2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-1999, 2001-2012
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../../info/os
7 @node System Interface, Packaging, Display, Top
8 @chapter Operating System Interface
10 This chapter is about starting and getting out of Emacs, access to
11 values in the operating system environment, and terminal input, output.
13 @xref{Building Emacs}, for related information. @xref{Display}, for
14 additional operating system status information pertaining to the
15 terminal and the screen.
18 * Starting Up:: Customizing Emacs startup processing.
19 * Getting Out:: How exiting works (permanent or temporary).
20 * System Environment:: Distinguish the name and kind of system.
21 * User Identification:: Finding the name and user id of the user.
22 * Time of Day:: Getting the current time.
23 * Time Conversion:: Converting a time from numeric form to
24 calendrical data and vice versa.
25 * Time Parsing:: Converting a time from numeric form to text
27 * Processor Run Time:: Getting the run time used by Emacs.
28 * Time Calculations:: Adding, subtracting, comparing times, etc.
29 * Timers:: Setting a timer to call a function at a certain time.
30 * Idle Timers:: Setting a timer to call a function when Emacs has
31 been idle for a certain length of time.
32 * Terminal Input:: Accessing and recording terminal input.
33 * Terminal Output:: Controlling and recording terminal output.
34 * Sound Output:: Playing sounds on the computer's speaker.
35 * X11 Keysyms:: Operating on key symbols for X Windows.
36 * Batch Mode:: Running Emacs without terminal interaction.
37 * Session Management:: Saving and restoring state with X Session Management.
38 * Dynamic Libraries:: On-demand loading of support libraries.
42 @section Starting Up Emacs
44 This section describes what Emacs does when it is started, and how you
45 can customize these actions.
48 * Startup Summary:: Sequence of actions Emacs performs at startup.
49 * Init File:: Details on reading the init file.
50 * Terminal-Specific:: How the terminal-specific Lisp file is read.
51 * Command-Line Arguments:: How command-line arguments are processed,
52 and how you can customize them.
56 @subsection Summary: Sequence of Actions at Startup
57 @cindex initialization of Emacs
58 @cindex startup of Emacs
59 @cindex @file{startup.el}
61 When Emacs is started up, it performs the following operations
62 (see @code{normal-top-level} in @file{startup.el}):
66 It adds subdirectories to @code{load-path}, by running the file named
67 @file{subdirs.el} in each directory in the list. Normally, this file
68 adds the directory's subdirectories to the list, and those are scanned
69 in their turn. The files @file{subdirs.el} are normally generated
70 automatically when Emacs is installed.
73 It registers input methods by loading any @file{leim-list.el} file
74 found in the @code{load-path}.
76 @c It removes PWD from the environment if it is not accurate.
77 @c It abbreviates default-directory.
79 @c Now normal-top-level calls command-line.
81 @vindex before-init-time
83 It sets the variable @code{before-init-time} to the value of
84 @code{current-time} (@pxref{Time of Day}). It also sets
85 @code{after-init-time} to @code{nil}, which signals to Lisp programs
86 that Emacs is being initialized.
88 @c set-locale-environment
90 It sets the language environment and the terminal coding system,
91 if requested by environment variables such as @code{LANG}.
94 It does some basic parsing of the command-line arguments.
96 @vindex initial-window-system@r{, and startup}
97 @vindex window-system-initialization-alist
99 If not running in batch mode, it initializes the window system that
100 the variable @code{initial-window-system} specifies (@pxref{Window
101 Systems, initial-window-system}). The initialization function for
102 each supported window system is specified by
103 @code{window-system-initialization-alist}. If the value
104 of @code{initial-window-system} is @var{windowsystem}, then the
105 appropriate initialization function is defined in the file
106 @file{term/@var{windowsystem}-win.el}. This file should have been
107 compiled into the Emacs executable when it was built.
110 It runs the normal hook @code{before-init-hook}.
113 If appropriate, it creates a graphical frame. This is not done if the
114 options @samp{--batch} or @samp{--daemon} were specified.
117 It initializes the initial frame's faces, and sets up the menu bar
118 and tool bar if needed. If graphical frames are supported, it sets up
119 the tool bar even if the current frame is not a graphical one, since a
120 graphical frame may be created later on.
123 It use @code{custom-reevaluate-setting} to re-initialize the members
124 of the list @code{custom-delayed-init-variables}. These are any
125 pre-loaded user options whose default value depends on the run-time,
126 rather than build-time, context.
127 @xref{Building Emacs, custom-initialize-delay}.
130 @c It registers the colors available for tty frames.
133 It loads the library @file{site-start}, if it exists. This is not
134 done if the options @samp{-Q} or @samp{--no-site-file} were specified.
135 @cindex @file{site-start.el}
138 It loads your init file (@pxref{Init File}). This is not done if the
139 options @samp{-q}, @samp{-Q}, or @samp{--batch} were specified. If
140 the @samp{-u} option was specified, Emacs looks for the init file in
141 that user's home directory instead.
144 It loads the library @file{default}, if it exists. This is not done
145 if @code{inhibit-default-init} is non-@code{nil}, nor if the options
146 @samp{-q}, @samp{-Q}, or @samp{--batch} were specified.
147 @cindex @file{default.el}
150 It loads your abbrevs from the file specified by
151 @code{abbrev-file-name}, if that file exists and can be read
152 (@pxref{Abbrev Files, abbrev-file-name}). This is not done if the
153 option @samp{--batch} was specified.
156 If @code{package-enable-at-startup} is non-@code{nil}, it calls the
157 function @code{package-initialize} to activate any optional Emacs Lisp
158 package that has been installed. @xref{Packaging Basics}.
160 @vindex after-init-time
162 It sets the variable @code{after-init-time} to the value of
163 @code{current-time}. This variable was set to @code{nil} earlier;
164 setting it to the current time signals that the initialization phase
165 is over, and, together with @code{before-init-time}, provides the
166 measurement of how long it took.
169 It runs the normal hook @code{after-init-hook}.
172 If the buffer @samp{*scratch*} exists and is still in Fundamental mode
173 (as it should be by default), it sets its major mode according to
174 @code{initial-major-mode}.
177 If started on a text terminal, it loads the terminal-specific
178 Lisp library, which is specified by the variable
179 @code{term-file-prefix} (@pxref{Terminal-Specific}). This is not done
180 in @code{--batch} mode, nor if @code{term-file-prefix} is @code{nil}.
182 @c Now command-line calls command-line-1.
185 It displays the initial echo area message, unless you have suppressed
186 that with @code{inhibit-startup-echo-area-message}.
189 It processes any command-line options that were not handled earlier.
191 @c This next one is back in command-line, but the remaining bits of
192 @c command-line-1 are not done if noninteractive.
194 It now exits if the option @code{--batch} was specified.
197 If @code{initial-buffer-choice} is a string, it visits the file with
198 that name. If the @samp{*scratch*} buffer exists and is
199 empty, it inserts @code{initial-scratch-message} into that buffer.
201 @c To make things nice and confusing, the next three items can be
202 @c called from two places. If displaying a startup screen, they are
203 @c called in command-line-1 before the startup screen is shown.
204 @c inhibit-startup-hooks is then set and window-setup-hook set to nil.
205 @c If not displaying a startup screen, they are are called in
207 @c FIXME? So it seems they can be called before or after the
208 @c daemon/session restore step?
211 It runs @code{emacs-startup-hook} and then @code{term-setup-hook}.
214 It calls @code{frame-notice-user-settings}, which modifies the
215 parameters of the selected frame according to whatever the init files
219 It runs @code{window-setup-hook}. @xref{Window Systems}.
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 @samp{*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 @samp{*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 Custom interface. Other methods of setting
293 @code{inhibit-startup-echo-area-message} to the same value do not
294 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 @samp{*scratch*} buffer when Emacs starts up. If it
302 is @code{nil}, the @samp{*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 @code{LOGNAME} environment
355 variable, or the @code{USER} (most systems) or @code{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 @code{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 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 @code{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 @code{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 @comment node-name, next, previous, up
615 @subsection Killing Emacs
616 @cindex killing Emacs
618 Killing Emacs means ending the execution of the Emacs process.
619 If you started Emacs from a terminal, the parent process normally
620 resumes control. The low-level primitive for killing Emacs is
623 @deffn Command kill-emacs &optional exit-data
624 This command calls the hook @code{kill-emacs-hook}, then exits the
625 Emacs process and kills it.
627 If @var{exit-data} is an integer, that is used as the exit status of
628 the Emacs process. (This is useful primarily in batch operation; see
631 If @var{exit-data} is a string, its contents are stuffed into the
632 terminal input buffer so that the shell (or whatever program next reads
633 input) can read them.
639 @cindex operating system signal
640 The @code{kill-emacs} function is normally called via the
641 higher-level command @kbd{C-x C-c}
642 (@code{save-buffers-kill-terminal}). @xref{Exiting,,, emacs, The GNU
643 Emacs Manual}. It is also called automatically if Emacs receives a
644 @code{SIGTERM} or @code{SIGHUP} operating system signal (e.g. when the
645 controlling terminal is disconnected), or if it receives a
646 @code{SIGINT} signal while running in batch mode (@pxref{Batch Mode}).
648 @defvar kill-emacs-hook
649 This normal hook is run by @code{kill-emacs}, before it kills Emacs.
651 Because @code{kill-emacs} can be called in situations where user
652 interaction is impossible (e.g. when the terminal is disconnected),
653 functions on this hook should not attempt to interact with the user.
654 If you want to interact with the user when Emacs is shutting down, use
655 @code{kill-emacs-query-functions}, described below.
658 When Emacs is killed, all the information in the Emacs process,
659 aside from files that have been saved, is lost. Because killing Emacs
660 inadvertently can lose a lot of work, the
661 @code{save-buffers-kill-terminal} command queries for confirmation if
662 you have buffers that need saving or subprocesses that are running.
663 It also runs the abnormal hook @code{kill-emacs-query-functions}:
665 @defvar kill-emacs-query-functions
666 When @code{save-buffers-kill-terminal} is killing Emacs, it calls the
667 functions in this hook, after asking the standard questions and before
668 calling @code{kill-emacs}. The functions are called in order of
669 appearance, with no arguments. Each function can ask for additional
670 confirmation from the user. If any of them returns @code{nil},
671 @code{save-buffers-kill-emacs} does not kill Emacs, and does not run
672 the remaining functions in this hook. Calling @code{kill-emacs}
673 directly does not run this hook.
676 @node Suspending Emacs
677 @subsection Suspending Emacs
678 @cindex suspending Emacs
680 On text terminals, it is possible to @dfn{suspend Emacs}, which
681 means stopping Emacs temporarily and returning control to its superior
682 process, which is usually the shell. This allows you to resume
683 editing later in the same Emacs process, with the same buffers, the
684 same kill ring, the same undo history, and so on. To resume Emacs,
685 use the appropriate command in the parent shell---most likely
688 @cindex controlling terminal
689 Suspending works only on a terminal device from which the Emacs
690 session was started. We call that device the @dfn{controlling
691 terminal} of the session. Suspending is not allowed if the
692 controlling terminal is a graphical terminal. Suspending is usually
693 not relevant in graphical environments, since you can simply switch to
694 another application without doing anything special to Emacs.
696 @c FIXME? Are there any systems Emacs still supports that do not
699 Some operating systems (those without @code{SIGTSTP}, or MS-DOS) do
700 not support suspension of jobs; on these systems, ``suspension''
701 actually creates a new shell temporarily as a subprocess of Emacs.
702 Then you would exit the shell to return to Emacs.
704 @deffn Command suspend-emacs &optional string
705 This function stops Emacs and returns control to the superior process.
706 If and when the superior process resumes Emacs, @code{suspend-emacs}
707 returns @code{nil} to its caller in Lisp.
709 This function works only on the controlling terminal of the Emacs
710 session; to relinquish control of other tty devices, use
711 @code{suspend-tty} (see below). If the Emacs session uses more than
712 one terminal, you must delete the frames on all the other terminals
713 before suspending Emacs, or this function signals an error.
714 @xref{Multiple Terminals}.
716 If @var{string} is non-@code{nil}, its characters are sent to Emacs's
717 superior shell, to be read as terminal input.
718 @c FIXME? It seems to me that shell does echo STRING.
719 The characters in @var{string} are not echoed by the superior shell;
720 only the results appear.
722 Before suspending, @code{suspend-emacs} runs the normal hook
723 @code{suspend-hook}. After the user resumes Emacs,
724 @code{suspend-emacs} runs the normal hook @code{suspend-resume-hook}.
727 The next redisplay after resumption will redraw the entire screen,
728 unless the variable @code{no-redraw-on-reenter} is non-@code{nil}.
729 @xref{Refresh Screen}.
731 Here is an example of how you could use these hooks:
735 (add-hook 'suspend-hook
736 (lambda () (or (y-or-n-p "Really suspend? ")
737 (error "Suspend canceled"))))
739 (add-hook 'suspend-resume-hook (lambda () (message "Resumed!")
742 @c The sit-for prevents the ``nil'' that suspend-emacs returns
743 @c hiding the message.
745 Here is what you would see upon evaluating @code{(suspend-emacs "pwd")}:
749 ---------- Buffer: Minibuffer ----------
750 Really suspend? @kbd{y}
751 ---------- Buffer: Minibuffer ----------
755 ---------- Parent Shell ----------
761 ---------- Echo Area ----------
766 @c FIXME? AFAICS, it is echoed.
767 Note that @samp{pwd} is not echoed after Emacs is suspended. But it
768 is read and executed by the shell.
772 This variable is a normal hook that Emacs runs before suspending.
775 @defvar suspend-resume-hook
776 This variable is a normal hook that Emacs runs on resuming
780 @defun suspend-tty &optional tty
781 If @var{tty} specifies a terminal device used by Emacs, this function
782 relinquishes the device and restores it to its prior state. Frames
783 that used the device continue to exist, but are not updated and Emacs
784 doesn't read input from them. @var{tty} can be a terminal object, a
785 frame (meaning the terminal for that frame), or @code{nil} (meaning
786 the terminal for the selected frame). @xref{Multiple Terminals}.
788 If @var{tty} is already suspended, this function does nothing.
790 @vindex suspend-tty-functions
791 This function runs the hook @code{suspend-tty-functions}, passing the
792 terminal object as an argument to each function.
795 @defun resume-tty &optional tty
796 This function resumes the previously suspended terminal device
797 @var{tty}; where @var{tty} has the same possible values as it does
798 for @code{suspend-tty}.
800 @vindex resume-tty-functions
801 This function reopens the terminal device, re-initializes it, and
802 redraws it with that terminal's selected frame. It then runs the
803 hook @code{resume-tty-functions}, passing the terminal object as an
804 argument to each function.
806 If the same device is already used by another Emacs terminal, this
807 function signals an error. If @var{tty} is not suspended, this
808 function does nothing.
811 @defun controlling-tty-p &optional tty
812 This function returns non-@code{nil} if @var{tty} is the
813 controlling terminal of the Emacs session; @var{tty} can be a
814 terminal object, a frame (meaning the terminal for that frame), or
815 @code{nil} (meaning the terminal for the selected frame).
818 @deffn Command suspend-frame
819 This command @dfn{suspends} a frame. For GUI frames, it calls
820 @code{iconify-frame} (@pxref{Visibility of Frames}); for frames on
821 text terminals, it calls either @code{suspend-emacs} or
822 @code{suspend-tty}, depending on whether the frame is displayed on the
823 controlling terminal device or not.
826 @node System Environment
827 @section Operating System Environment
828 @cindex operating system environment
830 Emacs provides access to variables in the operating system environment
831 through various functions. These variables include the name of the
832 system, the user's @acronym{UID}, and so on.
834 @defvar system-configuration
835 This variable holds the standard GNU configuration name for the
836 hardware/software configuration of your system, as a string. The
837 convenient way to test parts of this string is with
841 @cindex system type and name
843 The value of this variable is a symbol indicating the type of operating
844 system Emacs is operating on. Here is a table of the possible values:
851 Berkeley BSD and its variants.
854 Cygwin, a Posix layer on top of MS-Windows.
860 The GNU system (using the GNU kernel, which consists of the HURD and Mach).
863 A GNU/Linux system---that is, a variant GNU system, using the Linux
864 kernel. (These systems are the ones people often call ``Linux,'' but
865 actually Linux is just the kernel, not the whole system.)
868 A GNU (glibc-based) system with a FreeBSD kernel.
871 Hewlett-Packard HPUX operating system.
874 Silicon Graphics Irix system.
877 Microsoft MS-DOS ``operating system.'' Emacs compiled with DJGPP for
878 MS-DOS binds @code{system-type} to @code{ms-dos} even when you run it on
885 Microsoft Windows NT and later. The same executable supports Windows
886 9X, but the value of @code{system-type} is @code{windows-nt} in either
891 We do not wish to add new symbols to make finer distinctions unless it
892 is absolutely necessary! In fact, we hope to eliminate some of these
893 alternatives in the future. We recommend using
894 @code{system-configuration} to distinguish between different operating
899 This function returns the name of the machine you are running on.
902 @result{} "www.gnu.org"
906 The symbol @code{system-name} is a variable as well as a function. In
907 fact, the function returns whatever value the variable
908 @code{system-name} currently holds. Thus, you can set the variable
909 @code{system-name} in case Emacs is confused about the name of your
910 system. The variable is also useful for constructing frame titles
911 (@pxref{Frame Titles}).
913 @defopt mail-host-address
914 If this variable is non-@code{nil}, it is used instead of
915 @code{system-name} for purposes of generating email addresses. For
916 example, it is used when constructing the default value of
917 @code{user-mail-address}. @xref{User Identification}. (Since this is
918 done when Emacs starts up, the value actually used is the one saved when
919 Emacs was dumped. @xref{Building Emacs}.)
922 @deffn Command getenv var &optional frame
923 @cindex environment variable access
924 This function returns the value of the environment variable @var{var},
925 as a string. @var{var} should be a string. If @var{var} is undefined
926 in the environment, @code{getenv} returns @code{nil}. If returns
927 @samp{""} if @var{var} is set but null. Within Emacs, the environment
928 variable values are kept in the Lisp variable @code{process-environment}.
937 lewis@@slug[10] % printenv
938 PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
950 @deffn Command setenv variable &optional value
951 This command sets the value of the environment variable named
952 @var{variable} to @var{value}. @var{variable} should be a string.
953 Internally, Emacs Lisp can handle any string. However, normally
954 @var{variable} should be a valid shell identifier, that is, a sequence
955 of letters, digits and underscores, starting with a letter or
956 underscore. Otherwise, errors may occur if subprocesses of Emacs try
957 to access the value of @var{variable}. If @var{value} is omitted or
958 @code{nil}, @code{setenv} removes @var{variable} from the environment.
959 Otherwise, @var{value} should be a string.
961 @code{setenv} works by modifying @code{process-environment}; binding
962 that variable with @code{let} is also reasonable practice.
964 @code{setenv} returns the new value of @var{variable}, or @code{nil}
965 if it removed @var{variable} from the environment.
968 @defvar process-environment
969 This variable is a list of strings, each describing one environment
970 variable. The functions @code{getenv} and @code{setenv} work by means
976 @result{} ("l=/usr/stanford/lib/gnuemacs/lisp"
977 "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
987 If @code{process-environment} contains ``duplicate'' elements that
988 specify the same environment variable, the first of these elements
989 specifies the variable, and the other ``duplicates'' are ignored.
992 @defvar initial-environment
993 This variable holds the list of environment variables Emacs inherited
994 from its parent process. It is computed during startup, see
995 @ref{Startup Summary}.
998 @defvar path-separator
999 This variable holds a string which says which character separates
1000 directories in a search path (as found in an environment variable). Its
1001 value is @code{":"} for Unix and GNU systems, and @code{";"} for MS-DOS
1005 @defun parse-colon-path path
1006 This function takes a search path string such as would be the value of
1007 the @code{PATH} environment variable, and splits it at the separators,
1008 returning a list of directory names. @code{nil} in this list stands for
1009 ``use the current directory.'' Although the function's name says
1010 ``colon,'' it actually uses the value of @code{path-separator}.
1013 (parse-colon-path ":/foo:/bar")
1014 @result{} (nil "/foo/" "/bar/")
1018 @defvar invocation-name
1019 This variable holds the program name under which Emacs was invoked. The
1020 value is a string, and does not include a directory name.
1023 @defvar invocation-directory
1024 This variable holds the directory from which the Emacs executable was
1025 invoked, or perhaps @code{nil} if that directory cannot be determined.
1028 @defvar installation-directory
1029 If non-@code{nil}, this is a directory within which to look for the
1030 @file{lib-src} and @file{etc} subdirectories. This is non-@code{nil}
1031 when Emacs can't find those directories in their standard installed
1032 locations, but can find them in a directory related somehow to the one
1033 containing the Emacs executable.
1036 @defun load-average &optional use-float
1037 This function returns the current 1-minute, 5-minute, and 15-minute load
1038 averages, in a list.
1040 By default, the values are integers that are 100 times the system load
1041 averages, which indicate the average number of processes trying to run.
1042 If @var{use-float} is non-@code{nil}, then they are returned
1043 as floating point numbers and without multiplying by 100.
1045 If it is impossible to obtain the load average, this function signals
1046 an error. On some platforms, access to load averages requires
1047 installing Emacs as setuid or setgid so that it can read kernel
1048 information, and that usually isn't advisable.
1050 If the 1-minute load average is available, but the 5- or 15-minute
1051 averages are not, this function returns a shortened list containing
1052 the available averages.
1057 @result{} (169 48 36)
1061 @result{} (1.69 0.48 0.36)
1065 lewis@@rocky[5] % uptime
1066 11:55am up 1 day, 19:37, 3 users,
1067 load average: 1.69, 0.48, 0.36
1073 This function returns the process @acronym{ID} of the Emacs process,
1077 @defvar tty-erase-char
1078 This variable holds the erase character that was selected
1079 in the system's terminal driver, before Emacs was started.
1080 The value is @code{nil} if Emacs is running under a window system.
1083 @node User Identification
1084 @section User Identification
1085 @cindex user identification
1087 @defvar init-file-user
1088 This variable says which user's init files should be used by
1089 Emacs---or @code{nil} if none. @code{""} stands for the user who
1090 originally logged in. The value reflects command-line options such as
1091 @samp{-q} or @samp{-u @var{user}}.
1093 Lisp packages that load files of customizations, or any other sort of
1094 user profile, should obey this variable in deciding where to find it.
1095 They should load the profile of the user name found in this variable.
1096 If @code{init-file-user} is @code{nil}, meaning that the @samp{-q}
1097 option was used, then Lisp packages should not load any customization
1098 files or user profile.
1101 @defopt user-mail-address
1102 This holds the nominal email address of the user who is using Emacs.
1103 Emacs normally sets this variable to a default value after reading your
1104 init files, but not if you have already set it. So you can set the
1105 variable to some other value in your init file if you do not
1106 want to use the default value.
1109 @defun user-login-name &optional uid
1110 If you don't specify @var{uid}, this function returns the name under
1111 which the user is logged in. If the environment variable @code{LOGNAME}
1112 is set, that value is used. Otherwise, if the environment variable
1113 @code{USER} is set, that value is used. Otherwise, the value is based
1114 on the effective @acronym{UID}, not the real @acronym{UID}.
1116 If you specify @var{uid}, the value is the user name that corresponds
1117 to @var{uid} (which should be an integer), or @code{nil} if there is
1128 @defun user-real-login-name
1129 This function returns the user name corresponding to Emacs's real
1130 @acronym{UID}. This ignores the effective @acronym{UID} and ignores the
1131 environment variables @code{LOGNAME} and @code{USER}.
1134 @defun user-full-name &optional uid
1135 This function returns the full name of the logged-in user---or the value
1136 of the environment variable @code{NAME}, if that is set.
1138 @c "Bil" is the correct spelling.
1142 @result{} "Bil Lewis"
1146 If the Emacs job's user-id does not correspond to any known user (and
1147 provided @code{NAME} is not set), the value is @code{"unknown"}.
1149 If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
1150 or a string (a login name). Then @code{user-full-name} returns the full
1151 name corresponding to that user-id or login name. If you specify a
1152 user-id or login name that isn't defined, it returns @code{nil}.
1155 @vindex user-full-name
1156 @vindex user-real-login-name
1157 @vindex user-login-name
1158 The symbols @code{user-login-name}, @code{user-real-login-name} and
1159 @code{user-full-name} are variables as well as functions. The functions
1160 return the same values that the variables hold. These variables allow
1161 you to ``fake out'' Emacs by telling the functions what to return. The
1162 variables are also useful for constructing frame titles (@pxref{Frame
1165 @defun user-real-uid
1166 This function returns the real @acronym{UID} of the user.
1167 The value may be a floating point number.
1178 This function returns the effective @acronym{UID} of the user.
1179 The value may be a floating point number.
1183 @section Time of Day
1185 This section explains how to determine the current time and time
1189 Most of these functions represent time as a list of either three
1190 integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
1191 two integers, @code{(@var{sec-high} @var{sec-low})}. The integers
1192 @var{sec-high} and @var{sec-low} give the high and low bits of an
1193 integer number of seconds. This integer number,
1195 @var{high} * 2**16 + @var{low},
1200 is the number of seconds from the @dfn{epoch} (0:00 January 1, 1970
1201 UTC) to the specified time. The third list element @var{microsec}, if
1202 present, gives the number of microseconds from the start of that
1203 second to the specified time.
1205 The return value of @code{current-time} represents time using three
1206 integers, while the timestamps in the return value of
1207 @code{file-attributes} use two integers (@pxref{Definition of
1208 file-attributes}). In function arguments, e.g.@: the @var{time-value}
1209 argument to @code{current-time-string}, both two- and three-integer
1210 lists are accepted. You can convert times from the list
1211 representation into standard human-readable strings using
1212 @code{current-time}, or to other forms using the @code{decode-time}
1213 and @code{format-time-string} functions documented in the following
1216 @defun current-time-string &optional time-value
1217 This function returns the current time and date as a human-readable
1218 string. The format of the string is unvarying; the number of
1219 characters used for each part is always the same, so you can reliably
1220 use @code{substring} to extract pieces of it. You should count
1221 characters from the beginning of the string rather than from the end,
1222 as additional information may some day be added at the end.
1224 The argument @var{time-value}, if given, specifies a time to format
1225 (represented as a list of integers), instead of the current time.
1229 (current-time-string)
1230 @result{} "Wed Oct 14 22:21:05 1987"
1236 This function returns the current time, represented as a list of three
1237 integers @code{(@var{sec-high} @var{sec-low} @var{microsec})}. On
1238 systems with only one-second time resolutions, @var{microsec} is 0.
1241 @defun float-time &optional time-value
1242 This function returns the current time as a floating-point number of
1243 seconds since the epoch. The optional argument @var{time-value}, if
1244 given, specifies a time (represented as a list of integers) to convert
1245 instead of the current time.
1247 @emph{Warning}: Since the result is floating point, it may not be
1248 exact. Do not use this function if precise time stamps are required.
1251 @defun current-time-zone &optional time-value
1252 This function returns a list describing the time zone that the user is
1255 The value has the form @code{(@var{offset} @var{name})}. Here
1256 @var{offset} is an integer giving the number of seconds ahead of UTC
1257 (east of Greenwich). A negative value means west of Greenwich. The
1258 second element, @var{name}, is a string giving the name of the time
1259 zone. Both elements change when daylight saving time begins or ends;
1260 if the user has specified a time zone that does not use a seasonal time
1261 adjustment, then the value is constant through time.
1263 If the operating system doesn't supply all the information necessary to
1264 compute the value, the unknown elements of the list are @code{nil}.
1266 The argument @var{time-value}, if given, specifies a time (represented
1267 as a list of integers) to analyze instead of the current time.
1270 The current time zone is determined by the @samp{TZ} environment
1271 variable. @xref{System Environment}. For example, you can tell Emacs
1272 to use universal time with @code{(setenv "TZ" "UTC0")}. If @samp{TZ}
1273 is not in the environment, Emacs uses a platform-dependent default
1276 @node Time Conversion
1277 @section Time Conversion
1279 These functions convert time values (lists of two or three integers,
1280 as explained in the previous section) into calendrical information and
1283 Many 32-bit operating systems are limited to time values containing
1284 32 bits of information; these systems typically handle only the times
1285 from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC.
1286 However, 64-bit and some 32-bit operating systems have larger time
1287 values, and can represent times far in the past or future.
1289 Time conversion functions always use the Gregorian calendar, even
1290 for dates before the Gregorian calendar was introduced. Year numbers
1291 count the number of years since the year 1 B.C., and do not skip zero
1292 as traditional Gregorian years do; for example, the year number
1293 @minus{}37 represents the Gregorian year 38 B.C@.
1295 @defun decode-time &optional time
1296 This function converts a time value into calendrical information. If
1297 you don't specify @var{time}, it decodes the current time. The return
1298 value is a list of nine elements, as follows:
1301 (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
1304 Here is what the elements mean:
1308 The number of seconds past the minute, as an integer between 0 and 59.
1309 On some operating systems, this is 60 for leap seconds.
1311 The number of minutes past the hour, as an integer between 0 and 59.
1313 The hour of the day, as an integer between 0 and 23.
1315 The day of the month, as an integer between 1 and 31.
1317 The month of the year, as an integer between 1 and 12.
1319 The year, an integer typically greater than 1900.
1321 The day of week, as an integer between 0 and 6, where 0 stands for
1324 @code{t} if daylight saving time is effect, otherwise @code{nil}.
1326 An integer indicating the time zone, as the number of seconds east of
1330 @strong{Common Lisp Note:} Common Lisp has different meanings for
1331 @var{dow} and @var{zone}.
1334 @defun encode-time seconds minutes hour day month year &optional zone
1335 This function is the inverse of @code{decode-time}. It converts seven
1336 items of calendrical data into a time value. For the meanings of the
1337 arguments, see the table above under @code{decode-time}.
1339 Year numbers less than 100 are not treated specially. If you want them
1340 to stand for years above 1900, or years above 2000, you must alter them
1341 yourself before you call @code{encode-time}.
1343 The optional argument @var{zone} defaults to the current time zone and
1344 its daylight saving time rules. If specified, it can be either a list
1345 (as you would get from @code{current-time-zone}), a string as in the
1346 @code{TZ} environment variable, @code{t} for Universal Time, or an
1347 integer (as you would get from @code{decode-time}). The specified
1348 zone is used without any further alteration for daylight saving time.
1350 If you pass more than seven arguments to @code{encode-time}, the first
1351 six are used as @var{seconds} through @var{year}, the last argument is
1352 used as @var{zone}, and the arguments in between are ignored. This
1353 feature makes it possible to use the elements of a list returned by
1354 @code{decode-time} as the arguments to @code{encode-time}, like this:
1357 (apply 'encode-time (decode-time @dots{}))
1360 You can perform simple date arithmetic by using out-of-range values for
1361 the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
1362 arguments; for example, day 0 means the day preceding the given month.
1364 The operating system puts limits on the range of possible time values;
1365 if you try to encode a time that is out of range, an error results.
1366 For instance, years before 1970 do not work on some systems;
1367 on others, years as early as 1901 do work.
1371 @section Parsing and Formatting Times
1373 These functions convert time values (lists of two or three integers)
1374 to text in a string, and vice versa.
1376 @defun date-to-time string
1377 This function parses the time-string @var{string} and returns the
1378 corresponding time value.
1381 @defun format-time-string format-string &optional time universal
1382 This function converts @var{time} (or the current time, if @var{time} is
1383 omitted) to a string according to @var{format-string}. The argument
1384 @var{format-string} may contain @samp{%}-sequences which say to
1385 substitute parts of the time. Here is a table of what the
1386 @samp{%}-sequences mean:
1390 This stands for the abbreviated name of the day of week.
1392 This stands for the full name of the day of week.
1394 This stands for the abbreviated name of the month.
1396 This stands for the full name of the month.
1398 This is a synonym for @samp{%x %X}.
1400 This has a locale-specific meaning. In the default locale (named C), it
1401 is equivalent to @samp{%A, %B %e, %Y}.
1403 This stands for the day of month, zero-padded.
1405 This is a synonym for @samp{%m/%d/%y}.
1407 This stands for the day of month, blank-padded.
1409 This is a synonym for @samp{%b}.
1411 This stands for the hour (00-23).
1413 This stands for the hour (01-12).
1415 This stands for the day of the year (001-366).
1417 This stands for the hour (0-23), blank padded.
1419 This stands for the hour (1-12), blank padded.
1421 This stands for the month (01-12).
1423 This stands for the minute (00-59).
1425 This stands for a newline.
1427 This stands for the nanoseconds (000000000-999999999). To ask for
1428 fewer digits, use @samp{%3N} for milliseconds, @samp{%6N} for
1429 microseconds, etc. Any excess digits are discarded, without rounding.
1430 Currently Emacs time stamps are at best microsecond resolution so the
1431 last three digits generated by plain @samp{%N} are always zero.
1433 This stands for @samp{AM} or @samp{PM}, as appropriate.
1435 This is a synonym for @samp{%I:%M:%S %p}.
1437 This is a synonym for @samp{%H:%M}.
1439 This stands for the seconds (00-59).
1441 This stands for a tab character.
1443 This is a synonym for @samp{%H:%M:%S}.
1445 This stands for the week of the year (01-52), assuming that weeks
1448 This stands for the numeric day of week (0-6). Sunday is day 0.
1450 This stands for the week of the year (01-52), assuming that weeks
1453 This has a locale-specific meaning. In the default locale (named
1454 @samp{C}), it is equivalent to @samp{%D}.
1456 This has a locale-specific meaning. In the default locale (named
1457 @samp{C}), it is equivalent to @samp{%T}.
1459 This stands for the year without century (00-99).
1461 This stands for the year with century.
1463 This stands for the time zone abbreviation (e.g., @samp{EST}).
1465 This stands for the time zone numerical offset (e.g., @samp{-0500}).
1468 You can also specify the field width and type of padding for any of
1469 these @samp{%}-sequences. This works as in @code{printf}: you write
1470 the field width as digits in the middle of a @samp{%}-sequences. If you
1471 start the field width with @samp{0}, it means to pad with zeros. If you
1472 start the field width with @samp{_}, it means to pad with spaces.
1474 For example, @samp{%S} specifies the number of seconds since the minute;
1475 @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
1476 pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
1477 because that is how @samp{%S} normally pads to two positions.
1479 The characters @samp{E} and @samp{O} act as modifiers when used between
1480 @samp{%} and one of the letters in the table above. @samp{E} specifies
1481 using the current locale's ``alternative'' version of the date and time.
1482 In a Japanese locale, for example, @code{%Ex} might yield a date format
1483 based on the Japanese Emperors' reigns. @samp{E} is allowed in
1484 @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
1487 @samp{O} means to use the current locale's ``alternative''
1488 representation of numbers, instead of the ordinary decimal digits. This
1489 is allowed with most letters, all the ones that output numbers.
1491 If @var{universal} is non-@code{nil}, that means to describe the time as
1492 Universal Time; @code{nil} means describe it using what Emacs believes
1493 is the local time zone (see @code{current-time-zone}).
1495 This function uses the C library function @code{strftime}
1496 (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
1497 Manual}) to do most of the work. In order to communicate with that
1498 function, it first encodes its argument using the coding system
1499 specified by @code{locale-coding-system} (@pxref{Locales}); after
1500 @code{strftime} returns the resulting string,
1501 @code{format-time-string} decodes the string using that same coding
1505 @defun seconds-to-time seconds
1506 This function converts @var{seconds}, a floating point number of
1507 seconds since the epoch, to a time value and returns that. To perform
1508 the inverse conversion, use @code{float-time}.
1511 @defun format-seconds format-string seconds
1512 This function converts its argument @var{seconds} into a string of
1513 years, days, hours, etc., according to @var{format-string}. The
1514 argument @var{format-string} may contain @samp{%}-sequences which
1515 control the conversion. Here is a table of what the
1516 @samp{%}-sequences mean:
1521 The integer number of 365-day years.
1524 The integer number of days.
1527 The integer number of hours.
1530 The integer number of minutes.
1533 The integer number of seconds.
1535 Non-printing control flag. When it is used, other specifiers must be
1536 given in the order of decreasing size, i.e.@: years before days, hours
1537 before minutes, etc. Nothing will be produced in the result string to
1538 the left of @samp{%z} until the first non-zero conversion is
1539 encountered. For example, the default format used by
1540 @code{emacs-uptime} (@pxref{Processor Run Time, emacs-uptime})
1541 @w{@code{"%Y, %D, %H, %M, %z%S"}} means that the number of seconds
1542 will always be produced, but years, days, hours, and minutes will only
1543 be shown if they are non-zero.
1545 Produces a literal @samp{%}.
1548 Upper-case format sequences produce the units in addition to the
1549 numbers, lower-case formats produce only the numbers.
1551 You can also specify the field width by following the @samp{%} with a
1552 number; shorter numbers will be padded with blanks. An optional
1553 period before the width requests zero-padding instead. For example,
1554 @code{"%.3Y"} might produce @code{"004 years"}.
1556 @emph{Warning:} This function works only with values of @var{seconds}
1557 that don't exceed @code{most-positive-fixnum} (@pxref{Integer Basics,
1558 most-positive-fixnum}).
1561 @node Processor Run Time
1562 @section Processor Run time
1563 @cindex processor run time
1564 @cindex Emacs process run time
1566 Emacs provides several functions and primitives that return time,
1567 both elapsed and processor time, used by the Emacs process.
1569 @deffn Command emacs-uptime &optional format
1570 This function returns a string representing the Emacs
1571 @dfn{uptime}---the elapsed wall-clock time this instance of Emacs is
1572 running. The string is formatted by @code{format-seconds} according
1573 to the optional argument @var{format}. For the available format
1574 descriptors, see @ref{Time Parsing, format-seconds}. If @var{format}
1575 is @code{nil} or omitted, it defaults to @code{"%Y, %D, %H, %M,
1578 When called interactively, it prints the uptime in the echo area.
1581 @defun get-internal-run-time
1582 This function returns the processor run time used by Emacs as a list
1583 of three integers: @code{(@var{high} @var{low} @var{microsec})}. The
1584 integers @var{high} and @var{low} combine to give the number of
1587 @var{high} * 2**16 + @var{low}.
1593 The third element, @var{microsec}, gives the microseconds (or 0 for
1594 systems that return time with the resolution of only one second).
1596 Note that the time returned by this function excludes the time Emacs
1597 was not using the processor, and if the Emacs process has several
1598 threads, the returned value is the sum of the processor times used up
1599 by all Emacs threads.
1601 If the system doesn't provide a way to determine the processor run
1602 time, @code{get-internal-run-time} returns the same time as
1603 @code{current-time}.
1606 @deffn Command emacs-init-time
1607 This function returns the duration of the Emacs initialization
1608 (@pxref{Startup Summary}) in seconds, as a string. When called
1609 interactively, it prints the duration in the echo area.
1612 @node Time Calculations
1613 @section Time Calculations
1615 These functions perform calendrical computations using time values
1616 (the kind of list that @code{current-time} returns).
1618 @defun time-less-p t1 t2
1619 This returns @code{t} if time value @var{t1} is less than time value
1623 @defun time-subtract t1 t2
1624 This returns the time difference @var{t1} @minus{} @var{t2} between
1625 two time values, in the same format as a time value.
1628 @defun time-add t1 t2
1629 This returns the sum of two time values, one of which ought to
1630 represent a time difference rather than a point in time.
1631 Here is how to add a number of seconds to a time value:
1634 (time-add @var{time} (seconds-to-time @var{seconds}))
1638 @defun time-to-days time
1639 This function returns the number of days between the beginning of year
1643 @defun time-to-day-in-year time
1644 This returns the day number within the year corresponding to @var{time}.
1647 @defun date-leap-year-p year
1648 This function returns @code{t} if @var{year} is a leap year.
1652 @section Timers for Delayed Execution
1655 You can set up a @dfn{timer} to call a function at a specified
1656 future time or after a certain length of idleness.
1658 Emacs cannot run timers at any arbitrary point in a Lisp program; it
1659 can run them only when Emacs could accept output from a subprocess:
1660 namely, while waiting or inside certain primitive functions such as
1661 @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
1662 timer's execution may be delayed if Emacs is busy. However, the time of
1663 execution is very precise if Emacs is idle.
1665 Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
1666 function, because quitting out of many timer functions can leave
1667 things in an inconsistent state. This is normally unproblematical
1668 because most timer functions don't do a lot of work. Indeed, for a
1669 timer to call a function that takes substantial time to run is likely
1670 to be annoying. If a timer function needs to allow quitting, it
1671 should use @code{with-local-quit} (@pxref{Quitting}). For example, if
1672 a timer function calls @code{accept-process-output} to receive output
1673 from an external process, that call should be wrapped inside
1674 @code{with-local-quit}, to ensure that @kbd{C-g} works if the external
1677 It is usually a bad idea for timer functions to alter buffer
1678 contents. When they do, they usually should call @code{undo-boundary}
1679 both before and after changing the buffer, to separate the timer's
1680 changes from user commands' changes and prevent a single undo entry
1681 from growing to be quite large.
1683 Timer functions should also avoid calling functions that cause Emacs
1684 to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
1685 unpredictable effects, since other timers (or even the same timer) can
1686 run while waiting. If a timer function needs to perform an action
1687 after a certain time has elapsed, it can do this by scheduling a new
1690 If a timer function calls functions that can change the match data,
1691 it should save and restore the match data. @xref{Saving Match Data}.
1693 @deffn Command run-at-time time repeat function &rest args
1694 This sets up a timer that calls the function @var{function} with
1695 arguments @var{args} at time @var{time}. If @var{repeat} is a number
1696 (integer or floating point), the timer is scheduled to run again every
1697 @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
1698 the timer runs only once.
1700 @var{time} may specify an absolute or a relative time.
1702 Absolute times may be specified using a string with a limited variety
1703 of formats, and are taken to be times @emph{today}, even if already in
1704 the past. The recognized forms are @samp{@var{xxxx}},
1705 @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
1706 and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
1707 @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
1708 @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
1709 @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
1710 to separate the hour and minute parts.
1712 To specify a relative time as a string, use numbers followed by units.
1717 denotes 1 minute from now.
1719 denotes 65 seconds from now.
1720 @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
1721 denotes exactly 103 months, 123 days, and 10862 seconds from now.
1724 For relative time values, Emacs considers a month to be exactly thirty
1725 days, and a year to be exactly 365.25 days.
1727 Not all convenient formats are strings. If @var{time} is a number
1728 (integer or floating point), that specifies a relative time measured in
1729 seconds. The result of @code{encode-time} can also be used to specify
1730 an absolute value for @var{time}.
1732 In most cases, @var{repeat} has no effect on when @emph{first} call
1733 takes place---@var{time} alone specifies that. There is one exception:
1734 if @var{time} is @code{t}, then the timer runs whenever the time is a
1735 multiple of @var{repeat} seconds after the epoch. This is useful for
1736 functions like @code{display-time}.
1738 The function @code{run-at-time} returns a timer value that identifies
1739 the particular scheduled future action. You can use this value to call
1740 @code{cancel-timer} (see below).
1743 A repeating timer nominally ought to run every @var{repeat} seconds,
1744 but remember that any invocation of a timer can be late. Lateness of
1745 one repetition has no effect on the scheduled time of the next
1746 repetition. For instance, if Emacs is busy computing for long enough
1747 to cover three scheduled repetitions of the timer, and then starts to
1748 wait, it will immediately call the timer function three times in
1749 immediate succession (presuming no other timers trigger before or
1750 between them). If you want a timer to run again no less than @var{n}
1751 seconds after the last invocation, don't use the @var{repeat} argument.
1752 Instead, the timer function should explicitly reschedule the timer.
1754 @defvar timer-max-repeats
1755 This variable's value specifies the maximum number of times to repeat
1756 calling a timer function in a row, when many previously scheduled
1757 calls were unavoidably delayed.
1760 @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
1761 Execute @var{body}, but give up after @var{seconds} seconds. If
1762 @var{body} finishes before the time is up, @code{with-timeout} returns
1763 the value of the last form in @var{body}. If, however, the execution of
1764 @var{body} is cut short by the timeout, then @code{with-timeout}
1765 executes all the @var{timeout-forms} and returns the value of the last
1768 This macro works by setting a timer to run after @var{seconds} seconds. If
1769 @var{body} finishes before that time, it cancels the timer. If the
1770 timer actually runs, it terminates execution of @var{body}, then
1771 executes @var{timeout-forms}.
1773 Since timers can run within a Lisp program only when the program calls a
1774 primitive that can wait, @code{with-timeout} cannot stop executing
1775 @var{body} while it is in the midst of a computation---only when it
1776 calls one of those primitives. So use @code{with-timeout} only with a
1777 @var{body} that waits for input, not one that does a long computation.
1780 The function @code{y-or-n-p-with-timeout} provides a simple way to use
1781 a timer to avoid waiting too long for an answer. @xref{Yes-or-No
1784 @defun cancel-timer timer
1785 This cancels the requested action for @var{timer}, which should be a
1786 timer---usually, one previously returned by @code{run-at-time} or
1787 @code{run-with-idle-timer}. This cancels the effect of that call to
1788 one of these functions; the arrival of the specified time will not
1789 cause anything special to happen.
1793 @section Idle Timers
1795 Here is how to set up a timer that runs when Emacs is idle for a
1796 certain length of time. Aside from how to set them up, idle timers
1797 work just like ordinary timers.
1799 @deffn Command run-with-idle-timer secs repeat function &rest args
1800 Set up a timer which runs the next time Emacs is idle for @var{secs}
1801 seconds. The value of @var{secs} may be an integer or a floating
1802 point number; a value of the type returned by @code{current-idle-time}
1805 If @var{repeat} is @code{nil}, the timer runs just once, the first time
1806 Emacs remains idle for a long enough time. More often @var{repeat} is
1807 non-@code{nil}, which means to run the timer @emph{each time} Emacs
1808 remains idle for @var{secs} seconds.
1810 The function @code{run-with-idle-timer} returns a timer value which you
1811 can use in calling @code{cancel-timer} (@pxref{Timers}).
1815 Emacs becomes @dfn{idle} when it starts waiting for user input, and
1816 it remains idle until the user provides some input. If a timer is set
1817 for five seconds of idleness, it runs approximately five seconds after
1818 Emacs first becomes idle. Even if @var{repeat} is non-@code{nil},
1819 this timer will not run again as long as Emacs remains idle, because
1820 the duration of idleness will continue to increase and will not go
1821 down to five seconds again.
1823 Emacs can do various things while idle: garbage collect, autosave or
1824 handle data from a subprocess. But these interludes during idleness do
1825 not interfere with idle timers, because they do not reset the clock of
1826 idleness to zero. An idle timer set for 600 seconds will run when ten
1827 minutes have elapsed since the last user command was finished, even if
1828 subprocess output has been accepted thousands of times within those ten
1829 minutes, and even if there have been garbage collections and autosaves.
1831 When the user supplies input, Emacs becomes non-idle while executing the
1832 input. Then it becomes idle again, and all the idle timers that are
1833 set up to repeat will subsequently run another time, one by one.
1835 @defun current-idle-time
1836 If Emacs is idle, this function returns the length of time Emacs has
1837 been idle, as a list of three integers: @code{(@var{sec-high}
1838 @var{sec-low} @var{microsec})}, where @var{high} and @var{low} are the
1839 high and low bits for the number of seconds and @var{microsec} is the
1840 additional number of microseconds (@pxref{Time of Day}).
1842 When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
1843 This is a convenient way to test whether Emacs is idle.
1845 The main use of this function is when an idle timer function wants to
1846 ``take a break'' for a while. It can set up another idle timer to
1847 call the same function again, after a few seconds more idleness.
1851 (defvar resume-timer nil
1852 "Timer that `timer-function' used to reschedule itself, or nil.")
1854 (defun timer-function ()
1855 ;; @r{If the user types a command while @code{resume-timer}}
1856 ;; @r{is active, the next time this function is called from}
1857 ;; @r{its main idle timer, deactivate @code{resume-timer}.}
1859 (cancel-timer resume-timer))
1860 ...@var{do the work for a while}...
1861 (when @var{taking-a-break}
1863 (run-with-idle-timer
1864 ;; Compute an idle time @var{break-length}
1865 ;; more than the current value.
1866 (time-add (current-idle-time)
1867 (seconds-to-time @var{break-length}))
1873 Do not write an idle timer function containing a loop which does a
1874 certain amount of processing each time around, and exits when
1875 @code{(input-pending-p)} is non-@code{nil}. This approach seems very
1876 natural but has two problems:
1880 It blocks out all process output (since Emacs accepts process output
1881 only while waiting).
1884 It blocks out any idle timers that ought to run during that time.
1888 The correct approach is for the idle timer to reschedule itself after
1889 a brief pause, using the method in the @code{timer-function} example
1892 @node Terminal Input
1893 @section Terminal Input
1894 @cindex terminal input
1896 This section describes functions and variables for recording or
1897 manipulating terminal input. See @ref{Display}, for related
1901 * Input Modes:: Options for how input is processed.
1902 * Recording Input:: Saving histories of recent or all input events.
1906 @subsection Input Modes
1908 @cindex terminal input modes
1910 @defun set-input-mode interrupt flow meta &optional quit-char
1911 This function sets the mode for reading keyboard input. If
1912 @var{interrupt} is non-null, then Emacs uses input interrupts. If it is
1913 @code{nil}, then it uses @sc{cbreak} mode. The default setting is
1914 system-dependent. Some systems always use @sc{cbreak} mode regardless
1915 of what is specified.
1917 When Emacs communicates directly with X, it ignores this argument and
1918 uses interrupts if that is the way it knows how to communicate.
1920 If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
1921 (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
1922 has no effect except in @sc{cbreak} mode.
1925 The argument @var{meta} controls support for input character codes
1926 above 127. If @var{meta} is @code{t}, Emacs converts characters with
1927 the 8th bit set into Meta characters. If @var{meta} is @code{nil},
1928 Emacs disregards the 8th bit; this is necessary when the terminal uses
1929 it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
1930 Emacs uses all 8 bits of input unchanged. This is good for terminals
1931 that use 8-bit character sets.
1934 If @var{quit-char} is non-@code{nil}, it specifies the character to
1935 use for quitting. Normally this character is @kbd{C-g}.
1939 The @code{current-input-mode} function returns the input mode settings
1940 Emacs is currently using.
1943 @defun current-input-mode
1944 This function returns the current mode for reading keyboard input. It
1945 returns a list, corresponding to the arguments of @code{set-input-mode},
1946 of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
1950 is non-@code{nil} when Emacs is using interrupt-driven input. If
1951 @code{nil}, Emacs is using @sc{cbreak} mode.
1953 is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
1954 flow control for output to the terminal. This value is meaningful only
1955 when @var{interrupt} is @code{nil}.
1957 is @code{t} if Emacs treats the eighth bit of input characters as
1958 the meta bit; @code{nil} means Emacs clears the eighth bit of every
1959 input character; any other value means Emacs uses all eight bits as the
1960 basic character code.
1962 is the character Emacs currently uses for quitting, usually @kbd{C-g}.
1966 @node Recording Input
1967 @subsection Recording Input
1968 @cindex recording input
1971 This function returns a vector containing the last 300 input events from
1972 the keyboard or mouse. All input events are included, whether or not
1973 they were used as parts of key sequences. Thus, you always get the last
1974 100 input events, not counting events generated by keyboard macros.
1975 (These are excluded because they are less interesting for debugging; it
1976 should be enough to see the events that invoked the macros.)
1978 A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
1979 causes this function to return an empty vector immediately afterward.
1982 @deffn Command open-dribble-file filename
1983 @cindex dribble file
1984 This function opens a @dfn{dribble file} named @var{filename}. When a
1985 dribble file is open, each input event from the keyboard or mouse (but
1986 not those from keyboard macros) is written in that file. A
1987 non-character event is expressed using its printed representation
1988 surrounded by @samp{<@dots{}>}.
1990 You close the dribble file by calling this function with an argument
1993 This function is normally used to record the input necessary to
1994 trigger an Emacs bug, for the sake of a bug report.
1998 (open-dribble-file "~/dribble")
2004 See also the @code{open-termscript} function (@pxref{Terminal Output}).
2006 @node Terminal Output
2007 @section Terminal Output
2008 @cindex terminal output
2010 The terminal output functions send output to a text terminal, or keep
2011 track of output sent to the terminal. The variable @code{baud-rate}
2012 tells you what Emacs thinks is the output speed of the terminal.
2015 This variable's value is the output speed of the terminal, as far as
2016 Emacs knows. Setting this variable does not change the speed of actual
2017 data transmission, but the value is used for calculations such as
2020 It also affects decisions about whether to scroll part of the
2021 screen or repaint on text terminals. @xref{Forcing Redisplay},
2022 for the corresponding functionality on graphical terminals.
2024 The value is measured in baud.
2027 If you are running across a network, and different parts of the
2028 network work at different baud rates, the value returned by Emacs may be
2029 different from the value used by your local terminal. Some network
2030 protocols communicate the local terminal speed to the remote machine, so
2031 that Emacs and other programs can get the proper value, but others do
2032 not. If Emacs has the wrong value, it makes decisions that are less
2033 than optimal. To fix the problem, set @code{baud-rate}.
2035 @defun send-string-to-terminal string &optional terminal
2036 This function sends @var{string} to @var{terminal} without alteration.
2037 Control characters in @var{string} have terminal-dependent effects.
2038 This function operates only on text terminals. @var{terminal} may be
2039 a terminal object, a frame, or @code{nil} for the selected frame's
2040 terminal. In batch mode, @var{string} is sent to @code{stdout} when
2041 @var{terminal} is @code{nil}.
2043 One use of this function is to define function keys on terminals that
2044 have downloadable function key definitions. For example, this is how (on
2045 certain terminals) to define function key 4 to move forward four
2046 characters (by transmitting the characters @kbd{C-u C-f} to the
2051 (send-string-to-terminal "\eF4\^U\^F")
2057 @deffn Command open-termscript filename
2058 @cindex termscript file
2059 This function is used to open a @dfn{termscript file} that will record
2060 all the characters sent by Emacs to the terminal. It returns
2061 @code{nil}. Termscript files are useful for investigating problems
2062 where Emacs garbles the screen, problems that are due to incorrect
2063 Termcap entries or to undesirable settings of terminal options more
2064 often than to actual Emacs bugs. Once you are certain which characters
2065 were actually output, you can determine reliably whether they correspond
2066 to the Termcap specifications in use.
2068 You close the termscript file by calling this function with an
2069 argument of @code{nil}.
2071 See also @code{open-dribble-file} in @ref{Recording Input}.
2075 (open-termscript "../junk/termscript")
2082 @section Sound Output
2085 To play sound using Emacs, use the function @code{play-sound}. Only
2086 certain systems are supported; if you call @code{play-sound} on a
2087 system which cannot really do the job, it gives an error.
2089 The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
2090 or Sun Audio format (@samp{.au}).
2092 @defun play-sound sound
2093 This function plays a specified sound. The argument, @var{sound}, has
2094 the form @code{(sound @var{properties}...)}, where the @var{properties}
2095 consist of alternating keywords (particular symbols recognized
2096 specially) and values corresponding to them.
2098 Here is a table of the keywords that are currently meaningful in
2099 @var{sound}, and their meanings:
2102 @item :file @var{file}
2103 This specifies the file containing the sound to play.
2104 If the file name is not absolute, it is expanded against
2105 the directory @code{data-directory}.
2107 @item :data @var{data}
2108 This specifies the sound to play without need to refer to a file. The
2109 value, @var{data}, should be a string containing the same bytes as a
2110 sound file. We recommend using a unibyte string.
2112 @item :volume @var{volume}
2113 This specifies how loud to play the sound. It should be a number in the
2114 range of 0 to 1. The default is to use whatever volume has been
2117 @item :device @var{device}
2118 This specifies the system device on which to play the sound, as a
2119 string. The default device is system-dependent.
2122 Before actually playing the sound, @code{play-sound}
2123 calls the functions in the list @code{play-sound-functions}.
2124 Each function is called with one argument, @var{sound}.
2127 @defun play-sound-file file &optional volume device
2128 This function is an alternative interface to playing a sound @var{file}
2129 specifying an optional @var{volume} and @var{device}.
2132 @defvar play-sound-functions
2133 A list of functions to be called before playing a sound. Each function
2134 is called with one argument, a property list that describes the sound.
2138 @section Operating on X11 Keysyms
2141 To define system-specific X11 keysyms, set the variable
2142 @code{system-key-alist}.
2144 @defvar system-key-alist
2145 This variable's value should be an alist with one element for each
2146 system-specific keysym. Each element has the form @code{(@var{code}
2147 . @var{symbol})}, where @var{code} is the numeric keysym code (not
2148 including the ``vendor specific'' bit,
2155 and @var{symbol} is the name for the function key.
2157 For example @code{(168 . mute-acute)} defines a system-specific key (used
2158 by HP X servers) whose numeric code is
2167 It is not crucial to exclude from the alist the keysyms of other X
2168 servers; those do no harm, as long as they don't conflict with the ones
2169 used by the X server actually in use.
2171 The variable is always local to the current terminal, and cannot be
2172 buffer-local. @xref{Multiple Terminals}.
2175 You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
2177 @defvar x-alt-keysym
2178 @defvarx x-meta-keysym
2179 @defvarx x-hyper-keysym
2180 @defvarx x-super-keysym
2181 The name of the keysym that should stand for the Alt modifier
2182 (respectively, for Meta, Hyper, and Super). For example, here is
2183 how to swap the Meta and Alt modifiers within Emacs:
2185 (setq x-alt-keysym 'meta)
2186 (setq x-meta-keysym 'alt)
2194 The command-line option @samp{-batch} causes Emacs to run
2195 noninteractively. In this mode, Emacs does not read commands from the
2196 terminal, it does not alter the terminal modes, and it does not expect
2197 to be outputting to an erasable screen. The idea is that you specify
2198 Lisp programs to run; when they are finished, Emacs should exit. The
2199 way to specify the programs to run is with @samp{-l @var{file}}, which
2200 loads the library named @var{file}, or @samp{-f @var{function}}, which
2201 calls @var{function} with no arguments, or @samp{--eval @var{form}}.
2203 Any Lisp program output that would normally go to the echo area,
2204 either using @code{message}, or using @code{prin1}, etc., with @code{t}
2205 as the stream, goes instead to Emacs's standard error descriptor when
2206 in batch mode. Similarly, input that would normally come from the
2207 minibuffer is read from the standard input descriptor.
2208 Thus, Emacs behaves much like a noninteractive
2209 application program. (The echo area output that Emacs itself normally
2210 generates, such as command echoing, is suppressed entirely.)
2212 @defvar noninteractive
2213 This variable is non-@code{nil} when Emacs is running in batch mode.
2216 @node Session Management
2217 @section Session Management
2218 @cindex session manager
2220 Emacs supports the X Session Management Protocol, which is used to
2221 suspend and restart applications. In the X Window System, a program
2222 called the @dfn{session manager} is responsible for keeping track of
2223 the applications that are running. When the X server shuts down, the
2224 session manager asks applications to save their state, and delays the
2225 actual shutdown until they respond. An application can also cancel
2228 When the session manager restarts a suspended session, it directs
2229 these applications to individually reload their saved state. It does
2230 this by specifying a special command-line argument that says what
2231 saved session to restore. For Emacs, this argument is @samp{--smid
2234 @defvar emacs-save-session-functions
2235 Emacs supports saving state via a hook called
2236 @code{emacs-save-session-functions}. Emacs runs this hook when the
2237 session manager tells it that the window system is shutting down. The
2238 functions are called with no arguments, and with the current buffer
2239 set to a temporary buffer. Each function can use @code{insert} to add
2240 Lisp code to this buffer. At the end, Emacs saves the buffer in a
2241 file, called the @dfn{session file}.
2243 @findex emacs-session-restore
2244 Subsequently, when the session manager restarts Emacs, it loads the
2245 session file automatically (@pxref{Loading}). This is performed by a
2246 function named @code{emacs-session-restore}, which is called during
2247 startup. @xref{Startup Summary}.
2249 If a function in @code{emacs-save-session-functions} returns
2250 non-@code{nil}, Emacs tells the session manager to cancel the
2254 Here is an example that just inserts some text into @samp{*scratch*} when
2255 Emacs is restarted by the session manager.
2259 (add-hook 'emacs-save-session-functions 'save-yourself-test)
2263 (defun save-yourself-test ()
2264 (insert "(save-current-buffer
2265 (switch-to-buffer \"*scratch*\")
2266 (insert \"I am restored\"))")
2271 @node Dynamic Libraries
2272 @section Dynamically Loaded Libraries
2273 @cindex dynamic libraries
2275 A @dfn{dynamically loaded library} is a library that is loaded on
2276 demand, when its facilities are first needed. Emacs supports such
2277 on-demand loading of support libraries for some of its features.
2279 @defvar dynamic-library-alist
2280 This is an alist of dynamic libraries and external library files
2283 Each element is a list of the form
2284 @w{@code{(@var{library} @var{files}@dots{})}}, where the @code{car} is
2285 a symbol representing a supported external library, and the rest are
2286 strings giving alternate filenames for that library.
2288 Emacs tries to load the library from the files in the order they
2289 appear in the list; if none is found, the running session of Emacs
2290 won't have access to that library, and the features that depend on the
2291 library will be unavailable.
2293 Image support on some platforms uses this facility. Here's an example
2294 of setting this variable for supporting images on MS-Windows:
2297 (setq dynamic-library-alist
2298 '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")
2299 (png "libpng12d.dll" "libpng12.dll" "libpng.dll"
2300 "libpng13d.dll" "libpng13.dll")
2301 (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll" "jpeg.dll")
2302 (tiff "libtiff3.dll" "libtiff.dll")
2303 (gif "giflib4.dll" "libungif4.dll" "libungif.dll")
2304 (svg "librsvg-2-2.dll")
2305 (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")
2306 (glib "libglib-2.0-0.dll")
2307 (gobject "libgobject-2.0-0.dll")))
2310 Note that image types @code{pbm} and @code{xbm} do not need entries in
2311 this variable because they do not depend on external libraries and are
2312 always available in Emacs.
2314 Also note that this variable is not meant to be a generic facility for
2315 accessing external libraries; only those already known by Emacs can
2316 be loaded through it.
2318 This variable is ignored if the given @var{library} is statically