@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2001,
+@c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/os
-@node System Interface, Display, Processes, Top
+@node System Interface, Antinews, Display, Top
@chapter Operating System Interface
This chapter is about starting and getting out of Emacs, access to
pertaining to the terminal and the screen.
@menu
-* Starting Up:: Customizing Emacs start-up processing.
+* Starting Up:: Customizing Emacs startup processing.
* Getting Out:: How exiting works (permanent or temporary).
* System Environment:: Distinguish the name and kind of system.
* User Identification:: Finding the name and user id of the user.
* Time of Day:: Getting the current time.
-* Time Conversion:: Converting a time from numeric form to a string, or
- to calendrical data (or vice versa).
+* Time Conversion:: Converting a time from numeric form
+ to calendrical data, and vice versa).
+* Time Parsing:: Converting a time from numeric form to text
+ and vice versa.
+* Processor Run Time:: Getting the run time used by Emacs.
+* Time Calculations:: Adding, subtracting, comparing times, etc.
* Timers:: Setting a timer to call a function at a certain time.
-* Terminal Input:: Recording terminal input for debugging.
-* Terminal Output:: Recording terminal output for debugging.
-* Special Keysyms:: Defining system-specific key symbols for X windows.
-* Flow Control:: How to turn output flow control on or off.
+* Idle Timers:: Setting a timer to call a function when Emacs has
+ been idle for a certain length of time.
+* Terminal Input:: Accessing and recording terminal input.
+* Terminal Output:: Controlling and recording terminal output.
+* Sound Output:: Playing sounds on the computer's speaker.
+* X11 Keysyms:: Operating on key symbols for X Windows
* Batch Mode:: Running Emacs without terminal interaction.
+* Session Management:: Saving and restoring state with X Session Management.
@end menu
@node Starting Up
can customize these actions.
@menu
-* Start-up Summary:: Sequence of actions Emacs performs at start-up.
+* Startup Summary:: Sequence of actions Emacs performs at startup.
* Init File:: Details on reading the init file (@file{.emacs}).
* Terminal-Specific:: How the terminal-specific Lisp file is read.
-* Command Line Arguments:: How command line arguments are processed,
+* Command-Line Arguments:: How command-line arguments are processed,
and how you can customize them.
@end menu
-@node Start-up Summary
-@subsection Summary: Sequence of Actions at Start Up
-@cindex initialization
-@cindex start up of Emacs
+@node Startup Summary
+@subsection Summary: Sequence of Actions at Startup
+@cindex initialization of Emacs
+@cindex startup of Emacs
@cindex @file{startup.el}
The order of operations performed (in @file{startup.el}) by Emacs when
it is started up is as follows:
@enumerate
+@item
+It adds subdirectories to @code{load-path}, by running the file named
+@file{subdirs.el} in each directory in the list. Normally this file
+adds the directory's subdirectories to the list, and these will be
+scanned in their turn. The files @file{subdirs.el} are normally
+generated automatically by Emacs installation.
+
+@item
+It sets the language environment and the terminal coding system,
+if requested by environment variables such as @code{LANG}.
+
@item
It loads the initialization library for the window system, if you are
using a window system. This library's name is
even earlier than this.)
@item
-It initializes the X window frame and faces, if appropriate.
+It initializes the window frame and faces, if appropriate.
@item
It runs the normal hook @code{before-init-hook}.
@item
-It loads the library @file{site-start}, unless the option
-@samp{-no-site-file} was specified. The library's file name is usually
-@file{site-start.el}.
+It loads the library @file{site-start} (if any), unless the option
+@samp{-Q} (or @samp{--no-site-file}) was specified. The library's file
+name is usually @file{site-start.el}.
@cindex @file{site-start.el}
-@item
-It loads the file @file{~/.emacs} unless @samp{-q} was specified on
-the command line. (This is not done in @samp{-batch} mode.) The @samp{-u}
-option can specify the user name whose home directory should be used
-instead of @file{~}.
-
-@item
-It loads the library @file{default} unless @code{inhibit-default-init}
-is non-@code{nil}. (This is not done in @samp{-batch} mode or if
-@samp{-q} was specified on the command line.) The library's file name
-is usually @file{default.el}.
+@item
+It loads your init file (usually @file{~/.emacs}), unless the option
+@samp{-q} (or @samp{--no-init-file}), @samp{-Q}, or @samp{--batch} was
+specified on the command line. The @samp{-u} option can specify
+another user whose home directory should be used instead of @file{~}.
+
+@item
+It loads the library @file{default} (if any), unless
+@code{inhibit-default-init} is non-@code{nil}. (This is not done in
+@samp{-batch} mode, or if @samp{-Q} or @samp{-q} was specified on the
+command line.) The library's file name is usually @file{default.el}.
@cindex @file{default.el}
@item
the buffer @samp{*scratch*} is still current and still in Fundamental
mode.
-@item
+@item
It loads the terminal-specific Lisp file, if any, except when in batch
mode or using a window system.
It displays the initial echo area message, unless you have suppressed
that with @code{inhibit-startup-echo-area-message}.
-@item
+@item
It processes the action arguments from the command line.
-@item
-It runs @code{term-setup-hook}.
+@item
+It runs @code{emacs-startup-hook} and then @code{term-setup-hook}.
@item
It calls @code{frame-notice-user-settings}, which modifies the
parameters of the selected frame according to whatever the init files
specify.
-@item
+@item
It runs @code{window-setup-hook}. @xref{Window Systems}.
-@item
+@item
It displays copyleft, nonwarranty, and basic use information, provided
-there were no remaining command line arguments (a few steps above) and
-the value of @code{inhibit-startup-message} is @code{nil}.
+the value of @code{inhibit-startup-message} is @code{nil}, you didn't
+specify @samp{--no-splash} or @samp{-Q}.
@end enumerate
@defopt inhibit-startup-message
@defopt inhibit-startup-echo-area-message
This variable controls the display of the startup echo area message.
You can suppress the startup echo area message by adding text with this
-form to your @file{.emacs} file:
+form to your init file:
@example
(setq inhibit-startup-echo-area-message
"@var{your-login-name}")
@end example
-Simply setting @code{inhibit-startup-echo-area-message} to your login
-name is not sufficient to inhibit the message; Emacs explicitly checks
-whether @file{.emacs} contains an expression as shown above. Your login
-name must appear in the expression as a Lisp string constant.
+Emacs explicitly checks for an expression as shown above in your init
+file; your login name must appear in the expression as a Lisp string
+constant. Other methods of setting
+@code{inhibit-startup-echo-area-message} to the same value do not
+inhibit the startup message.
This way, you can easily inhibit the message for yourself if you wish,
-but thoughtless copying of your @file{.emacs} file will not inhibit the
-message for someone else.
+but thoughtless copying of your init file will not inhibit the message
+for someone else.
@end defopt
@node Init File
-@subsection The Init File: @file{.emacs}
+@subsection The Init File, @file{.emacs}
@cindex init file
@cindex @file{.emacs}
- When you start Emacs, it normally attempts to load the file
-@file{.emacs} from your home directory. This file, if it exists, must
-contain Lisp code. It is called your @dfn{init file}. The command line
-switches @samp{-q} and @samp{-u} affect the use of the init file;
-@samp{-q} says not to load an init file, and @samp{-u} says to load a
-specified user's init file instead of yours. @xref{Entering Emacs,,,
-emacs, The GNU Emacs Manual}.
+ When you start Emacs, it normally attempts to load your @dfn{init
+file}, a file in your home directory. Its normal name is
+@file{.emacs}, but you can also call it @file{.emacs.el}.
+Alternatively, you can use a file named @file{init.el} in a
+subdirectory @file{.emacs.d}. Whichever place you use, you can also
+compile the file (@pxref{Byte Compilation}); then the actual file
+loaded will be @file{.emacs.elc} or @file{init.elc}.
+
+ The command-line switches @samp{-q}, @samp{-Q}, and @samp{-u}
+control whether and where to find the init file; @samp{-q} (and the
+stronger @samp{-Q}) says not to load an init file, while @samp{-u
+@var{user}} says to load @var{user}'s init file instead of yours.
+@xref{Entering Emacs,,, emacs, The GNU Emacs Manual}. If neither
+option is specified, Emacs uses the @code{LOGNAME} environment
+variable, or the @code{USER} (most systems) or @code{USERNAME} (MS
+systems) variable, to find your home directory and thus your init
+file; this way, even if you have su'd, Emacs still loads your own init
+file. If those environment variables are absent, though, Emacs uses
+your user-id to find your home directory.
@cindex default init file
- A site may have a @dfn{default init file}, which is the library named
-@file{default.el}. Emacs finds the @file{default.el} file through the
-standard search path for libraries (@pxref{How Programs Do Loading}).
-The Emacs distribution does not come with this file; sites may provide
-one for local customizations. If the default init file exists, it is
-loaded whenever you start Emacs, except in batch mode or if @samp{-q} is
-specified. But your own personal init file, if any, is loaded first; if
-it sets @code{inhibit-default-init} to a non-@code{nil} value, then
-Emacs does not subsequently load the @file{default.el} file.
+ A site may have a @dfn{default init file}, which is the library
+named @file{default.el}. Emacs finds the @file{default.el} file
+through the standard search path for libraries (@pxref{How Programs Do
+Loading}). The Emacs distribution does not come with this file; sites
+may provide one for local customizations. If the default init file
+exists, it is loaded whenever you start Emacs, except in batch mode or
+if @samp{-q} (or @samp{-Q}) is specified. But your own personal init
+file, if any, is loaded first; if it sets @code{inhibit-default-init}
+to a non-@code{nil} value, then Emacs does not subsequently load the
+@file{default.el} file.
Another file for site-customization is @file{site-start.el}. Emacs
loads this @emph{before} the user's init file. You can inhibit the
-loading of this file with the option @samp{-no-site-file}.
+loading of this file with the option @samp{--no-site-file}.
@defvar site-run-file
-This variable specifies the site-customization file to load
-before the user's init file. Its normal value is @code{"site-start"}.
+This variable specifies the site-customization file to load before the
+user's init file. Its normal value is @code{"site-start"}. The only
+way you can change it with real effect is to do so before dumping
+Emacs.
@end defvar
- If there is a great deal of code in your @file{.emacs} file, you
-should move it into another file named @file{@var{something}.el},
-byte-compile it (@pxref{Byte Compilation}), and make your @file{.emacs}
-file load the other file using @code{load} (@pxref{Loading}).
-
- @xref{Init File Examples,,, emacs, The GNU Emacs Manual}, for
+ @xref{Init Examples,, Init File Examples, emacs, The GNU Emacs Manual}, for
examples of how to make various commonly desired customizations in your
@file{.emacs} file.
@end defopt
@defvar before-init-hook
-@defvarx after-init-hook
-These two normal hooks are run just before, and just after, loading of
-the user's init file, @file{default.el}, and/or @file{site-start.el}.
+This normal hook is run, once, just before loading all the init files
+(the user's init file, @file{default.el}, and/or @file{site-start.el}).
+(The only way to change it with real effect is before dumping Emacs.)
+@end defvar
+
+@defvar after-init-hook
+This normal hook is run, once, just after loading all the init files
+(the user's init file, @file{default.el}, and/or @file{site-start.el}),
+before loading the terminal-specific library and processing the
+command-line action arguments.
+@end defvar
+
+@defvar emacs-startup-hook
+This normal hook is run, once, just after handling the command line
+arguments, just before @code{term-setup-hook}.
+@end defvar
+
+@defvar user-init-file
+This variable holds the absolute file name of the user's init file. If the
+actual init file loaded is a compiled file, such as @file{.emacs.elc},
+the value refers to the corresponding source file.
@end defvar
@node Terminal-Specific
@cindex terminal-specific initialization
Each terminal type can have its own Lisp library that Emacs loads when
-run on that type of terminal. For a terminal type named @var{termtype},
-the library is called @file{term/@var{termtype}}. Emacs finds the file
-by searching the @code{load-path} directories as it does for other
-files, and trying the @samp{.elc} and @samp{.el} suffixes. Normally,
-terminal-specific Lisp library is located in @file{emacs/lisp/term}, a
-subdirectory of the @file{emacs/lisp} directory in which most Emacs Lisp
-libraries are kept.@refill
-
- The library's name is constructed by concatenating the value of the
-variable @code{term-file-prefix} and the terminal type. Normally,
-@code{term-file-prefix} has the value @code{"term/"}; changing this
-is not recommended.
-
- The usual function of a terminal-specific library is to enable special
-keys to send sequences that Emacs can recognize. It may also need to
-set or add to @code{function-key-map} if the Termcap entry does not
-specify all the terminal's function keys. @xref{Terminal Input}.
+run on that type of terminal. The library's name is constructed by
+concatenating the value of the variable @code{term-file-prefix} and the
+terminal type (specified by the environment variable @code{TERM}).
+Normally, @code{term-file-prefix} has the value
+@code{"term/"}; changing this is not recommended. Emacs finds the file
+in the normal manner, by searching the @code{load-path} directories, and
+trying the @samp{.elc} and @samp{.el} suffixes.
@cindex Termcap
- When the name of the terminal type contains a hyphen, only the part of
-the name before the first hyphen is significant in choosing the library
-name. Thus, terminal types @samp{aaa-48} and @samp{aaa-30-rv} both use
-the @file{term/aaa} library. If necessary, the library can evaluate
-@code{(getenv "TERM")} to find the full name of the terminal
-type.@refill
-
- Your @file{.emacs} file can prevent the loading of the
+ The usual function of a terminal-specific library is to enable
+special keys to send sequences that Emacs can recognize. It may also
+need to set or add to @code{function-key-map} if the Termcap or
+Terminfo entry does not specify all the terminal's function keys.
+@xref{Terminal Input}.
+
+ When the name of the terminal type contains a hyphen, and no library
+is found whose name is identical to the terminal's name, Emacs strips
+from the terminal's name the last hyphen and everything that follows
+it, and tries again. This process is repeated until Emacs finds a
+matching library or until there are no more hyphens in the name (the
+latter means the terminal doesn't have any library specific to it).
+Thus, for example, if there are no @samp{aaa-48} and @samp{aaa-30}
+libraries, Emacs will try the same library @file{term/aaa.el} for
+terminal types @samp{aaa-48} and @samp{aaa-30-rv}. If necessary, the
+library can evaluate @code{(getenv "TERM")} to find the full name of
+the terminal type.@refill
+
+ Your init file can prevent the loading of the
terminal-specific library by setting the variable
@code{term-file-prefix} to @code{nil}. This feature is useful when
experimenting with your own peculiar customizations.
terminal-specific library by setting the variable
@code{term-setup-hook}. This is a normal hook which Emacs runs using
@code{run-hooks} at the end of Emacs initialization, after loading both
-your @file{.emacs} file and any terminal-specific libraries. You can
+your init file and any terminal-specific libraries. You can
use this variable to define initializations for terminals that do not
have their own libraries. @xref{Hooks}.
@noindent
You may set the @code{term-file-prefix} variable to @code{nil} in your
-@file{.emacs} file if you do not wish to load the
+init file if you do not wish to load the
terminal-initialization file. To do this, put the following in
-your @file{.emacs} file: @code{(setq term-file-prefix nil)}.
+your init file: @code{(setq term-file-prefix nil)}.
+
+On MS-DOS, if the environment variable @code{TERM} is not set, Emacs
+uses @samp{internal} as the terminal type.
@end defvar
-@defvar term-setup-hook
+@defvar term-setup-hook
This variable is a normal hook that Emacs runs after loading your
-@file{.emacs} file, the default initialization file (if any) and the
+init file, the default initialization file (if any) and the
terminal-specific Lisp file.
You can use @code{term-setup-hook} to override the definitions made by a
See @code{window-setup-hook} in @ref{Window Systems}, for a related
feature.
-@node Command Line Arguments
-@subsection Command Line Arguments
-@cindex command line arguments
+@node Command-Line Arguments
+@subsection Command-Line Arguments
+@cindex command-line arguments
- You can use command line arguments to request various actions when you
+ You can use command-line arguments to request various actions when you
start Emacs. Since you do not need to start Emacs more than once per
day, and will often leave your Emacs session running longer than that,
-command line arguments are hardly ever used. As a practical matter, it
+command-line arguments are hardly ever used. As a practical matter, it
is best to avoid making the habit of using them, since this habit would
encourage you to kill and restart Emacs unnecessarily often. These
options exist for two reasons: to be compatible with other editors (for
invocation by other programs) and to enable shell scripts to run
specific Lisp programs.
- This section describes how Emacs processes command line arguments,
+ This section describes how Emacs processes command-line arguments,
and how you can customize them.
@ignore
(Note that some other editors require you to start afresh each time
you want to edit a file. With this kind of editor, you will probably
-specify the file as a command line argument. The recommended way to
+specify the file as a command-line argument. The recommended way to
use GNU Emacs is to start it only once, just after you log in, and do
all your editing in the same Emacs process. Each time you want to edit
a different file, you visit it with the existing Emacs, which eventually
@defun command-line
This function parses the command line that Emacs was called with,
-processes it, loads the user's @file{.emacs} file and displays the
+processes it, loads the user's init file and displays the
startup messages.
@end defun
If you redump Emacs by calling @code{dump-emacs}, you may wish to set
this variable to @code{nil} first in order to cause the new dumped Emacs
-to process its new command line arguments.
+to process its new command-line arguments.
@end defvar
@defvar command-switch-alist
@cindex switches on command line
@cindex options on command line
-@cindex command line options
+@cindex command-line options
The value of this variable is an alist of user-defined command-line
options and associated handler functions. This variable exists so you
can add elements to it.
-A @dfn{command line option} is an argument on the command line of the
-form:
+A @dfn{command-line option} is an argument on the command line, which
+has the form:
@example
-@var{option}
@end example
-The elements of the @code{command-switch-alist} look like this:
+The elements of the @code{command-switch-alist} look like this:
@example
(@var{option} . @var{handler-function})
@end example
-The @var{handler-function} is called to handle @var{option} and receives
-the option name as its sole argument.
+The @sc{car}, @var{option}, is a string, the name of a command-line
+option (not including the initial hyphen). The @var{handler-function}
+is called to handle @var{option}, and receives the option name as its
+sole argument.
In some cases, the option is followed in the command line by an
argument. In these cases, the @var{handler-function} can find all the
@code{command-line-args-left}. (The entire list of command-line
arguments is in @code{command-line-args}.)
-The command line arguments are parsed by the @code{command-line-1}
-function in the @file{startup.el} file. See also @ref{Command
-Switches, , Command Line Switches and Arguments, emacs, The GNU Emacs
-Manual}.
+The command-line arguments are parsed by the @code{command-line-1}
+function in the @file{startup.el} file. See also @ref{Emacs
+Invocation, , Command Line Arguments for Emacs Invocation, emacs, The
+GNU Emacs Manual}.
@end defvar
@defvar command-line-args
-The value of this variable is the list of command line arguments passed
+The value of this variable is the list of command-line arguments passed
to Emacs.
@end defvar
These functions are called with no arguments. They can access the
command-line argument under consideration through the variable
-@code{argi}. The remaining arguments (not including the current one)
-are in the variable @code{command-line-args-left}.
+@code{argi}, which is bound temporarily at this point. The remaining
+arguments (not including the current one) are in the variable
+@code{command-line-args-left}.
When a function recognizes and processes the argument in @code{argi}, it
should return a non-@code{nil} value to say it has dealt with that
@end defun
All the information in the Emacs process, aside from files that have
-been saved, is lost when the Emacs is killed. Because killing Emacs
-inadvertently can lose a lot of work, Emacs queries for confirmation
-before actually terminating if you have buffers that need saving or
-subprocesses that are running. This is done in the function
-@code{save-buffers-kill-emacs}.
+been saved, is lost when the Emacs process is killed. Because killing
+Emacs inadvertently can lose a lot of work, Emacs queries for
+confirmation before actually terminating if you have buffers that need
+saving or subprocesses that are running. This is done in the function
+@code{save-buffers-kill-emacs}, the higher level function from which
+@code{kill-emacs} is usually called.
@defvar kill-emacs-query-functions
After asking the standard questions, @code{save-buffers-kill-emacs}
-calls the functions in the list @code{kill-buffer-query-functions}, in
+calls the functions in the list @code{kill-emacs-query-functions}, in
order of appearance, with no arguments. These functions can ask for
additional confirmation from the user. If any of them returns
-non-@code{nil}, Emacs is not killed.
+@code{nil}, @code{save-buffers-kill-emacs} does not kill Emacs, and
+does not run the remaining functions in this hook. Calling
+@code{kill-emacs} directly does not run this hook.
@end defvar
@defvar kill-emacs-hook
This variable is a normal hook; once @code{save-buffers-kill-emacs} is
-finished with all file saving and confirmation, it runs the functions in
-this hook.
+finished with all file saving and confirmation, it calls
+@code{kill-emacs} which runs the functions in this hook.
+@code{kill-emacs} does not run this hook in batch mode.
+
+@code{kill-emacs} may be invoked directly (that is not via
+@code{save-buffers-kill-emacs}) if the terminal is disconnected, or in
+similar situations where interaction with the user is not possible.
+Thus, if your hook needs to interact with the user, put it on
+@code{kill-emacs-query-functions}; if it needs to run regardless of
+how Emacs is killed, put it on @code{kill-emacs-hook}.
@end defvar
@node Suspending Emacs
systems, ``suspension'' actually creates a new shell temporarily as a
subprocess of Emacs. Then you would exit the shell to return to Emacs.
- Suspension is not useful with window systems such as X, because the
-Emacs job may not have a parent that can resume it again, and in any
-case you can give input to some other job such as a shell merely by
-moving to a different window. Therefore, suspending is not allowed
-when Emacs is an X client.
+ Suspension is not useful with window systems, because the Emacs job
+may not have a parent that can resume it again, and in any case you can
+give input to some other job such as a shell merely by moving to a
+different window. Therefore, suspending is not allowed when Emacs is using
+a window system (X, MS Windows, or Mac).
-@defun suspend-emacs string
+@defun suspend-emacs &optional string
This function stops Emacs and returns control to the superior process.
If and when the superior process resumes Emacs, @code{suspend-emacs}
returns @code{nil} to its caller in Lisp.
appear.
Before suspending, @code{suspend-emacs} runs the normal hook
-@code{suspend-hook}. In Emacs version 18, @code{suspend-hook} was not a
-normal hook; its value was a single function, and if its value was
-non-@code{nil}, then @code{suspend-emacs} returned immediately without
-actually suspending anything.
+@code{suspend-hook}.
After the user resumes Emacs, @code{suspend-emacs} runs the normal hook
@code{suspend-resume-hook}. @xref{Hooks}.
(function (lambda ()
(or (y-or-n-p
"Really suspend? ")
- (error "Suspend cancelled")))))
+ (error "Suspend canceled")))))
@result{} (lambda nil
(or (y-or-n-p "Really suspend? ")
- (error "Suspend cancelled")))
+ (error "Suspend canceled")))
@end group
@group
(add-hook 'suspend-resume-hook
@end defun
@defvar suspend-hook
-This variable is a normal hook run before suspending.
+This variable is a normal hook that Emacs runs before suspending.
@end defvar
@defvar suspend-resume-hook
-This variable is a normal hook run after suspending.
+This variable is a normal hook that Emacs runs on resuming
+after a suspension.
@end defvar
@node System Environment
Emacs provides access to variables in the operating system environment
through various functions. These variables include the name of the
-system, the user's @sc{uid}, and so on.
+system, the user's @acronym{UID}, and so on.
+@defvar system-configuration
+This variable holds the standard GNU configuration name for the
+hardware/software configuration of your system, as a string. The
+convenient way to test parts of this string is with
+@code{string-match}.
+@end defvar
+
+@cindex system type and name
@defvar system-type
The value of this variable is a symbol indicating the type of operating
system Emacs is operating on. Here is a table of the possible values:
@table @code
+@item alpha-vms
+VMS on the Alpha.
+
@item aix-v3
AIX.
@item berkeley-unix
Berkeley BSD.
+@item cygwin
+Cygwin.
+
@item dgux
Data General DGUX operating system.
@item gnu
-A GNU system using the GNU HURD and Mach.
+the GNU system (using the GNU kernel, which consists of the HURD and Mach).
+
+@item gnu/linux
+A GNU/Linux system---that is, a variant GNU system, using the Linux
+kernel. (These systems are the ones people often call ``Linux,'' but
+actually Linux is just the kernel, not the whole system.)
@item hpux
Hewlett-Packard HPUX operating system.
@item irix
Silicon Graphics Irix system.
-@item linux
-A GNU system using the Linux kernel.
-
@item ms-dos
-Microsoft MS-DOS ``operating system.''
+Microsoft MS-DOS ``operating system.'' Emacs compiled with DJGPP for
+MS-DOS binds @code{system-type} to @code{ms-dos} even when you run it on
+MS-Windows.
@item next-mach
NeXT Mach-based system.
VAX VMS.
@item windows-nt
-Microsoft windows NT.
+Microsoft windows NT. The same executable supports Windows 9X, but the
+value of @code{system-type} is @code{windows-nt} in either case.
@item xenix
SCO Xenix 386.
systems.
@end defvar
-@defvar system-configuration
-This variable holds the three-part configuration name for the
-hardware/software configuration of your system, as a string. The
-convenient way to test parts of this string is with @code{string-match}.
-@end defvar
-
@defun system-name
This function returns the name of the machine you are running on.
@example
(system-name)
- @result{} "prep.ai.mit.edu"
+ @result{} "www.gnu.org"
@end example
@end defun
-@vindex system-name
The symbol @code{system-name} is a variable as well as a function. In
fact, the function returns whatever value the variable
@code{system-name} currently holds. Thus, you can set the variable
Emacs was dumped. @xref{Building Emacs}.)
@end defvar
-@defun getenv var
+@deffn Command getenv var
@cindex environment variable access
This function returns the value of the environment variable @var{var},
-as a string. Within Emacs, the environment variable values are kept in
-the Lisp variable @code{process-environment}.
+as a string. @var{var} should be a string. If @var{var} is undefined
+in the environment, @code{getenv} returns @code{nil}. If returns
+@samp{""} if @var{var} is set but null. Within Emacs, the environment
+variable values are kept in the Lisp variable @code{process-environment}.
@example
@group
HOME=/user/lewis
@end group
@end example
-@end defun
+@end deffn
@c Emacs 19 feature
-@deffn Command setenv variable value
+@deffn Command setenv variable &optional value
This command sets the value of the environment variable named
-@var{variable} to @var{value}. Both arguments should be strings. This
-function works by modifying @code{process-environment}; binding that
-variable with @code{let} is also reasonable practice.
+@var{variable} to @var{value}. @var{variable} should be a string.
+Internally, Emacs Lisp can handle any string. However, normally
+@var{variable} should be a valid shell identifier, that is, a sequence
+of letters, digits and underscores, starting with a letter or
+underscore. Otherwise, errors may occur if subprocesses of Emacs try
+to access the value of @var{variable}. If @var{value} is omitted or
+@code{nil}, @code{setenv} removes @var{variable} from the environment.
+Otherwise, @var{value} should be a string.
+
+@code{setenv} works by modifying @code{process-environment}; binding
+that variable with @code{let} is also reasonable practice.
+
+@code{setenv} returns the new value of @var{variable}, or @code{nil}
+if it removed @var{variable} from the environment.
@end deffn
@defvar process-environment
process-environment
@result{} ("l=/usr/stanford/lib/gnuemacs/lisp"
"PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
- "USER=lewis"
+ "USER=lewis"
@end group
@group
- "TERM=ibmapa16"
+ "TERM=ibmapa16"
"SHELL=/bin/csh"
"HOME=/user/lewis")
@end group
@end smallexample
+
+If @code{process-environment} contains ``duplicate'' elements that
+specify the same environment variable, the first of these elements
+specifies the variable, and the other ``duplicates'' are ignored.
@end defvar
@defvar path-separator
This variable holds a string which says which character separates
directories in a search path (as found in an environment variable). Its
value is @code{":"} for Unix and GNU systems, and @code{";"} for MS-DOS
-and Windows NT.
+and MS-Windows.
@end defvar
+@defun parse-colon-path path
+This function takes a search path string such as would be the value of
+the @code{PATH} environment variable, and splits it at the separators,
+returning a list of directory names. @code{nil} in this list stands for
+``use the current directory.'' Although the function's name says
+``colon,'' it actually uses the value of @code{path-separator}.
+
+@example
+(parse-colon-path ":/foo:/bar")
+ @result{} (nil "/foo/" "/bar/")
+@end example
+@end defun
+
@defvar invocation-name
This variable holds the program name under which Emacs was invoked. The
value is a string, and does not include a directory name.
containing the Emacs executable.
@end defvar
-@defun load-average
-This function returns the current 1-minute, 5-minute and 15-minute
-load averages in a list. The values are integers that are 100 times
-the system load averages. (The load averages indicate the number of
-processes trying to run.)
+@defun load-average &optional use-float
+This function returns the current 1-minute, 5-minute, and 15-minute load
+averages, in a list.
+
+By default, the values are integers that are 100 times the system load
+averages, which indicate the average number of processes trying to run.
+If @var{use-float} is non-@code{nil}, then they are returned
+as floating point numbers and without multiplying by 100.
+
+If it is impossible to obtain the load average, this function signals
+an error. On some platforms, access to load averages requires
+installing Emacs as setuid or setgid so that it can read kernel
+information, and that usually isn't advisable.
+
+If the 1-minute load average is available, but the 5- or 15-minute
+averages are not, this function returns a shortened list containing
+the available averages.
@example
@group
(load-average)
@result{} (169 48 36)
@end group
+@group
+(load-average t)
+ @result{} (1.69 0.48 0.36)
+@end group
@group
lewis@@rocky[5] % uptime
@end defun
@defun emacs-pid
-This function returns the process @sc{id} of the Emacs process.
+This function returns the process @acronym{ID} of the Emacs process,
+as an integer.
@end defun
+@defvar tty-erase-char
+This variable holds the erase character that was selected
+in the system's terminal driver, before Emacs was started.
+The value is @code{nil} if Emacs is running under a window system.
+@end defvar
+
@defun setprv privilege-name &optional setp getprv
This function sets or resets a VMS privilege. (It does not exist on
-Unix.) The first arg is the privilege name, as a string. The second
-argument, @var{setp}, is @code{t} or @code{nil}, indicating whether the
-privilege is to be turned on or off. Its default is @code{nil}. The
-function returns @code{t} if successful, @code{nil} otherwise.
+other systems.) The first argument is the privilege name, as a string.
+The second argument, @var{setp}, is @code{t} or @code{nil}, indicating
+whether the privilege is to be turned on or off. Its default is
+@code{nil}. The function returns @code{t} if successful, @code{nil}
+otherwise.
- If the third argument, @var{getprv}, is non-@code{nil}, @code{setprv}
+If the third argument, @var{getprv}, is non-@code{nil}, @code{setprv}
does not change the privilege, but returns @code{t} or @code{nil}
indicating whether the privilege is currently enabled.
@end defun
@node User Identification
@section User Identification
+@cindex user identification
+
+@defvar init-file-user
+This variable says which user's init files should be used by
+Emacs---or @code{nil} if none. @code{""} stands for the user who
+originally logged in. The value reflects command-line options such as
+@samp{-q} or @samp{-u @var{user}}.
+
+Lisp packages that load files of customizations, or any other sort of
+user profile, should obey this variable in deciding where to find it.
+They should load the profile of the user name found in this variable.
+If @code{init-file-user} is @code{nil}, meaning that the @samp{-q}
+option was used, then Lisp packages should not load any customization
+files or user profile.
+@end defvar
@defvar user-mail-address
This holds the nominal email address of the user who is using Emacs.
Emacs normally sets this variable to a default value after reading your
init files, but not if you have already set it. So you can set the
-variable to some other value in your @file{~/.emacs} file if you do not
+variable to some other value in your init file if you do not
want to use the default value.
@end defvar
which the user is logged in. If the environment variable @code{LOGNAME}
is set, that value is used. Otherwise, if the environment variable
@code{USER} is set, that value is used. Otherwise, the value is based
-on the effective @sc{uid}, not the real @sc{uid}.
+on the effective @acronym{UID}, not the real @acronym{UID}.
If you specify @var{uid}, the value is the user name that corresponds
-to @var{uid} (which should be an integer).
+to @var{uid} (which should be an integer), or @code{nil} if there is
+no such user.
@example
@group
@defun user-real-login-name
This function returns the user name corresponding to Emacs's real
-@sc{uid}. This ignores the effective @sc{uid} and ignores the
+@acronym{UID}. This ignores the effective @acronym{UID} and ignores the
environment variables @code{LOGNAME} and @code{USER}.
@end defun
-@defun user-full-name
-This function returns the full name of the user.
+@defun user-full-name &optional uid
+This function returns the full name of the logged-in user---or the value
+of the environment variable @code{NAME}, if that is set.
+@c "Bil" is the correct spelling.
@example
@group
(user-full-name)
@result{} "Bil Lewis"
@end group
@end example
+
+If the Emacs job's user-id does not correspond to any known user (and
+provided @code{NAME} is not set), the value is @code{"unknown"}.
+
+If @var{uid} is non-@code{nil}, then it should be a number (a user-id)
+or a string (a login name). Then @code{user-full-name} returns the full
+name corresponding to that user-id or login name. If you specify a
+user-id or login name that isn't defined, it returns @code{nil}.
@end defun
@vindex user-full-name
Titles}).
@defun user-real-uid
-This function returns the real @sc{uid} of the user.
+This function returns the real @acronym{UID} of the user.
+The value may be a floating point number.
@example
@group
@end defun
@defun user-uid
-This function returns the effective @sc{uid} of the user.
+This function returns the effective @acronym{UID} of the user.
+The value may be a floating point number.
@end defun
@node Time of Day
zone.
@defun current-time-string &optional time-value
-This function returns the current time and date as a humanly-readable
+This function returns the current time and date as a human-readable
string. The format of the string is unvarying; the number of characters
used for each part is always the same, so you can reliably use
@code{substring} to extract pieces of it. It is wise to count the
characters from the beginning of the string rather than from the end, as
-additional information may be added at the end.
+additional information may some day be added at the end.
@c Emacs 19 feature
The argument @var{time-value}, if given, specifies a time to format
instead of the current time. The argument should be a list whose first
two elements are integers. Thus, you can use times obtained from
@code{current-time} (see below) and from @code{file-attributes}
-(@pxref{File Attributes}).
+(@pxref{Definition of file-attributes}). @var{time-value} can also be
+a cons of two integers, but this is considered obsolete.
@example
@group
This function returns the system's time value as a list of three
integers: @code{(@var{high} @var{low} @var{microsec})}. The integers
@var{high} and @var{low} combine to give the number of seconds since
-0:00 January 1, 1970, which is
-@ifinfo
+0:00 January 1, 1970 UTC (Coordinated Universal Time), which is
+@ifnottex
@var{high} * 2**16 + @var{low}.
-@end ifinfo
+@end ifnottex
@tex
$high*2^{16}+low$.
@end tex
The third element, @var{microsec}, gives the microseconds since the
-start of the current second (or 0 for systems that return time only on
-the resolution of a second).
+start of the current second (or 0 for systems that return time with
+the resolution of only one second).
The first two elements can be compared with file time values such as you
-get with the function @code{file-attributes}. @xref{File Attributes}.
+get with the function @code{file-attributes}.
+@xref{Definition of file-attributes}.
@end defun
@c Emacs 19 feature
The value has the form @code{(@var{offset} @var{name})}. Here
@var{offset} is an integer giving the number of seconds ahead of UTC
(east of Greenwich). A negative value means west of Greenwich. The
-second element, @var{name} is a string giving the name of the time
-zone. Both elements change when daylight savings time begins or ends;
+second element, @var{name}, is a string giving the name of the time
+zone. Both elements change when daylight saving time begins or ends;
if the user has specified a time zone that does not use a seasonal time
adjustment, then the value is constant through time.
If the operating system doesn't supply all the information necessary to
-compute the value, both elements of the list are @code{nil}.
+compute the value, the unknown elements of the list are @code{nil}.
The argument @var{time-value}, if given, specifies a time to analyze
-instead of the current time. The argument should be a cons cell
-containing two integers, or a list whose first two elements are
-integers. Thus, you can use times obtained from @code{current-time}
-(see above) and from @code{file-attributes} (@pxref{File Attributes}).
+instead of the current time. The argument should have the same form
+as for @code{current-time-string} (see above). Thus, you can use
+times obtained from @code{current-time} (see above) and from
+@code{file-attributes}. @xref{Definition of file-attributes}.
+@end defun
+
+@defun set-time-zone-rule tz
+This function specifies the local time zone according to @var{tz}. If
+@var{tz} is @code{nil}, that means to use an implementation-defined
+default time zone. If @var{tz} is @code{t}, that means to use
+Universal Time. Otherwise, @var{tz} should be a string specifying a
+time zone rule.
+@end defun
+
+@defun float-time &optional time-value
+This function returns the current time as a floating-point number of
+seconds since the epoch. The argument @var{time-value}, if given,
+specifies a time to convert instead of the current time. The argument
+should have the same form as for @code{current-time-string} (see
+above). Thus, it accepts the output of @code{current-time} and
+@code{file-attributes}.
+
+@emph{Warning}: Since the result is floating point, it may not be
+exact. Do not use this function if precise time stamps are required.
@end defun
@node Time Conversion
@section Time Conversion
These functions convert time values (lists of two or three integers)
-to strings or to calendrical information. There is also a function to
-convert calendrical information to a time value. You can get time
-values from the functions @code{current-time} (@pxref{Time of Day}) and
-@code{file-attributes} (@pxref{File Attributes}).
+to calendrical information and vice versa. You can get time values
+from the functions @code{current-time} (@pxref{Time of Day}) and
+@code{file-attributes} (@pxref{Definition of file-attributes}).
+
+ Many operating systems are limited to time values that contain 32 bits
+of information; these systems typically handle only the times from
+1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some
+operating systems have larger time values, and can represent times far
+in the past or future.
+
+ Time conversion functions always use the Gregorian calendar, even
+for dates before the Gregorian calendar was introduced. Year numbers
+count the number of years since the year 1 B.C., and do not skip zero
+as traditional Gregorian years do; for example, the year number
+@minus{}37 represents the Gregorian year 38 B.C@.
+
+@defun decode-time &optional time
+This function converts a time value into calendrical information. If
+you don't specify @var{time}, it decodes the current time. The return
+value is a list of nine elements, as follows:
-@defun format-time-string format-string time
-This function converts @var{time} to a string according to
-@var{format-string}. The argument @var{format-string} may contain
-@samp{%}-sequences which say to substitute parts of the time. Here is a
-table of what the @samp{%}-sequences mean:
+@example
+(@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
+@end example
+
+Here is what the elements mean:
+
+@table @var
+@item seconds
+The number of seconds past the minute, as an integer between 0 and 59.
+On some operating systems, this is 60 for leap seconds.
+@item minutes
+The number of minutes past the hour, as an integer between 0 and 59.
+@item hour
+The hour of the day, as an integer between 0 and 23.
+@item day
+The day of the month, as an integer between 1 and 31.
+@item month
+The month of the year, as an integer between 1 and 12.
+@item year
+The year, an integer typically greater than 1900.
+@item dow
+The day of week, as an integer between 0 and 6, where 0 stands for
+Sunday.
+@item dst
+@code{t} if daylight saving time is effect, otherwise @code{nil}.
+@item zone
+An integer indicating the time zone, as the number of seconds east of
+Greenwich.
+@end table
+
+@strong{Common Lisp Note:} Common Lisp has different meanings for
+@var{dow} and @var{zone}.
+@end defun
+
+@defun encode-time seconds minutes hour day month year &optional zone
+This function is the inverse of @code{decode-time}. It converts seven
+items of calendrical data into a time value. For the meanings of the
+arguments, see the table above under @code{decode-time}.
+
+Year numbers less than 100 are not treated specially. If you want them
+to stand for years above 1900, or years above 2000, you must alter them
+yourself before you call @code{encode-time}.
+
+The optional argument @var{zone} defaults to the current time zone and
+its daylight saving time rules. If specified, it can be either a list
+(as you would get from @code{current-time-zone}), a string as in the
+@code{TZ} environment variable, @code{t} for Universal Time, or an
+integer (as you would get from @code{decode-time}). The specified
+zone is used without any further alteration for daylight saving time.
+
+If you pass more than seven arguments to @code{encode-time}, the first
+six are used as @var{seconds} through @var{year}, the last argument is
+used as @var{zone}, and the arguments in between are ignored. This
+feature makes it possible to use the elements of a list returned by
+@code{decode-time} as the arguments to @code{encode-time}, like this:
+
+@example
+(apply 'encode-time (decode-time @dots{}))
+@end example
+
+You can perform simple date arithmetic by using out-of-range values for
+the @var{seconds}, @var{minutes}, @var{hour}, @var{day}, and @var{month}
+arguments; for example, day 0 means the day preceding the given month.
+
+The operating system puts limits on the range of possible time values;
+if you try to encode a time that is out of range, an error results.
+For instance, years before 1970 do not work on some systems;
+on others, years as early as 1901 do work.
+@end defun
+
+@node Time Parsing
+@section Parsing and Formatting Times
+
+ These functions convert time values (lists of two or three integers)
+to text in a string, and vice versa.
+
+@defun date-to-time string
+This function parses the time-string @var{string} and returns the
+corresponding time value.
+@end defun
+
+@defun format-time-string format-string &optional time universal
+This function converts @var{time} (or the current time, if @var{time} is
+omitted) to a string according to @var{format-string}. The argument
+@var{format-string} may contain @samp{%}-sequences which say to
+substitute parts of the time. Here is a table of what the
+@samp{%}-sequences mean:
@table @samp
@item %a
@item %H
This stands for the hour (00-23).
@item %I
-This stands for the hour (00-12).
+This stands for the hour (01-12).
@item %j
This stands for the day of the year (001-366).
@item %k
@item %R
This is a synonym for @samp{%H:%M}.
@item %S
-This stands for the seconds (00-60).
+This stands for the seconds (00-59).
@item %t
This stands for a tab character.
@item %T
This stands for the week of the year (01-52), assuming that weeks
start on Monday.
@item %x
-This has a locale-specific meaning. In the default locale (named C), it
-is equivalent to @samp{%D}.
+This has a locale-specific meaning. In the default locale (named
+@samp{C}), it is equivalent to @samp{%D}.
@item %X
-This has a locale-specific meaning. In the default locale (named C), it
-is equivalent to @samp{%T}.
+This has a locale-specific meaning. In the default locale (named
+@samp{C}), it is equivalent to @samp{%T}.
@item %y
This stands for the year without century (00-99).
@item %Y
This stands for the year with century.
@item %Z
-This stands for the time zone abbreviation.
+This stands for the time zone abbreviation (e.g., @samp{EST}).
+@item %z
+This stands for the time zone numerical offset (e.g., @samp{-0500}).
@end table
+
+You can also specify the field width and type of padding for any of
+these @samp{%}-sequences. This works as in @code{printf}: you write
+the field width as digits in the middle of a @samp{%}-sequences. If you
+start the field width with @samp{0}, it means to pad with zeros. If you
+start the field width with @samp{_}, it means to pad with spaces.
+
+For example, @samp{%S} specifies the number of seconds since the minute;
+@samp{%03S} means to pad this with zeros to 3 positions, @samp{%_3S} to
+pad with spaces to 3 positions. Plain @samp{%3S} pads with zeros,
+because that is how @samp{%S} normally pads to two positions.
+
+The characters @samp{E} and @samp{O} act as modifiers when used between
+@samp{%} and one of the letters in the table above. @samp{E} specifies
+using the current locale's ``alternative'' version of the date and time.
+In a Japanese locale, for example, @code{%Ex} might yield a date format
+based on the Japanese Emperors' reigns. @samp{E} is allowed in
+@samp{%Ec}, @samp{%EC}, @samp{%Ex}, @samp{%EX}, @samp{%Ey}, and
+@samp{%EY}.
+
+@samp{O} means to use the current locale's ``alternative''
+representation of numbers, instead of the ordinary decimal digits. This
+is allowed with most letters, all the ones that output numbers.
+
+If @var{universal} is non-@code{nil}, that means to describe the time as
+Universal Time; @code{nil} means describe it using what Emacs believes
+is the local time zone (see @code{current-time-zone}).
+
+This function uses the C library function @code{strftime}
+(@pxref{Formatting Calendar Time,,, libc, The GNU C Library Reference
+Manual}) to do most of the work. In order to communicate with that
+function, it first encodes its argument using the coding system
+specified by @code{locale-coding-system} (@pxref{Locales}); after
+@code{strftime} returns the resulting string,
+@code{format-time-string} decodes the string using that same coding
+system.
@end defun
-@defun decode-time time
-This function converts a time value into calendrical information. The
-return value is a list of nine elements, as follows:
+@defun seconds-to-time seconds
+This function converts @var{seconds}, a floating point number of
+seconds since the epoch, to a time value and returns that. To perform
+the inverse conversion, use @code{float-time}.
+@end defun
-@example
-(@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year} @var{dow} @var{dst} @var{zone})
-@end example
+@node Processor Run Time
+@section Processor Run time
+@cindex processor run time
-Here is what the elements mean:
+@defun get-internal-run-time
+This function returns the processor run time used by Emacs as a list
+of three integers: @code{(@var{high} @var{low} @var{microsec})}. The
+integers @var{high} and @var{low} combine to give the number of
+seconds, which is
+@ifnottex
+@var{high} * 2**16 + @var{low}.
+@end ifnottex
+@tex
+$high*2^{16}+low$.
+@end tex
-@table @var
-@item sec
-The number of seconds past the minute, as an integer between 0 and 59.
-@item minute
-The number of minutes past the hour, as an integer between 0 and 59.
-@item hour
-The hour of the day, as an integer between 0 and 23.
-@item day
-The day of the month, as an integer between 1 and 31.
-@item month
-The month of the year, as an integer between 1 and 12.
-@item year
-The year, an integer typically greater than 1900.
-@item dow
-The day of week, as an integer between 0 and 6, where 0 stands for
-Sunday.
-@item dst
-@code{t} if daylight savings time is effect, otherwise @code{nil}.
-@item zone
-An integer indicating the time zone, as the number of seconds east of
-Greenwich.
-@end table
+The third element, @var{microsec}, gives the microseconds (or 0 for
+systems that return time with the resolution of only one second).
-Note that Common Lisp has different meanings for @var{dow} and
-@var{zone}.
+If the system doesn't provide a way to determine the processor run
+time, get-internal-run-time returns the same time as current-time.
@end defun
-@defun encode-time seconds minutes hour day month year &optional zone
-This function is the inverse of @code{decode-time}. It converts seven
-items of calendrical data into a time value. For the meanings of the
-arguments, see the table above under @code{decode-time}.
+@node Time Calculations
+@section Time Calculations
-Year numbers less than 100 are treated just like other year numbers. If
-you want them to stand for years above 1900, you must alter them yourself
-before you call @code{encode-time}.
+ These functions perform calendrical computations using time values
+(the kind of list that @code{current-time} returns).
-The optional argument @var{zone} defaults to the current time zone and
-its daylight savings time rules. If specified, it can be either a list
-(as you would get from @code{current-time-zone}) or an integer (as you
-would get from @code{decode-time}). The specified zone is used without
-any further alteration for daylight savings time.
+@defun time-less-p t1 t2
+This returns @code{t} if time value @var{t1} is less than time value
+@var{t2}.
@end defun
-@node Timers
-@section Timers for Delayed Execution
+@defun time-subtract t1 t2
+This returns the time difference @var{t1} @minus{} @var{t2} between
+two time values, in the same format as a time value.
+@end defun
-You can set up a timer to call a function at a specified future time.
+@defun time-add t1 t2
+This returns the sum of two time values, one of which ought to
+represent a time difference rather than a point in time.
+Here is how to add a number of seconds to a time value:
-@defun run-at-time time repeat function &rest args
-This function arranges to call @var{function} with arguments @var{args}
-at time @var{time}. The argument @var{function} is a function to call
-later, and @var{args} are the arguments to give it when it is called.
-The time @var{time} is specified as a string.
+@example
+(time-add @var{time} (seconds-to-time @var{seconds}))
+@end example
+@end defun
-Absolute times may be specified in a wide variety of formats; The form
-@samp{@var{hour}:@var{min}:@var{sec} @var{timezone}
-@var{month}/@var{day}/@var{year}}, where all fields are numbers, works;
-the format that @code{current-time-string} returns is also allowed.
+@defun time-to-days time
+This function returns the number of days between the beginning of year
+1 and @var{time}.
+@end defun
-To specify a relative time, use numbers followed by units.
+@defun time-to-day-in-year time
+This returns the day number within the year corresponding to @var{time}.
+@end defun
+
+@defun date-leap-year-p year
+This function returns @code{t} if @var{year} is a leap year.
+@end defun
+
+@node Timers
+@section Timers for Delayed Execution
+@cindex timer
+
+ You can set up a @dfn{timer} to call a function at a specified
+future time or after a certain length of idleness.
+
+ Emacs cannot run timers at any arbitrary point in a Lisp program; it
+can run them only when Emacs could accept output from a subprocess:
+namely, while waiting or inside certain primitive functions such as
+@code{sit-for} or @code{read-event} which @emph{can} wait. Therefore, a
+timer's execution may be delayed if Emacs is busy. However, the time of
+execution is very precise if Emacs is idle.
+
+ Emacs binds @code{inhibit-quit} to @code{t} before calling the timer
+function, because quitting out of many timer functions can leave
+things in an inconsistent state. This is normally unproblematical
+because most timer functions don't do a lot of work. Indeed, for a
+timer to call a function that takes substantial time to run is likely
+to be annoying. If a timer function needs to allow quitting, it
+should use @code{with-local-quit} (@pxref{Quitting}). For example, if
+a timer function calls @code{accept-process-output} to receive output
+from an external process, that call should be wrapped inside
+@code{with-local-quit}, to ensure that @kbd{C-g} works if the external
+process hangs.
+
+ It is usually a bad idea for timer functions to alter buffer
+contents. When they do, they usually should call @code{undo-boundary}
+both before and after changing the buffer, to separate the timer's
+changes from user commands' changes and prevent a single undo entry
+from growing to be quite large.
+
+ Timer functions should also avoid calling functions that cause Emacs
+to wait, such as @code{sit-for} (@pxref{Waiting}). This can lead to
+unpredictable effects, since other timers (or even the same timer) can
+run while waiting. If a timer function needs to perform an action
+after a certain time has elapsed, it can do this by scheduling a new
+timer.
+
+ If a timer function calls functions that can change the match data,
+it should save and restore the match data. @xref{Saving Match Data}.
+
+@deffn Command run-at-time time repeat function &rest args
+This sets up a timer that calls the function @var{function} with
+arguments @var{args} at time @var{time}. If @var{repeat} is a number
+(integer or floating point), the timer is scheduled to run again every
+@var{repeat} seconds after @var{time}. If @var{repeat} is @code{nil},
+the timer runs only once.
+
+@var{time} may specify an absolute or a relative time.
+
+Absolute times may be specified using a string with a limited variety
+of formats, and are taken to be times @emph{today}, even if already in
+the past. The recognized forms are @samp{@var{xxxx}},
+@samp{@var{x}:@var{xx}}, or @samp{@var{xx}:@var{xx}} (military time),
+and @samp{@var{xx}am}, @samp{@var{xx}AM}, @samp{@var{xx}pm},
+@samp{@var{xx}PM}, @samp{@var{xx}:@var{xx}am},
+@samp{@var{xx}:@var{xx}AM}, @samp{@var{xx}:@var{xx}pm}, or
+@samp{@var{xx}:@var{xx}PM}. A period can be used instead of a colon
+to separate the hour and minute parts.
+
+To specify a relative time as a string, use numbers followed by units.
For example:
@table @samp
denotes exactly 103 months, 123 days, and 10862 seconds from now.
@end table
-If @var{time} is an integer, that specifies a relative time measured in
-seconds.
+For relative time values, Emacs considers a month to be exactly thirty
+days, and a year to be exactly 365.25 days.
+
+Not all convenient formats are strings. If @var{time} is a number
+(integer or floating point), that specifies a relative time measured in
+seconds. The result of @code{encode-time} can also be used to specify
+an absolute value for @var{time}.
-The argument @var{repeat} specifies how often to repeat the call. If
-@var{repeat} is @code{nil}, there are no repetitions; @var{function} is
-called just once, at @var{time}. If @var{repeat} is an integer, it
-specifies a repetition period measured in seconds. In any case, @var{repeat}
-has no effect on when @emph{first} call takes place---@var{time} specifies
-that.
+In most cases, @var{repeat} has no effect on when @emph{first} call
+takes place---@var{time} alone specifies that. There is one exception:
+if @var{time} is @code{t}, then the timer runs whenever the time is a
+multiple of @var{repeat} seconds after the epoch. This is useful for
+functions like @code{display-time}.
The function @code{run-at-time} returns a timer value that identifies
the particular scheduled future action. You can use this value to call
-@code{cancel-timer}.
-@end defun
+@code{cancel-timer} (see below).
+@end deffn
+
+ A repeating timer nominally ought to run every @var{repeat} seconds,
+but remember that any invocation of a timer can be late. Lateness of
+one repetition has no effect on the scheduled time of the next
+repetition. For instance, if Emacs is busy computing for long enough
+to cover three scheduled repetitions of the timer, and then starts to
+wait, it will immediately call the timer function three times in
+immediate succession (presuming no other timers trigger before or
+between them). If you want a timer to run again no less than @var{n}
+seconds after the last invocation, don't use the @var{repeat} argument.
+Instead, the timer function should explicitly reschedule the timer.
+
+@defvar timer-max-repeats
+This variable's value specifies the maximum number of times to repeat
+calling a timer function in a row, when many previously scheduled
+calls were unavoidably delayed.
+@end defvar
+
+@defmac with-timeout (seconds timeout-forms@dots{}) body@dots{}
+Execute @var{body}, but give up after @var{seconds} seconds. If
+@var{body} finishes before the time is up, @code{with-timeout} returns
+the value of the last form in @var{body}. If, however, the execution of
+@var{body} is cut short by the timeout, then @code{with-timeout}
+executes all the @var{timeout-forms} and returns the value of the last
+of them.
+
+This macro works by setting a timer to run after @var{seconds} seconds. If
+@var{body} finishes before that time, it cancels the timer. If the
+timer actually runs, it terminates execution of @var{body}, then
+executes @var{timeout-forms}.
+
+Since timers can run within a Lisp program only when the program calls a
+primitive that can wait, @code{with-timeout} cannot stop executing
+@var{body} while it is in the midst of a computation---only when it
+calls one of those primitives. So use @code{with-timeout} only with a
+@var{body} that waits for input, not one that does a long computation.
+@end defmac
+
+ The function @code{y-or-n-p-with-timeout} provides a simple way to use
+a timer to avoid waiting too long for an answer. @xref{Yes-or-No
+Queries}.
@defun cancel-timer timer
-Cancel the requested action for @var{timer}, which should be a value
-previously returned by @code{run-at-time}. This cancels the effect of
-that call to @code{run-at-time}; the arrival of the specified time will
-not cause anything special to happen.
+This cancels the requested action for @var{timer}, which should be a
+timer---usually, one previously returned by @code{run-at-time} or
+@code{run-with-idle-timer}. This cancels the effect of that call to
+one of these functions; the arrival of the specified time will not
+cause anything special to happen.
+@end defun
+
+@node Idle Timers
+@section Idle Timers
+
+ Here is how to set up a timer that runs when Emacs is idle for a
+certain length of time. Aside from how to set them up, idle timers
+work just like ordinary timers.
+
+@deffn Command run-with-idle-timer secs repeat function &rest args
+Set up a timer which runs when Emacs has been idle for @var{secs}
+seconds. The value of @var{secs} may be an integer or a floating point
+number; a value of the type returned by @code{current-idle-time}
+is also allowed.
+
+If @var{repeat} is @code{nil}, the timer runs just once, the first time
+Emacs remains idle for a long enough time. More often @var{repeat} is
+non-@code{nil}, which means to run the timer @emph{each time} Emacs
+remains idle for @var{secs} seconds.
+
+The function @code{run-with-idle-timer} returns a timer value which you
+can use in calling @code{cancel-timer} (@pxref{Timers}).
+@end deffn
+
+@cindex idleness
+ Emacs becomes ``idle'' when it starts waiting for user input, and it
+remains idle until the user provides some input. If a timer is set for
+five seconds of idleness, it runs approximately five seconds after Emacs
+first becomes idle. Even if @var{repeat} is non-@code{nil}, this timer
+will not run again as long as Emacs remains idle, because the duration
+of idleness will continue to increase and will not go down to five
+seconds again.
+
+ Emacs can do various things while idle: garbage collect, autosave or
+handle data from a subprocess. But these interludes during idleness do
+not interfere with idle timers, because they do not reset the clock of
+idleness to zero. An idle timer set for 600 seconds will run when ten
+minutes have elapsed since the last user command was finished, even if
+subprocess output has been accepted thousands of times within those ten
+minutes, and even if there have been garbage collections and autosaves.
+
+ When the user supplies input, Emacs becomes non-idle while executing the
+input. Then it becomes idle again, and all the idle timers that are
+set up to repeat will subsequently run another time, one by one.
+
+@c Emacs 19 feature
+@defun current-idle-time
+If Emacs is idle, this function returns the length of time Emacs has
+been idle, as a list of three integers: @code{(@var{high} @var{low}
+@var{microsec})}. The integers @var{high} and @var{low} combine to
+give the number of seconds of idleness, which is
+@ifnottex
+@var{high} * 2**16 + @var{low}.
+@end ifnottex
+@tex
+$high*2^{16}+low$.
+@end tex
+
+The third element, @var{microsec}, gives the microseconds since the
+start of the current second (or 0 for systems that return time with
+the resolution of only one second).
+
+When Emacs is not idle, @code{current-idle-time} returns @code{nil}.
+This is a convenient way to test whether Emacs is idle.
+
+The main use of this function is when an idle timer function wants to
+``take a break'' for a while. It can set up another idle timer to
+call the same function again, after a few seconds more idleness.
+Here's an example:
+
+@smallexample
+(defvar resume-timer nil
+ "Timer that `timer-function' used to reschedule itself, or nil.")
+
+(defun timer-function ()
+ ;; @r{If the user types a command while @code{resume-timer}}
+ ;; @r{is active, the next time this function is called from}
+ ;; @r{its main idle timer, deactivate @code{resume-timer}.}
+ (when resume-timer
+ (cancel-timer resume-timer))
+ ...@var{do the work for a while}...
+ (when @var{taking-a-break}
+ (setq resume-timer
+ (run-with-idle-timer
+ ;; Compute an idle time @var{break-length}
+ ;; more than the current value.
+ (time-add (current-idle-time)
+ (seconds-to-time @var{break-length}))
+ nil
+ 'timer-function))))
+@end smallexample
@end defun
+ Some idle timer functions in user Lisp packages have a loop that
+does a certain amount of processing each time around, and exits when
+@code{(input-pending-p)} is non-@code{nil}. That approach seems very
+natural but has two problems:
+
+@itemize
+@item
+It blocks out all process output (since Emacs accepts process output
+only while waiting).
+
+@item
+It blocks out any idle timers that ought to run during that time.
+@end itemize
+
+@noindent
+To avoid these problems, don't use that technique. Instead, write
+such idle timers to reschedule themselves after a brief pause, using
+the method in the @code{timer-function} example above.
+
@node Terminal Input
@section Terminal Input
@cindex terminal input
@menu
* Input Modes:: Options for how input is processed.
-* Translating Input:: Low level conversion of some characters or events
- into others.
* Recording Input:: Saving histories of recent or all input events.
@end menu
@cindex input modes
@cindex terminal input modes
-@defun set-input-mode interrupt flow meta quit-char
+@defun set-input-mode interrupt flow meta &optional quit-char
This function sets the mode for reading keyboard input. If
@var{interrupt} is non-null, then Emacs uses input interrupts. If it is
-@code{nil}, then it uses @sc{cbreak} mode. When Emacs communicates
-directly with X, it ignores this argument and uses interrupts if that is
-the way it knows how to communicate.
+@code{nil}, then it uses @sc{cbreak} mode. The default setting is
+system-dependent. Some systems always use @sc{cbreak} mode regardless
+of what is specified.
-If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff} (@kbd{C-q},
-@kbd{C-s}) flow control for output to the terminal. This has no effect except
-in @sc{cbreak} mode. @xref{Flow Control}.
+When Emacs communicates directly with X, it ignores this argument and
+uses interrupts if that is the way it knows how to communicate.
-The default setting is system dependent. Some systems always use
-@sc{cbreak} mode regardless of what is specified.
+If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff}
+(@kbd{C-q}, @kbd{C-s}) flow control for output to the terminal. This
+has no effect except in @sc{cbreak} mode.
@c Emacs 19 feature
The argument @var{meta} controls support for input character codes
Emacs disregards the 8th bit; this is necessary when the terminal uses
it as a parity bit. If @var{meta} is neither @code{t} nor @code{nil},
Emacs uses all 8 bits of input unchanged. This is good for terminals
-using European 8-bit character sets.
+that use 8-bit character sets.
@c Emacs 19 feature
If @var{quit-char} is non-@code{nil}, it specifies the character to
@c Emacs 19 feature
@defun current-input-mode
-This function returns current mode for reading keyboard input. It
+This function returns the current mode for reading keyboard input. It
returns a list, corresponding to the arguments of @code{set-input-mode},
of the form @code{(@var{interrupt} @var{flow} @var{meta} @var{quit})} in
which:
@code{nil}, Emacs is using @sc{cbreak} mode.
@item flow
is non-@code{nil} if Emacs uses @sc{xon/xoff} (@kbd{C-q}, @kbd{C-s})
-flow control for output to the terminal. This value has no effect
-unless @var{interrupt} is non-@code{nil}.
+flow control for output to the terminal. This value is meaningful only
+when @var{interrupt} is @code{nil}.
@item meta
is @code{t} if Emacs treats the eighth bit of input characters as
the meta bit; @code{nil} means Emacs clears the eighth bit of every
@end table
@end defun
-@node Translating Input
-@subsection Translating Input Events
-@cindex translating input events
-
- This section describes features for translating input events into other
-input events before they become part of key sequences.
-
-@c Emacs 19 feature
-@defvar extra-keyboard-modifiers
-This variable lets Lisp programs ``press'' the modifier keys on the
-keyboard. The value is a bit mask:
-
-@table @asis
-@item 1
-The @key{SHIFT} key.
-@item 2
-The @key{LOCK} key.
-@item 4
-The @key{CTL} key.
-@item 8
-The @key{META} key.
-@end table
-
-Each time the user types a keyboard key, it is altered as if the
-modifier keys specified in the bit mask were held down.
-
-When using X windows, the program can ``press'' any of the modifier
-keys in this way. Otherwise, only the @key{CTL} and @key{META} keys can
-be virtually pressed.
-@end defvar
-
-@defvar keyboard-translate-table
-This variable is the translate table for keyboard characters. It lets
-you reshuffle the keys on the keyboard without changing any command
-bindings. Its value must be a string or @code{nil}.
-
-If @code{keyboard-translate-table} is a string, then each character read
-from the keyboard is looked up in this string and the character in the
-string is used instead. If the string is of length @var{n}, character codes
-@var{n} and up are untranslated.
-
-In the example below, we set @code{keyboard-translate-table} to a
-string of 128 characters. Then we fill it in to swap the characters
-@kbd{C-s} and @kbd{C-\} and the characters @kbd{C-q} and @kbd{C-^}.
-Subsequently, typing @kbd{C-\} has all the usual effects of typing
-@kbd{C-s}, and vice versa. (@xref{Flow Control} for more information on
-this subject.)
-
-@cindex flow control example
-@example
-@group
-(defun evade-flow-control ()
- "Replace C-s with C-\ and C-q with C-^."
- (interactive)
-@end group
-@group
- (let ((the-table (make-string 128 0)))
- (let ((i 0))
- (while (< i 128)
- (aset the-table i i)
- (setq i (1+ i))))
-@end group
- ;; @r{Swap @kbd{C-s} and @kbd{C-\}.}
- (aset the-table ?\034 ?\^s)
- (aset the-table ?\^s ?\034)
-@group
- ;; @r{Swap @kbd{C-q} and @kbd{C-^}.}
- (aset the-table ?\036 ?\^q)
- (aset the-table ?\^q ?\036)
- (setq keyboard-translate-table the-table)))
-@end group
-@end example
-
-Note that this translation is the first thing that happens to a
-character after it is read from the terminal. Record-keeping features
-such as @code{recent-keys} and dribble files record the characters after
-translation.
-@end defvar
-
-@defun keyboard-translate from to
-This function modifies @code{keyboard-translate-table} to translate
-character code @var{from} into character code @var{to}. It creates
-or enlarges the translate table if necessary.
-@end defun
-
-@defvar function-key-map
-This variable holds a keymap that describes the character sequences
-sent by function keys on an ordinary character terminal. This keymap
-uses the same data structure as other keymaps, but is used differently: it
-specifies translations to make while reading events.
-
-If @code{function-key-map} ``binds'' a key sequence @var{k} to a vector
-@var{v}, then when @var{k} appears as a subsequence @emph{anywhere} in a
-key sequence, it is replaced with the events in @var{v}.
-
-For example, VT100 terminals send @kbd{@key{ESC} O P} when the
-keypad PF1 key is pressed. Therefore, we want Emacs to translate
-that sequence of events into the single event @code{pf1}. We accomplish
-this by ``binding'' @kbd{@key{ESC} O P} to @code{[pf1]} in
-@code{function-key-map}, when using a VT100.
-
-Thus, typing @kbd{C-c @key{PF1}} sends the character sequence @kbd{C-c
-@key{ESC} O P}; later the function @code{read-key-sequence} translates
-this back into @kbd{C-c @key{PF1}}, which it returns as the vector
-@code{[?\C-c pf1]}.
-
-Entries in @code{function-key-map} are ignored if they conflict with
-bindings made in the minor mode, local, or global keymaps. The intent
-is that the character sequences that function keys send should not have
-command bindings in their own right.
-
-The value of @code{function-key-map} is usually set up automatically
-according to the terminal's Terminfo or Termcap entry, but sometimes
-those need help from terminal-specific Lisp files. Emacs comes with
-terminal-specific files for many common terminals; their main purpose is
-to make entries in @code{function-key-map} beyond those that can be
-deduced from Termcap and Terminfo. @xref{Terminal-Specific}.
-
-Emacs versions 18 and earlier used totally different means of detecting
-the character sequences that represent function keys.
-@end defvar
-
-@defvar key-translation-map
-This variable is another keymap used just like @code{function-key-map}
-to translate input events into other events. It differs from
-@code{function-key-map} in two ways:
-
-@itemize @bullet
-@item
-@code{key-translation-map} goes to work after @code{function-key-map} is
-finished; it receives the results of translation by
-@code{function-key-map}.
-
-@item
-@code{key-translation-map} overrides actual key bindings.
-@end itemize
-
-The intent of @code{key-translation-map} is for users to map one
-character set to another, including ordinary characters normally bound
-to @code{self-insert-command}.
-@end defvar
-
-@cindex key translation function
-You can use @code{function-key-map} or @code{key-translation-map} for
-more than simple aliases, by using a function, instead of a key
-sequence, as the ``translation'' of a key. Then this function is called
-to compute the translation of that key.
-
-The key translation function receives one argument, which is the prompt
-that was specified in @code{read-key-sequence}---or @code{nil} if the
-key sequence is being read by the editor command loop. In most cases
-you can ignore the prompt value.
-
-If the function reads input itself, it can have the effect of altering
-the event that follows. For example, here's how to define @kbd{C-c h}
-to turn the character that follows into a Hyper character:
-
-@example
-@group
-(defun hyperify (prompt)
- (let ((e (read-event)))
- (vector (if (numberp e)
- (logior (lsh 1 20) e)
- (if (memq 'hyper (event-modifiers e))
- e
- (add-event-modifier "H-" e))))))
-
-(defun add-event-modifier (string e)
- (let ((symbol (if (symbolp e) e (car e))))
- (setq symbol (intern (concat string
- (symbol-name symbol))))
-@end group
-@group
- (if (symbolp e)
- symbol
- (cons symbol (cdr e)))))
-
-(define-key function-key-map "\C-ch" 'hyperify)
-@end group
-@end example
-
-@pindex iso-transl
-@cindex Latin-1 character set (input)
-@cindex ISO Latin-1 characters (input)
-The @file{iso-transl} library uses this feature to provide a way of
-inputting non-ASCII Latin-1 characters.
-
@node Recording Input
@subsection Recording Input
+@cindex recording input
@defun recent-keys
-This function returns a vector containing the last 100 input events
-from the keyboard or mouse. All input events are included, whether or
-not they were used as parts of key sequences. Thus, you always get the
-last 100 inputs, not counting keyboard macros. (Events from keyboard
-macros are excluded because they are less interesting for debugging; it
+This function returns a vector containing the last 300 input events from
+the keyboard or mouse. All input events are included, whether or not
+they were used as parts of key sequences. Thus, you always get the last
+100 input events, not counting events generated by keyboard macros.
+(These are excluded because they are less interesting for debugging; it
should be enough to see the events that invoked the macros.)
+
+A call to @code{clear-this-command-keys} (@pxref{Command Loop Info})
+causes this function to return an empty vector immediately afterward.
@end defun
-@deffn Command open-dribble-file filename
+@deffn Command open-dribble-file filename
@cindex dribble file
This function opens a @dfn{dribble file} named @var{filename}. When a
dribble file is open, each input event from the keyboard or mouse (but
@section Terminal Output
@cindex terminal output
- The terminal output functions send output to the terminal or keep
+ The terminal output functions send output to a text terminal, or keep
track of output sent to the terminal. The variable @code{baud-rate}
tells you what Emacs thinks is the output speed of the terminal.
This variable's value is the output speed of the terminal, as far as
Emacs knows. Setting this variable does not change the speed of actual
data transmission, but the value is used for calculations such as
-padding. It also affects decisions about whether to scroll part of the
-screen or repaint---even when using a window system. (We designed it
-this way despite the fact that a window system has no true ``output
-speed'', to give you a way to tune these decisions.)
+padding.
+
+ It also affects decisions about whether to scroll part of the
+screen or repaint on text terminals. @xref{Forcing Redisplay},
+for the corresponding functionality on graphical terminals.
The value is measured in baud.
@end defvar
than optimal. To fix the problem, set @code{baud-rate}.
@defun baud-rate
-This function returns the value of the variable @code{baud-rate}. In
-Emacs versions 18 and earlier, this was the only way to find out the
-terminal speed.
+This obsolete function returns the value of the variable
+@code{baud-rate}.
@end defun
@defun send-string-to-terminal string
This function sends @var{string} to the terminal without alteration.
Control characters in @var{string} have terminal-dependent effects.
+This function operates only on text terminals.
One use of this function is to define function keys on terminals that
-have downloadable function key definitions. For example, this is how on
-certain terminals to define function key 4 to move forward four
+have downloadable function key definitions. For example, this is how (on
+certain terminals) to define function key 4 to move forward four
characters (by transmitting the characters @kbd{C-u C-f} to the
computer):
were actually output, you can determine reliably whether they correspond
to the Termcap specifications in use.
-See also @code{open-dribble-file} in @ref{Terminal Input}.
+You close the termscript file by calling this function with an
+argument of @code{nil}.
+
+See also @code{open-dribble-file} in @ref{Recording Input}.
@example
@group
@end example
@end deffn
-@node Special Keysyms
-@section System-Specific X11 Keysyms
+@node Sound Output
+@section Sound Output
+@cindex sound
-To define system-specific X11 keysyms, set the variable
-@code{system-key-alist}.
+ To play sound using Emacs, use the function @code{play-sound}. Only
+certain systems are supported; if you call @code{play-sound} on a system
+which cannot really do the job, it gives an error. Emacs version 20 and
+earlier did not support sound at all.
-@defvar system-key-alist
-This variable's value should be an alist with one element for each
-system-specific keysym. An element has this form: @code{(@var{code}
-. @var{symbol})}, where @var{code} is the numeric keysym code (not
-including the ``vendor specific'' bit, 1 << 28), and @var{symbol} is the
-name for the function key.
+ The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
+or Sun Audio format (@samp{.au}).
-For example @code{(168 . mute-acute)} defines a system-specific key used
-by HP X servers whose numeric code is (1 << 28) + 168.
+@defun play-sound sound
+This function plays a specified sound. The argument, @var{sound}, has
+the form @code{(sound @var{properties}...)}, where the @var{properties}
+consist of alternating keywords (particular symbols recognized
+specially) and values corresponding to them.
-It is not a problem if the alist defines keysyms for other X servers, as
-long as they don't conflict with the ones used by the X server actually
-in use.
+Here is a table of the keywords that are currently meaningful in
+@var{sound}, and their meanings:
-The variable is always local to the current X terminal and cannot be
-buffer-local. @xref{Multiple Displays}.
-@end defvar
+@table @code
+@item :file @var{file}
+This specifies the file containing the sound to play.
+If the file name is not absolute, it is expanded against
+the directory @code{data-directory}.
+
+@item :data @var{data}
+This specifies the sound to play without need to refer to a file. The
+value, @var{data}, should be a string containing the same bytes as a
+sound file. We recommend using a unibyte string.
+
+@item :volume @var{volume}
+This specifies how loud to play the sound. It should be a number in the
+range of 0 to 1. The default is to use whatever volume has been
+specified before.
+
+@item :device @var{device}
+This specifies the system device on which to play the sound, as a
+string. The default device is system-dependent.
+@end table
+
+Before actually playing the sound, @code{play-sound}
+calls the functions in the list @code{play-sound-functions}.
+Each function is called with one argument, @var{sound}.
+@end defun
-@node Flow Control
-@section Flow Control
-@cindex flow control characters
-
- This section attempts to answer the question ``Why does Emacs choose
-to use flow-control characters in its command character set?'' For a
-second view on this issue, read the comments on flow control in the
-@file{emacs/INSTALL} file from the distribution; for help with Termcap
-entries and DEC terminal concentrators, see @file{emacs/etc/TERMS}.
-
-@cindex @kbd{C-s}
-@cindex @kbd{C-q}
- At one time, most terminals did not need flow control, and none used
-@code{C-s} and @kbd{C-q} for flow control. Therefore, the choice of
-@kbd{C-s} and @kbd{C-q} as command characters was uncontroversial.
-Emacs, for economy of keystrokes and portability, used nearly all the
-@sc{ASCII} control characters, with mnemonic meanings when possible;
-thus, @kbd{C-s} for search and @kbd{C-q} for quote.
-
- Later, some terminals were introduced which required these characters
-for flow control. They were not very good terminals for full-screen
-editing, so Emacs maintainers did not pay attention. In later years,
-flow control with @kbd{C-s} and @kbd{C-q} became widespread among
-terminals, but by this time it was usually an option. And the majority
-of users, who can turn flow control off, were unwilling to switch to
-less mnemonic key bindings for the sake of flow control.
-
- So which usage is ``right'', Emacs's or that of some terminal and
-concentrator manufacturers? This question has no simple answer.
-
- One reason why we are reluctant to cater to the problems caused by
-@kbd{C-s} and @kbd{C-q} is that they are gratuitous. There are other
-techniques (albeit less common in practice) for flow control that
-preserve transparency of the character stream. Note also that their use
-for flow control is not an official standard. Interestingly, on the
-model 33 teletype with a paper tape punch (which is very old), @kbd{C-s}
-and @kbd{C-q} were sent by the computer to turn the punch on and off!
-
- As X servers and other window systems replace character-only
-terminals, this problem is gradually being cured. For the mean time,
-Emacs provides a convenient way of enabling flow control if you want it:
-call the function @code{enable-flow-control}.
-
-@defun enable-flow-control
-This function enables use of @kbd{C-s} and @kbd{C-q} for output flow
-control, and provides the characters @kbd{C-\} and @kbd{C-^} as aliases
-for them using @code{keyboard-translate-table} (@pxref{Translating Input}).
+@defun play-sound-file file &optional volume device
+This function is an alternative interface to playing a sound @var{file}
+specifying an optional @var{volume} and @var{device}.
@end defun
-You can use the function @code{enable-flow-control-on} in your
-@file{.emacs} file to enable flow control automatically on certain
-terminal types.
+@defvar play-sound-functions
+A list of functions to be called before playing a sound. Each function
+is called with one argument, a property list that describes the sound.
+@end defvar
-@defun enable-flow-control-on &rest termtypes
-This function enables flow control, and the aliases @kbd{C-\} and @kbd{C-^},
-if the terminal type is one of @var{termtypes}. For example:
+@node X11 Keysyms
+@section Operating on X11 Keysyms
+@cindex X11 keysyms
-@smallexample
-(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
-@end smallexample
-@end defun
+To define system-specific X11 keysyms, set the variable
+@code{system-key-alist}.
- Here is how @code{enable-flow-control} does its job:
+@defvar system-key-alist
+This variable's value should be an alist with one element for each
+system-specific keysym. Each element has the form @code{(@var{code}
+. @var{symbol})}, where @var{code} is the numeric keysym code (not
+including the ``vendor specific'' bit,
+@ifnottex
+-2**28),
+@end ifnottex
+@tex
+$-2^{28}$),
+@end tex
+and @var{symbol} is the name for the function key.
-@enumerate
-@item
-@cindex @sc{cbreak}
-It sets @sc{cbreak} mode for terminal input, and tells the operating
-system to handle flow control, with @code{(set-input-mode nil t)}.
+For example @code{(168 . mute-acute)} defines a system-specific key (used
+by HP X servers) whose numeric code is
+@ifnottex
+-2**28
+@end ifnottex
+@tex
+$-2^{28}$
+@end tex
++ 168.
-@item
-It sets up @code{keyboard-translate-table} to translate @kbd{C-\} and
-@kbd{C-^} into @kbd{C-s} and @kbd{C-q}. Except at its very
-lowest level, Emacs never knows that the characters typed were anything
-but @kbd{C-s} and @kbd{C-q}, so you can in effect type them as @kbd{C-\}
-and @kbd{C-^} even when they are input for other commands.
-@xref{Translating Input}.
-@end enumerate
+It is not crucial to exclude from the alist the keysyms of other X
+servers; those do no harm, as long as they don't conflict with the ones
+used by the X server actually in use.
-If the terminal is the source of the flow control characters, then once
-you enable kernel flow control handling, you probably can make do with
-less padding than normal for that terminal. You can reduce the amount
-of padding by customizing the Termcap entry. You can also reduce it by
-setting @code{baud-rate} to a smaller value so that Emacs uses a smaller
-speed when calculating the padding needed. @xref{Terminal Output}.
+The variable is always local to the current terminal, and cannot be
+buffer-local. @xref{Multiple Displays}.
+@end defvar
+
+You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
+
+@defvar x-alt-keysym
+@defvarx x-meta-keysym
+@defvarx x-hyper-keysym
+@defvarx x-super-keysym
+The name of the keysym that should stand for the Alt modifier
+(respectively, for Meta, Hyper, and Super). For example, here is
+how to swap the Meta and Alt modifiers within Emacs:
+@lisp
+(setq x-alt-keysym 'meta)
+(setq x-meta-keysym 'alt)
+@end lisp
+@end defvar
@node Batch Mode
@section Batch Mode
@cindex batch mode
-@cindex noninteractive use
- The command line option @samp{-batch} causes Emacs to run
+ The command-line option @samp{-batch} causes Emacs to run
noninteractively. In this mode, Emacs does not read commands from the
terminal, it does not alter the terminal modes, and it does not expect
to be outputting to an erasable screen. The idea is that you specify
Lisp programs to run; when they are finished, Emacs should exit. The
way to specify the programs to run is with @samp{-l @var{file}}, which
-loads the library named @var{file}, and @samp{-f @var{function}}, which
-calls @var{function} with no arguments.
+loads the library named @var{file}, or @samp{-f @var{function}}, which
+calls @var{function} with no arguments, or @samp{--eval @var{form}}.
Any Lisp program output that would normally go to the echo area,
-either using @code{message} or using @code{prin1}, etc., with @code{t}
+either using @code{message}, or using @code{prin1}, etc., with @code{t}
as the stream, goes instead to Emacs's standard error descriptor when
-in batch mode. Thus, Emacs behaves much like a noninteractive
+in batch mode. Similarly, input that would normally come from the
+minibuffer is read from the standard input descriptor.
+Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
@defvar noninteractive
This variable is non-@code{nil} when Emacs is running in batch mode.
@end defvar
+
+@node Session Management
+@section Session Management
+@cindex session manager
+
+Emacs supports the X Session Management Protocol for suspension and
+restart of applications. In the X Window System, a program called the
+@dfn{session manager} has the responsibility to keep track of the
+applications that are running. During shutdown, the session manager
+asks applications to save their state, and delays the actual shutdown
+until they respond. An application can also cancel the shutdown.
+
+When the session manager restarts a suspended session, it directs
+these applications to individually reload their saved state. It does
+this by specifying a special command-line argument that says what
+saved session to restore. For Emacs, this argument is @samp{--smid
+@var{session}}.
+
+@defvar emacs-save-session-functions
+Emacs supports saving state by using a hook called
+@code{emacs-save-session-functions}. Each function in this hook is
+called when the session manager tells Emacs that the window system is
+shutting down. The functions are called with no arguments and with the
+current buffer set to a temporary buffer. Each function can use
+@code{insert} to add Lisp code to this buffer. At the end, Emacs
+saves the buffer in a file that a subsequent Emacs invocation will
+load in order to restart the saved session.
+
+If a function in @code{emacs-save-session-functions} returns
+non-@code{nil}, Emacs tells the session manager to cancel the
+shutdown.
+@end defvar
+
+Here is an example that just inserts some text into @samp{*scratch*} when
+Emacs is restarted by the session manager.
+
+@example
+@group
+(add-hook 'emacs-save-session-functions 'save-yourself-test)
+@end group
+
+@group
+(defun save-yourself-test ()
+ (insert "(save-excursion
+ (switch-to-buffer \"*scratch*\")
+ (insert \"I am restored\"))")
+ nil)
+@end group
+@end example
+
+@ignore
+ arch-tag: 8378814a-30d7-467c-9615-74a80b9988a7
+@end ignore
HCoop / bpt / emacs.git / blobdiff