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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
b3d90e46 GM |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001, |
4 | @c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. | |
73804d4b RS |
5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/os | |
52a1d3b7 | 7 | @node System Interface, Antinews, Display, Top |
73804d4b RS |
8 | @chapter Operating System Interface |
9 | ||
10 | This chapter is about starting and getting out of Emacs, access to | |
78608595 | 11 | values in the operating system environment, and terminal input, output, |
73804d4b RS |
12 | and flow control. |
13 | ||
14 | @xref{Building Emacs}, for related information. See also | |
15 | @ref{Display}, for additional operating system status information | |
16 | pertaining to the terminal and the screen. | |
17 | ||
18 | @menu | |
8241495d | 19 | * Starting Up:: Customizing Emacs startup processing. |
73804d4b RS |
20 | * Getting Out:: How exiting works (permanent or temporary). |
21 | * System Environment:: Distinguish the name and kind of system. | |
22 | * User Identification:: Finding the name and user id of the user. | |
23 | * Time of Day:: Getting the current time. | |
4bdbd317 RS |
24 | * Time Conversion:: Converting a time from numeric form |
25 | to calendrical data, and vice versa). | |
26 | * Time Parsing:: Converting a time from numeric form to text | |
27 | and vice versa. | |
2f6037a5 | 28 | * Processor Run Time:: Getting the run time used by Emacs. |
baee1397 | 29 | * Time Calculations:: Adding, subtracting, comparing times, etc. |
73804d4b | 30 | * Timers:: Setting a timer to call a function at a certain time. |
9d45757a RS |
31 | * Idle Timers:: Setting a timer to call a function when Emacs has |
32 | been idle for a certain length of time. | |
13bdd945 RS |
33 | * Terminal Input:: Accessing and recording terminal input. |
34 | * Terminal Output:: Controlling and recording terminal output. | |
8241495d | 35 | * Sound Output:: Playing sounds on the computer's speaker. |
1ce58cc0 | 36 | * X11 Keysyms:: Operating on key symbols for X Windows |
73804d4b | 37 | * Batch Mode:: Running Emacs without terminal interaction. |
750c3b02 | 38 | * Session Management:: Saving and restoring state with X Session Management. |
73804d4b RS |
39 | @end menu |
40 | ||
41 | @node Starting Up | |
42 | @section Starting Up Emacs | |
43 | ||
44 | This section describes what Emacs does when it is started, and how you | |
45 | can customize these actions. | |
46 | ||
47 | @menu | |
8241495d | 48 | * Startup Summary:: Sequence of actions Emacs performs at startup. |
73804d4b RS |
49 | * Init File:: Details on reading the init file (@file{.emacs}). |
50 | * Terminal-Specific:: How the terminal-specific Lisp file is read. | |
8241495d | 51 | * Command-Line Arguments:: How command-line arguments are processed, |
73804d4b RS |
52 | and how you can customize them. |
53 | @end menu | |
54 | ||
8241495d RS |
55 | @node Startup Summary |
56 | @subsection Summary: Sequence of Actions at Startup | |
bbb9c4e1 | 57 | @cindex initialization of Emacs |
8241495d | 58 | @cindex startup of Emacs |
73804d4b RS |
59 | @cindex @file{startup.el} |
60 | ||
61 | The order of operations performed (in @file{startup.el}) by Emacs when | |
62 | it is started up is as follows: | |
63 | ||
64 | @enumerate | |
a9f0a989 | 65 | @item |
5858d11f RS |
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 these will be | |
69 | scanned in their turn. The files @file{subdirs.el} are normally | |
70 | generated automatically by Emacs installation. | |
a9f0a989 RS |
71 | |
72 | @item | |
73 | It sets the language environment and the terminal coding system, | |
74 | if requested by environment variables such as @code{LANG}. | |
75 | ||
73804d4b RS |
76 | @item |
77 | It loads the initialization library for the window system, if you are | |
78 | using a window system. This library's name is | |
79 | @file{term/@var{windowsystem}-win.el}. | |
80 | ||
bfe721d1 KH |
81 | @item |
82 | It processes the initial options. (Some of them are handled | |
83 | even earlier than this.) | |
84 | ||
73804d4b | 85 | @item |
969fe9b5 | 86 | It initializes the window frame and faces, if appropriate. |
73804d4b RS |
87 | |
88 | @item | |
89 | It runs the normal hook @code{before-init-hook}. | |
90 | ||
91 | @item | |
9775b550 RS |
92 | It loads the library @file{site-start} (if any), unless the option |
93 | @samp{-Q} (or @samp{--no-site-file}) was specified. The library's file | |
94 | name is usually @file{site-start.el}. | |
73804d4b RS |
95 | @cindex @file{site-start.el} |
96 | ||
c60ee5e7 | 97 | @item |
342fd6cd RS |
98 | It loads your init file (usually @file{~/.emacs}), unless the option |
99 | @samp{-q} (or @samp{--no-init-file}), @samp{-Q}, or @samp{--batch} was | |
100 | specified on the command line. The @samp{-u} option can specify | |
101 | another user whose home directory should be used instead of @file{~}. | |
73804d4b | 102 | |
c60ee5e7 | 103 | @item |
9775b550 RS |
104 | It loads the library @file{default} (if any), unless |
105 | @code{inhibit-default-init} is non-@code{nil}. (This is not done in | |
106 | @samp{-batch} mode, or if @samp{-Q} or @samp{-q} was specified on the | |
107 | command line.) The library's file name is usually @file{default.el}. | |
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108 | @cindex @file{default.el} |
109 | ||
110 | @item | |
111 | It runs the normal hook @code{after-init-hook}. | |
112 | ||
113 | @item | |
114 | It sets the major mode according to @code{initial-major-mode}, provided | |
115 | the buffer @samp{*scratch*} is still current and still in Fundamental | |
116 | mode. | |
117 | ||
c60ee5e7 | 118 | @item |
73804d4b RS |
119 | It loads the terminal-specific Lisp file, if any, except when in batch |
120 | mode or using a window system. | |
121 | ||
122 | @item | |
123 | It displays the initial echo area message, unless you have suppressed | |
ebc78e8d | 124 | that with @code{inhibit-startup-echo-area-message}. |
73804d4b | 125 | |
c60ee5e7 | 126 | @item |
bfe721d1 | 127 | It processes the action arguments from the command line. |
73804d4b | 128 | |
c60ee5e7 | 129 | @item |
7ba6d818 | 130 | It runs @code{emacs-startup-hook} and then @code{term-setup-hook}. |
73804d4b RS |
131 | |
132 | @item | |
133 | It calls @code{frame-notice-user-settings}, which modifies the | |
134 | parameters of the selected frame according to whatever the init files | |
135 | specify. | |
136 | ||
c60ee5e7 | 137 | @item |
73804d4b RS |
138 | It runs @code{window-setup-hook}. @xref{Window Systems}. |
139 | ||
c60ee5e7 | 140 | @item |
78608595 | 141 | It displays copyleft, nonwarranty, and basic use information, provided |
9775b550 | 142 | the value of @code{inhibit-startup-message} is @code{nil}, you didn't |
ebc78e8d | 143 | specify @samp{--no-splash} or @samp{-Q}. |
73804d4b RS |
144 | @end enumerate |
145 | ||
146 | @defopt inhibit-startup-message | |
147 | This variable inhibits the initial startup messages (the nonwarranty, | |
148 | etc.). If it is non-@code{nil}, then the messages are not printed. | |
149 | ||
150 | This variable exists so you can set it in your personal init file, once | |
151 | you are familiar with the contents of the startup message. Do not set | |
152 | this variable in the init file of a new user, or in a way that affects | |
153 | more than one user, because that would prevent new users from receiving | |
154 | the information they are supposed to see. | |
155 | @end defopt | |
156 | ||
157 | @defopt inhibit-startup-echo-area-message | |
158 | This variable controls the display of the startup echo area message. | |
159 | You can suppress the startup echo area message by adding text with this | |
a40d4712 | 160 | form to your init file: |
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161 | |
162 | @example | |
163 | (setq inhibit-startup-echo-area-message | |
164 | "@var{your-login-name}") | |
165 | @end example | |
166 | ||
a40d4712 PR |
167 | Emacs explicitly checks for an expression as shown above in your init |
168 | file; your login name must appear in the expression as a Lisp string | |
169 | constant. Other methods of setting | |
a9f0a989 RS |
170 | @code{inhibit-startup-echo-area-message} to the same value do not |
171 | inhibit the startup message. | |
73804d4b RS |
172 | |
173 | This way, you can easily inhibit the message for yourself if you wish, | |
a40d4712 PR |
174 | but thoughtless copying of your init file will not inhibit the message |
175 | for someone else. | |
73804d4b RS |
176 | @end defopt |
177 | ||
178 | @node Init File | |
a40d4712 | 179 | @subsection The Init File, @file{.emacs} |
73804d4b RS |
180 | @cindex init file |
181 | @cindex @file{.emacs} | |
182 | ||
a40d4712 | 183 | When you start Emacs, it normally attempts to load your @dfn{init |
9775b550 | 184 | file}, a file in your home directory. Its normal name is |
f0cdd9e4 CY |
185 | @file{.emacs}, but you can also call it @file{.emacs.el}. |
186 | Alternatively, you can use a file named @file{init.el} in a | |
187 | subdirectory @file{.emacs.d}. Whichever place you use, you can also | |
188 | compile the file (@pxref{Byte Compilation}); then the actual file | |
189 | loaded will be @file{.emacs.elc} or @file{init.elc}. | |
9775b550 RS |
190 | |
191 | The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u} | |
192 | control whether and where to find the init file; @samp{-q} (and the | |
193 | stronger @samp{-Q}) says not to load an init file, while @samp{-u | |
194 | @var{user}} says to load @var{user}'s init file instead of yours. | |
195 | @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither | |
196 | option is specified, Emacs uses the @code{LOGNAME} environment | |
a40d4712 | 197 | variable, or the @code{USER} (most systems) or @code{USERNAME} (MS |
9775b550 RS |
198 | systems) variable, to find your home directory and thus your init |
199 | file; this way, even if you have su'd, Emacs still loads your own init | |
200 | file. If those environment variables are absent, though, Emacs uses | |
201 | your user-id to find your home directory. | |
73804d4b RS |
202 | |
203 | @cindex default init file | |
9775b550 RS |
204 | A site may have a @dfn{default init file}, which is the library |
205 | named @file{default.el}. Emacs finds the @file{default.el} file | |
206 | through the standard search path for libraries (@pxref{How Programs Do | |
207 | Loading}). The Emacs distribution does not come with this file; sites | |
208 | may provide one for local customizations. If the default init file | |
209 | exists, it is loaded whenever you start Emacs, except in batch mode or | |
210 | if @samp{-q} (or @samp{-Q}) is specified. But your own personal init | |
211 | file, if any, is loaded first; if it sets @code{inhibit-default-init} | |
212 | to a non-@code{nil} value, then Emacs does not subsequently load the | |
213 | @file{default.el} file. | |
73804d4b RS |
214 | |
215 | Another file for site-customization is @file{site-start.el}. Emacs | |
216 | loads this @emph{before} the user's init file. You can inhibit the | |
9775b550 | 217 | loading of this file with the option @samp{--no-site-file}. |
73804d4b | 218 | |
bfe721d1 | 219 | @defvar site-run-file |
ebc6903b RS |
220 | This variable specifies the site-customization file to load before the |
221 | user's init file. Its normal value is @code{"site-start"}. The only | |
222 | way you can change it with real effect is to do so before dumping | |
223 | Emacs. | |
bfe721d1 KH |
224 | @end defvar |
225 | ||
333c5fc5 | 226 | @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for |
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227 | examples of how to make various commonly desired customizations in your |
228 | @file{.emacs} file. | |
229 | ||
230 | @defopt inhibit-default-init | |
231 | This variable prevents Emacs from loading the default initialization | |
232 | library file for your session of Emacs. If its value is non-@code{nil}, | |
233 | then the default library is not loaded. The default value is | |
234 | @code{nil}. | |
235 | @end defopt | |
236 | ||
237 | @defvar before-init-hook | |
1911e6e5 | 238 | This normal hook is run, once, just before loading all the init files |
a9f0a989 | 239 | (the user's init file, @file{default.el}, and/or @file{site-start.el}). |
1911e6e5 | 240 | (The only way to change it with real effect is before dumping Emacs.) |
a9f0a989 RS |
241 | @end defvar |
242 | ||
243 | @defvar after-init-hook | |
1911e6e5 | 244 | This normal hook is run, once, just after loading all the init files |
a9f0a989 | 245 | (the user's init file, @file{default.el}, and/or @file{site-start.el}), |
7ba6d818 | 246 | before loading the terminal-specific library and processing the |
339902ec | 247 | command-line action arguments. |
7ba6d818 RS |
248 | @end defvar |
249 | ||
250 | @defvar emacs-startup-hook | |
7ba6d818 RS |
251 | This normal hook is run, once, just after handling the command line |
252 | arguments, just before @code{term-setup-hook}. | |
253 | @end defvar | |
254 | ||
255 | @defvar user-init-file | |
339902ec | 256 | This variable holds the absolute file name of the user's init file. If the |
7ba6d818 RS |
257 | actual init file loaded is a compiled file, such as @file{.emacs.elc}, |
258 | the value refers to the corresponding source file. | |
73804d4b RS |
259 | @end defvar |
260 | ||
261 | @node Terminal-Specific | |
262 | @subsection Terminal-Specific Initialization | |
263 | @cindex terminal-specific initialization | |
264 | ||
265 | Each terminal type can have its own Lisp library that Emacs loads when | |
a9f0a989 RS |
266 | run on that type of terminal. The library's name is constructed by |
267 | concatenating the value of the variable @code{term-file-prefix} and the | |
8241495d RS |
268 | terminal type (specified by the environment variable @code{TERM}). |
269 | Normally, @code{term-file-prefix} has the value | |
a9f0a989 RS |
270 | @code{"term/"}; changing this is not recommended. Emacs finds the file |
271 | in the normal manner, by searching the @code{load-path} directories, and | |
272 | trying the @samp{.elc} and @samp{.el} suffixes. | |
73804d4b | 273 | |
73804d4b | 274 | @cindex Termcap |
1299a5a4 EZ |
275 | The usual function of a terminal-specific library is to enable |
276 | special keys to send sequences that Emacs can recognize. It may also | |
277 | need to set or add to @code{function-key-map} if the Termcap or | |
278 | Terminfo entry does not specify all the terminal's function keys. | |
279 | @xref{Terminal Input}. | |
280 | ||
281 | When the name of the terminal type contains a hyphen, and no library | |
282 | is found whose name is identical to the terminal's name, Emacs strips | |
283 | from the terminal's name the last hyphen and everything that follows | |
284 | it, and tries again. This process is repeated until Emacs finds a | |
285 | matching library or until there are no more hyphens in the name (the | |
286 | latter means the terminal doesn't have any library specific to it). | |
287 | Thus, for example, if there are no @samp{aaa-48} and @samp{aaa-30} | |
288 | libraries, Emacs will try the same library @file{term/aaa.el} for | |
289 | terminal types @samp{aaa-48} and @samp{aaa-30-rv}. If necessary, the | |
290 | library can evaluate @code{(getenv "TERM")} to find the full name of | |
291 | the terminal type.@refill | |
73804d4b | 292 | |
a40d4712 | 293 | Your init file can prevent the loading of the |
73804d4b RS |
294 | terminal-specific library by setting the variable |
295 | @code{term-file-prefix} to @code{nil}. This feature is useful when | |
296 | experimenting with your own peculiar customizations. | |
297 | ||
298 | You can also arrange to override some of the actions of the | |
299 | terminal-specific library by setting the variable | |
300 | @code{term-setup-hook}. This is a normal hook which Emacs runs using | |
301 | @code{run-hooks} at the end of Emacs initialization, after loading both | |
a40d4712 | 302 | your init file and any terminal-specific libraries. You can |
73804d4b RS |
303 | use this variable to define initializations for terminals that do not |
304 | have their own libraries. @xref{Hooks}. | |
305 | ||
306 | @defvar term-file-prefix | |
307 | @cindex @code{TERM} environment variable | |
308 | If the @code{term-file-prefix} variable is non-@code{nil}, Emacs loads | |
309 | a terminal-specific initialization file as follows: | |
310 | ||
311 | @example | |
312 | (load (concat term-file-prefix (getenv "TERM"))) | |
313 | @end example | |
314 | ||
315 | @noindent | |
316 | You may set the @code{term-file-prefix} variable to @code{nil} in your | |
a40d4712 | 317 | init file if you do not wish to load the |
73804d4b | 318 | terminal-initialization file. To do this, put the following in |
a40d4712 | 319 | your init file: @code{(setq term-file-prefix nil)}. |
8241495d RS |
320 | |
321 | On MS-DOS, if the environment variable @code{TERM} is not set, Emacs | |
322 | uses @samp{internal} as the terminal type. | |
73804d4b RS |
323 | @end defvar |
324 | ||
c60ee5e7 | 325 | @defvar term-setup-hook |
78608595 | 326 | This variable is a normal hook that Emacs runs after loading your |
a40d4712 | 327 | init file, the default initialization file (if any) and the |
73804d4b RS |
328 | terminal-specific Lisp file. |
329 | ||
330 | You can use @code{term-setup-hook} to override the definitions made by a | |
331 | terminal-specific file. | |
332 | @end defvar | |
333 | ||
334 | See @code{window-setup-hook} in @ref{Window Systems}, for a related | |
335 | feature. | |
336 | ||
8241495d RS |
337 | @node Command-Line Arguments |
338 | @subsection Command-Line Arguments | |
339 | @cindex command-line arguments | |
73804d4b | 340 | |
8241495d | 341 | You can use command-line arguments to request various actions when you |
73804d4b RS |
342 | start Emacs. Since you do not need to start Emacs more than once per |
343 | day, and will often leave your Emacs session running longer than that, | |
8241495d | 344 | command-line arguments are hardly ever used. As a practical matter, it |
73804d4b RS |
345 | is best to avoid making the habit of using them, since this habit would |
346 | encourage you to kill and restart Emacs unnecessarily often. These | |
347 | options exist for two reasons: to be compatible with other editors (for | |
348 | invocation by other programs) and to enable shell scripts to run | |
349 | specific Lisp programs. | |
350 | ||
8241495d | 351 | This section describes how Emacs processes command-line arguments, |
73804d4b RS |
352 | and how you can customize them. |
353 | ||
354 | @ignore | |
355 | (Note that some other editors require you to start afresh each time | |
356 | you want to edit a file. With this kind of editor, you will probably | |
8241495d | 357 | specify the file as a command-line argument. The recommended way to |
73804d4b RS |
358 | use GNU Emacs is to start it only once, just after you log in, and do |
359 | all your editing in the same Emacs process. Each time you want to edit | |
360 | a different file, you visit it with the existing Emacs, which eventually | |
361 | comes to have many files in it ready for editing. Usually you do not | |
362 | kill the Emacs until you are about to log out.) | |
363 | @end ignore | |
364 | ||
365 | @defun command-line | |
78608595 | 366 | This function parses the command line that Emacs was called with, |
a40d4712 | 367 | processes it, loads the user's init file and displays the |
78608595 | 368 | startup messages. |
73804d4b RS |
369 | @end defun |
370 | ||
371 | @defvar command-line-processed | |
372 | The value of this variable is @code{t} once the command line has been | |
373 | processed. | |
374 | ||
375 | If you redump Emacs by calling @code{dump-emacs}, you may wish to set | |
376 | this variable to @code{nil} first in order to cause the new dumped Emacs | |
8241495d | 377 | to process its new command-line arguments. |
73804d4b RS |
378 | @end defvar |
379 | ||
380 | @defvar command-switch-alist | |
381 | @cindex switches on command line | |
382 | @cindex options on command line | |
8241495d | 383 | @cindex command-line options |
73804d4b RS |
384 | The value of this variable is an alist of user-defined command-line |
385 | options and associated handler functions. This variable exists so you | |
386 | can add elements to it. | |
387 | ||
8241495d RS |
388 | A @dfn{command-line option} is an argument on the command line, which |
389 | has the form: | |
73804d4b RS |
390 | |
391 | @example | |
392 | -@var{option} | |
393 | @end example | |
394 | ||
c60ee5e7 | 395 | The elements of the @code{command-switch-alist} look like this: |
73804d4b RS |
396 | |
397 | @example | |
398 | (@var{option} . @var{handler-function}) | |
399 | @end example | |
400 | ||
8241495d RS |
401 | The @sc{car}, @var{option}, is a string, the name of a command-line |
402 | option (not including the initial hyphen). The @var{handler-function} | |
403 | is called to handle @var{option}, and receives the option name as its | |
404 | sole argument. | |
73804d4b RS |
405 | |
406 | In some cases, the option is followed in the command line by an | |
407 | argument. In these cases, the @var{handler-function} can find all the | |
408 | remaining command-line arguments in the variable | |
409 | @code{command-line-args-left}. (The entire list of command-line | |
410 | arguments is in @code{command-line-args}.) | |
411 | ||
8241495d | 412 | The command-line arguments are parsed by the @code{command-line-1} |
0462a47d EZ |
413 | function in the @file{startup.el} file. See also @ref{Emacs |
414 | Invocation, , Command Line Arguments for Emacs Invocation, emacs, The | |
415 | GNU Emacs Manual}. | |
73804d4b RS |
416 | @end defvar |
417 | ||
418 | @defvar command-line-args | |
8241495d | 419 | The value of this variable is the list of command-line arguments passed |
73804d4b RS |
420 | to Emacs. |
421 | @end defvar | |
422 | ||
423 | @defvar command-line-functions | |
424 | This variable's value is a list of functions for handling an | |
425 | unrecognized command-line argument. Each time the next argument to be | |
426 | processed has no special meaning, the functions in this list are called, | |
78608595 | 427 | in order of appearance, until one of them returns a non-@code{nil} |
73804d4b RS |
428 | value. |
429 | ||
430 | These functions are called with no arguments. They can access the | |
431 | command-line argument under consideration through the variable | |
f9f59935 RS |
432 | @code{argi}, which is bound temporarily at this point. The remaining |
433 | arguments (not including the current one) are in the variable | |
434 | @code{command-line-args-left}. | |
73804d4b RS |
435 | |
436 | When a function recognizes and processes the argument in @code{argi}, it | |
437 | should return a non-@code{nil} value to say it has dealt with that | |
438 | argument. If it has also dealt with some of the following arguments, it | |
439 | can indicate that by deleting them from @code{command-line-args-left}. | |
440 | ||
441 | If all of these functions return @code{nil}, then the argument is used | |
442 | as a file name to visit. | |
443 | @end defvar | |
444 | ||
445 | @node Getting Out | |
446 | @section Getting Out of Emacs | |
447 | @cindex exiting Emacs | |
448 | ||
449 | There are two ways to get out of Emacs: you can kill the Emacs job, | |
450 | which exits permanently, or you can suspend it, which permits you to | |
451 | reenter the Emacs process later. As a practical matter, you seldom kill | |
452 | Emacs---only when you are about to log out. Suspending is much more | |
453 | common. | |
454 | ||
455 | @menu | |
456 | * Killing Emacs:: Exiting Emacs irreversibly. | |
457 | * Suspending Emacs:: Exiting Emacs reversibly. | |
458 | @end menu | |
459 | ||
460 | @node Killing Emacs | |
461 | @comment node-name, next, previous, up | |
462 | @subsection Killing Emacs | |
463 | @cindex killing Emacs | |
464 | ||
465 | Killing Emacs means ending the execution of the Emacs process. The | |
466 | parent process normally resumes control. The low-level primitive for | |
467 | killing Emacs is @code{kill-emacs}. | |
468 | ||
469 | @defun kill-emacs &optional exit-data | |
470 | This function exits the Emacs process and kills it. | |
471 | ||
472 | If @var{exit-data} is an integer, then it is used as the exit status | |
473 | of the Emacs process. (This is useful primarily in batch operation; see | |
474 | @ref{Batch Mode}.) | |
475 | ||
476 | If @var{exit-data} is a string, its contents are stuffed into the | |
477 | terminal input buffer so that the shell (or whatever program next reads | |
478 | input) can read them. | |
479 | @end defun | |
480 | ||
481 | All the information in the Emacs process, aside from files that have | |
8241495d RS |
482 | been saved, is lost when the Emacs process is killed. Because killing |
483 | Emacs inadvertently can lose a lot of work, Emacs queries for | |
484 | confirmation before actually terminating if you have buffers that need | |
485 | saving or subprocesses that are running. This is done in the function | |
339902ec LT |
486 | @code{save-buffers-kill-emacs}, the higher level function from which |
487 | @code{kill-emacs} is usually called. | |
73804d4b RS |
488 | |
489 | @defvar kill-emacs-query-functions | |
490 | After asking the standard questions, @code{save-buffers-kill-emacs} | |
f9f59935 | 491 | calls the functions in the list @code{kill-emacs-query-functions}, in |
73804d4b RS |
492 | order of appearance, with no arguments. These functions can ask for |
493 | additional confirmation from the user. If any of them returns | |
339902ec LT |
494 | @code{nil}, @code{save-buffers-kill-emacs} does not kill Emacs, and |
495 | does not run the remaining functions in this hook. Calling | |
496 | @code{kill-emacs} directly does not run this hook. | |
73804d4b RS |
497 | @end defvar |
498 | ||
499 | @defvar kill-emacs-hook | |
500 | This variable is a normal hook; once @code{save-buffers-kill-emacs} is | |
339902ec LT |
501 | finished with all file saving and confirmation, it calls |
502 | @code{kill-emacs} which runs the functions in this hook. | |
503 | @code{kill-emacs} does not run this hook in batch mode. | |
504 | ||
505 | @code{kill-emacs} may be invoked directly (that is not via | |
506 | @code{save-buffers-kill-emacs}) if the terminal is disconnected, or in | |
507 | similar situations where interaction with the user is not possible. | |
508 | Thus, if your hook needs to interact with the user, put it on | |
509 | @code{kill-emacs-query-functions}; if it needs to run regardless of | |
510 | how Emacs is killed, put it on @code{kill-emacs-hook}. | |
73804d4b RS |
511 | @end defvar |
512 | ||
513 | @node Suspending Emacs | |
514 | @subsection Suspending Emacs | |
515 | @cindex suspending Emacs | |
516 | ||
517 | @dfn{Suspending Emacs} means stopping Emacs temporarily and returning | |
518 | control to its superior process, which is usually the shell. This | |
519 | allows you to resume editing later in the same Emacs process, with the | |
520 | same buffers, the same kill ring, the same undo history, and so on. To | |
521 | resume Emacs, use the appropriate command in the parent shell---most | |
522 | likely @code{fg}. | |
523 | ||
524 | Some operating systems do not support suspension of jobs; on these | |
525 | systems, ``suspension'' actually creates a new shell temporarily as a | |
526 | subprocess of Emacs. Then you would exit the shell to return to Emacs. | |
527 | ||
969fe9b5 RS |
528 | Suspension is not useful with window systems, because the Emacs job |
529 | may not have a parent that can resume it again, and in any case you can | |
530 | give input to some other job such as a shell merely by moving to a | |
531 | different window. Therefore, suspending is not allowed when Emacs is using | |
4b3b6396 | 532 | a window system (X, MS Windows, or Mac). |
73804d4b | 533 | |
339902ec | 534 | @defun suspend-emacs &optional string |
73804d4b RS |
535 | This function stops Emacs and returns control to the superior process. |
536 | If and when the superior process resumes Emacs, @code{suspend-emacs} | |
537 | returns @code{nil} to its caller in Lisp. | |
538 | ||
539 | If @var{string} is non-@code{nil}, its characters are sent to be read | |
540 | as terminal input by Emacs's superior shell. The characters in | |
541 | @var{string} are not echoed by the superior shell; only the results | |
542 | appear. | |
543 | ||
544 | Before suspending, @code{suspend-emacs} runs the normal hook | |
969fe9b5 | 545 | @code{suspend-hook}. |
73804d4b | 546 | |
78608595 | 547 | After the user resumes Emacs, @code{suspend-emacs} runs the normal hook |
73804d4b RS |
548 | @code{suspend-resume-hook}. @xref{Hooks}. |
549 | ||
550 | The next redisplay after resumption will redraw the entire screen, | |
551 | unless the variable @code{no-redraw-on-reenter} is non-@code{nil} | |
552 | (@pxref{Refresh Screen}). | |
553 | ||
554 | In the following example, note that @samp{pwd} is not echoed after | |
555 | Emacs is suspended. But it is read and executed by the shell. | |
556 | ||
557 | @smallexample | |
558 | @group | |
559 | (suspend-emacs) | |
560 | @result{} nil | |
561 | @end group | |
562 | ||
563 | @group | |
564 | (add-hook 'suspend-hook | |
565 | (function (lambda () | |
566 | (or (y-or-n-p | |
567 | "Really suspend? ") | |
339902ec | 568 | (error "Suspend canceled"))))) |
73804d4b RS |
569 | @result{} (lambda nil |
570 | (or (y-or-n-p "Really suspend? ") | |
339902ec | 571 | (error "Suspend canceled"))) |
73804d4b RS |
572 | @end group |
573 | @group | |
574 | (add-hook 'suspend-resume-hook | |
575 | (function (lambda () (message "Resumed!")))) | |
576 | @result{} (lambda nil (message "Resumed!")) | |
577 | @end group | |
578 | @group | |
579 | (suspend-emacs "pwd") | |
580 | @result{} nil | |
581 | @end group | |
582 | @group | |
583 | ---------- Buffer: Minibuffer ---------- | |
584 | Really suspend? @kbd{y} | |
585 | ---------- Buffer: Minibuffer ---------- | |
586 | @end group | |
587 | ||
588 | @group | |
589 | ---------- Parent Shell ---------- | |
590 | lewis@@slug[23] % /user/lewis/manual | |
591 | lewis@@slug[24] % fg | |
592 | @end group | |
593 | ||
594 | @group | |
595 | ---------- Echo Area ---------- | |
596 | Resumed! | |
597 | @end group | |
598 | @end smallexample | |
599 | @end defun | |
600 | ||
601 | @defvar suspend-hook | |
8241495d | 602 | This variable is a normal hook that Emacs runs before suspending. |
73804d4b RS |
603 | @end defvar |
604 | ||
605 | @defvar suspend-resume-hook | |
8241495d RS |
606 | This variable is a normal hook that Emacs runs on resuming |
607 | after a suspension. | |
73804d4b RS |
608 | @end defvar |
609 | ||
610 | @node System Environment | |
611 | @section Operating System Environment | |
612 | @cindex operating system environment | |
613 | ||
614 | Emacs provides access to variables in the operating system environment | |
615 | through various functions. These variables include the name of the | |
ad800164 | 616 | system, the user's @acronym{UID}, and so on. |
73804d4b | 617 | |
969fe9b5 | 618 | @defvar system-configuration |
342fd6cd RS |
619 | This variable holds the standard GNU configuration name for the |
620 | hardware/software configuration of your system, as a string. The | |
621 | convenient way to test parts of this string is with | |
622 | @code{string-match}. | |
969fe9b5 RS |
623 | @end defvar |
624 | ||
1db203ff | 625 | @cindex system type and name |
73804d4b | 626 | @defvar system-type |
bfe721d1 KH |
627 | The value of this variable is a symbol indicating the type of operating |
628 | system Emacs is operating on. Here is a table of the possible values: | |
73804d4b RS |
629 | |
630 | @table @code | |
1911e6e5 RS |
631 | @item alpha-vms |
632 | VMS on the Alpha. | |
633 | ||
73804d4b RS |
634 | @item aix-v3 |
635 | AIX. | |
636 | ||
637 | @item berkeley-unix | |
638 | Berkeley BSD. | |
639 | ||
c60ee5e7 JB |
640 | @item cygwin |
641 | Cygwin. | |
642 | ||
bfe721d1 KH |
643 | @item dgux |
644 | Data General DGUX operating system. | |
645 | ||
646 | @item gnu | |
969fe9b5 | 647 | the GNU system (using the GNU kernel, which consists of the HURD and Mach). |
0c124126 RS |
648 | |
649 | @item gnu/linux | |
969fe9b5 RS |
650 | A GNU/Linux system---that is, a variant GNU system, using the Linux |
651 | kernel. (These systems are the ones people often call ``Linux,'' but | |
652 | actually Linux is just the kernel, not the whole system.) | |
bfe721d1 | 653 | |
73804d4b | 654 | @item hpux |
bfe721d1 | 655 | Hewlett-Packard HPUX operating system. |
73804d4b RS |
656 | |
657 | @item irix | |
658 | Silicon Graphics Irix system. | |
659 | ||
bfe721d1 | 660 | @item ms-dos |
8241495d RS |
661 | Microsoft MS-DOS ``operating system.'' Emacs compiled with DJGPP for |
662 | MS-DOS binds @code{system-type} to @code{ms-dos} even when you run it on | |
663 | MS-Windows. | |
bfe721d1 KH |
664 | |
665 | @item next-mach | |
666 | NeXT Mach-based system. | |
6705a2a6 | 667 | |
73804d4b RS |
668 | @item rtu |
669 | Masscomp RTU, UCB universe. | |
670 | ||
671 | @item unisoft-unix | |
672 | UniSoft UniPlus. | |
673 | ||
674 | @item usg-unix-v | |
675 | AT&T System V. | |
676 | ||
677 | @item vax-vms | |
678 | VAX VMS. | |
679 | ||
bfe721d1 | 680 | @item windows-nt |
8241495d RS |
681 | Microsoft windows NT. The same executable supports Windows 9X, but the |
682 | value of @code{system-type} is @code{windows-nt} in either case. | |
bfe721d1 | 683 | |
73804d4b RS |
684 | @item xenix |
685 | SCO Xenix 386. | |
686 | @end table | |
687 | ||
688 | We do not wish to add new symbols to make finer distinctions unless it | |
689 | is absolutely necessary! In fact, we hope to eliminate some of these | |
690 | alternatives in the future. We recommend using | |
691 | @code{system-configuration} to distinguish between different operating | |
692 | systems. | |
693 | @end defvar | |
694 | ||
73804d4b RS |
695 | @defun system-name |
696 | This function returns the name of the machine you are running on. | |
697 | @example | |
698 | (system-name) | |
a9f0a989 | 699 | @result{} "www.gnu.org" |
73804d4b RS |
700 | @end example |
701 | @end defun | |
702 | ||
22697dac KH |
703 | The symbol @code{system-name} is a variable as well as a function. In |
704 | fact, the function returns whatever value the variable | |
705 | @code{system-name} currently holds. Thus, you can set the variable | |
706 | @code{system-name} in case Emacs is confused about the name of your | |
707 | system. The variable is also useful for constructing frame titles | |
708 | (@pxref{Frame Titles}). | |
709 | ||
710 | @defvar mail-host-address | |
711 | If this variable is non-@code{nil}, it is used instead of | |
712 | @code{system-name} for purposes of generating email addresses. For | |
713 | example, it is used when constructing the default value of | |
714 | @code{user-mail-address}. @xref{User Identification}. (Since this is | |
715 | done when Emacs starts up, the value actually used is the one saved when | |
716 | Emacs was dumped. @xref{Building Emacs}.) | |
717 | @end defvar | |
718 | ||
5633ded3 | 719 | @deffn Command getenv var |
73804d4b RS |
720 | @cindex environment variable access |
721 | This function returns the value of the environment variable @var{var}, | |
339902ec LT |
722 | as a string. @var{var} should be a string. If @var{var} is undefined |
723 | in the environment, @code{getenv} returns @code{nil}. If returns | |
724 | @samp{""} if @var{var} is set but null. Within Emacs, the environment | |
725 | variable values are kept in the Lisp variable @code{process-environment}. | |
73804d4b RS |
726 | |
727 | @example | |
728 | @group | |
729 | (getenv "USER") | |
730 | @result{} "lewis" | |
731 | @end group | |
732 | ||
733 | @group | |
734 | lewis@@slug[10] % printenv | |
735 | PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin | |
736 | USER=lewis | |
737 | @end group | |
738 | @group | |
739 | TERM=ibmapa16 | |
740 | SHELL=/bin/csh | |
741 | HOME=/user/lewis | |
742 | @end group | |
743 | @end example | |
a0b972de | 744 | @end deffn |
73804d4b RS |
745 | |
746 | @c Emacs 19 feature | |
339902ec | 747 | @deffn Command setenv variable &optional value |
73804d4b | 748 | This command sets the value of the environment variable named |
339902ec LT |
749 | @var{variable} to @var{value}. @var{variable} should be a string. |
750 | Internally, Emacs Lisp can handle any string. However, normally | |
751 | @var{variable} should be a valid shell identifier, that is, a sequence | |
752 | of letters, digits and underscores, starting with a letter or | |
753 | underscore. Otherwise, errors may occur if subprocesses of Emacs try | |
754 | to access the value of @var{variable}. If @var{value} is omitted or | |
755 | @code{nil}, @code{setenv} removes @var{variable} from the environment. | |
756 | Otherwise, @var{value} should be a string. | |
757 | ||
758 | @code{setenv} works by modifying @code{process-environment}; binding | |
759 | that variable with @code{let} is also reasonable practice. | |
760 | ||
761 | @code{setenv} returns the new value of @var{variable}, or @code{nil} | |
762 | if it removed @var{variable} from the environment. | |
73804d4b RS |
763 | @end deffn |
764 | ||
765 | @defvar process-environment | |
766 | This variable is a list of strings, each describing one environment | |
767 | variable. The functions @code{getenv} and @code{setenv} work by means | |
768 | of this variable. | |
769 | ||
770 | @smallexample | |
771 | @group | |
772 | process-environment | |
773 | @result{} ("l=/usr/stanford/lib/gnuemacs/lisp" | |
774 | "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" | |
c60ee5e7 | 775 | "USER=lewis" |
73804d4b RS |
776 | @end group |
777 | @group | |
c60ee5e7 | 778 | "TERM=ibmapa16" |
73804d4b RS |
779 | "SHELL=/bin/csh" |
780 | "HOME=/user/lewis") | |
781 | @end group | |
782 | @end smallexample | |
9cee54f8 RS |
783 | |
784 | If @code{process-environment} contains ``duplicate'' elements that | |
785 | specify the same environment variable, the first of these elements | |
786 | specifies the variable, and the other ``duplicates'' are ignored. | |
73804d4b RS |
787 | @end defvar |
788 | ||
bfe721d1 KH |
789 | @defvar path-separator |
790 | This variable holds a string which says which character separates | |
791 | directories in a search path (as found in an environment variable). Its | |
792 | value is @code{":"} for Unix and GNU systems, and @code{";"} for MS-DOS | |
8241495d | 793 | and MS-Windows. |
bfe721d1 KH |
794 | @end defvar |
795 | ||
5557b83b | 796 | @defun parse-colon-path path |
5557b83b RS |
797 | This function takes a search path string such as would be the value of |
798 | the @code{PATH} environment variable, and splits it at the separators, | |
799 | returning a list of directory names. @code{nil} in this list stands for | |
800 | ``use the current directory.'' Although the function's name says | |
801 | ``colon,'' it actually uses the value of @code{path-separator}. | |
802 | ||
803 | @example | |
804 | (parse-colon-path ":/foo:/bar") | |
805 | @result{} (nil "/foo/" "/bar/") | |
806 | @end example | |
807 | @end defun | |
808 | ||
a890e1b0 RS |
809 | @defvar invocation-name |
810 | This variable holds the program name under which Emacs was invoked. The | |
811 | value is a string, and does not include a directory name. | |
812 | @end defvar | |
813 | ||
814 | @defvar invocation-directory | |
815 | This variable holds the directory from which the Emacs executable was | |
816 | invoked, or perhaps @code{nil} if that directory cannot be determined. | |
817 | @end defvar | |
818 | ||
819 | @defvar installation-directory | |
820 | If non-@code{nil}, this is a directory within which to look for the | |
821 | @file{lib-src} and @file{etc} subdirectories. This is non-@code{nil} | |
822 | when Emacs can't find those directories in their standard installed | |
78608595 RS |
823 | locations, but can find them in a directory related somehow to the one |
824 | containing the Emacs executable. | |
a890e1b0 RS |
825 | @end defvar |
826 | ||
a9f0a989 | 827 | @defun load-average &optional use-float |
1911e6e5 RS |
828 | This function returns the current 1-minute, 5-minute, and 15-minute load |
829 | averages, in a list. | |
a9f0a989 RS |
830 | |
831 | By default, the values are integers that are 100 times the system load | |
832 | averages, which indicate the average number of processes trying to run. | |
833 | If @var{use-float} is non-@code{nil}, then they are returned | |
1911e6e5 | 834 | as floating point numbers and without multiplying by 100. |
73804d4b | 835 | |
7c47f838 RS |
836 | If it is impossible to obtain the load average, this function signals |
837 | an error. On some platforms, access to load averages requires | |
838 | installing Emacs as setuid or setgid so that it can read kernel | |
839 | information, and that usually isn't advisable. | |
6b7a4323 | 840 | |
339902ec LT |
841 | If the 1-minute load average is available, but the 5- or 15-minute |
842 | averages are not, this function returns a shortened list containing | |
843 | the available averages. | |
844 | ||
73804d4b RS |
845 | @example |
846 | @group | |
847 | (load-average) | |
848 | @result{} (169 48 36) | |
849 | @end group | |
a9f0a989 RS |
850 | @group |
851 | (load-average t) | |
852 | @result{} (1.69 0.48 0.36) | |
853 | @end group | |
73804d4b RS |
854 | |
855 | @group | |
856 | lewis@@rocky[5] % uptime | |
857 | 11:55am up 1 day, 19:37, 3 users, | |
858 | load average: 1.69, 0.48, 0.36 | |
859 | @end group | |
860 | @end example | |
861 | @end defun | |
862 | ||
863 | @defun emacs-pid | |
339902ec LT |
864 | This function returns the process @acronym{ID} of the Emacs process, |
865 | as an integer. | |
73804d4b RS |
866 | @end defun |
867 | ||
f9f59935 RS |
868 | @defvar tty-erase-char |
869 | This variable holds the erase character that was selected | |
870 | in the system's terminal driver, before Emacs was started. | |
339902ec | 871 | The value is @code{nil} if Emacs is running under a window system. |
f9f59935 RS |
872 | @end defvar |
873 | ||
73804d4b RS |
874 | @defun setprv privilege-name &optional setp getprv |
875 | This function sets or resets a VMS privilege. (It does not exist on | |
8241495d RS |
876 | other systems.) The first argument is the privilege name, as a string. |
877 | The second argument, @var{setp}, is @code{t} or @code{nil}, indicating | |
878 | whether the privilege is to be turned on or off. Its default is | |
879 | @code{nil}. The function returns @code{t} if successful, @code{nil} | |
880 | otherwise. | |
73804d4b | 881 | |
339902ec | 882 | If the third argument, @var{getprv}, is non-@code{nil}, @code{setprv} |
73804d4b RS |
883 | does not change the privilege, but returns @code{t} or @code{nil} |
884 | indicating whether the privilege is currently enabled. | |
885 | @end defun | |
886 | ||
887 | @node User Identification | |
888 | @section User Identification | |
1db203ff | 889 | @cindex user identification |
73804d4b | 890 | |
f9f59935 | 891 | @defvar init-file-user |
339902ec LT |
892 | This variable says which user's init files should be used by |
893 | Emacs---or @code{nil} if none. @code{""} stands for the user who | |
894 | originally logged in. The value reflects command-line options such as | |
f9f59935 RS |
895 | @samp{-q} or @samp{-u @var{user}}. |
896 | ||
897 | Lisp packages that load files of customizations, or any other sort of | |
898 | user profile, should obey this variable in deciding where to find it. | |
899 | They should load the profile of the user name found in this variable. | |
900 | If @code{init-file-user} is @code{nil}, meaning that the @samp{-q} | |
901 | option was used, then Lisp packages should not load any customization | |
902 | files or user profile. | |
903 | @end defvar | |
904 | ||
22697dac KH |
905 | @defvar user-mail-address |
906 | This holds the nominal email address of the user who is using Emacs. | |
485dbcf2 RS |
907 | Emacs normally sets this variable to a default value after reading your |
908 | init files, but not if you have already set it. So you can set the | |
a40d4712 | 909 | variable to some other value in your init file if you do not |
485dbcf2 | 910 | want to use the default value. |
22697dac KH |
911 | @end defvar |
912 | ||
913 | @defun user-login-name &optional uid | |
914 | If you don't specify @var{uid}, this function returns the name under | |
915 | which the user is logged in. If the environment variable @code{LOGNAME} | |
916 | is set, that value is used. Otherwise, if the environment variable | |
917 | @code{USER} is set, that value is used. Otherwise, the value is based | |
ad800164 | 918 | on the effective @acronym{UID}, not the real @acronym{UID}. |
22697dac KH |
919 | |
920 | If you specify @var{uid}, the value is the user name that corresponds | |
339902ec LT |
921 | to @var{uid} (which should be an integer), or @code{nil} if there is |
922 | no such user. | |
73804d4b RS |
923 | |
924 | @example | |
925 | @group | |
926 | (user-login-name) | |
927 | @result{} "lewis" | |
928 | @end group | |
929 | @end example | |
930 | @end defun | |
931 | ||
932 | @defun user-real-login-name | |
933 | This function returns the user name corresponding to Emacs's real | |
ad800164 | 934 | @acronym{UID}. This ignores the effective @acronym{UID} and ignores the |
73804d4b RS |
935 | environment variables @code{LOGNAME} and @code{USER}. |
936 | @end defun | |
937 | ||
f9f59935 RS |
938 | @defun user-full-name &optional uid |
939 | This function returns the full name of the logged-in user---or the value | |
8241495d | 940 | of the environment variable @code{NAME}, if that is set. |
73804d4b | 941 | |
8241495d | 942 | @c "Bil" is the correct spelling. |
73804d4b RS |
943 | @example |
944 | @group | |
945 | (user-full-name) | |
946 | @result{} "Bil Lewis" | |
947 | @end group | |
948 | @end example | |
f9f59935 | 949 | |
52f51621 KH |
950 | If the Emacs job's user-id does not correspond to any known user (and |
951 | provided @code{NAME} is not set), the value is @code{"unknown"}. | |
952 | ||
339902ec | 953 | If @var{uid} is non-@code{nil}, then it should be a number (a user-id) |
52f51621 KH |
954 | or a string (a login name). Then @code{user-full-name} returns the full |
955 | name corresponding to that user-id or login name. If you specify a | |
956 | user-id or login name that isn't defined, it returns @code{nil}. | |
73804d4b RS |
957 | @end defun |
958 | ||
22697dac KH |
959 | @vindex user-full-name |
960 | @vindex user-real-login-name | |
961 | @vindex user-login-name | |
962 | The symbols @code{user-login-name}, @code{user-real-login-name} and | |
963 | @code{user-full-name} are variables as well as functions. The functions | |
964 | return the same values that the variables hold. These variables allow | |
965 | you to ``fake out'' Emacs by telling the functions what to return. The | |
966 | variables are also useful for constructing frame titles (@pxref{Frame | |
967 | Titles}). | |
968 | ||
73804d4b | 969 | @defun user-real-uid |
ad800164 | 970 | This function returns the real @acronym{UID} of the user. |
dd726314 | 971 | The value may be a floating point number. |
73804d4b RS |
972 | |
973 | @example | |
974 | @group | |
975 | (user-real-uid) | |
976 | @result{} 19 | |
977 | @end group | |
978 | @end example | |
979 | @end defun | |
980 | ||
981 | @defun user-uid | |
ad800164 | 982 | This function returns the effective @acronym{UID} of the user. |
dd726314 | 983 | The value may be a floating point number. |
73804d4b RS |
984 | @end defun |
985 | ||
986 | @node Time of Day | |
987 | @section Time of Day | |
988 | ||
989 | This section explains how to determine the current time and the time | |
990 | zone. | |
991 | ||
992 | @defun current-time-string &optional time-value | |
a9f0a989 | 993 | This function returns the current time and date as a human-readable |
73804d4b RS |
994 | string. The format of the string is unvarying; the number of characters |
995 | used for each part is always the same, so you can reliably use | |
bfe721d1 KH |
996 | @code{substring} to extract pieces of it. It is wise to count the |
997 | characters from the beginning of the string rather than from the end, as | |
f9f59935 | 998 | additional information may some day be added at the end. |
73804d4b RS |
999 | |
1000 | @c Emacs 19 feature | |
1001 | The argument @var{time-value}, if given, specifies a time to format | |
bfe721d1 KH |
1002 | instead of the current time. The argument should be a list whose first |
1003 | two elements are integers. Thus, you can use times obtained from | |
1004 | @code{current-time} (see below) and from @code{file-attributes} | |
339902ec LT |
1005 | (@pxref{Definition of file-attributes}). @var{time-value} can also be |
1006 | a cons of two integers, but this is considered obsolete. | |
73804d4b RS |
1007 | |
1008 | @example | |
1009 | @group | |
1010 | (current-time-string) | |
1011 | @result{} "Wed Oct 14 22:21:05 1987" | |
1012 | @end group | |
1013 | @end example | |
1014 | @end defun | |
1015 | ||
1016 | @c Emacs 19 feature | |
1017 | @defun current-time | |
1018 | This function returns the system's time value as a list of three | |
1019 | integers: @code{(@var{high} @var{low} @var{microsec})}. The integers | |
1020 | @var{high} and @var{low} combine to give the number of seconds since | |
339902ec | 1021 | 0:00 January 1, 1970 UTC (Coordinated Universal Time), which is |
37680279 | 1022 | @ifnottex |
73804d4b | 1023 | @var{high} * 2**16 + @var{low}. |
37680279 | 1024 | @end ifnottex |
73804d4b | 1025 | @tex |
78608595 | 1026 | $high*2^{16}+low$. |
73804d4b RS |
1027 | @end tex |
1028 | ||
1029 | The third element, @var{microsec}, gives the microseconds since the | |
8241495d RS |
1030 | start of the current second (or 0 for systems that return time with |
1031 | the resolution of only one second). | |
73804d4b RS |
1032 | |
1033 | The first two elements can be compared with file time values such as you | |
339902ec LT |
1034 | get with the function @code{file-attributes}. |
1035 | @xref{Definition of file-attributes}. | |
73804d4b RS |
1036 | @end defun |
1037 | ||
1038 | @c Emacs 19 feature | |
1039 | @defun current-time-zone &optional time-value | |
1040 | This function returns a list describing the time zone that the user is | |
1041 | in. | |
1042 | ||
1043 | The value has the form @code{(@var{offset} @var{name})}. Here | |
1044 | @var{offset} is an integer giving the number of seconds ahead of UTC | |
1045 | (east of Greenwich). A negative value means west of Greenwich. The | |
8241495d | 1046 | second element, @var{name}, is a string giving the name of the time |
18629155 | 1047 | zone. Both elements change when daylight saving time begins or ends; |
73804d4b RS |
1048 | if the user has specified a time zone that does not use a seasonal time |
1049 | adjustment, then the value is constant through time. | |
1050 | ||
1051 | If the operating system doesn't supply all the information necessary to | |
339902ec | 1052 | compute the value, the unknown elements of the list are @code{nil}. |
73804d4b RS |
1053 | |
1054 | The argument @var{time-value}, if given, specifies a time to analyze | |
339902ec LT |
1055 | instead of the current time. The argument should have the same form |
1056 | as for @code{current-time-string} (see above). Thus, you can use | |
1057 | times obtained from @code{current-time} (see above) and from | |
1058 | @code{file-attributes}. @xref{Definition of file-attributes}. | |
22697dac KH |
1059 | @end defun |
1060 | ||
76aac1c1 RS |
1061 | @defun set-time-zone-rule tz |
1062 | This function specifies the local time zone according to @var{tz}. If | |
1063 | @var{tz} is @code{nil}, that means to use an implementation-defined | |
1064 | default time zone. If @var{tz} is @code{t}, that means to use | |
339902ec LT |
1065 | Universal Time. Otherwise, @var{tz} should be a string specifying a |
1066 | time zone rule. | |
76aac1c1 RS |
1067 | @end defun |
1068 | ||
de0df8e2 EZ |
1069 | @defun float-time &optional time-value |
1070 | This function returns the current time as a floating-point number of | |
1071 | seconds since the epoch. The argument @var{time-value}, if given, | |
1072 | specifies a time to convert instead of the current time. The argument | |
1073 | should have the same form as for @code{current-time-string} (see | |
339902ec | 1074 | above). Thus, it accepts the output of @code{current-time} and |
de0df8e2 EZ |
1075 | @code{file-attributes}. |
1076 | ||
1077 | @emph{Warning}: Since the result is floating point, it may not be | |
1078 | exact. Do not use this function if precise time stamps are required. | |
1079 | @end defun | |
1080 | ||
22697dac KH |
1081 | @node Time Conversion |
1082 | @section Time Conversion | |
1083 | ||
1084 | These functions convert time values (lists of two or three integers) | |
4bdbd317 RS |
1085 | to calendrical information and vice versa. You can get time values |
1086 | from the functions @code{current-time} (@pxref{Time of Day}) and | |
339902ec | 1087 | @code{file-attributes} (@pxref{Definition of file-attributes}). |
22697dac | 1088 | |
4bdbd317 | 1089 | Many operating systems are limited to time values that contain 32 bits |
cfbaa90c RS |
1090 | of information; these systems typically handle only the times from |
1091 | 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some | |
1092 | operating systems have larger time values, and can represent times far | |
1093 | in the past or future. | |
1094 | ||
4bdbd317 RS |
1095 | Time conversion functions always use the Gregorian calendar, even |
1096 | for dates before the Gregorian calendar was introduced. Year numbers | |
1097 | count the number of years since the year 1 B.C., and do not skip zero | |
1098 | as traditional Gregorian years do; for example, the year number | |
1099 | @minus{}37 represents the Gregorian year 38 B.C@. | |
1100 | ||
1101 | @defun decode-time &optional time | |
1102 | This function converts a time value into calendrical information. If | |
1103 | you don't specify @var{time}, it decodes the current time. The return | |
1104 | value is a list of nine elements, as follows: | |
1105 | ||
1106 | @example | |
1107 | (@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone}) | |
1108 | @end example | |
1109 | ||
1110 | Here is what the elements mean: | |
1111 | ||
1112 | @table @var | |
1113 | @item seconds | |
1114 | The number of seconds past the minute, as an integer between 0 and 59. | |
1115 | On some operating systems, this is 60 for leap seconds. | |
1116 | @item minutes | |
1117 | The number of minutes past the hour, as an integer between 0 and 59. | |
1118 | @item hour | |
1119 | The hour of the day, as an integer between 0 and 23. | |
1120 | @item day | |
1121 | The day of the month, as an integer between 1 and 31. | |
1122 | @item month | |
1123 | The month of the year, as an integer between 1 and 12. | |
1124 | @item year | |
1125 | The year, an integer typically greater than 1900. | |
1126 | @item dow | |
1127 | The day of week, as an integer between 0 and 6, where 0 stands for | |
1128 | Sunday. | |
1129 | @item dst | |
18629155 | 1130 | @code{t} if daylight saving time is effect, otherwise @code{nil}. |
4bdbd317 RS |
1131 | @item zone |
1132 | An integer indicating the time zone, as the number of seconds east of | |
1133 | Greenwich. | |
1134 | @end table | |
1135 | ||
1136 | @strong{Common Lisp Note:} Common Lisp has different meanings for | |
1137 | @var{dow} and @var{zone}. | |
1138 | @end defun | |
1139 | ||
1140 | @defun encode-time seconds minutes hour day month year &optional zone | |
1141 | This function is the inverse of @code{decode-time}. It converts seven | |
1142 | items of calendrical data into a time value. For the meanings of the | |
1143 | arguments, see the table above under @code{decode-time}. | |
1144 | ||
1145 | Year numbers less than 100 are not treated specially. If you want them | |
1146 | to stand for years above 1900, or years above 2000, you must alter them | |
1147 | yourself before you call @code{encode-time}. | |
1148 | ||
1149 | The optional argument @var{zone} defaults to the current time zone and | |
18629155 | 1150 | its daylight saving time rules. If specified, it can be either a list |
4bdbd317 RS |
1151 | (as you would get from @code{current-time-zone}), a string as in the |
1152 | @code{TZ} environment variable, @code{t} for Universal Time, or an | |
1153 | integer (as you would get from @code{decode-time}). The specified | |
18629155 | 1154 | zone is used without any further alteration for daylight saving time. |
4bdbd317 RS |
1155 | |
1156 | If you pass more than seven arguments to @code{encode-time}, the first | |
1157 | six are used as @var{seconds} through @var{year}, the last argument is | |
1158 | used as @var{zone}, and the arguments in between are ignored. This | |
1159 | feature makes it possible to use the elements of a list returned by | |
1160 | @code{decode-time} as the arguments to @code{encode-time}, like this: | |
1161 | ||
1162 | @example | |
1163 | (apply 'encode-time (decode-time @dots{})) | |
1164 | @end example | |
1165 | ||
1166 | You can perform simple date arithmetic by using out-of-range values for | |
1167 | the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month} | |
1168 | arguments; for example, day 0 means the day preceding the given month. | |
1169 | ||
1170 | The operating system puts limits on the range of possible time values; | |
1171 | if you try to encode a time that is out of range, an error results. | |
1172 | For instance, years before 1970 do not work on some systems; | |
1173 | on others, years as early as 1901 do work. | |
1174 | @end defun | |
1175 | ||
1176 | @node Time Parsing | |
1177 | @section Parsing and Formatting Times | |
1178 | ||
1179 | These functions convert time values (lists of two or three integers) | |
1180 | to text in a string, and vice versa. | |
cfbaa90c | 1181 | |
baee1397 RS |
1182 | @defun date-to-time string |
1183 | This function parses the time-string @var{string} and returns the | |
1184 | corresponding time value. | |
1185 | @end defun | |
1186 | ||
3f705836 GM |
1187 | @defun format-time-string format-string &optional time universal |
1188 | This function converts @var{time} (or the current time, if @var{time} is | |
1189 | omitted) to a string according to @var{format-string}. The argument | |
1190 | @var{format-string} may contain @samp{%}-sequences which say to | |
1191 | substitute parts of the time. Here is a table of what the | |
1192 | @samp{%}-sequences mean: | |
22697dac KH |
1193 | |
1194 | @table @samp | |
1195 | @item %a | |
1196 | This stands for the abbreviated name of the day of week. | |
1197 | @item %A | |
1198 | This stands for the full name of the day of week. | |
1199 | @item %b | |
1200 | This stands for the abbreviated name of the month. | |
1201 | @item %B | |
1202 | This stands for the full name of the month. | |
1203 | @item %c | |
1204 | This is a synonym for @samp{%x %X}. | |
1205 | @item %C | |
bfe721d1 KH |
1206 | This has a locale-specific meaning. In the default locale (named C), it |
1207 | is equivalent to @samp{%A, %B %e, %Y}. | |
22697dac KH |
1208 | @item %d |
1209 | This stands for the day of month, zero-padded. | |
1210 | @item %D | |
1211 | This is a synonym for @samp{%m/%d/%y}. | |
1212 | @item %e | |
1213 | This stands for the day of month, blank-padded. | |
1214 | @item %h | |
1215 | This is a synonym for @samp{%b}. | |
1216 | @item %H | |
1217 | This stands for the hour (00-23). | |
1218 | @item %I | |
8241495d | 1219 | This stands for the hour (01-12). |
22697dac KH |
1220 | @item %j |
1221 | This stands for the day of the year (001-366). | |
1222 | @item %k | |
1223 | This stands for the hour (0-23), blank padded. | |
1224 | @item %l | |
1225 | This stands for the hour (1-12), blank padded. | |
1226 | @item %m | |
1227 | This stands for the month (01-12). | |
1228 | @item %M | |
1229 | This stands for the minute (00-59). | |
1230 | @item %n | |
1231 | This stands for a newline. | |
1232 | @item %p | |
1233 | This stands for @samp{AM} or @samp{PM}, as appropriate. | |
1234 | @item %r | |
1235 | This is a synonym for @samp{%I:%M:%S %p}. | |
1236 | @item %R | |
1237 | This is a synonym for @samp{%H:%M}. | |
1238 | @item %S | |
8241495d | 1239 | This stands for the seconds (00-59). |
22697dac KH |
1240 | @item %t |
1241 | This stands for a tab character. | |
1242 | @item %T | |
1243 | This is a synonym for @samp{%H:%M:%S}. | |
1244 | @item %U | |
1245 | This stands for the week of the year (01-52), assuming that weeks | |
1246 | start on Sunday. | |
1247 | @item %w | |
1248 | This stands for the numeric day of week (0-6). Sunday is day 0. | |
1249 | @item %W | |
1250 | This stands for the week of the year (01-52), assuming that weeks | |
1251 | start on Monday. | |
1252 | @item %x | |
969fe9b5 RS |
1253 | This has a locale-specific meaning. In the default locale (named |
1254 | @samp{C}), it is equivalent to @samp{%D}. | |
22697dac | 1255 | @item %X |
969fe9b5 RS |
1256 | This has a locale-specific meaning. In the default locale (named |
1257 | @samp{C}), it is equivalent to @samp{%T}. | |
22697dac KH |
1258 | @item %y |
1259 | This stands for the year without century (00-99). | |
1260 | @item %Y | |
1261 | This stands for the year with century. | |
1262 | @item %Z | |
78e5d549 EZ |
1263 | This stands for the time zone abbreviation (e.g., @samp{EST}). |
1264 | @item %z | |
1265 | This stands for the time zone numerical offset (e.g., @samp{-0500}). | |
22697dac | 1266 | @end table |
f9f59935 RS |
1267 | |
1268 | You can also specify the field width and type of padding for any of | |
969fe9b5 RS |
1269 | these @samp{%}-sequences. This works as in @code{printf}: you write |
1270 | the field width as digits in the middle of a @samp{%}-sequences. If you | |
a9f0a989 RS |
1271 | start the field width with @samp{0}, it means to pad with zeros. If you |
1272 | start the field width with @samp{_}, it means to pad with spaces. | |
f9f59935 RS |
1273 | |
1274 | For example, @samp{%S} specifies the number of seconds since the minute; | |
1275 | @samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to | |
1276 | pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros, | |
1277 | because that is how @samp{%S} normally pads to two positions. | |
3f705836 GM |
1278 | |
1279 | The characters @samp{E} and @samp{O} act as modifiers when used between | |
1280 | @samp{%} and one of the letters in the table above. @samp{E} specifies | |
79ddc9c9 GM |
1281 | using the current locale's ``alternative'' version of the date and time. |
1282 | In a Japanese locale, for example, @code{%Ex} might yield a date format | |
1283 | based on the Japanese Emperors' reigns. @samp{E} is allowed in | |
1284 | @samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and | |
1285 | @samp{%EY}. | |
1286 | ||
1287 | @samp{O} means to use the current locale's ``alternative'' | |
1288 | representation of numbers, instead of the ordinary decimal digits. This | |
1289 | is allowed with most letters, all the ones that output numbers. | |
3f705836 GM |
1290 | |
1291 | If @var{universal} is non-@code{nil}, that means to describe the time as | |
1292 | Universal Time; @code{nil} means describe it using what Emacs believes | |
1293 | is the local time zone (see @code{current-time-zone}). | |
2468d0c0 | 1294 | |
78e5d549 EZ |
1295 | This function uses the C library function @code{strftime} |
1296 | (@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference | |
1297 | Manual}) to do most of the work. In order to communicate with that | |
1298 | function, it first encodes its argument using the coding system | |
1299 | specified by @code{locale-coding-system} (@pxref{Locales}); after | |
1300 | @code{strftime} returns the resulting string, | |
1301 | @code{format-time-string} decodes the string using that same coding | |
1302 | system. | |
22697dac KH |
1303 | @end defun |
1304 | ||
baee1397 RS |
1305 | @defun seconds-to-time seconds |
1306 | This function converts @var{seconds}, a floating point number of | |
1307 | seconds since the epoch, to a time value and returns that. To perform | |
1308 | the inverse conversion, use @code{float-time}. | |
1309 | @end defun | |
1310 | ||
2f6037a5 EZ |
1311 | @node Processor Run Time |
1312 | @section Processor Run time | |
ad8d30b3 | 1313 | @cindex processor run time |
2f6037a5 EZ |
1314 | |
1315 | @defun get-internal-run-time | |
1316 | This function returns the processor run time used by Emacs as a list | |
1317 | of three integers: @code{(@var{high} @var{low} @var{microsec})}. The | |
1318 | integers @var{high} and @var{low} combine to give the number of | |
1319 | seconds, which is | |
1320 | @ifnottex | |
1321 | @var{high} * 2**16 + @var{low}. | |
1322 | @end ifnottex | |
1323 | @tex | |
1324 | $high*2^{16}+low$. | |
1325 | @end tex | |
1326 | ||
1327 | The third element, @var{microsec}, gives the microseconds (or 0 for | |
1328 | systems that return time with the resolution of only one second). | |
1329 | ||
1330 | If the system doesn't provide a way to determine the processor run | |
1331 | time, get-internal-run-time returns the same time as current-time. | |
1332 | @end defun | |
1333 | ||
baee1397 RS |
1334 | @node Time Calculations |
1335 | @section Time Calculations | |
1336 | ||
1337 | These functions perform calendrical computations using time values | |
1338 | (the kind of list that @code{current-time} returns). | |
1339 | ||
1340 | @defun time-less-p t1 t2 | |
1341 | This returns @code{t} if time value @var{t1} is less than time value | |
1342 | @var{t2}. | |
1343 | @end defun | |
1344 | ||
1345 | @defun time-subtract t1 t2 | |
1346 | This returns the time difference @var{t1} @minus{} @var{t2} between | |
1347 | two time values, in the same format as a time value. | |
1348 | @end defun | |
1349 | ||
1350 | @defun time-add t1 t2 | |
1351 | This returns the sum of two time values, one of which ought to | |
1352 | represent a time difference rather than a point in time. | |
1353 | Here is how to add a number of seconds to a time value: | |
1354 | ||
1355 | @example | |
1356 | (time-add @var{time} (seconds-to-time @var{seconds})) | |
1357 | @end example | |
1358 | @end defun | |
1359 | ||
1360 | @defun time-to-days time | |
1361 | This function returns the number of days between the beginning of year | |
1362 | 1 and @var{time}. | |
1363 | @end defun | |
1364 | ||
1365 | @defun time-to-day-in-year time | |
1366 | This returns the day number within the year corresponding to @var{time}. | |
1367 | @end defun | |
1368 | ||
1369 | @defun date-leap-year-p year | |
1370 | This function returns @code{t} if @var{year} is a leap year. | |
1371 | @end defun | |
1372 | ||
73804d4b | 1373 | @node Timers |
bfe721d1 | 1374 | @section Timers for Delayed Execution |
0c124126 | 1375 | @cindex timer |
73804d4b | 1376 | |
d64f1a9d RS |
1377 | You can set up a @dfn{timer} to call a function at a specified |
1378 | future time or after a certain length of idleness. | |
0c124126 | 1379 | |
969fe9b5 | 1380 | Emacs cannot run timers at any arbitrary point in a Lisp program; it |
0c124126 RS |
1381 | can run them only when Emacs could accept output from a subprocess: |
1382 | namely, while waiting or inside certain primitive functions such as | |
1911e6e5 | 1383 | @code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a |
0c124126 RS |
1384 | timer's execution may be delayed if Emacs is busy. However, the time of |
1385 | execution is very precise if Emacs is idle. | |
73804d4b | 1386 | |
d64f1a9d RS |
1387 | Emacs binds @code{inhibit-quit} to @code{t} before calling the timer |
1388 | function, because quitting out of many timer functions can leave | |
1389 | things in an inconsistent state. This is normally unproblematical | |
1390 | because most timer functions don't do a lot of work. Indeed, for a | |
c2d8228a | 1391 | timer to call a function that takes substantial time to run is likely |
2d56beed CY |
1392 | to be annoying. If a timer function needs to allow quitting, it |
1393 | should use @code{with-local-quit} (@pxref{Quitting}). For example, if | |
1394 | a timer function calls @code{accept-process-output} to receive output | |
1395 | from an external process, that call should be wrapped inside | |
1396 | @code{with-local-quit}, to ensure that @kbd{C-g} works if the external | |
1397 | process hangs. | |
d64f1a9d | 1398 | |
c734ae59 RS |
1399 | It is usually a bad idea for timer functions to alter buffer |
1400 | contents. When they do, they usually should call @code{undo-boundary} | |
1401 | both before and after changing the buffer, to separate the timer's | |
a5c81331 RS |
1402 | changes from user commands' changes and prevent a single undo entry |
1403 | from growing to be quite large. | |
e756f049 | 1404 | |
fda97484 CY |
1405 | Timer functions should also avoid calling functions that cause Emacs |
1406 | to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to | |
1407 | unpredictable effects, since other timers (or even the same timer) can | |
1408 | run while waiting. If a timer function needs to perform an action | |
1409 | after a certain time has elapsed, it can do this by scheduling a new | |
1410 | timer. | |
1411 | ||
df05ea85 LT |
1412 | If a timer function calls functions that can change the match data, |
1413 | it should save and restore the match data. @xref{Saving Match Data}. | |
1414 | ||
339902ec LT |
1415 | @deffn Command run-at-time time repeat function &rest args |
1416 | This sets up a timer that calls the function @var{function} with | |
1417 | arguments @var{args} at time @var{time}. If @var{repeat} is a number | |
79d41bd0 RS |
1418 | (integer or floating point), the timer is scheduled to run again every |
1419 | @var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil}, | |
1420 | the timer runs only once. | |
339902ec LT |
1421 | |
1422 | @var{time} may specify an absolute or a relative time. | |
73804d4b | 1423 | |
bbb9c4e1 RS |
1424 | Absolute times may be specified using a string with a limited variety |
1425 | of formats, and are taken to be times @emph{today}, even if already in | |
1426 | the past. The recognized forms are @samp{@var{xxxx}}, | |
1427 | @samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time), | |
1428 | and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm}, | |
1429 | @samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am}, | |
1430 | @samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or | |
1431 | @samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon | |
1432 | to separate the hour and minute parts. | |
73804d4b | 1433 | |
339902ec | 1434 | To specify a relative time as a string, use numbers followed by units. |
73804d4b RS |
1435 | For example: |
1436 | ||
1437 | @table @samp | |
1438 | @item 1 min | |
1439 | denotes 1 minute from now. | |
1440 | @item 1 min 5 sec | |
1441 | denotes 65 seconds from now. | |
1442 | @item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year | |
1443 | denotes exactly 103 months, 123 days, and 10862 seconds from now. | |
1444 | @end table | |
1445 | ||
8241495d RS |
1446 | For relative time values, Emacs considers a month to be exactly thirty |
1447 | days, and a year to be exactly 365.25 days. | |
1448 | ||
339902ec | 1449 | Not all convenient formats are strings. If @var{time} is a number |
e42b9a33 GM |
1450 | (integer or floating point), that specifies a relative time measured in |
1451 | seconds. The result of @code{encode-time} can also be used to specify | |
1452 | an absolute value for @var{time}. | |
f9f59935 RS |
1453 | |
1454 | In most cases, @var{repeat} has no effect on when @emph{first} call | |
1455 | takes place---@var{time} alone specifies that. There is one exception: | |
1456 | if @var{time} is @code{t}, then the timer runs whenever the time is a | |
1457 | multiple of @var{repeat} seconds after the epoch. This is useful for | |
1458 | functions like @code{display-time}. | |
78608595 RS |
1459 | |
1460 | The function @code{run-at-time} returns a timer value that identifies | |
1461 | the particular scheduled future action. You can use this value to call | |
0c124126 | 1462 | @code{cancel-timer} (see below). |
339902ec | 1463 | @end deffn |
0c124126 | 1464 | |
79d41bd0 RS |
1465 | A repeating timer nominally ought to run every @var{repeat} seconds, |
1466 | but remember that any invocation of a timer can be late. Lateness of | |
1467 | one repetition has no effect on the scheduled time of the next | |
1468 | repetition. For instance, if Emacs is busy computing for long enough | |
1469 | to cover three scheduled repetitions of the timer, and then starts to | |
1470 | wait, it will immediately call the timer function three times in | |
1471 | immediate succession (presuming no other timers trigger before or | |
1472 | between them). If you want a timer to run again no less than @var{n} | |
1473 | seconds after the last invocation, don't use the @var{repeat} argument. | |
1474 | Instead, the timer function should explicitly reschedule the timer. | |
1475 | ||
17947151 RS |
1476 | @defvar timer-max-repeats |
1477 | This variable's value specifies the maximum number of times to repeat | |
1478 | calling a timer function in a row, when many previously scheduled | |
1479 | calls were unavoidably delayed. | |
1480 | @end defvar | |
1481 | ||
0c124126 RS |
1482 | @defmac with-timeout (seconds timeout-forms@dots{}) body@dots{} |
1483 | Execute @var{body}, but give up after @var{seconds} seconds. If | |
1484 | @var{body} finishes before the time is up, @code{with-timeout} returns | |
1485 | the value of the last form in @var{body}. If, however, the execution of | |
1486 | @var{body} is cut short by the timeout, then @code{with-timeout} | |
1487 | executes all the @var{timeout-forms} and returns the value of the last | |
1488 | of them. | |
1489 | ||
a9f0a989 | 1490 | This macro works by setting a timer to run after @var{seconds} seconds. If |
0c124126 RS |
1491 | @var{body} finishes before that time, it cancels the timer. If the |
1492 | timer actually runs, it terminates execution of @var{body}, then | |
1493 | executes @var{timeout-forms}. | |
1494 | ||
1495 | Since timers can run within a Lisp program only when the program calls a | |
1496 | primitive that can wait, @code{with-timeout} cannot stop executing | |
1497 | @var{body} while it is in the midst of a computation---only when it | |
1498 | calls one of those primitives. So use @code{with-timeout} only with a | |
1499 | @var{body} that waits for input, not one that does a long computation. | |
1500 | @end defmac | |
1501 | ||
1502 | The function @code{y-or-n-p-with-timeout} provides a simple way to use | |
1503 | a timer to avoid waiting too long for an answer. @xref{Yes-or-No | |
1504 | Queries}. | |
1505 | ||
9d45757a RS |
1506 | @defun cancel-timer timer |
1507 | This cancels the requested action for @var{timer}, which should be a | |
1508 | timer---usually, one previously returned by @code{run-at-time} or | |
1509 | @code{run-with-idle-timer}. This cancels the effect of that call to | |
1510 | one of these functions; the arrival of the specified time will not | |
1511 | cause anything special to happen. | |
1512 | @end defun | |
1513 | ||
1514 | @node Idle Timers | |
1515 | @section Idle Timers | |
1516 | ||
1517 | Here is how to set up a timer that runs when Emacs is idle for a | |
15fe0825 | 1518 | certain length of time. Aside from how to set them up, idle timers |
9d45757a RS |
1519 | work just like ordinary timers. |
1520 | ||
339902ec | 1521 | @deffn Command run-with-idle-timer secs repeat function &rest args |
0c124126 RS |
1522 | Set up a timer which runs when Emacs has been idle for @var{secs} |
1523 | seconds. The value of @var{secs} may be an integer or a floating point | |
73c24ae8 RS |
1524 | number; a value of the type returned by @code{current-idle-time} |
1525 | is also allowed. | |
0c124126 RS |
1526 | |
1527 | If @var{repeat} is @code{nil}, the timer runs just once, the first time | |
1528 | Emacs remains idle for a long enough time. More often @var{repeat} is | |
1529 | non-@code{nil}, which means to run the timer @emph{each time} Emacs | |
1530 | remains idle for @var{secs} seconds. | |
1531 | ||
1532 | The function @code{run-with-idle-timer} returns a timer value which you | |
73c24ae8 | 1533 | can use in calling @code{cancel-timer} (@pxref{Timers}). |
339902ec | 1534 | @end deffn |
73804d4b | 1535 | |
0c124126 RS |
1536 | @cindex idleness |
1537 | Emacs becomes ``idle'' when it starts waiting for user input, and it | |
1538 | remains idle until the user provides some input. If a timer is set for | |
1539 | five seconds of idleness, it runs approximately five seconds after Emacs | |
8241495d RS |
1540 | first becomes idle. Even if @var{repeat} is non-@code{nil}, this timer |
1541 | will not run again as long as Emacs remains idle, because the duration | |
1542 | of idleness will continue to increase and will not go down to five | |
1543 | seconds again. | |
0c124126 RS |
1544 | |
1545 | Emacs can do various things while idle: garbage collect, autosave or | |
969fe9b5 RS |
1546 | handle data from a subprocess. But these interludes during idleness do |
1547 | not interfere with idle timers, because they do not reset the clock of | |
1548 | idleness to zero. An idle timer set for 600 seconds will run when ten | |
1549 | minutes have elapsed since the last user command was finished, even if | |
1550 | subprocess output has been accepted thousands of times within those ten | |
8241495d | 1551 | minutes, and even if there have been garbage collections and autosaves. |
0c124126 RS |
1552 | |
1553 | When the user supplies input, Emacs becomes non-idle while executing the | |
1554 | input. Then it becomes idle again, and all the idle timers that are | |
1555 | set up to repeat will subsequently run another time, one by one. | |
1556 | ||
9d45757a RS |
1557 | @c Emacs 19 feature |
1558 | @defun current-idle-time | |
1559 | This function returns the length of time Emacs has been idle, as a | |
1560 | list of three integers: @code{(@var{high} @var{low} @var{microsec})}. | |
1561 | The integers @var{high} and @var{low} combine to give the number of | |
1562 | seconds of idleness, which is | |
1563 | @ifnottex | |
1564 | @var{high} * 2**16 + @var{low}. | |
1565 | @end ifnottex | |
1566 | @tex | |
1567 | $high*2^{16}+low$. | |
1568 | @end tex | |
1569 | ||
1570 | The third element, @var{microsec}, gives the microseconds since the | |
1571 | start of the current second (or 0 for systems that return time with | |
1572 | the resolution of only one second). | |
1573 | ||
1574 | The main use of this function is when an idle timer function wants to | |
1575 | ``take a break'' for a while. It can set up another idle timer to | |
1576 | call the same function again, after a few seconds more idleness. | |
1577 | Here's an example: | |
1578 | ||
1579 | @smallexample | |
1580 | (defvar resume-timer nil | |
1581 | "Timer that `timer-function' used to reschedule itself, or nil.") | |
1582 | ||
1583 | (defun timer-function () | |
1584 | ;; @r{If the user types a command while @code{resume-timer}} | |
1585 | ;; @r{is active, the next time this function is called from} | |
1586 | ;; @r{its main idle timer, deactivate @code{resume-timer}.} | |
1587 | (when resume-timer | |
1588 | (cancel-timer resume-timer)) | |
1589 | ...@var{do the work for a while}... | |
1590 | (when @var{taking-a-break} | |
1591 | (setq resume-timer | |
1592 | (run-with-idle-timer | |
15fe0825 | 1593 | ;; Compute an idle time @var{break-length} |
9d45757a RS |
1594 | ;; more than the current value. |
1595 | (time-add (current-idle-time) | |
1596 | (seconds-to-time @var{break-length})) | |
1597 | nil | |
1598 | 'timer-function)))) | |
1599 | @end smallexample | |
73804d4b RS |
1600 | @end defun |
1601 | ||
0a369706 RS |
1602 | Some idle timer functions in user Lisp packages have a loop that |
1603 | does a certain amount of processing each time around, and exits when | |
1604 | @code{(input-pending-p)} is non-@code{nil}. That approach seems very | |
1605 | natural but has two problems: | |
1606 | ||
1607 | @itemize | |
1608 | @item | |
1609 | It blocks out all process output (since Emacs accepts process output | |
1610 | only while waiting). | |
1611 | ||
1612 | @item | |
1613 | It blocks out any idle timers that ought to run during that time. | |
1614 | @end itemize | |
1615 | ||
1616 | @noindent | |
1617 | To avoid these problems, don't use that technique. Instead, write | |
1618 | such idle timers to reschedule themselves after a brief pause, using | |
1619 | the method in the @code{timer-function} example above. | |
1620 | ||
73804d4b RS |
1621 | @node Terminal Input |
1622 | @section Terminal Input | |
1623 | @cindex terminal input | |
1624 | ||
1625 | This section describes functions and variables for recording or | |
1626 | manipulating terminal input. See @ref{Display}, for related | |
1627 | functions. | |
1628 | ||
1629 | @menu | |
1630 | * Input Modes:: Options for how input is processed. | |
73804d4b RS |
1631 | * Recording Input:: Saving histories of recent or all input events. |
1632 | @end menu | |
1633 | ||
1634 | @node Input Modes | |
1635 | @subsection Input Modes | |
1636 | @cindex input modes | |
1637 | @cindex terminal input modes | |
1638 | ||
339902ec | 1639 | @defun set-input-mode interrupt flow meta &optional quit-char |
73804d4b RS |
1640 | This function sets the mode for reading keyboard input. If |
1641 | @var{interrupt} is non-null, then Emacs uses input interrupts. If it is | |
969fe9b5 | 1642 | @code{nil}, then it uses @sc{cbreak} mode. The default setting is |
8241495d | 1643 | system-dependent. Some systems always use @sc{cbreak} mode regardless |
969fe9b5 | 1644 | of what is specified. |
73804d4b | 1645 | |
969fe9b5 RS |
1646 | When Emacs communicates directly with X, it ignores this argument and |
1647 | uses interrupts if that is the way it knows how to communicate. | |
73804d4b | 1648 | |
969fe9b5 RS |
1649 | If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff} |
1650 | (@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This | |
9775b550 | 1651 | has no effect except in @sc{cbreak} mode. |
73804d4b RS |
1652 | |
1653 | @c Emacs 19 feature | |
1654 | The argument @var{meta} controls support for input character codes | |
1655 | above 127. If @var{meta} is @code{t}, Emacs converts characters with | |
1656 | the 8th bit set into Meta characters. If @var{meta} is @code{nil}, | |
1657 | Emacs disregards the 8th bit; this is necessary when the terminal uses | |
1658 | it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil}, | |
1659 | Emacs uses all 8 bits of input unchanged. This is good for terminals | |
969fe9b5 | 1660 | that use 8-bit character sets. |
73804d4b RS |
1661 | |
1662 | @c Emacs 19 feature | |
1663 | If @var{quit-char} is non-@code{nil}, it specifies the character to | |
1664 | use for quitting. Normally this character is @kbd{C-g}. | |
1665 | @xref{Quitting}. | |
1666 | @end defun | |
1667 | ||
1668 | The @code{current-input-mode} function returns the input mode settings | |
1669 | Emacs is currently using. | |
1670 | ||
1671 | @c Emacs 19 feature | |
1672 | @defun current-input-mode | |
8241495d | 1673 | This function returns the current mode for reading keyboard input. It |
73804d4b RS |
1674 | returns a list, corresponding to the arguments of @code{set-input-mode}, |
1675 | of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in | |
1676 | which: | |
1677 | @table @var | |
1678 | @item interrupt | |
1679 | is non-@code{nil} when Emacs is using interrupt-driven input. If | |
1680 | @code{nil}, Emacs is using @sc{cbreak} mode. | |
1681 | @item flow | |
1682 | is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s}) | |
a9f0a989 RS |
1683 | flow control for output to the terminal. This value is meaningful only |
1684 | when @var{interrupt} is @code{nil}. | |
73804d4b | 1685 | @item meta |
bfe721d1 | 1686 | is @code{t} if Emacs treats the eighth bit of input characters as |
73804d4b RS |
1687 | the meta bit; @code{nil} means Emacs clears the eighth bit of every |
1688 | input character; any other value means Emacs uses all eight bits as the | |
1689 | basic character code. | |
1690 | @item quit | |
1691 | is the character Emacs currently uses for quitting, usually @kbd{C-g}. | |
1692 | @end table | |
1693 | @end defun | |
1694 | ||
73804d4b RS |
1695 | @node Recording Input |
1696 | @subsection Recording Input | |
5e472eb6 | 1697 | @cindex recording input |
73804d4b RS |
1698 | |
1699 | @defun recent-keys | |
520a1273 | 1700 | This function returns a vector containing the last 300 input events from |
969fe9b5 RS |
1701 | the keyboard or mouse. All input events are included, whether or not |
1702 | they were used as parts of key sequences. Thus, you always get the last | |
1703 | 100 input events, not counting events generated by keyboard macros. | |
1704 | (These are excluded because they are less interesting for debugging; it | |
78608595 | 1705 | should be enough to see the events that invoked the macros.) |
de0df8e2 EZ |
1706 | |
1707 | A call to @code{clear-this-command-keys} (@pxref{Command Loop Info}) | |
caae20c7 | 1708 | causes this function to return an empty vector immediately afterward. |
73804d4b RS |
1709 | @end defun |
1710 | ||
3f705836 | 1711 | @deffn Command open-dribble-file filename |
73804d4b RS |
1712 | @cindex dribble file |
1713 | This function opens a @dfn{dribble file} named @var{filename}. When a | |
1714 | dribble file is open, each input event from the keyboard or mouse (but | |
1715 | not those from keyboard macros) is written in that file. A | |
1716 | non-character event is expressed using its printed representation | |
1717 | surrounded by @samp{<@dots{}>}. | |
1718 | ||
1719 | You close the dribble file by calling this function with an argument | |
1720 | of @code{nil}. | |
1721 | ||
1722 | This function is normally used to record the input necessary to | |
1723 | trigger an Emacs bug, for the sake of a bug report. | |
1724 | ||
1725 | @example | |
1726 | @group | |
1727 | (open-dribble-file "~/dribble") | |
1728 | @result{} nil | |
1729 | @end group | |
1730 | @end example | |
1731 | @end deffn | |
1732 | ||
1733 | See also the @code{open-termscript} function (@pxref{Terminal Output}). | |
1734 | ||
1735 | @node Terminal Output | |
1736 | @section Terminal Output | |
1737 | @cindex terminal output | |
1738 | ||
9775b550 | 1739 | The terminal output functions send output to a text terminal, or keep |
73804d4b RS |
1740 | track of output sent to the terminal. The variable @code{baud-rate} |
1741 | tells you what Emacs thinks is the output speed of the terminal. | |
1742 | ||
1743 | @defvar baud-rate | |
1744 | This variable's value is the output speed of the terminal, as far as | |
1745 | Emacs knows. Setting this variable does not change the speed of actual | |
1746 | data transmission, but the value is used for calculations such as | |
532ddb4c KS |
1747 | padding. |
1748 | ||
1749 | It also affects decisions about whether to scroll part of the | |
ffe379cb KS |
1750 | screen or repaint on text terminals. @xref{Forcing Redisplay}, |
1751 | for the corresponding functionality on graphical terminals. | |
73804d4b RS |
1752 | |
1753 | The value is measured in baud. | |
1754 | @end defvar | |
1755 | ||
1756 | If you are running across a network, and different parts of the | |
1757 | network work at different baud rates, the value returned by Emacs may be | |
1758 | different from the value used by your local terminal. Some network | |
1759 | protocols communicate the local terminal speed to the remote machine, so | |
1760 | that Emacs and other programs can get the proper value, but others do | |
1761 | not. If Emacs has the wrong value, it makes decisions that are less | |
1762 | than optimal. To fix the problem, set @code{baud-rate}. | |
1763 | ||
1764 | @defun baud-rate | |
969fe9b5 RS |
1765 | This obsolete function returns the value of the variable |
1766 | @code{baud-rate}. | |
73804d4b RS |
1767 | @end defun |
1768 | ||
1769 | @defun send-string-to-terminal string | |
1770 | This function sends @var{string} to the terminal without alteration. | |
1771 | Control characters in @var{string} have terminal-dependent effects. | |
9775b550 | 1772 | This function operates only on text terminals. |
73804d4b RS |
1773 | |
1774 | One use of this function is to define function keys on terminals that | |
8241495d RS |
1775 | have downloadable function key definitions. For example, this is how (on |
1776 | certain terminals) to define function key 4 to move forward four | |
73804d4b RS |
1777 | characters (by transmitting the characters @kbd{C-u C-f} to the |
1778 | computer): | |
1779 | ||
1780 | @example | |
1781 | @group | |
1782 | (send-string-to-terminal "\eF4\^U\^F") | |
1783 | @result{} nil | |
1784 | @end group | |
1785 | @end example | |
1786 | @end defun | |
1787 | ||
1788 | @deffn Command open-termscript filename | |
1789 | @cindex termscript file | |
1790 | This function is used to open a @dfn{termscript file} that will record | |
1791 | all the characters sent by Emacs to the terminal. It returns | |
1792 | @code{nil}. Termscript files are useful for investigating problems | |
1793 | where Emacs garbles the screen, problems that are due to incorrect | |
1794 | Termcap entries or to undesirable settings of terminal options more | |
1795 | often than to actual Emacs bugs. Once you are certain which characters | |
1796 | were actually output, you can determine reliably whether they correspond | |
1797 | to the Termcap specifications in use. | |
1798 | ||
339902ec LT |
1799 | You close the termscript file by calling this function with an |
1800 | argument of @code{nil}. | |
1801 | ||
1802 | See also @code{open-dribble-file} in @ref{Recording Input}. | |
73804d4b RS |
1803 | |
1804 | @example | |
1805 | @group | |
1806 | (open-termscript "../junk/termscript") | |
1807 | @result{} nil | |
1808 | @end group | |
1809 | @end example | |
1810 | @end deffn | |
1811 | ||
8241495d RS |
1812 | @node Sound Output |
1813 | @section Sound Output | |
1814 | @cindex sound | |
1815 | ||
1816 | To play sound using Emacs, use the function @code{play-sound}. Only | |
1817 | certain systems are supported; if you call @code{play-sound} on a system | |
1818 | which cannot really do the job, it gives an error. Emacs version 20 and | |
1819 | earlier did not support sound at all. | |
1820 | ||
1821 | The sound must be stored as a file in RIFF-WAVE format (@samp{.wav}) | |
1822 | or Sun Audio format (@samp{.au}). | |
1823 | ||
8241495d RS |
1824 | @defun play-sound sound |
1825 | This function plays a specified sound. The argument, @var{sound}, has | |
1826 | the form @code{(sound @var{properties}...)}, where the @var{properties} | |
1827 | consist of alternating keywords (particular symbols recognized | |
1828 | specially) and values corresponding to them. | |
1829 | ||
1830 | Here is a table of the keywords that are currently meaningful in | |
1831 | @var{sound}, and their meanings: | |
1832 | ||
1833 | @table @code | |
1834 | @item :file @var{file} | |
1835 | This specifies the file containing the sound to play. | |
1836 | If the file name is not absolute, it is expanded against | |
1837 | the directory @code{data-directory}. | |
1838 | ||
8f3efb4e RS |
1839 | @item :data @var{data} |
1840 | This specifies the sound to play without need to refer to a file. The | |
1841 | value, @var{data}, should be a string containing the same bytes as a | |
1842 | sound file. We recommend using a unibyte string. | |
1843 | ||
8241495d RS |
1844 | @item :volume @var{volume} |
1845 | This specifies how loud to play the sound. It should be a number in the | |
1846 | range of 0 to 1. The default is to use whatever volume has been | |
1847 | specified before. | |
a6b8df2f DL |
1848 | |
1849 | @item :device @var{device} | |
1850 | This specifies the system device on which to play the sound, as a | |
1851 | string. The default device is system-dependent. | |
8241495d RS |
1852 | @end table |
1853 | ||
1854 | Before actually playing the sound, @code{play-sound} | |
1855 | calls the functions in the list @code{play-sound-functions}. | |
1856 | Each function is called with one argument, @var{sound}. | |
1857 | @end defun | |
1858 | ||
a6b8df2f | 1859 | @defun play-sound-file file &optional volume device |
a6b8df2f DL |
1860 | This function is an alternative interface to playing a sound @var{file} |
1861 | specifying an optional @var{volume} and @var{device}. | |
1862 | @end defun | |
1863 | ||
8241495d RS |
1864 | @defvar play-sound-functions |
1865 | A list of functions to be called before playing a sound. Each function | |
1866 | is called with one argument, a property list that describes the sound. | |
1867 | @end defvar | |
1868 | ||
1ce58cc0 RS |
1869 | @node X11 Keysyms |
1870 | @section Operating on X11 Keysyms | |
bbb9c4e1 | 1871 | @cindex X11 keysyms |
73804d4b RS |
1872 | |
1873 | To define system-specific X11 keysyms, set the variable | |
1874 | @code{system-key-alist}. | |
1875 | ||
1876 | @defvar system-key-alist | |
1877 | This variable's value should be an alist with one element for each | |
8241495d | 1878 | system-specific keysym. Each element has the form @code{(@var{code} |
73804d4b | 1879 | . @var{symbol})}, where @var{code} is the numeric keysym code (not |
c60ee5e7 | 1880 | including the ``vendor specific'' bit, |
37680279 | 1881 | @ifnottex |
86494bd5 | 1882 | -2**28), |
37680279 | 1883 | @end ifnottex |
c60ee5e7 | 1884 | @tex |
86494bd5 | 1885 | $-2^{28}$), |
969fe9b5 RS |
1886 | @end tex |
1887 | and @var{symbol} is the name for the function key. | |
73804d4b | 1888 | |
8241495d RS |
1889 | For example @code{(168 . mute-acute)} defines a system-specific key (used |
1890 | by HP X servers) whose numeric code is | |
37680279 | 1891 | @ifnottex |
969fe9b5 | 1892 | -2**28 |
37680279 | 1893 | @end ifnottex |
c60ee5e7 | 1894 | @tex |
969fe9b5 RS |
1895 | $-2^{28}$ |
1896 | @end tex | |
1897 | + 168. | |
73804d4b | 1898 | |
969fe9b5 RS |
1899 | It is not crucial to exclude from the alist the keysyms of other X |
1900 | servers; those do no harm, as long as they don't conflict with the ones | |
1901 | used by the X server actually in use. | |
22697dac | 1902 | |
1911e6e5 | 1903 | The variable is always local to the current terminal, and cannot be |
22697dac | 1904 | buffer-local. @xref{Multiple Displays}. |
73804d4b RS |
1905 | @end defvar |
1906 | ||
1ce58cc0 RS |
1907 | You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables: |
1908 | ||
1909 | @defvar x-alt-keysym | |
1910 | @defvarx x-meta-keysym | |
1911 | @defvarx x-hyper-keysym | |
1912 | @defvarx x-super-keysym | |
1913 | The name of the keysym that should stand for the Alt modifier | |
1914 | (respectively, for Meta, Hyper, and Super). For example, here is | |
1915 | how to swap the Meta and Alt modifiers within Emacs: | |
1916 | @lisp | |
1917 | (setq x-alt-keysym 'meta) | |
1918 | (setq x-meta-keysym 'alt) | |
1919 | @end lisp | |
1920 | @end defvar | |
1921 | ||
73804d4b RS |
1922 | @node Batch Mode |
1923 | @section Batch Mode | |
1924 | @cindex batch mode | |
73804d4b | 1925 | |
8241495d | 1926 | The command-line option @samp{-batch} causes Emacs to run |
73804d4b RS |
1927 | noninteractively. In this mode, Emacs does not read commands from the |
1928 | terminal, it does not alter the terminal modes, and it does not expect | |
1929 | to be outputting to an erasable screen. The idea is that you specify | |
1930 | Lisp programs to run; when they are finished, Emacs should exit. The | |
1931 | way to specify the programs to run is with @samp{-l @var{file}}, which | |
9775b550 RS |
1932 | loads the library named @var{file}, or @samp{-f @var{function}}, which |
1933 | calls @var{function} with no arguments, or @samp{--eval @var{form}}. | |
73804d4b RS |
1934 | |
1935 | Any Lisp program output that would normally go to the echo area, | |
8241495d | 1936 | either using @code{message}, or using @code{prin1}, etc., with @code{t} |
bfe721d1 | 1937 | as the stream, goes instead to Emacs's standard error descriptor when |
d70ba855 DL |
1938 | in batch mode. Similarly, input that would normally come from the |
1939 | minibuffer is read from the standard input descriptor. | |
1940 | Thus, Emacs behaves much like a noninteractive | |
73804d4b RS |
1941 | application program. (The echo area output that Emacs itself normally |
1942 | generates, such as command echoing, is suppressed entirely.) | |
1943 | ||
1944 | @defvar noninteractive | |
1945 | This variable is non-@code{nil} when Emacs is running in batch mode. | |
1946 | @end defvar | |
750c3b02 JD |
1947 | |
1948 | @node Session Management | |
1949 | @section Session Management | |
f8e7eebe | 1950 | @cindex session manager |
750c3b02 | 1951 | |
f8e7eebe RS |
1952 | Emacs supports the X Session Management Protocol for suspension and |
1953 | restart of applications. In the X Window System, a program called the | |
1954 | @dfn{session manager} has the responsibility to keep track of the | |
1955 | applications that are running. During shutdown, the session manager | |
1956 | asks applications to save their state, and delays the actual shutdown | |
1957 | until they respond. An application can also cancel the shutdown. | |
750c3b02 | 1958 | |
f8e7eebe RS |
1959 | When the session manager restarts a suspended session, it directs |
1960 | these applications to individually reload their saved state. It does | |
1961 | this by specifying a special command-line argument that says what | |
1962 | saved session to restore. For Emacs, this argument is @samp{--smid | |
1963 | @var{session}}. | |
750c3b02 JD |
1964 | |
1965 | @defvar emacs-save-session-functions | |
750c3b02 JD |
1966 | Emacs supports saving state by using a hook called |
1967 | @code{emacs-save-session-functions}. Each function in this hook is | |
1968 | called when the session manager tells Emacs that the window system is | |
339902ec LT |
1969 | shutting down. The functions are called with no arguments and with the |
1970 | current buffer set to a temporary buffer. Each function can use | |
1971 | @code{insert} to add Lisp code to this buffer. At the end, Emacs | |
1972 | saves the buffer in a file that a subsequent Emacs invocation will | |
1973 | load in order to restart the saved session. | |
f8e7eebe RS |
1974 | |
1975 | If a function in @code{emacs-save-session-functions} returns | |
1976 | non-@code{nil}, Emacs tells the session manager to cancel the | |
1977 | shutdown. | |
750c3b02 JD |
1978 | @end defvar |
1979 | ||
fe3b7e35 | 1980 | Here is an example that just inserts some text into @samp{*scratch*} when |
f8e7eebe | 1981 | Emacs is restarted by the session manager. |
750c3b02 JD |
1982 | |
1983 | @example | |
1984 | @group | |
1985 | (add-hook 'emacs-save-session-functions 'save-yourself-test) | |
1986 | @end group | |
1987 | ||
1988 | @group | |
1989 | (defun save-yourself-test () | |
f8e7eebe RS |
1990 | (insert "(save-excursion |
1991 | (switch-to-buffer \"*scratch*\") | |
1992 | (insert \"I am restored\"))") | |
1993 | nil) | |
750c3b02 JD |
1994 | @end group |
1995 | @end example | |
ab5796a9 MB |
1996 | |
1997 | @ignore | |
1998 | arch-tag: 8378814a-30d7-467c-9615-74a80b9988a7 | |
1999 | @end ignore |