@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 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, Calendar, 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.
* 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.
+* Sound Output:: Playing sounds on the computer's speaker.
* Special Keysyms:: Defining system-specific key symbols for X windows.
* Flow Control:: How to turn output flow control on or off.
* Batch Mode:: Running Emacs without terminal interaction.
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
+@node Startup Summary
+@subsection Summary: Sequence of Actions at Startup
@cindex initialization
-@cindex start up 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 that is listed.
+
+@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}.
@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{~}.
+It loads your init file (usually @file{~/.emacs}), unless @samp{-q},
+@samp{-no-init-file}, 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} unless @code{inhibit-default-init}
+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 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}.
+there were no remaining command-line arguments (a few steps above),
+the value of @code{inhibit-startup-message} is @code{nil}, and the
+buffer is still empty.
@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 alternatively call it @file{.emacs.el}, which enables you to
+byte-compile it (@pxref{Byte Compilation}); then the actual file loaded
+will be @file{.emacs.elc}.
+
+ The command-line switches @samp{-q} and @samp{-u} control whether and
+where to find the init file; @samp{-q} says not to load an init file,
+and @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
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
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 the terminal-specific initialization.
@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.
+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.
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
@code{(getenv "TERM")} to find the full name of the terminal
type.@refill
- Your @file{.emacs} file can prevent the loading of the
+ 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
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}
(@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}
+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}.
@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
+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}.
@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}, Emacs is not killed.
@end defvar
@defvar kill-emacs-hook
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 Windows or MS Windows).
@defun suspend-emacs string
This function stops Emacs and returns control to the superior process.
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}.
@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
through various functions. These variables include the name of the
system, the user's @sc{uid}, and so on.
+@defvar system-configuration
+This variable holds the 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
+
@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.
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
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
@defvar invocation-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.
@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
This function returns the process @sc{id} of the Emacs process.
@end defun
+@defvar tty-erase-char
+@tindex tty-erase-char
+This variable holds the erase character that was selected
+in the system's terminal driver, before Emacs was started.
+@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}
does not change the privilege, but returns @code{t} or @code{nil}
@node User Identification
@section User Identification
+@defvar init-file-user
+This variable says which user's init files should be used by Emacs---or
+@code{nil} if none. 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
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 an integer (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
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
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
+0:00 January 1, 1970 (local time), which is
@ifinfo
@var{high} * 2**16 + @var{low}.
@end ifinfo
@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}.
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
+second element, @var{name}, is a string giving the name of the time
zone. Both elements change when daylight savings 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.
values from the functions @code{current-time} (@pxref{Time of Day}) and
@code{file-attributes} (@pxref{File Attributes}).
-@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:
+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 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
@item %Z
This stands for the time zone abbreviation.
@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}).
@end defun
@defun decode-time time
Here is what the elements mean:
@table @var
-@item sec
+@item seconds
The number of seconds past the minute, as an integer between 0 and 59.
-@item minute
+@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.
Greenwich.
@end table
-Note that Common Lisp has different meanings for @var{dow} and
-@var{zone}.
+@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
+@defun encode-time seconds minutes hour day month year &optional @dots{}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 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}.
+Year numbers less than 100 are not treated specially. If you want them
+to stand for years above 1900, 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 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.
+(as you would get from @code{current-time-zone}), a string as in the
+@code{TZ} environment variable, or an integer (as you would get from
+@code{decode-time}). The specified zone is used without any further
+alteration for daylight savings 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.
@end defun
@node Timers
@section Timers for Delayed Execution
+@cindex timer
-You can set up a timer to call a function at a specified future time.
+ 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.
@defun run-at-time time repeat function &rest args
This function arranges to call @var{function} with arguments @var{args}
later, and @var{args} are the arguments to give it when it is called.
The time @var{time} is specified as a string.
-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.
+Absolute times may be specified in a wide variety of formats; this
+function tries to accept all the commonly used date formats. Valid
+formats include these two,
+
+@example
+@var{year}-@var{month}-@var{day} @var{hour}:@var{min}:@var{sec} @var{timezone}
+
+@var{hour}:@var{min}:@var{sec} @var{timezone} @var{month}/@var{day}/@var{year}
+@end example
+
+@noindent
+where in both examples all fields are numbers; the format that
+@code{current-time-string} returns is also allowed, and many others
+as well.
To specify a relative time, use numbers followed by units.
For example:
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.
+
+If @var{time} is a number (integer or floating point), that specifies a
+relative time measured in seconds.
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.
+called just once, at @var{time}. If @var{repeat} is a number, it
+specifies a repetition period measured in seconds.
+
+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}.
+@code{cancel-timer} (see below).
@end defun
+@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 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.
+
+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} (see below).
+@end defun
+
+@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.
+
@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.
+previously returned by @code{run-at-time} or @code{run-with-idle-timer}.
+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.
@end defun
@node Terminal Input
@defun set-input-mode interrupt flow meta 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. @xref{Flow Control}.
@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
@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.
+ This section describes features for translating input events into
+other input events before they become part of key sequences. These
+features apply to each event in the order they are described here: each
+event is first modified according to @code{extra-keyboard-modifiers},
+then translated through @code{keyboard-translate-table} (if applicable),
+and finally decoded with the specified keyboard coding system. If it is
+being read as part of a key sequence, it is then added to the sequence
+being read; then subsequences containing it are checked first with
+@code{function-key-map} and then with @code{key-translation-map}.
@c Emacs 19 feature
@defvar extra-keyboard-modifiers
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.
+When using a window system, 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}.
+bindings. Its value is normally a char-table, or else @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.
+If @code{keyboard-translate-table} is a char-table
+(@pxref{Char-Tables}), then each character read from the keyboard is
+looked up in this char-table. If the value found there is
+non-@code{nil}, then it is used instead of the actual input character.
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.)
+char-table. 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
(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))))
+ (setq keyboard-translate-table
+ (make-char-table 'keyboard-translate-table nil))
+@end group
+@group
+ ;; @r{Swap @kbd{C-s} and @kbd{C-\}.}
+ (aset keyboard-translate-table ?\034 ?\^s)
+ (aset keyboard-translate-table ?\^s ?\034)
@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)))
+ ;; @r{Swap @kbd{C-q} and @kbd{C-^}.}
+ (aset keyboard-translate-table ?\036 ?\^q)
+ (aset keyboard-translate-table ?\^q ?\036))
@end group
@end example
@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.
+the keyboard translate table if necessary.
@end defun
+ The remaining translation features translate subsequences of key
+sequences being read. They are implemented in @code{read-key-sequence}
+and have no effect on input read with @code{read-event}.
+
@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.
+This variable holds a keymap that describes the character sequences sent
+by function keys on an ordinary character terminal. This keymap has the
+same structure as other keymaps, but is used differently: it specifies
+translations to make while reading key sequences, rather than bindings
+for key sequences.
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
+keypad @key{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.
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.
+command bindings in their own right---but if they do, the ordinary
+bindings take priority.
The value of @code{function-key-map} is usually set up automatically
according to the terminal's Terminfo or Termcap entry, but sometimes
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
@code{function-key-map}.
@item
-@code{key-translation-map} overrides actual key bindings.
+@code{key-translation-map} overrides actual key bindings. For example,
+if @kbd{C-x f} has a binding in @code{key-translation-map}, that
+translation takes effect even though @kbd{C-x f} also has a key binding
+in the global map.
@end itemize
The intent of @code{key-translation-map} is for users to map one
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
- (logior (lsh 1 20) e)
+ (logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
@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.
+Finally, if you have enabled keyboard character set decoding using
+@code{set-keyboard-coding-system}, decoding is done after the
+translations listed above. @xref{Specifying Coding Systems}. In future
+Emacs versions, character set decoding may be done before the other
+translations.
@node Recording Input
@subsection 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 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 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.)
@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 the 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.
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
Control characters in @var{string} have terminal-dependent effects.
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):
@end example
@end deffn
+@node Sound Output
+@section Sound Output
+@cindex sound
+
+ 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.
+
+ The sound must be stored as a file in RIFF-WAVE format (@samp{.wav})
+or Sun Audio format (@samp{.au}).
+
+@tindex play-sound
+@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.
+
+Here is a table of the keywords that are currently meaningful in
+@var{sound}, and their meanings:
+
+@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 :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.
+@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
+
+@tindex play-sound-functions
+@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
+
@node Special Keysyms
@section System-Specific X11 Keysyms
@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}
+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, 1 << 28), and @var{symbol} is the
-name for the function key.
+including the ``vendor specific'' bit,
+@ifinfo
+-2**28),
+@end ifinfo
+@tex
+$-2^{28}$),
+@end tex
+and @var{symbol} is the name for the function key.
-For example @code{(168 . mute-acute)} defines a system-specific key used
-by HP X servers whose numeric code is (1 << 28) + 168.
+For example @code{(168 . mute-acute)} defines a system-specific key (used
+by HP X servers) whose numeric code is
+@ifinfo
+-2**28
+@end ifinfo
+@tex
+$-2^{28}$
+@end tex
++ 168.
-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.
+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.
-The variable is always local to the current X terminal and cannot be
+The variable is always local to the current terminal, and cannot be
buffer-local. @xref{Multiple Displays}.
@end defvar
@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
+ This section attempts to answer the question ``Why does Emacs 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-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.
+@kbd{C-s} and @kbd{C-q} as command characters for searching and quoting
+was natural and uncontroversial. With so many commands needing key
+assignments, of course we assigned meanings to nearly all @sc{ascii}
+control characters.
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.
+editing, so Emacs maintainers ignored them. 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 Emacs
+users, who can turn flow control off, did not want 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
+ 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
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!
+model 33 teletype with a paper tape punch (around 1970), @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}.
+ As window systems and PC terminal emulators replace character-only
+terminals, the flow control problem is gradually disappearing. 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
+@deffn Command 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}).
-@end defun
+@end deffn
You can use the function @code{enable-flow-control-on} in your
-@file{.emacs} file to enable flow control automatically on certain
+init file to enable flow control automatically on certain
terminal types.
@defun enable-flow-control-on &rest termtypes
@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
calls @var{function} with no arguments.
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
application program. (The echo area output that Emacs itself normally
HCoop / bpt / emacs.git / blobdiff