use for quitting. Normally this character is @kbd{C-g}.
1945 The @code{current-input-mode} function returns the input mode settings
1946 Emacs is currently using.
1948 @defun current-input-mode
1949 This function returns the current mode for reading keyboard input. It
1950 returns a list, corresponding to the arguments of @code{set-input-mode},
1951 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1955 is non-@code{nil} when Emacs is using interrupt-driven input. If
1956 @code{nil}, Emacs is using @sc{cbreak} mode.
1958 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1959 flow control for output to the terminal. This value is meaningful only
1960 when @var{interrupt} is @code{nil}.
1962 is @code{t} if Emacs treats the eighth bit of input characters as
1963 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1964 input character; any other value means Emacs uses all eight bits as the
1965 basic character code.
1967 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1971 @node Recording Input
1972 @subsection Recording Input
1973 @cindex recording input
1976 This function returns a vector containing the last 300 input events from
1977 the keyboard or mouse. All input events are included, whether or not
1978 they were used as parts of key sequences. Thus, you always get the last
1979 300 input events, not counting events generated by keyboard macros.
1980 (These are excluded because they are less interesting for debugging; it
1981 should be enough to see the events that invoked the macros.)
1983 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1984 causes this function to return an empty vector immediately afterward.
1987 @deffn Command open-dribble-file filename
1988 @cindex dribble file
1989 This function opens a @dfn{dribble file} named @var{filename}. When a
1990 dribble file is open, each input event from the keyboard or mouse (but
1991 not those from keyboard macros) is written in that file. A
1992 non-character event is expressed using its printed representation
1993 surrounded by @samp{<@dots{}>}.
1995 You close the dribble file by calling this function with an argument
1998 This function is normally used to record the input necessary to
1999 trigger an Emacs bug, for the sake of a bug report.
2003 (open-dribble-file "~/dribble")
2009 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2011 @node Terminal Output
2012 @section Terminal Output
2013 @cindex terminal output
2015 The terminal output functions send output to a text terminal, or keep
2016 track of output sent to the terminal. The variable @code{baud-rate}
2017 tells you what Emacs thinks is the output speed of the terminal.
2020 This variable's value is the output speed of the terminal, as far as
2021 Emacs knows. Setting this variable does not change the speed of actual
2022 data transmission, but the value is used for calculations such as
2025 It also affects decisions about whether to scroll part of the
2026 screen or repaint on text terminals. @xref{Forcing Redisplay},
2027 for the corresponding functionality on graphical terminals.
2029 The value is measured in baud.
2032 If you are running across a network, and different parts of the
2033 network work at different baud rates, the value returned by Emacs may be
2034 different from the value used by your local terminal. Some network
2035 protocols communicate the local terminal speed to the remote machine, so
2036 that Emacs and other programs can get the proper value, but others do
2037 not. If Emacs has the wrong value, it makes decisions that are less
2038 than optimal. To fix the problem, set @code{baud-rate}.
2040 @defun send-string-to-terminal string &optional terminal
2041 This function sends @var{string} to @var{terminal} without alteration.
2042 Control characters in @var{string} have terminal-dependent effects.
2043 This function operates only on text terminals. @var{terminal} may be
2044 a terminal object, a frame, or @code{nil} for the selected frame's
2045 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2046 @var{terminal} is @code{nil}.
2048 One use of this function is to define function keys on terminals that
2049 have downloadable function key definitions. For example, this is how (on
2050 certain terminals) to define function key 4 to move forward four
2051 characters (by transmitting the characters @kbd{C-u C-f} to the
2056 (send-string-to-terminal "\eF4\^U\^F")
2062 @deffn Command open-termscript filename
2063 @cindex termscript file
2064 This function is used to open a @dfn{termscript file} that will record
2065 all the characters sent by Emacs to the terminal. It returns
2066 @code{nil}. Termscript files are useful for investigating problems
2067 where Emacs garbles the screen, problems that are due to incorrect
2068 Termcap entries or to undesirable settings of terminal options more
2069 often than to actual Emacs bugs. Once you are certain which characters
2070 were actually output, you can determine reliably whether they correspond
2071 to the Termcap specifications in use.
2073 You close the termscript file by calling this function with an
2074 argument of @code{nil}.
2076 See also @code{open-dribble-file} in @ref{Recording Input}.
2080 (open-termscript "../junk/termscript")
2087 @section Sound Output
2090 To play sound using Emacs, use the function @code{play-sound}. Only
2091 certain systems are supported; if you call @code{play-sound} on a
2092 system which cannot really do the job, it gives an error.
2094 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2095 or Sun Audio format (@samp{.au}).
2097 @defun play-sound sound
2098 This function plays a specified sound. The argument, @var{sound}, has
2099 the form @code{(sound @var{properties}...)}, where the @var{properties}
2100 consist of alternating keywords (particular symbols recognized
2101 specially) and values corresponding to them.
2103 Here is a table of the keywords that are currently meaningful in
2104 @var{sound}, and their meanings:
2107 @item :file @var{file}
2108 This specifies the file containing the sound to play.
2109 If the file name is not absolute, it is expanded against
2110 the directory @code{data-directory}.
2112 @item :data @var{data}
2113 This specifies the sound to play without need to refer to a file. The
2114 value, @var{data}, should be a string containing the same bytes as a
2115 sound file. We recommend using a unibyte string.
2117 @item :volume @var{volume}
2118 This specifies how loud to play the sound. It should be a number in the
2119 range of 0 to 1. The default is to use whatever volume has been
2122 @item :device @var{device}
2123 This specifies the system device on which to play the sound, as a
2124 string. The default device is system-dependent.
2127 Before actually playing the sound, @code{play-sound}
2128 calls the functions in the list @code{play-sound-functions}.
2129 Each function is called with one argument, @var{sound}.
2132 @deffn Command play-sound-file file &optional volume device
2133 This function is an alternative interface to playing a sound @var{file}
2134 specifying an optional @var{volume} and @var{device}.
2137 @defvar play-sound-functions
2138 A list of functions to be called before playing a sound. Each function
2139 is called with one argument, a property list that describes the sound.
2143 @section Operating on X11 Keysyms
2146 To define system-specific X11 keysyms, set the variable
2147 @code{system-key-alist}.
2149 @defvar system-key-alist
2150 This variable's value should be an alist with one element for each
2151 system-specific keysym. Each element has the form @code{(@var{code}
2152 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2153 including the ``vendor specific'' bit,
2160 and @var{symbol} is the name for the function key.
2162 For example @code{(168 . mute-acute)} defines a system-specific key (used
2163 by HP X servers) whose numeric code is
2172 It is not crucial to exclude from the alist the keysyms of other X
2173 servers; those do no harm, as long as they don't conflict with the ones
2174 used by the X server actually in use.
2176 The variable is always local to the current terminal, and cannot be
2177 buffer-local. @xref{Multiple Terminals}.
2180 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2182 @defvar x-alt-keysym
2183 @defvarx x-meta-keysym
2184 @defvarx x-hyper-keysym
2185 @defvarx x-super-keysym
2186 The name of the keysym that should stand for the Alt modifier
2187 (respectively, for Meta, Hyper, and Super). For example, here is
2188 how to swap the Meta and Alt modifiers within Emacs:
2190 (setq x-alt-keysym 'meta)
2191 (setq x-meta-keysym 'alt)
2199 The command-line option @samp{-batch} causes Emacs to run
2200 noninteractively. In this mode, Emacs does not read commands from the
2201 terminal, it does not alter the terminal modes, and it does not expect
2202 to be outputting to an erasable screen. The idea is that you specify
2203 Lisp programs to run; when they are finished, Emacs should exit. The
2204 way to specify the programs to run is with @samp{-l @var{file}}, which
2205 loads the library named @var{file}, or @samp{-f @var{function}}, which
2206 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2208 Any Lisp program output that would normally go to the echo area,
2209 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2210 as the stream, goes instead to Emacs's standard error descriptor when
2211 in batch mode. Similarly, input that would normally come from the
2212 minibuffer is read from the standard input descriptor.
2213 Thus, Emacs behaves much like a noninteractive
2214 application program. (The echo area output that Emacs itself normally
2215 generates, such as command echoing, is suppressed entirely.)
2217 @defvar noninteractive
2218 This variable is non-@code{nil} when Emacs is running in batch mode.
2221 @node Session Management
2222 @section Session Management
2223 @cindex session manager
2225 Emacs supports the X Session Management Protocol, which is used to
2226 suspend and restart applications. In the X Window System, a program
2227 called the @dfn{session manager} is responsible for keeping track of
2228 the applications that are running. When the X server shuts down, the
2229 session manager asks applications to save their state, and delays the
2230 actual shutdown until they respond. An application can also cancel
2233 When the session manager restarts a suspended session, it directs
2234 these applications to individually reload their saved state. It does
2235 this by specifying a special command-line argument that says what
2236 saved session to restore. For Emacs, this argument is @samp{--smid
2239 @defvar emacs-save-session-functions
2240 Emacs supports saving state via a hook called
2241 @code{emacs-save-session-functions}. Emacs runs this hook when the
2242 session manager tells it that the window system is shutting down. The
2243 functions are called with no arguments, and with the current buffer
2244 set to a temporary buffer. Each function can use @code{insert} to add
2245 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2246 file, called the @dfn{session file}.
2248 @findex emacs-session-restore
2249 Subsequently, when the session manager restarts Emacs, it loads the
2250 session file automatically (@pxref{Loading}). This is performed by a
2251 function named @code{emacs-session-restore}, which is called during
2252 startup. @xref{Startup Summary}.
2254 If a function in @code{emacs-save-session-functions} returns
2255 non-@code{nil}, Emacs tells the session manager to cancel the
2259 Here is an example that just inserts some text into @file{*scratch*} when
2260 Emacs is restarted by the session manager.
2264 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2268 (defun save-yourself-test ()
2269 (insert "(save-current-buffer
2270 (switch-to-buffer \"*scratch*\")
2271 (insert \"I am restored\"))")
2276 @node Desktop Notifications
2277 @section Desktop Notifications
2278 @cindex desktop notifications
2280 Emacs is able to send @dfn{notifications} on systems that support the
2281 freedesktop.org Desktop Notifications Specification. In order to use
2282 this functionality, Emacs must have been compiled with D-Bus support,
2283 and the @code{notifications} library must be loaded.
2285 @defun notifications-notify &rest params
2286 This function sends a notification to the desktop via D-Bus,
2287 consisting of the parameters specified by the @var{params} arguments.
2288 These arguments should consist of alternating keyword and value pairs.
2289 The supported keywords and values are as follows:
2292 @item :bus @var{bus}
2293 The D-Bus bus. This argument is needed only if a bus other than
2294 @code{:session} shall be used.
2296 @item :title @var{title}
2297 The notification title.
2299 @item :body @var{text}
2300 The notification body text. Depending on the implementation of the
2301 notification server, the text could contain HTML markups, like
2302 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2303 characters must be encoded, as @samp{"Contact
2304 <postmaster@@localhost>!"}.
2306 @item :app-name @var{name}
2307 The name of the application sending the notification. The default is
2308 @code{notifications-application-name}.
2310 @item :replaces-id @var{id}
2311 The notification @var{id} that this notification replaces. @var{id}
2312 must be the result of a previous @code{notifications-notify} call.
2314 @item :app-icon @var{icon-file}
2315 The file name of the notification icon. If set to @code{nil}, no icon
2316 is displayed. The default is @code{notifications-application-icon}.
2318 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2319 A list of actions to be applied. @var{key} and @var{title} are both
2320 strings. The default action (usually invoked by clicking the
2321 notification) should have a key named @samp{"default"}. The title can
2322 be anything, though implementations are free not to display it.
2324 @item :timeout @var{timeout}
2325 The timeout time in milliseconds since the display of the notification
2326 at which the notification should automatically close. If -1, the
2327 notification's expiration time is dependent on the notification
2328 server's settings, and may vary for the type of notification. If 0,
2329 the notification never expires. Default value is -1.
2331 @item :urgency @var{urgency}
2332 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2335 When this keyword is given, the @var{title} string of the actions is
2336 interpreted as icon name.
2338 @item :category @var{category}
2339 The type of notification this is, a string. See the
2340 @uref{http://developer.gnome.org/notification-spec/#categories,
2341 Desktop Notifications Specification} for a list of standard
2344 @item :desktop-entry @var{filename}
2345 This specifies the name of the desktop filename representing the
2346 calling program, like @samp{"emacs"}.
2348 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2349 This is a raw data image format that describes the width, height,
2350 rowstride, whether there is an alpha channel, bits per sample,
2351 channels and image data, respectively.
2353 @item :image-path @var{path}
2354 This is represented either as a URI (@samp{file://} is the only URI
2355 schema supported right now) or a name in a freedesktop.org-compliant
2356 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2358 @item :sound-file @var{filename}
2359 The path to a sound file to play when the notification pops up.
2361 @item :sound-name @var{name}
2362 A themable named sound from the freedesktop.org sound naming
2363 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2364 notification pops up. Similar to the icon name, only for sounds. An
2365 example would be @samp{"message-new-instant"}.
2367 @item :suppress-sound
2368 Causes the server to suppress playing any sounds, if it has that
2372 When set the server will not automatically remove the notification
2373 when an action has been invoked. The notification will remain resident
2374 in the server until it is explicitly removed by the user or by the
2375 sender. This hint is likely only useful when the server has the
2376 @code{:persistence} capability.
2379 When set the server will treat the notification as transient and
2380 by-pass the server's persistence capability, if it should exist.
2382 @item :x @var{position}
2383 @itemx :y @var{position}
2384 Specifies the X, Y location on the screen that the
2385 notification should point to. Both arguments must be used together.
2387 @item :on-action @var{function}
2388 Function to call when an action is invoked. The notification @var{id}
2389 and the @var{key} of the action are passed as arguments to the
2392 @item :on-close @var{function}
2393 Function to call when the notification has been closed by timeout or
2394 by the user. The function receive the notification @var{id} and the closing
2395 @var{reason} as arguments:
2398 @item @code{expired} if the notification has expired
2399 @item @code{dismissed} if the notification was dismissed by the user
2400 @item @code{close-notification} if the notification was closed by a call to
2401 @code{notifications-close-notification}
2402 @item @code{undefined} if the notification server hasn't provided a reason
2406 Which parameters are accepted by the notification server can be
2407 checked via @code{notifications-get-capabilities}.
2409 This function returns a notification id, an integer, which can be used
2410 to manipulate the notification item with
2411 @code{notifications-close-notification} or the @code{:replaces-id}
2412 argument of another @code{notifications-notify} call. For example:
2416 (defun my-on-action-function (id key)
2417 (message "Message %d, key \"%s\" pressed" id key))
2418 @result{} my-on-action-function
2422 (defun my-on-close-function (id reason)
2423 (message "Message %d, closed due to \"%s\"" id reason))
2424 @result{} my-on-close-function
2428 (notifications-notify
2430 :body "This is <b>important</b>."
2431 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2432 :on-action 'my-on-action-function
2433 :on-close 'my-on-close-function)
2438 A message window opens on the desktop. Press "I agree"
2439 @result{} Message 22, key "Confirm" pressed
2440 Message 22, closed due to "dismissed"
2445 @defun notifications-close-notification id &optional bus
2446 This function closes a notification with identifier @var{id}.
2447 @var{bus} can be a string denoting a D-Bus connection, the default is
2451 @defun notifications-get-capabilities &optional bus
2452 Returns the capabilities of the notification server, a list of
2453 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2454 default is @code{:session}. The following capabilities can be
2459 The server will provide the specified actions to the user.
2464 @item :body-hyperlinks
2465 The server supports hyperlinks in the notifications.
2468 The server supports images in the notifications.
2471 Supports markup in the body text.
2474 The server will render an animation of all the frames in a given image
2478 Supports display of exactly 1 frame of any given image array. This
2479 value is mutually exclusive with @code{:icon-multi}.
2482 The server supports persistence of notifications.
2485 The server supports sounds on notifications.
2488 Further vendor-specific caps start with @code{:x-vendor}, like
2489 @code{:x-gnome-foo-cap}.
2492 @defun notifications-get-server-information &optional bus
2493 Return information on the notification server, a list of strings.
2494 @var{bus} can be a string denoting a D-Bus connection, the default is
2495 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2496 @var{version} @var{spec-version})}.
2500 The product name of the server.
2503 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2506 The server's version number.
2509 The specification version the server is compliant with.
2512 If @var{SPEC_VERSION} is @code{nil}, the server supports a
2513 specification prior to @samp{"1.0"}.
2516 @node File Notifications
2517 @section Notifications on File Changes
2518 @cindex file notifications
2520 Several operating systems support watching of filesystems for changes
2521 of files. If configured properly, Emacs links a respective library
2522 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2523 statically. These libraries enable watching of filesystems on the
2526 It is also possible to watch filesystems on remote machines,
2527 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2528 This does not depend on one of the libraries linked to Emacs.
2530 Since all these libraries emit different events on notified file
2531 changes, there is the Emacs library @code{filenotify} which provides a
2534 @defun file-notify-add-watch file flags callback
2535 Add a watch for filesystem events pertaining to @var{file}. This
2536 arranges for filesystem events pertaining to @var{file} to be reported
2539 The returned value is a descriptor for the added watch. Its type
2540 depends on the underlying library, it cannot be assumed to be an
2541 integer as in the example below. It should be used for comparison by
2544 If the @var{file} cannot be watched for some reason, this function
2545 signals a @code{file-notify-error} error.
2547 Sometimes, mounted filesystems cannot be watched for file changes.
2548 This is not detected by this function, a non-@code{nil} return value
2549 does not guarantee that changes on @var{file} will be notified.
2551 @var{flags} is a list of conditions to set what will be watched for.
2552 It can include the following symbols:
2556 watch for file changes
2557 @item attribute-change
2558 watch for file attribute changes, like permissions or modification
2562 If @var{file} is a directory, changes for all files in that directory
2563 will be notified. This does not work recursively.
2565 When any event happens, Emacs will call the @var{callback} function
2566 passing it a single argument @var{event}, which is of the form
2569 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2572 @var{descriptor} is the same object as the one returned by this
2573 function. @var{action} is the description of the event. It could be
2574 any one of the following symbols:
2578 @var{file} was created
2580 @var{file} was deleted
2582 @var{file} has changed
2584 @var{file} has been renamed to @var{file1}
2585 @item attribute-changed
2586 a @var{file} attribute was changed
2589 @var{file} and @var{file1} are the name of the file(s) whose event is
2590 being reported. For example:
2594 (require 'filenotify)
2595 @result{} filenotify
2599 (defun my-notify-callback (event)
2600 (message "Event %S" event))
2601 @result{} my-notify-callback
2605 (file-notify-add-watch
2606 "/tmp" '(change attribute-change) 'my-notify-callback)
2611 (write-region "foo" nil "/tmp/foo")
2612 @result{} Event (35025468 created "/tmp/.#foo")
2613 Event (35025468 created "/tmp/foo")
2614 Event (35025468 changed "/tmp/foo")
2615 Event (35025468 deleted "/tmp/.#foo")
2619 (write-region "bla" nil "/tmp/foo")
2620 @result{} Event (35025468 created "/tmp/.#foo")
2621 Event (35025468 changed "/tmp/foo") [2 times]
2622 Event (35025468 deleted "/tmp/.#foo")
2626 (set-file-modes "/tmp/foo" (default-file-modes))
2627 @result{} Event (35025468 attribute-changed "/tmp/foo")
2631 Whether the action @code{renamed} is returned, depends on the used
2632 watch library. It can be expected, when a directory is watched, and
2633 both @var{file} and @var{file1} belong to this directory. Otherwise,
2634 the actions @code{deleted} and @code{created} could be returned in a
2639 (rename-file "/tmp/foo" "/tmp/bla")
2640 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2644 (file-notify-add-watch
2645 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2650 (rename-file "/tmp/bla" "/var/tmp/bla")
2651 @result{} ;; gfilenotify
2652 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2654 @result{} ;; inotify
2655 Event (35025504 created "/var/tmp/bla")
2656 Event (35025468 deleted "/tmp/bla")
2661 @defun file-notify-rm-watch descriptor
2662 Removes an existing file watch specified by its @var{descriptor}.
2663 @var{descriptor} should be an object returned by
2664 @code{file-notify-add-watch}.
2667 @node Dynamic Libraries
2668 @section Dynamically Loaded Libraries
2669 @cindex dynamic libraries
2671 A @dfn{dynamically loaded library} is a library that is loaded on
2672 demand, when its facilities are first needed. Emacs supports such
2673 on-demand loading of support libraries for some of its features.
2675 @defvar dynamic-library-alist
2676 This is an alist of dynamic libraries and external library files
2679 Each element is a list of the form
2680 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2681 a symbol representing a supported external library, and the rest are
2682 strings giving alternate filenames for that library.
2684 Emacs tries to load the library from the files in the order they
2685 appear in the list; if none is found, the Emacs session won't have
2686 access to that library, and the features it provides will be
2689 Image support on some platforms uses this facility. Here's an example
2690 of setting this variable for supporting images on MS-Windows:
2693 (setq dynamic-library-alist
2694 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2695 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2696 "libpng13d.dll" "libpng13.dll")
2697 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2699 (tiff "libtiff3.dll" "libtiff.dll")
2700 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2701 (svg "librsvg-2-2.dll")
2702 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2703 (glib "libglib-2.0-0.dll")
2704 (gobject "libgobject-2.0-0.dll")))
2707 Note that image types @code{pbm} and @code{xbm} do not need entries in
2708 this variable because they do not depend on external libraries and are
2709 always available in Emacs.
2711 Also note that this variable is not meant to be a generic facility for
2712 accessing external libraries; only those already known by Emacs can
2713 be loaded through it.
2715 This variable is ignored if the given @var{library} is statically