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}, you may wish to set
521 this variable to @code{nil} first in order to cause the new dumped Emacs
522 to process its new command-line arguments.
525 @defvar command-switch-alist
526 @cindex switches on command line
527 @cindex options on command line
528 @cindex command-line options
529 This variable is an alist of user-defined command-line options and
530 associated handler functions. By default it is empty, but you can
531 add elements if you wish.
533 A @dfn{command-line option} is an argument on the command line, which
540 The elements of the @code{command-switch-alist} look like this:
543 (@var{option} . @var{handler-function})
546 The @sc{car}, @var{option}, is a string, the name of a command-line
547 option (not including the initial hyphen). The @var{handler-function}
548 is called to handle @var{option}, and receives the option name as its
551 In some cases, the option is followed in the command line by an
552 argument. In these cases, the @var{handler-function} can find all the
553 remaining command-line arguments in the variable
554 @code{command-line-args-left}. (The entire list of command-line
555 arguments is in @code{command-line-args}.)
557 The command-line arguments are parsed by the @code{command-line-1}
558 function in the @file{startup.el} file. See also @ref{Emacs
559 Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
563 @defvar command-line-args
564 The value of this variable is the list of command-line arguments passed
568 @defvar command-line-args-left
570 The value of this variable is the list of command-line arguments that
571 have not yet been processed.
572 @c Don't mention this, since it is a "bad name for a dynamically bound variable"
573 @c @code{argv} is an alias for this.
576 @defvar command-line-functions
577 This variable's value is a list of functions for handling an
578 unrecognized command-line argument. Each time the next argument to be
579 processed has no special meaning, the functions in this list are called,
580 in order of appearance, until one of them returns a non-@code{nil}
583 These functions are called with no arguments. They can access the
584 command-line argument under consideration through the variable
585 @code{argi}, which is bound temporarily at this point. The remaining
586 arguments (not including the current one) are in the variable
587 @code{command-line-args-left}.
589 When a function recognizes and processes the argument in @code{argi}, it
590 should return a non-@code{nil} value to say it has dealt with that
591 argument. If it has also dealt with some of the following arguments, it
592 can indicate that by deleting them from @code{command-line-args-left}.
594 If all of these functions return @code{nil}, then the argument is treated
595 as a file name to visit.
599 @section Getting Out of Emacs
600 @cindex exiting Emacs
602 There are two ways to get out of Emacs: you can kill the Emacs job,
603 which exits permanently, or you can suspend it, which permits you to
604 reenter the Emacs process later. (In a graphical environment, you can
605 of course simply switch to another application without doing anything
606 special to Emacs, then switch back to Emacs when you want.)
609 * Killing Emacs:: Exiting Emacs irreversibly.
610 * Suspending Emacs:: Exiting Emacs reversibly.
614 @subsection Killing Emacs
615 @cindex killing Emacs
617 Killing Emacs means ending the execution of the Emacs process.
618 If you started Emacs from a terminal, the parent process normally
619 resumes control. The low-level primitive for killing Emacs is
622 @deffn Command kill-emacs &optional exit-data
623 This command calls the hook @code{kill-emacs-hook}, then exits the
624 Emacs process and kills it.
626 If @var{exit-data} is an integer, that is used as the exit status of
627 the Emacs process. (This is useful primarily in batch operation; see
630 If @var{exit-data} is a string, its contents are stuffed into the
631 terminal input buffer so that the shell (or whatever program next reads
632 input) can read them.
638 @cindex operating system signal
639 The @code{kill-emacs} function is normally called via the
640 higher-level command @kbd{C-x C-c}
641 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
642 Emacs Manual}. It is also called automatically if Emacs receives a
643 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g., when the
644 controlling terminal is disconnected), or if it receives a
645 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
647 @defvar kill-emacs-hook
648 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
650 Because @code{kill-emacs} can be called in situations where user
651 interaction is impossible (e.g., when the terminal is disconnected),
652 functions on this hook should not attempt to interact with the user.
653 If you want to interact with the user when Emacs is shutting down, use
654 @code{kill-emacs-query-functions}, described below.
657 When Emacs is killed, all the information in the Emacs process,
658 aside from files that have been saved, is lost. Because killing Emacs
659 inadvertently can lose a lot of work, the
660 @code{save-buffers-kill-terminal} command queries for confirmation if
661 you have buffers that need saving or subprocesses that are running.
662 It also runs the abnormal hook @code{kill-emacs-query-functions}:
664 @defvar kill-emacs-query-functions
665 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
666 functions in this hook, after asking the standard questions and before
667 calling @code{kill-emacs}. The functions are called in order of
668 appearance, with no arguments. Each function can ask for additional
669 confirmation from the user. If any of them returns @code{nil},
670 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
671 the remaining functions in this hook. Calling @code{kill-emacs}
672 directly does not run this hook.
675 @node Suspending Emacs
676 @subsection Suspending Emacs
677 @cindex suspending Emacs
679 On text terminals, it is possible to @dfn{suspend Emacs}, which
680 means stopping Emacs temporarily and returning control to its superior
681 process, which is usually the shell. This allows you to resume
682 editing later in the same Emacs process, with the same buffers, the
683 same kill ring, the same undo history, and so on. To resume Emacs,
684 use the appropriate command in the parent shell---most likely
687 @cindex controlling terminal
688 Suspending works only on a terminal device from which the Emacs
689 session was started. We call that device the @dfn{controlling
690 terminal} of the session. Suspending is not allowed if the
691 controlling terminal is a graphical terminal. Suspending is usually
692 not relevant in graphical environments, since you can simply switch to
693 another application without doing anything special to Emacs.
695 @c FIXME? Are there any systems Emacs still supports that do not
698 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
699 not support suspension of jobs; on these systems, ``suspension''
700 actually creates a new shell temporarily as a subprocess of Emacs.
701 Then you would exit the shell to return to Emacs.
703 @deffn Command suspend-emacs &optional string
704 This function stops Emacs and returns control to the superior process.
705 If and when the superior process resumes Emacs, @code{suspend-emacs}
706 returns @code{nil} to its caller in Lisp.
708 This function works only on the controlling terminal of the Emacs
709 session; to relinquish control of other tty devices, use
710 @code{suspend-tty} (see below). If the Emacs session uses more than
711 one terminal, you must delete the frames on all the other terminals
712 before suspending Emacs, or this function signals an error.
713 @xref{Multiple Terminals}.
715 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
716 superior shell, to be read as terminal input.
717 @c FIXME? It seems to me that shell does echo STRING.
718 The characters in @var{string} are not echoed by the superior shell;
719 only the results appear.
721 Before suspending, @code{suspend-emacs} runs the normal hook
722 @code{suspend-hook}. After the user resumes Emacs,
723 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
726 The next redisplay after resumption will redraw the entire screen,
727 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
728 @xref{Refresh Screen}.
730 Here is an example of how you could use these hooks:
734 (add-hook 'suspend-hook
735 (lambda () (or (y-or-n-p "Really suspend? ")
736 (error "Suspend canceled"))))
738 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
741 @c The sit-for prevents the ``nil'' that suspend-emacs returns
742 @c hiding the message.
744 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
748 ---------- Buffer: Minibuffer ----------
749 Really suspend? @kbd{y}
750 ---------- Buffer: Minibuffer ----------
754 ---------- Parent Shell ----------
760 ---------- Echo Area ----------
765 @c FIXME? AFAICS, it is echoed.
766 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
767 is read and executed by the shell.
771 This variable is a normal hook that Emacs runs before suspending.
774 @defvar suspend-resume-hook
775 This variable is a normal hook that Emacs runs on resuming
779 @defun suspend-tty &optional tty
780 If @var{tty} specifies a terminal device used by Emacs, this function
781 relinquishes the device and restores it to its prior state. Frames
782 that used the device continue to exist, but are not updated and Emacs
783 doesn't read input from them. @var{tty} can be a terminal object, a
784 frame (meaning the terminal for that frame), or @code{nil} (meaning
785 the terminal for the selected frame). @xref{Multiple Terminals}.
787 If @var{tty} is already suspended, this function does nothing.
789 @vindex suspend-tty-functions
790 This function runs the hook @code{suspend-tty-functions}, passing the
791 terminal object as an argument to each function.
794 @defun resume-tty &optional tty
795 This function resumes the previously suspended terminal device
796 @var{tty}; where @var{tty} has the same possible values as it does
797 for @code{suspend-tty}.
799 @vindex resume-tty-functions
800 This function reopens the terminal device, re-initializes it, and
801 redraws it with that terminal's selected frame. It then runs the
802 hook @code{resume-tty-functions}, passing the terminal object as an
803 argument to each function.
805 If the same device is already used by another Emacs terminal, this
806 function signals an error. If @var{tty} is not suspended, this
807 function does nothing.
810 @defun controlling-tty-p &optional tty
811 This function returns non-@code{nil} if @var{tty} is the
812 controlling terminal of the Emacs session; @var{tty} can be a
813 terminal object, a frame (meaning the terminal for that frame), or
814 @code{nil} (meaning the terminal for the selected frame).
817 @deffn Command suspend-frame
818 This command @dfn{suspends} a frame. For GUI frames, it calls
819 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
820 text terminals, it calls either @code{suspend-emacs} or
821 @code{suspend-tty}, depending on whether the frame is displayed on the
822 controlling terminal device or not.
825 @node System Environment
826 @section Operating System Environment
827 @cindex operating system environment
829 Emacs provides access to variables in the operating system environment
830 through various functions. These variables include the name of the
831 system, the user's @acronym{UID}, and so on.
833 @defvar system-configuration
834 This variable holds the standard GNU configuration name for the
835 hardware/software configuration of your system, as a string. For
836 example, a typical value for a 64-bit GNU/Linux system is
837 @samp{"x86_64-unknown-linux-gnu"}.
840 @cindex system type and name
842 The value of this variable is a symbol indicating the type of operating
843 system Emacs is running on. The possible values are:
850 Berkeley BSD and its variants.
853 Cygwin, a Posix layer on top of MS-Windows.
859 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
862 A GNU/Linux system---that is, a variant GNU system, using the Linux
863 kernel. (These systems are the ones people often call ``Linux'', but
864 actually Linux is just the kernel, not the whole system.)
867 A GNU (glibc-based) system with a FreeBSD kernel.
870 Hewlett-Packard HPUX operating system.
873 Silicon Graphics Irix system.
876 Microsoft's DOS@. Emacs compiled with DJGPP for MS-DOS binds
877 @code{system-type} to @code{ms-dos} even when you run it on MS-Windows.
883 Microsoft Windows NT, 9X and later. The value of @code{system-type}
884 is always @code{windows-nt}, e.g., even on Windows 7.
888 We do not wish to add new symbols to make finer distinctions unless it
889 is absolutely necessary! In fact, we hope to eliminate some of these
890 alternatives in the future. If you need to make a finer distinction
891 than @code{system-type} allows for, you can test
892 @code{system-configuration}, e.g., against a regexp.
896 This function returns the name of the machine you are running on, as a
900 The symbol @code{system-name} is a variable as well as a function. In
901 fact, the function returns whatever value the variable
902 @code{system-name} currently holds. Thus, you can set the variable
903 @code{system-name} in case Emacs is confused about the name of your
904 system. The variable is also useful for constructing frame titles
905 (@pxref{Frame Titles}).
907 @c FIXME seems like this section is not the best place for this option?
908 @defopt mail-host-address
909 If this variable is non-@code{nil}, it is used instead of
910 @code{system-name} for purposes of generating email addresses. For
911 example, it is used when constructing the default value of
912 @code{user-mail-address}. @xref{User Identification}. (Since this is
913 done when Emacs starts up, the value actually used is the one saved when
914 Emacs was dumped. @xref{Building Emacs}.)
915 @c FIXME sounds like should probably give this a :set-after and some
916 @c custom-initialize-delay voodoo.
919 @deffn Command getenv var &optional frame
920 @cindex environment variable access
921 This function returns the value of the environment variable @var{var},
922 as a string. @var{var} should be a string. If @var{var} is undefined
923 in the environment, @code{getenv} returns @code{nil}. It returns
924 @samp{""} if @var{var} is set but null. Within Emacs, a list of environment
925 variables and their values is kept in the variable @code{process-environment}.
934 The shell command @code{printenv} prints all or part of the environment:
939 PATH=/usr/local/bin:/usr/bin:/bin
951 @deffn Command setenv variable &optional value substitute
952 This command sets the value of the environment variable named
953 @var{variable} to @var{value}. @var{variable} should be a string.
954 Internally, Emacs Lisp can handle any string. However, normally
955 @var{variable} should be a valid shell identifier, that is, a sequence
956 of letters, digits and underscores, starting with a letter or
957 underscore. Otherwise, errors may occur if subprocesses of Emacs try
958 to access the value of @var{variable}. If @var{value} is omitted or
959 @code{nil} (or, interactively, with a prefix argument), @code{setenv}
960 removes @var{variable} from the environment. Otherwise, @var{value}
963 If the optional argument @var{substitute} is non-@code{nil}, Emacs
964 calls the function @code{substitute-env-vars} to expand any
965 environment variables in @var{value}.
967 @code{setenv} works by modifying @code{process-environment}; binding
968 that variable with @code{let} is also reasonable practice.
970 @code{setenv} returns the new value of @var{variable}, or @code{nil}
971 if it removed @var{variable} from the environment.
974 @defvar process-environment
975 This variable is a list of strings, each describing one environment
976 variable. The functions @code{getenv} and @code{setenv} work by means
982 @result{} ("PATH=/usr/local/bin:/usr/bin:/bin"
993 If @code{process-environment} contains ``duplicate'' elements that
994 specify the same environment variable, the first of these elements
995 specifies the variable, and the other ``duplicates'' are ignored.
998 @defvar initial-environment
999 This variable holds the list of environment variables Emacs inherited
1000 from its parent process when Emacs started.
1003 @defvar path-separator
1004 This variable holds a string that says which character separates
1005 directories in a search path (as found in an environment variable). Its
1006 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
1009 @defun parse-colon-path path
1010 This function takes a search path string such as the value of
1011 the @env{PATH} environment variable, and splits it at the separators,
1012 returning a list of directory names. @code{nil} in this list means
1013 the current directory. Although the function's name says
1014 ``colon'', it actually uses the value of @code{path-separator}.
1017 (parse-colon-path ":/foo:/bar")
1018 @result{} (nil "/foo/" "/bar/")
1022 @defvar invocation-name
1023 This variable holds the program name under which Emacs was invoked. The
1024 value is a string, and does not include a directory name.
1027 @defvar invocation-directory
1028 This variable holds the directory from which the Emacs executable was
1029 invoked, or @code{nil} if that directory cannot be determined.
1032 @defvar installation-directory
1033 If non-@code{nil}, this is a directory within which to look for the
1034 @file{lib-src} and @file{etc} subdirectories. In an installed Emacs,
1035 it is normally @code{nil}. It is non-@code{nil}
1036 when Emacs can't find those directories in their standard installed
1037 locations, but can find them in a directory related somehow to the one
1038 containing the Emacs executable (i.e., @code{invocation-directory}).
1041 @defun load-average &optional use-float
1042 This function returns the current 1-minute, 5-minute, and 15-minute
1043 system load averages, in a list. The load average indicates the
1044 number of processes trying to run on the system.
1046 By default, the values are integers that are 100 times the system load
1047 averages, but if @var{use-float} is non-@code{nil}, then they are
1048 returned as floating point numbers without multiplying by 100.
1050 If it is impossible to obtain the load average, this function signals
1051 an error. On some platforms, access to load averages requires
1052 installing Emacs as setuid or setgid so that it can read kernel
1053 information, and that usually isn't advisable.
1054 @c FIXME which platforms are these? Are they still relevant?
1056 If the 1-minute load average is available, but the 5- or 15-minute
1057 averages are not, this function returns a shortened list containing
1058 the available averages.
1063 @result{} (169 48 36)
1067 @result{} (1.69 0.48 0.36)
1071 The shell command @code{uptime} returns similar information.
1075 This function returns the process @acronym{ID} of the Emacs process,
1079 @defvar tty-erase-char
1080 This variable holds the erase character that was selected
1081 in the system's terminal driver, before Emacs was started.
1082 @c FIXME? Seems untrue since 23.1. For me, it is 0.
1083 @c The value is @code{nil} if Emacs is running under a window system.
1086 @node User Identification
1087 @section User Identification
1088 @cindex user identification
1090 @defvar init-file-user
1091 This variable says which user's init files should be used by
1092 Emacs---or @code{nil} if none. @code{""} stands for the user who
1093 originally logged in. The value reflects command-line options such as
1094 @samp{-q} or @samp{-u @var{user}}.
1096 Lisp packages that load files of customizations, or any other sort of
1097 user profile, should obey this variable in deciding where to find it.
1098 They should load the profile of the user name found in this variable.
1099 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q}
1100 option was used, then Lisp packages should not load any customization
1101 files or user profile.
1104 @defopt user-mail-address
1105 This holds the nominal email address of the user who is using Emacs.
1106 Emacs normally sets this variable to a default value after reading your
1107 init files, but not if you have already set it. So you can set the
1108 variable to some other value in your init file if you do not
1109 want to use the default value.
1112 @defun user-login-name &optional uid
1113 This function returns the name under which the user is logged in.
1114 It uses the environment variables @env{LOGNAME} or @env{USER} if
1115 either is set. Otherwise, the value is based on the effective
1116 @acronym{UID}, not the real @acronym{UID}.
1118 If you specify @var{uid} (a number), the result is the user name that
1119 corresponds to @var{uid}, or @code{nil} if there is no such user.
1122 @defun user-real-login-name
1123 This function returns the user name corresponding to Emacs's real
1124 @acronym{UID}. This ignores the effective @acronym{UID}, and the
1125 environment variables @env{LOGNAME} and @env{USER}.
1128 @defun user-full-name &optional uid
1129 This function returns the full name of the logged-in user---or the value
1130 of the environment variable @env{NAME}, if that is set.
1132 If the Emacs process's user-id does not correspond to any known user (and
1133 provided @code{NAME} is not set), the result is @code{"unknown"}.
1135 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1136 or a string (a login name). Then @code{user-full-name} returns the full
1137 name corresponding to that user-id or login name. If you specify a
1138 user-id or login name that isn't defined, it returns @code{nil}.
1141 @vindex user-full-name
1142 @vindex user-real-login-name
1143 @vindex user-login-name
1144 The symbols @code{user-login-name}, @code{user-real-login-name} and
1145 @code{user-full-name} are variables as well as functions. The functions
1146 return the same values that the variables hold. These variables allow
1147 you to ``fake out'' Emacs by telling the functions what to return. The
1148 variables are also useful for constructing frame titles (@pxref{Frame
1151 @defun user-real-uid
1152 This function returns the real @acronym{UID} of the user.
1153 The value may be a floating point number, in the (unlikely) event that
1154 the UID is too large to fit in a Lisp integer.
1158 This function returns the effective @acronym{UID} of the user.
1159 The value may be a floating point number.
1163 This function returns the effective @acronym{GID} of the Emacs process.
1164 The value may be a floating point number.
1167 @defun group-real-gid
1168 This function returns the real @acronym{GID} of the Emacs process.
1169 The value may be a floating point number.
1173 This function returns a list of strings, listing the user names on the
1174 system. If Emacs cannot retrieve this information, the return value
1175 is a list containing just the value of @code{user-real-login-name}.
1179 @defun system-groups
1180 This function returns a list of strings, listing the names of user
1181 groups on the system. If Emacs cannot retrieve this information, the
1182 return value is @code{nil}.
1187 @section Time of Day
1189 This section explains how to determine the current time and time
1193 Most of these functions represent time as a list of either four
1194 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
1195 @var{picosec})}, or of three
1196 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1197 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1198 @var{sec-high} and @var{sec-low} give the high and low bits of an
1199 integer number of seconds. This integer number,
1201 @var{high} * 2**16 + @var{low},
1206 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1207 UTC) to the specified time. The third list element @var{microsec}, if
1208 present, gives the number of microseconds from the start of that
1209 second to the specified time.
1210 Similarly, the fourth list element @var{picosec}, if present, gives
1211 the number of picoseconds from the start of that microsecond to the
1214 The return value of @code{current-time} represents time using four
1215 integers, as do the timestamps in the return value of
1216 @code{file-attributes} (@pxref{Definition of
1217 file-attributes}). In function arguments, e.g., the @var{time-value}
1218 argument to @code{current-time-string}, two-, three-, and four-integer
1219 lists are accepted. You can convert times from the list
1220 representation into standard human-readable strings using
1221 @code{current-time}, or to other forms using the @code{decode-time}
1222 and @code{format-time-string} functions documented in the following
1225 @defun current-time-string &optional time-value
1226 This function returns the current time and date as a human-readable
1227 string. The format does not vary for the initial part of the string,
1228 which contains the day of week, month, day of month, and time of day
1229 in that order: the number of characters used for these fields is
1230 always the same, so you can reliably
1231 use @code{substring} to extract them. You should count
1232 characters from the beginning of the string rather than from the end,
1233 as the year might not have exactly four digits, and additional
1234 information may some day be added at the end.
1236 The argument @var{time-value}, if given, specifies a time to format
1237 (represented as a list of integers), instead of the current time.
1241 (current-time-string)
1242 @result{} "Wed Oct 14 22:21:05 1987"
1248 This function returns the current time, represented as a list of four
1249 integers @code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
1250 These integers have trailing zeros on systems that return time with
1251 lower resolutions. On all current machines @var{picosec} is a
1252 multiple of 1000, but this may change as higher-resolution clocks
1256 @defun float-time &optional time-value
1257 This function returns the current time as a floating-point number of
1258 seconds since the epoch. The optional argument @var{time-value}, if
1259 given, specifies a time (represented as a list of integers) to convert
1260 instead of the current time.
1262 @emph{Warning}: Since the result is floating point, it may not be
1263 exact. Do not use this function if precise time stamps are required.
1266 @defun current-time-zone &optional time-value
1267 This function returns a list describing the time zone that the user is
1270 The value has the form @code{(@var{offset} @var{name})}. Here
1271 @var{offset} is an integer giving the number of seconds ahead of UTC
1272 (east of Greenwich). A negative value means west of Greenwich. The
1273 second element, @var{name}, is a string giving the name of the time
1274 zone. Both elements change when daylight saving time begins or ends;
1275 if the user has specified a time zone that does not use a seasonal time
1276 adjustment, then the value is constant through time.
1278 If the operating system doesn't supply all the information necessary to
1279 compute the value, the unknown elements of the list are @code{nil}.
1281 The argument @var{time-value}, if given, specifies a time (represented
1282 as a list of integers) to analyze instead of the current time.
1285 The current time zone is determined by the @env{TZ} environment
1286 variable. @xref{System Environment}. For example, you can tell Emacs
1287 to use universal time with @code{(setenv "TZ" "UTC0")}. If @env{TZ}
1288 is not in the environment, Emacs uses a platform-dependent default
1291 @node Time Conversion
1292 @section Time Conversion
1294 These functions convert time values (lists of two to four integers,
1295 as explained in the previous section) into calendrical information and
1298 Many 32-bit operating systems are limited to time values containing
1299 32 bits of information; these systems typically handle only the times
1300 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
1301 However, 64-bit and some 32-bit operating systems have larger time
1302 values, and can represent times far in the past or future.
1304 Time conversion functions always use the Gregorian calendar, even
1305 for dates before the Gregorian calendar was introduced. Year numbers
1306 count the number of years since the year 1 B.C., and do not skip zero
1307 as traditional Gregorian years do; for example, the year number
1308 @minus{}37 represents the Gregorian year 38 B.C@.
1310 @defun decode-time &optional time
1311 This function converts a time value into calendrical information. If
1312 you don't specify @var{time}, it decodes the current time. The return
1313 value is a list of nine elements, as follows:
1316 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1319 Here is what the elements mean:
1323 The number of seconds past the minute, as an integer between 0 and 59.
1324 On some operating systems, this is 60 for leap seconds.
1326 The number of minutes past the hour, as an integer between 0 and 59.
1328 The hour of the day, as an integer between 0 and 23.
1330 The day of the month, as an integer between 1 and 31.
1332 The month of the year, as an integer between 1 and 12.
1334 The year, an integer typically greater than 1900.
1336 The day of week, as an integer between 0 and 6, where 0 stands for
1339 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1341 An integer indicating the time zone, as the number of seconds east of
1345 @strong{Common Lisp Note:} Common Lisp has different meanings for
1346 @var{dow} and @var{zone}.
1349 @defun encode-time seconds minutes hour day month year &optional zone
1350 This function is the inverse of @code{decode-time}. It converts seven
1351 items of calendrical data into a time value. For the meanings of the
1352 arguments, see the table above under @code{decode-time}.
1354 Year numbers less than 100 are not treated specially. If you want them
1355 to stand for years above 1900, or years above 2000, you must alter them
1356 yourself before you call @code{encode-time}.
1358 The optional argument @var{zone} defaults to the current time zone and
1359 its daylight saving time rules. If specified, it can be either a list
1360 (as you would get from @code{current-time-zone}), a string as in the
1361 @env{TZ} environment variable, @code{t} for Universal Time, or an
1362 integer (as you would get from @code{decode-time}). The specified
1363 zone is used without any further alteration for daylight saving time.
1365 If you pass more than seven arguments to @code{encode-time}, the first
1366 six are used as @var{seconds} through @var{year}, the last argument is
1367 used as @var{zone}, and the arguments in between are ignored. This
1368 feature makes it possible to use the elements of a list returned by
1369 @code{decode-time} as the arguments to @code{encode-time}, like this:
1372 (apply 'encode-time (decode-time @dots{}))
1375 You can perform simple date arithmetic by using out-of-range values for
1376 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1377 arguments; for example, day 0 means the day preceding the given month.
1379 The operating system puts limits on the range of possible time values;
1380 if you try to encode a time that is out of range, an error results.
1381 For instance, years before 1970 do not work on some systems;
1382 on others, years as early as 1901 do work.
1386 @section Parsing and Formatting Times
1388 These functions convert time values to text in a string, and vice versa.
1389 Time values are lists of two to four integers (@pxref{Time of Day}).
1391 @defun date-to-time string
1392 This function parses the time-string @var{string} and returns the
1393 corresponding time value.
1396 @defun format-time-string format-string &optional time universal
1397 This function converts @var{time} (or the current time, if @var{time} is
1398 omitted) to a string according to @var{format-string}. The argument
1399 @var{format-string} may contain @samp{%}-sequences which say to
1400 substitute parts of the time. Here is a table of what the
1401 @samp{%}-sequences mean:
1405 This stands for the abbreviated name of the day of week.
1407 This stands for the full name of the day of week.
1409 This stands for the abbreviated name of the month.
1411 This stands for the full name of the month.
1413 This is a synonym for @samp{%x %X}.
1415 This has a locale-specific meaning. In the default locale (named C), it
1416 is equivalent to @samp{%A, %B %e, %Y}.
1418 This stands for the day of month, zero-padded.
1420 This is a synonym for @samp{%m/%d/%y}.
1422 This stands for the day of month, blank-padded.
1424 This is a synonym for @samp{%b}.
1426 This stands for the hour (00--23).
1428 This stands for the hour (01--12).
1430 This stands for the day of the year (001--366).
1432 This stands for the hour (0--23), blank padded.
1434 This stands for the hour (1--12), blank padded.
1436 This stands for the month (01--12).
1438 This stands for the minute (00--59).
1440 This stands for a newline.
1442 This stands for the nanoseconds (000000000--999999999). To ask for
1443 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1444 microseconds, etc. Any excess digits are discarded, without rounding.
1446 This stands for @samp{AM} or @samp{PM}, as appropriate.
1448 This is a synonym for @samp{%I:%M:%S %p}.
1450 This is a synonym for @samp{%H:%M}.
1452 This stands for the seconds (00--59).
1454 This stands for a tab character.
1456 This is a synonym for @samp{%H:%M:%S}.
1458 This stands for the week of the year (01--52), assuming that weeks
1461 This stands for the numeric day of week (0--6). Sunday is day 0.
1463 This stands for the week of the year (01--52), assuming that weeks
1466 This has a locale-specific meaning. In the default locale (named
1467 @samp{C}), it is equivalent to @samp{%D}.
1469 This has a locale-specific meaning. In the default locale (named
1470 @samp{C}), it is equivalent to @samp{%T}.
1472 This stands for the year without century (00--99).
1474 This stands for the year with century.
1476 This stands for the time zone abbreviation (e.g., @samp{EST}).
1478 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1481 You can also specify the field width and type of padding for any of
1482 these @samp{%}-sequences. This works as in @code{printf}: you write
1483 the field width as digits in the middle of a @samp{%}-sequences. If you
1484 start the field width with @samp{0}, it means to pad with zeros. If you
1485 start the field width with @samp{_}, it means to pad with spaces.
1487 For example, @samp{%S} specifies the number of seconds since the minute;
1488 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1489 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1490 because that is how @samp{%S} normally pads to two positions.
1492 The characters @samp{E} and @samp{O} act as modifiers when used between
1493 @samp{%} and one of the letters in the table above. @samp{E} specifies
1494 using the current locale's ``alternative'' version of the date and time.
1495 In a Japanese locale, for example, @code{%Ex} might yield a date format
1496 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1497 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1500 @samp{O} means to use the current locale's ``alternative''
1501 representation of numbers, instead of the ordinary decimal digits. This
1502 is allowed with most letters, all the ones that output numbers.
1504 If @var{universal} is non-@code{nil}, that means to describe the time as
1505 Universal Time; @code{nil} means describe it using what Emacs believes
1506 is the local time zone (see @code{current-time-zone}).
1508 This function uses the C library function @code{strftime}
1509 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1510 Manual}) to do most of the work. In order to communicate with that
1511 function, it first encodes its argument using the coding system
1512 specified by @code{locale-coding-system} (@pxref{Locales}); after
1513 @code{strftime} returns the resulting string,
1514 @code{format-time-string} decodes the string using that same coding
1518 @defun seconds-to-time seconds
1519 This function converts @var{seconds}, a floating point number of
1520 seconds since the epoch, to a time value and returns that. To perform
1521 the inverse conversion, use @code{float-time}.
1524 @defun format-seconds format-string seconds
1525 This function converts its argument @var{seconds} into a string of
1526 years, days, hours, etc., according to @var{format-string}. The
1527 argument @var{format-string} may contain @samp{%}-sequences which
1528 control the conversion. Here is a table of what the
1529 @samp{%}-sequences mean:
1534 The integer number of 365-day years.
1537 The integer number of days.
1540 The integer number of hours.
1543 The integer number of minutes.
1546 The integer number of seconds.
1548 Non-printing control flag. When it is used, other specifiers must be
1549 given in the order of decreasing size, i.e., years before days, hours
1550 before minutes, etc. Nothing will be produced in the result string to
1551 the left of @samp{%z} until the first non-zero conversion is
1552 encountered. For example, the default format used by
1553 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1554 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1555 will always be produced, but years, days, hours, and minutes will only
1556 be shown if they are non-zero.
1558 Produces a literal @samp{%}.
1561 Upper-case format sequences produce the units in addition to the
1562 numbers, lower-case formats produce only the numbers.
1564 You can also specify the field width by following the @samp{%} with a
1565 number; shorter numbers will be padded with blanks. An optional
1566 period before the width requests zero-padding instead. For example,
1567 @code{"%.3Y"} might produce @code{"004 years"}.
1569 @emph{Warning:} This function works only with values of @var{seconds}
1570 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1571 most-positive-fixnum}).
1574 @node Processor Run Time
1575 @section Processor Run time
1576 @cindex processor run time
1577 @cindex Emacs process run time
1579 Emacs provides several functions and primitives that return time,
1580 both elapsed and processor time, used by the Emacs process.
1582 @deffn Command emacs-uptime &optional format
1583 This function returns a string representing the Emacs
1584 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1585 running. The string is formatted by @code{format-seconds} according
1586 to the optional argument @var{format}. For the available format
1587 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1588 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1591 When called interactively, it prints the uptime in the echo area.
1594 @defun get-internal-run-time
1595 This function returns the processor run time used by Emacs as a list
1596 of four integers: @code{(@var{high} @var{low} @var{microsec}
1597 @var{picosec})}, using the same format as @code{current-time}
1598 (@pxref{Time of Day}).
1600 Note that the time returned by this function excludes the time Emacs
1601 was not using the processor, and if the Emacs process has several
1602 threads, the returned value is the sum of the processor times used up
1603 by all Emacs threads.
1605 If the system doesn't provide a way to determine the processor run
1606 time, @code{get-internal-run-time} returns the same time as
1607 @code{current-time}.
1610 @deffn Command emacs-init-time
1611 This function returns the duration of the Emacs initialization
1612 (@pxref{Startup Summary}) in seconds, as a string. When called
1613 interactively, it prints the duration in the echo area.
1616 @node Time Calculations
1617 @section Time Calculations
1619 These functions perform calendrical computations using time values
1620 (the kind of list that @code{current-time} returns).
1622 @defun time-less-p t1 t2
1623 This returns @code{t} if time value @var{t1} is less than time value
1627 @defun time-subtract t1 t2
1628 This returns the time difference @var{t1} @minus{} @var{t2} between
1629 two time values, in the same format as a time value.
1632 @defun time-add t1 t2
1633 This returns the sum of two time values, one of which ought to
1634 represent a time difference rather than a point in time.
1635 Here is how to add a number of seconds to a time value:
1638 (time-add @var{time} (seconds-to-time @var{seconds}))
1642 @defun time-to-days time
1643 This function returns the number of days between the beginning of year
1647 @defun time-to-day-in-year time
1648 This returns the day number within the year corresponding to @var{time}.
1651 @defun date-leap-year-p year
1652 This function returns @code{t} if @var{year} is a leap year.
1656 @section Timers for Delayed Execution
1659 You can set up a @dfn{timer} to call a function at a specified
1660 future time or after a certain length of idleness.
1662 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1663 can run them only when Emacs could accept output from a subprocess:
1664 namely, while waiting or inside certain primitive functions such as
1665 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1666 timer's execution may be delayed if Emacs is busy. However, the time of
1667 execution is very precise if Emacs is idle.
1669 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1670 function, because quitting out of many timer functions can leave
1671 things in an inconsistent state. This is normally unproblematical
1672 because most timer functions don't do a lot of work. Indeed, for a
1673 timer to call a function that takes substantial time to run is likely
1674 to be annoying. If a timer function needs to allow quitting, it
1675 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1676 a timer function calls @code{accept-process-output} to receive output
1677 from an external process, that call should be wrapped inside
1678 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1681 It is usually a bad idea for timer functions to alter buffer
1682 contents. When they do, they usually should call @code{undo-boundary}
1683 both before and after changing the buffer, to separate the timer's
1684 changes from user commands' changes and prevent a single undo entry
1685 from growing to be quite large.
1687 Timer functions should also avoid calling functions that cause Emacs
1688 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1689 unpredictable effects, since other timers (or even the same timer) can
1690 run while waiting. If a timer function needs to perform an action
1691 after a certain time has elapsed, it can do this by scheduling a new
1694 If a timer function calls functions that can change the match data,
1695 it should save and restore the match data. @xref{Saving Match Data}.
1697 @deffn Command run-at-time time repeat function &rest args
1698 This sets up a timer that calls the function @var{function} with
1699 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1700 (integer or floating point), the timer is scheduled to run again every
1701 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1702 the timer runs only once.
1704 @var{time} may specify an absolute or a relative time.
1706 Absolute times may be specified using a string with a limited variety
1707 of formats, and are taken to be times @emph{today}, even if already in
1708 the past. The recognized forms are @samp{@var{xxxx}},
1709 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1710 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1711 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1712 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1713 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1714 to separate the hour and minute parts.
1716 To specify a relative time as a string, use numbers followed by units.
1721 denotes 1 minute from now.
1723 denotes 65 seconds from now.
1724 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1725 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1728 For relative time values, Emacs considers a month to be exactly thirty
1729 days, and a year to be exactly 365.25 days.
1731 Not all convenient formats are strings. If @var{time} is a number
1732 (integer or floating point), that specifies a relative time measured in
1733 seconds. The result of @code{encode-time} can also be used to specify
1734 an absolute value for @var{time}.
1736 In most cases, @var{repeat} has no effect on when @emph{first} call
1737 takes place---@var{time} alone specifies that. There is one exception:
1738 if @var{time} is @code{t}, then the timer runs whenever the time is a
1739 multiple of @var{repeat} seconds after the epoch. This is useful for
1740 functions like @code{display-time}.
1742 The function @code{run-at-time} returns a timer value that identifies
1743 the particular scheduled future action. You can use this value to call
1744 @code{cancel-timer} (see below).
1747 A repeating timer nominally ought to run every @var{repeat} seconds,
1748 but remember that any invocation of a timer can be late. Lateness of
1749 one repetition has no effect on the scheduled time of the next
1750 repetition. For instance, if Emacs is busy computing for long enough
1751 to cover three scheduled repetitions of the timer, and then starts to
1752 wait, it will immediately call the timer function three times in
1753 immediate succession (presuming no other timers trigger before or
1754 between them). If you want a timer to run again no less than @var{n}
1755 seconds after the last invocation, don't use the @var{repeat} argument.
1756 Instead, the timer function should explicitly reschedule the timer.
1758 @defopt timer-max-repeats
1759 This variable's value specifies the maximum number of times to repeat
1760 calling a timer function in a row, when many previously scheduled
1761 calls were unavoidably delayed.
1764 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1765 Execute @var{body}, but give up after @var{seconds} seconds. If
1766 @var{body} finishes before the time is up, @code{with-timeout} returns
1767 the value of the last form in @var{body}. If, however, the execution of
1768 @var{body} is cut short by the timeout, then @code{with-timeout}
1769 executes all the @var{timeout-forms} and returns the value of the last
1772 This macro works by setting a timer to run after @var{seconds} seconds. If
1773 @var{body} finishes before that time, it cancels the timer. If the
1774 timer actually runs, it terminates execution of @var{body}, then
1775 executes @var{timeout-forms}.
1777 Since timers can run within a Lisp program only when the program calls a
1778 primitive that can wait, @code{with-timeout} cannot stop executing
1779 @var{body} while it is in the midst of a computation---only when it
1780 calls one of those primitives. So use @code{with-timeout} only with a
1781 @var{body} that waits for input, not one that does a long computation.
1784 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1785 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1788 @defun cancel-timer timer
1789 This cancels the requested action for @var{timer}, which should be a
1790 timer---usually, one previously returned by @code{run-at-time} or
1791 @code{run-with-idle-timer}. This cancels the effect of that call to
1792 one of these functions; the arrival of the specified time will not
1793 cause anything special to happen.
1797 @section Idle Timers
1799 Here is how to set up a timer that runs when Emacs is idle for a
1800 certain length of time. Aside from how to set them up, idle timers
1801 work just like ordinary timers.
1803 @deffn Command run-with-idle-timer secs repeat function &rest args
1804 Set up a timer which runs the next time Emacs is idle for @var{secs}
1805 seconds. The value of @var{secs} may be an integer or a floating
1806 point number; a value of the type returned by @code{current-idle-time}
1809 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1810 Emacs remains idle for a long enough time. More often @var{repeat} is
1811 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1812 remains idle for @var{secs} seconds.
1814 The function @code{run-with-idle-timer} returns a timer value which you
1815 can use in calling @code{cancel-timer} (@pxref{Timers}).
1819 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1820 it remains idle until the user provides some input. If a timer is set
1821 for five seconds of idleness, it runs approximately five seconds after
1822 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1823 this timer will not run again as long as Emacs remains idle, because
1824 the duration of idleness will continue to increase and will not go
1825 down to five seconds again.
1827 Emacs can do various things while idle: garbage collect, autosave or
1828 handle data from a subprocess. But these interludes during idleness do
1829 not interfere with idle timers, because they do not reset the clock of
1830 idleness to zero. An idle timer set for 600 seconds will run when ten
1831 minutes have elapsed since the last user command was finished, even if
1832 subprocess output has been accepted thousands of times within those ten
1833 minutes, and even if there have been garbage collections and autosaves.
1835 When the user supplies input, Emacs becomes non-idle while executing the
1836 input. Then it becomes idle again, and all the idle timers that are
1837 set up to repeat will subsequently run another time, one by one.
1839 Do not write an idle timer function containing a loop which does a
1840 certain amount of processing each time around, and exits when
1841 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1842 natural but has two problems:
1846 It blocks out all process output (since Emacs accepts process output
1847 only while waiting).
1850 It blocks out any idle timers that ought to run during that time.
1854 Similarly, do not write an idle timer function that sets up another
1855 idle timer (including the same idle timer) with @var{secs} argument
1856 less than or equal to the current idleness time. Such a timer will
1857 run almost immediately, and continue running again and again, instead
1858 of waiting for the next time Emacs becomes idle. The correct approach
1859 is to reschedule with an appropriate increment of the current value of
1860 the idleness time, as described below.
1862 @defun current-idle-time
1863 If Emacs is idle, this function returns the length of time Emacs has
1864 been idle, as a list of four integers: @code{(@var{sec-high}
1865 @var{sec-low} @var{microsec} @var{picosec})}, using the same format as
1866 @code{current-time} (@pxref{Time of Day}).
1868 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1869 This is a convenient way to test whether Emacs is idle.
1872 The main use of @code{current-idle-time} is when an idle timer
1873 function wants to ``take a break'' for a while. It can set up another
1874 idle timer to call the same function again, after a few seconds more
1875 idleness. Here's an example:
1878 (defvar my-resume-timer nil
1879 "Timer for `my-timer-function' to reschedule itself, or nil.")
1881 (defun my-timer-function ()
1882 ;; @r{If the user types a command while @code{my-resume-timer}}
1883 ;; @r{is active, the next time this function is called from}
1884 ;; @r{its main idle timer, deactivate @code{my-resume-timer}.}
1885 (when my-resume-timer
1886 (cancel-timer my-resume-timer))
1887 ...@var{do the work for a while}...
1888 (when @var{taking-a-break}
1889 (setq my-resume-timer
1890 (run-with-idle-timer
1891 ;; Compute an idle time @var{break-length}
1892 ;; more than the current value.
1893 (time-add (current-idle-time)
1894 (seconds-to-time @var{break-length}))
1896 'my-timer-function))))
1899 @node Terminal Input
1900 @section Terminal Input
1901 @cindex terminal input
1903 This section describes functions and variables for recording or
1904 manipulating terminal input. See @ref{Display}, for related
1908 * Input Modes:: Options for how input is processed.
1909 * Recording Input:: Saving histories of recent or all input events.
1913 @subsection Input Modes
1915 @cindex terminal input modes
1917 @defun set-input-mode interrupt flow meta &optional quit-char
1918 This function sets the mode for reading keyboard input. If
1919 @var{interrupt} is non-null, then Emacs uses input interrupts. If it is
1920 @code{nil}, then it uses @sc{cbreak} mode. The default setting is
1921 system-dependent. Some systems always use @sc{cbreak} mode regardless
1922 of what is specified.
1924 When Emacs communicates directly with X, it ignores this argument and
1925 uses interrupts if that is the way it knows how to communicate.
1927 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1928 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1929 has no effect except in @sc{cbreak} mode.
1931 The argument @var{meta} controls support for input character codes
1932 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1933 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1934 Emacs disregards the 8th bit; this is necessary when the terminal uses
1935 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1936 Emacs uses all 8 bits of input unchanged. This is good for terminals
1937 that use 8-bit character sets.
1939 If @var{quit-char} is non-@code{nil}, it specifies the character to
1940 use for quitting. Normally this character is @kbd{C-g}.
1944 The @code{current-input-mode} function returns the input mode settings
1945 Emacs is currently using.
1947 @defun current-input-mode
1948 This function returns the current mode for reading keyboard input. It
1949 returns a list, corresponding to the arguments of @code{set-input-mode},
1950 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1954 is non-@code{nil} when Emacs is using interrupt-driven input. If
1955 @code{nil}, Emacs is using @sc{cbreak} mode.
1957 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1958 flow control for output to the terminal. This value is meaningful only
1959 when @var{interrupt} is @code{nil}.
1961 is @code{t} if Emacs treats the eighth bit of input characters as
1962 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1963 input character; any other value means Emacs uses all eight bits as the
1964 basic character code.
1966 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1970 @node Recording Input
1971 @subsection Recording Input
1972 @cindex recording input
1975 This function returns a vector containing the last 300 input events from
1976 the keyboard or mouse. All input events are included, whether or not
1977 they were used as parts of key sequences. Thus, you always get the last
1978 300 input events, not counting events generated by keyboard macros.
1979 (These are excluded because they are less interesting for debugging; it
1980 should be enough to see the events that invoked the macros.)
1982 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1983 causes this function to return an empty vector immediately afterward.
1986 @deffn Command open-dribble-file filename
1987 @cindex dribble file
1988 This function opens a @dfn{dribble file} named @var{filename}. When a
1989 dribble file is open, each input event from the keyboard or mouse (but
1990 not those from keyboard macros) is written in that file. A
1991 non-character event is expressed using its printed representation
1992 surrounded by @samp{<@dots{}>}.
1994 You close the dribble file by calling this function with an argument
1997 This function is normally used to record the input necessary to
1998 trigger an Emacs bug, for the sake of a bug report.
2002 (open-dribble-file "~/dribble")
2008 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2010 @node Terminal Output
2011 @section Terminal Output
2012 @cindex terminal output
2014 The terminal output functions send output to a text terminal, or keep
2015 track of output sent to the terminal. The variable @code{baud-rate}
2016 tells you what Emacs thinks is the output speed of the terminal.
2019 This variable's value is the output speed of the terminal, as far as
2020 Emacs knows. Setting this variable does not change the speed of actual
2021 data transmission, but the value is used for calculations such as
2024 It also affects decisions about whether to scroll part of the
2025 screen or repaint on text terminals. @xref{Forcing Redisplay},
2026 for the corresponding functionality on graphical terminals.
2028 The value is measured in baud.
2031 If you are running across a network, and different parts of the
2032 network work at different baud rates, the value returned by Emacs may be
2033 different from the value used by your local terminal. Some network
2034 protocols communicate the local terminal speed to the remote machine, so
2035 that Emacs and other programs can get the proper value, but others do
2036 not. If Emacs has the wrong value, it makes decisions that are less
2037 than optimal. To fix the problem, set @code{baud-rate}.
2039 @defun send-string-to-terminal string &optional terminal
2040 This function sends @var{string} to @var{terminal} without alteration.
2041 Control characters in @var{string} have terminal-dependent effects.
2042 This function operates only on text terminals. @var{terminal} may be
2043 a terminal object, a frame, or @code{nil} for the selected frame's
2044 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2045 @var{terminal} is @code{nil}.
2047 One use of this function is to define function keys on terminals that
2048 have downloadable function key definitions. For example, this is how (on
2049 certain terminals) to define function key 4 to move forward four
2050 characters (by transmitting the characters @kbd{C-u C-f} to the
2055 (send-string-to-terminal "\eF4\^U\^F")
2061 @deffn Command open-termscript filename
2062 @cindex termscript file
2063 This function is used to open a @dfn{termscript file} that will record
2064 all the characters sent by Emacs to the terminal. It returns
2065 @code{nil}. Termscript files are useful for investigating problems
2066 where Emacs garbles the screen, problems that are due to incorrect
2067 Termcap entries or to undesirable settings of terminal options more
2068 often than to actual Emacs bugs. Once you are certain which characters
2069 were actually output, you can determine reliably whether they correspond
2070 to the Termcap specifications in use.
2072 You close the termscript file by calling this function with an
2073 argument of @code{nil}.
2075 See also @code{open-dribble-file} in @ref{Recording Input}.
2079 (open-termscript "../junk/termscript")
2086 @section Sound Output
2089 To play sound using Emacs, use the function @code{play-sound}. Only
2090 certain systems are supported; if you call @code{play-sound} on a
2091 system which cannot really do the job, it gives an error.
2093 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2094 or Sun Audio format (@samp{.au}).
2096 @defun play-sound sound
2097 This function plays a specified sound. The argument, @var{sound}, has
2098 the form @code{(sound @var{properties}...)}, where the @var{properties}
2099 consist of alternating keywords (particular symbols recognized
2100 specially) and values corresponding to them.
2102 Here is a table of the keywords that are currently meaningful in
2103 @var{sound}, and their meanings:
2106 @item :file @var{file}
2107 This specifies the file containing the sound to play.
2108 If the file name is not absolute, it is expanded against
2109 the directory @code{data-directory}.
2111 @item :data @var{data}
2112 This specifies the sound to play without need to refer to a file. The
2113 value, @var{data}, should be a string containing the same bytes as a
2114 sound file. We recommend using a unibyte string.
2116 @item :volume @var{volume}
2117 This specifies how loud to play the sound. It should be a number in the
2118 range of 0 to 1. The default is to use whatever volume has been
2121 @item :device @var{device}
2122 This specifies the system device on which to play the sound, as a
2123 string. The default device is system-dependent.
2126 Before actually playing the sound, @code{play-sound}
2127 calls the functions in the list @code{play-sound-functions}.
2128 Each function is called with one argument, @var{sound}.
2131 @deffn Command play-sound-file file &optional volume device
2132 This function is an alternative interface to playing a sound @var{file}
2133 specifying an optional @var{volume} and @var{device}.
2136 @defvar play-sound-functions
2137 A list of functions to be called before playing a sound. Each function
2138 is called with one argument, a property list that describes the sound.
2142 @section Operating on X11 Keysyms
2145 To define system-specific X11 keysyms, set the variable
2146 @code{system-key-alist}.
2148 @defvar system-key-alist
2149 This variable's value should be an alist with one element for each
2150 system-specific keysym. Each element has the form @code{(@var{code}
2151 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2152 including the ``vendor specific'' bit,
2159 and @var{symbol} is the name for the function key.
2161 For example @code{(168 . mute-acute)} defines a system-specific key (used
2162 by HP X servers) whose numeric code is
2171 It is not crucial to exclude from the alist the keysyms of other X
2172 servers; those do no harm, as long as they don't conflict with the ones
2173 used by the X server actually in use.
2175 The variable is always local to the current terminal, and cannot be
2176 buffer-local. @xref{Multiple Terminals}.
2179 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2181 @defvar x-alt-keysym
2182 @defvarx x-meta-keysym
2183 @defvarx x-hyper-keysym
2184 @defvarx x-super-keysym
2185 The name of the keysym that should stand for the Alt modifier
2186 (respectively, for Meta, Hyper, and Super). For example, here is
2187 how to swap the Meta and Alt modifiers within Emacs:
2189 (setq x-alt-keysym 'meta)
2190 (setq x-meta-keysym 'alt)
2198 The command-line option @samp{-batch} causes Emacs to run
2199 noninteractively. In this mode, Emacs does not read commands from the
2200 terminal, it does not alter the terminal modes, and it does not expect
2201 to be outputting to an erasable screen. The idea is that you specify
2202 Lisp programs to run; when they are finished, Emacs should exit. The
2203 way to specify the programs to run is with @samp{-l @var{file}}, which
2204 loads the library named @var{file}, or @samp{-f @var{function}}, which
2205 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2207 Any Lisp program output that would normally go to the echo area,
2208 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2209 as the stream, goes instead to Emacs's standard error descriptor when
2210 in batch mode. Similarly, input that would normally come from the
2211 minibuffer is read from the standard input descriptor.
2212 Thus, Emacs behaves much like a noninteractive
2213 application program. (The echo area output that Emacs itself normally
2214 generates, such as command echoing, is suppressed entirely.)
2216 @defvar noninteractive
2217 This variable is non-@code{nil} when Emacs is running in batch mode.
2220 @node Session Management
2221 @section Session Management
2222 @cindex session manager
2224 Emacs supports the X Session Management Protocol, which is used to
2225 suspend and restart applications. In the X Window System, a program
2226 called the @dfn{session manager} is responsible for keeping track of
2227 the applications that are running. When the X server shuts down, the
2228 session manager asks applications to save their state, and delays the
2229 actual shutdown until they respond. An application can also cancel
2232 When the session manager restarts a suspended session, it directs
2233 these applications to individually reload their saved state. It does
2234 this by specifying a special command-line argument that says what
2235 saved session to restore. For Emacs, this argument is @samp{--smid
2238 @defvar emacs-save-session-functions
2239 Emacs supports saving state via a hook called
2240 @code{emacs-save-session-functions}. Emacs runs this hook when the
2241 session manager tells it that the window system is shutting down. The
2242 functions are called with no arguments, and with the current buffer
2243 set to a temporary buffer. Each function can use @code{insert} to add
2244 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2245 file, called the @dfn{session file}.
2247 @findex emacs-session-restore
2248 Subsequently, when the session manager restarts Emacs, it loads the
2249 session file automatically (@pxref{Loading}). This is performed by a
2250 function named @code{emacs-session-restore}, which is called during
2251 startup. @xref{Startup Summary}.
2253 If a function in @code{emacs-save-session-functions} returns
2254 non-@code{nil}, Emacs tells the session manager to cancel the
2258 Here is an example that just inserts some text into @file{*scratch*} when
2259 Emacs is restarted by the session manager.
2263 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2267 (defun save-yourself-test ()
2268 (insert "(save-current-buffer
2269 (switch-to-buffer \"*scratch*\")
2270 (insert \"I am restored\"))")
2275 @node Desktop Notifications
2276 @section Desktop Notifications
2277 @cindex desktop notifications
2279 Emacs is able to send @dfn{notifications} on systems that support the
2280 freedesktop.org Desktop Notifications Specification. In order to use
2281 this functionality, Emacs must have been compiled with D-Bus support,
2282 and the @code{notifications} library must be loaded.
2284 @defun notifications-notify &rest params
2285 This function sends a notification to the desktop via D-Bus,
2286 consisting of the parameters specified by the @var{params} arguments.
2287 These arguments should consist of alternating keyword and value pairs.
2288 The supported keywords and values are as follows:
2291 @item :bus @var{bus}
2292 The D-Bus bus. This argument is needed only if a bus other than
2293 @code{:session} shall be used.
2295 @item :title @var{title}
2296 The notification title.
2298 @item :body @var{text}
2299 The notification body text. Depending on the implementation of the
2300 notification server, the text could contain HTML markups, like
2301 @samp{"<b>bold text</b>"}, hyperlinks, or images. Special HTML
2302 characters must be encoded, as @samp{"Contact
2303 <postmaster@@localhost>!"}.
2305 @item :app-name @var{name}
2306 The name of the application sending the notification. The default is
2307 @code{notifications-application-name}.
2309 @item :replaces-id @var{id}
2310 The notification @var{id} that this notification replaces. @var{id}
2311 must be the result of a previous @code{notifications-notify} call.
2313 @item :app-icon @var{icon-file}
2314 The file name of the notification icon. If set to @code{nil}, no icon
2315 is displayed. The default is @code{notifications-application-icon}.
2317 @item :actions (@var{key} @var{title} @var{key} @var{title} ...)
2318 A list of actions to be applied. @var{key} and @var{title} are both
2319 strings. The default action (usually invoked by clicking the
2320 notification) should have a key named @samp{"default"}. The title can
2321 be anything, though implementations are free not to display it.
2323 @item :timeout @var{timeout}
2324 The timeout time in milliseconds since the display of the notification
2325 at which the notification should automatically close. If -1, the
2326 notification's expiration time is dependent on the notification
2327 server's settings, and may vary for the type of notification. If 0,
2328 the notification never expires. Default value is -1.
2330 @item :urgency @var{urgency}
2331 The urgency level. It can be @code{low}, @code{normal}, or @code{critical}.
2334 When this keyword is given, the @var{title} string of the actions is
2335 interpreted as icon name.
2337 @item :category @var{category}
2338 The type of notification this is, a string. See the
2339 @uref{http://developer.gnome.org/notification-spec/#categories,
2340 Desktop Notifications Specification} for a list of standard
2343 @item :desktop-entry @var{filename}
2344 This specifies the name of the desktop filename representing the
2345 calling program, like @samp{"emacs"}.
2347 @item :image-data (@var{width} @var{height} @var{rowstride} @var{has-alpha} @var{bits} @var{channels} @var{data})
2348 This is a raw data image format that describes the width, height,
2349 rowstride, whether there is an alpha channel, bits per sample,
2350 channels and image data, respectively.
2352 @item :image-path @var{path}
2353 This is represented either as a URI (@samp{file://} is the only URI
2354 schema supported right now) or a name in a freedesktop.org-compliant
2355 icon theme from @samp{$XDG_DATA_DIRS/icons}.
2357 @item :sound-file @var{filename}
2358 The path to a sound file to play when the notification pops up.
2360 @item :sound-name @var{name}
2361 A themable named sound from the freedesktop.org sound naming
2362 specification from @samp{$XDG_DATA_DIRS/sounds}, to play when the
2363 notification pops up. Similar to the icon name, only for sounds. An
2364 example would be @samp{"message-new-instant"}.
2366 @item :suppress-sound
2367 Causes the server to suppress playing any sounds, if it has that
2371 When set the server will not automatically remove the notification
2372 when an action has been invoked. The notification will remain resident
2373 in the server until it is explicitly removed by the user or by the
2374 sender. This hint is likely only useful when the server has the
2375 @code{:persistence} capability.
2378 When set the server will treat the notification as transient and
2379 by-pass the server's persistence capability, if it should exist.
2381 @item :x @var{position}
2382 @itemx :y @var{position}
2383 Specifies the X, Y location on the screen that the
2384 notification should point to. Both arguments must be used together.
2386 @item :on-action @var{function}
2387 Function to call when an action is invoked. The notification @var{id}
2388 and the @var{key} of the action are passed as arguments to the
2391 @item :on-close @var{function}
2392 Function to call when the notification has been closed by timeout or
2393 by the user. The function receive the notification @var{id} and the closing
2394 @var{reason} as arguments:
2397 @item @code{expired} if the notification has expired
2398 @item @code{dismissed} if the notification was dismissed by the user
2399 @item @code{close-notification} if the notification was closed by a call to
2400 @code{notifications-close-notification}
2401 @item @code{undefined} if the notification server hasn't provided a reason
2405 Which parameters are accepted by the notification server can be
2406 checked via @code{notifications-get-capabilities}.
2408 This function returns a notification id, an integer, which can be used
2409 to manipulate the notification item with
2410 @code{notifications-close-notification} or the @code{:replaces-id}
2411 argument of another @code{notifications-notify} call. For example:
2415 (defun my-on-action-function (id key)
2416 (message "Message %d, key \"%s\" pressed" id key))
2417 @result{} my-on-action-function
2421 (defun my-on-close-function (id reason)
2422 (message "Message %d, closed due to \"%s\"" id reason))
2423 @result{} my-on-close-function
2427 (notifications-notify
2429 :body "This is <b>important</b>."
2430 :actions '("Confirm" "I agree" "Refuse" "I disagree")
2431 :on-action 'my-on-action-function
2432 :on-close 'my-on-close-function)
2437 A message window opens on the desktop. Press "I agree"
2438 @result{} Message 22, key "Confirm" pressed
2439 Message 22, closed due to "dismissed"
2444 @defun notifications-close-notification id &optional bus
2445 This function closes a notification with identifier @var{id}.
2446 @var{bus} can be a string denoting a D-Bus connection, the default is
2450 @defun notifications-get-capabilities &optional bus
2451 Returns the capabilities of the notification server, a list of
2452 symbols. @var{bus} can be a string denoting a D-Bus connection, the
2453 default is @code{:session}. The following capabilities can be
2458 The server will provide the specified actions to the user.
2463 @item :body-hyperlinks
2464 The server supports hyperlinks in the notifications.
2467 The server supports images in the notifications.
2470 Supports markup in the body text.
2473 The server will render an animation of all the frames in a given image
2477 Supports display of exactly 1 frame of any given image array. This
2478 value is mutually exclusive with @code{:icon-multi}.
2481 The server supports persistence of notifications.
2484 The server supports sounds on notifications.
2487 Further vendor-specific caps start with @code{:x-vendor}, like
2488 @code{:x-gnome-foo-cap}.
2491 @defun notifications-get-server-information &optional bus
2492 Return information on the notification server, a list of strings.
2493 @var{bus} can be a string denoting a D-Bus connection, the default is
2494 @code{:session}. The returned list is @code{(@var{name} @var{vendor}
2495 @var{version} @var{spec-version})}.
2499 The product name of the server.
2502 The vendor name. For example, @samp{"KDE"}, @samp{"GNOME"}.
2505 The server's version number.
2508 The specification version the server is compliant with.
2511 If @var{SPEC_VERSION} is @code{nil}, the server supports a
2512 specification prior to @samp{"1.0"}.
2515 @node File Notifications
2516 @section Notifications on File Changes
2517 @cindex file notifications
2519 Several operating systems support watching of filesystems for changes
2520 of files. If configured properly, Emacs links a respective library
2521 like @file{gfilenotify}, @file{inotify}, or @file{w32notify}
2522 statically. These libraries enable watching of filesystems on the
2525 It is also possible to watch filesystems on remote machines,
2526 @pxref{Remote Files,, Remote Files, emacs, The GNU Emacs Manual}
2527 This does not depend on one of the libraries linked to Emacs.
2529 Since all these libraries emit different events on notified file
2530 changes, there is the Emacs library @code{filenotify} which provides a
2533 @defun file-notify-add-watch file flags callback
2534 Add a watch for filesystem events pertaining to @var{file}. This
2535 arranges for filesystem events pertaining to @var{file} to be reported
2538 The returned value is a descriptor for the added watch. Its type
2539 depends on the underlying library, it cannot be assumed to be an
2540 integer as in the example below. It should be used for comparison by
2543 If the @var{file} cannot be watched for some reason, this function
2544 signals a @code{file-notify-error} error.
2546 Sometimes, mounted filesystems cannot be watched for file changes.
2547 This is not detected by this function, a non-@code{nil} return value
2548 does not guarantee that changes on @var{file} will be notified.
2550 @var{flags} is a list of conditions to set what will be watched for.
2551 It can include the following symbols:
2555 watch for file changes
2556 @item attribute-change
2557 watch for file attribute changes, like permissions or modification
2561 If @var{file} is a directory, changes for all files in that directory
2562 will be notified. This does not work recursively.
2564 When any event happens, Emacs will call the @var{callback} function
2565 passing it a single argument @var{event}, which is of the form
2568 (@var{descriptor} @var{action} @var{file} [@var{file1}])
2571 @var{descriptor} is the same object as the one returned by this
2572 function. @var{action} is the description of the event. It could be
2573 any one of the following symbols:
2577 @var{file} was created
2579 @var{file} was deleted
2581 @var{file} has changed
2583 @var{file} has been renamed to @var{file1}
2584 @item attribute-changed
2585 a @var{file} attribute was changed
2588 @var{file} and @var{file1} are the name of the file(s) whose event is
2589 being reported. For example:
2593 (require 'filenotify)
2594 @result{} filenotify
2598 (defun my-notify-callback (event)
2599 (message "Event %S" event))
2600 @result{} my-notify-callback
2604 (file-notify-add-watch
2605 "/tmp" '(change attribute-change) 'my-notify-callback)
2610 (write-region "foo" nil "/tmp/foo")
2611 @result{} Event (35025468 created "/tmp/.#foo")
2612 Event (35025468 created "/tmp/foo")
2613 Event (35025468 changed "/tmp/foo")
2614 Event (35025468 deleted "/tmp/.#foo")
2618 (write-region "bla" nil "/tmp/foo")
2619 @result{} Event (35025468 created "/tmp/.#foo")
2620 Event (35025468 changed "/tmp/foo") [2 times]
2621 Event (35025468 deleted "/tmp/.#foo")
2625 (set-file-modes "/tmp/foo" (default-file-modes))
2626 @result{} Event (35025468 attribute-changed "/tmp/foo")
2630 Whether the action @code{renamed} is returned, depends on the used
2631 watch library. It can be expected, when a directory is watched, and
2632 both @var{file} and @var{file1} belong to this directory. Otherwise,
2633 the actions @code{deleted} and @code{created} could be returned in a
2638 (rename-file "/tmp/foo" "/tmp/bla")
2639 @result{} Event (35025468 renamed "/tmp/foo" "/tmp/bla")
2643 (file-notify-add-watch
2644 "/var/tmp" '(change attribute-change) 'my-notify-callback)
2649 (rename-file "/tmp/bla" "/var/tmp/bla")
2650 @result{} ;; gfilenotify
2651 Event (35025468 renamed "/tmp/bla" "/var/tmp/bla")
2653 @result{} ;; inotify
2654 Event (35025504 created "/var/tmp/bla")
2655 Event (35025468 deleted "/tmp/bla")
2660 @defun file-notify-rm-watch descriptor
2661 Removes an existing file watch specified by its @var{descriptor}.
2662 @var{descriptor} should be an object returned by
2663 @code{file-notify-add-watch}.
2666 @node Dynamic Libraries
2667 @section Dynamically Loaded Libraries
2668 @cindex dynamic libraries
2670 A @dfn{dynamically loaded library} is a library that is loaded on
2671 demand, when its facilities are first needed. Emacs supports such
2672 on-demand loading of support libraries for some of its features.
2674 @defvar dynamic-library-alist
2675 This is an alist of dynamic libraries and external library files
2678 Each element is a list of the form
2679 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2680 a symbol representing a supported external library, and the rest are
2681 strings giving alternate filenames for that library.
2683 Emacs tries to load the library from the files in the order they
2684 appear in the list; if none is found, the Emacs session won't have
2685 access to that library, and the features it provides will be
2688 Image support on some platforms uses this facility. Here's an example
2689 of setting this variable for supporting images on MS-Windows:
2692 (setq dynamic-library-alist
2693 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2694 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2695 "libpng13d.dll" "libpng13.dll")
2696 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll"
2698 (tiff "libtiff3.dll" "libtiff.dll")
2699 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2700 (svg "librsvg-2-2.dll")
2701 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2702 (glib "libglib-2.0-0.dll")
2703 (gobject "libgobject-2.0-0.dll")))
2706 Note that image types @code{pbm} and @code{xbm} do not need entries in
2707 this variable because they do not depend on external libraries and are
2708 always available in Emacs.
2710 Also note that this variable is not meant to be a generic facility for
2711 accessing external libraries; only those already known by Emacs can
2712 be loaded through it.
2714 This variable is ignored if the given @var{library} is statically