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+@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 See the file elisp.texi for copying conditions.
+@setfilename ../info/os
+@node System Interface, Display, Processes, Top
+@chapter Operating System Interface
+
+  This chapter is about starting and getting out of Emacs, access to
+values in the operating system environment, and terminal input, output
+and flow control.
+
+  @xref{Building Emacs}, for related information.  See also
+@ref{Display}, for additional operating system status information
+pertaining to the terminal and the screen.
+
+@menu
+* Starting Up::         Customizing Emacs start-up 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.
+* 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.
+* Batch Mode::          Running Emacs without terminal interaction.
+@end menu
+
+@node Starting Up
+@section Starting Up Emacs
+
+  This section describes what Emacs does when it is started, and how you
+can customize these actions.
+
+@menu
+* Start-up Summary::        Sequence of actions Emacs performs at start-up.
+* 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,
+                              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
+@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 loads the initialization library for the window system, if you are
+using a window system.  This library's name is
+@file{term/@var{windowsystem}-win.el}.
+
+@item
+It initializes the X 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}.
+@cindex @file{site-start.el}
+
+@item 
+It loads the file @file{~/.emacs} unless @samp{-q} was specified on
+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 command line.)  The library's file name is
+usually @file{default.el}.
+@cindex @file{default.el}
+
+@item
+It runs the normal hook @code{after-init-hook}.
+
+@item
+It sets the major mode according to @code{initial-major-mode}, provided
+the buffer @samp{*scratch*} is still current and still in Fundamental
+mode.
+
+@item 
+It loads the terminal-specific Lisp file, if any, except when in batch
+mode or using a window system.
+
+@item
+It displays the initial echo area message, unless you have suppressed
+that with @code{inhibit-startup-echo-area-message}.
+
+@item 
+It processes any remaining command line arguments.
+
+@item 
+It runs @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 
+It runs @code{window-setup-hook}.  @xref{Window Systems}.
+
+@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}.
+@end enumerate
+
+@defopt inhibit-startup-message
+This variable inhibits the initial startup messages (the nonwarranty,
+etc.).  If it is non-@code{nil}, then the messages are not printed.
+
+This variable exists so you can set it in your personal init file, once
+you are familiar with the contents of the startup message.  Do not set
+this variable in the init file of a new user, or in a way that affects
+more than one user, because that would prevent new users from receiving
+the information they are supposed to see.
+@end defopt
+
+@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:
+
+@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.
+
+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.
+@end defopt
+
+@node Init File
+@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}.
+
+@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.
+
+  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}.
+
+  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.
+
+@defopt inhibit-default-init
+This variable prevents Emacs from loading the default initialization
+library file for your session of Emacs.  If its value is non-@code{nil},
+then the default library is not loaded.  The default value is
+@code{nil}.
+@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}.
+@end defvar
+
+@node Terminal-Specific
+@subsection Terminal-Specific Initialization
+@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}.
+
+@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
+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.
+
+  You can also arrange to override some of the actions of the
+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
+use this variable to define initializations for terminals that do not
+have their own libraries.  @xref{Hooks}.
+
+@defvar term-file-prefix
+@cindex @code{TERM} environment variable
+If the @code{term-file-prefix} variable is non-@code{nil}, Emacs loads
+a terminal-specific initialization file as follows:
+
+@example
+(load (concat term-file-prefix (getenv "TERM")))
+@end example
+
+@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
+terminal-initialization file.  To do this, put the following in
+your @file{.emacs} file: @code{(setq term-file-prefix nil)}.
+@end defvar
+
+@defvar term-setup-hook 
+This variable is a normal hook which Emacs runs after loading your
+@file{.emacs} 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
+terminal-specific file.
+@end defvar
+
+  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
+
+  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
+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,
+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
+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
+comes to have many files in it ready for editing.  Usually you do not
+kill the Emacs until you are about to log out.)
+@end ignore
+
+@defun command-line
+This function parses the command line which Emacs was called with,
+processes it, loads the user's @file{.emacs} file and displays the
+initial nonwarranty information, etc.
+@end defun
+
+@defvar command-line-processed
+The value of this variable is @code{t} once the command line has been
+processed.
+
+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.
+@end defvar
+
+@defvar command-switch-alist
+@cindex switches on command line
+@cindex options on command line
+@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:
+
+@example
+-@var{option}
+@end example
+
+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.
+
+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
+remaining command-line arguments in the variable
+@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}.
+@end defvar
+
+@defvar command-line-args
+The value of this variable is the list of command line arguments passed
+to Emacs.
+@end defvar
+
+@defvar command-line-functions
+This variable's value is a list of functions for handling an
+unrecognized command-line argument.  Each time the next argument to be
+processed has no special meaning, the functions in this list are called,
+in the order they appear, until one of them returns a non-@code{nil}
+value.
+
+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}.
+
+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
+argument.  If it has also dealt with some of the following arguments, it
+can indicate that by deleting them from @code{command-line-args-left}.
+
+If all of these functions return @code{nil}, then the argument is used
+as a file name to visit.
+@end defvar
+
+@node Getting Out
+@section Getting Out of Emacs
+@cindex exiting Emacs
+
+  There are two ways to get out of Emacs: you can kill the Emacs job,
+which exits permanently, or you can suspend it, which permits you to
+reenter the Emacs process later.  As a practical matter, you seldom kill
+Emacs---only when you are about to log out.  Suspending is much more
+common.
+
+@menu
+* Killing Emacs::        Exiting Emacs irreversibly.
+* Suspending Emacs::     Exiting Emacs reversibly.
+@end menu
+
+@node Killing Emacs
+@comment  node-name,  next,  previous,  up
+@subsection Killing Emacs
+@cindex killing Emacs
+
+  Killing Emacs means ending the execution of the Emacs process.  The
+parent process normally resumes control.  The low-level primitive for
+killing Emacs is @code{kill-emacs}.
+
+@defun kill-emacs &optional exit-data
+This function exits the Emacs process and kills it.
+
+If @var{exit-data} is an integer, then it is used as the exit status
+of the Emacs process.  (This is useful primarily in batch operation; see
+@ref{Batch Mode}.)
+
+If @var{exit-data} is a string, its contents are stuffed into the
+terminal input buffer so that the shell (or whatever program next reads
+input) can read them.
+@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}.
+
+@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
+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.
+@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.
+@end defvar
+
+@node Suspending Emacs
+@subsection Suspending Emacs
+@cindex suspending Emacs
+
+  @dfn{Suspending Emacs} means stopping Emacs temporarily and returning
+control to its superior process, which is usually the shell.  This
+allows you to resume editing later in the same Emacs process, with the
+same buffers, the same kill ring, the same undo history, and so on.  To
+resume Emacs, use the appropriate command in the parent shell---most
+likely @code{fg}.
+
+  Some operating systems do not support suspension of jobs; on these
+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.
+
+@defun suspend-emacs 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.
+
+If @var{string} is non-@code{nil}, its characters are sent to be read
+as terminal input by Emacs's superior shell.  The characters in
+@var{string} are not echoed by the superior shell; only the results
+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.
+
+After the user resumes Emacs, it runs the normal hook
+@code{suspend-resume-hook}.  @xref{Hooks}.
+
+The next redisplay after resumption will redraw the entire screen,
+unless the variable @code{no-redraw-on-reenter} is non-@code{nil}
+(@pxref{Refresh Screen}).
+
+In the following example, note that @samp{pwd} is not echoed after
+Emacs is suspended.  But it is read and executed by the shell.
+
+@smallexample
+@group
+(suspend-emacs)
+     @result{} nil
+@end group
+
+@group
+(add-hook 'suspend-hook
+          (function (lambda ()
+                      (or (y-or-n-p
+                            "Really suspend? ")
+                          (error "Suspend cancelled")))))
+     @result{} (lambda nil
+          (or (y-or-n-p "Really suspend? ")
+              (error "Suspend cancelled")))
+@end group
+@group
+(add-hook 'suspend-resume-hook
+          (function (lambda () (message "Resumed!"))))
+     @result{} (lambda nil (message "Resumed!"))
+@end group
+@group
+(suspend-emacs "pwd")
+     @result{} nil
+@end group
+@group
+---------- Buffer: Minibuffer ----------
+Really suspend? @kbd{y}
+---------- Buffer: Minibuffer ----------
+@end group
+
+@group
+---------- Parent Shell ----------
+lewis@@slug[23] % /user/lewis/manual
+lewis@@slug[24] % fg
+@end group
+
+@group
+---------- Echo Area ----------
+Resumed!
+@end group
+@end smallexample
+@end defun
+
+@defvar suspend-hook
+This variable is a normal hook run before suspending.
+@end defvar
+
+@defvar suspend-resume-hook
+This variable is a normal hook run after suspending.
+@end defvar
+
+@node System Environment
+@section Operating System Environment
+@cindex operating 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.
+
+@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 symbols
+for the operating systems that Emacs can run on up to version 19.1.
+
+@table @code
+@item aix-v3
+AIX.
+
+@item berkeley-unix
+Berkeley BSD.
+
+@item hpux
+Hewlett-Packard operating system.
+
+@item irix
+Silicon Graphics Irix system.
+
+@item rtu
+Masscomp RTU, UCB universe.
+
+@item unisoft-unix
+UniSoft UniPlus.
+
+@item usg-unix-v
+AT&T System V.
+
+@item vax-vms
+VAX VMS.
+
+@item xenix
+SCO Xenix 386.
+@end table
+
+We do not wish to add new symbols to make finer distinctions unless it
+is absolutely necessary!  In fact, we hope to eliminate some of these
+alternatives in the future.  We recommend using
+@code{system-configuration} to distinguish between different operating
+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"
+@end example
+@end defun
+
+@defun 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}.
+
+@example
+@group
+(getenv "USER")
+     @result{} "lewis"
+@end group
+
+@group
+lewis@@slug[10] % printenv
+PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
+USER=lewis
+@end group
+@group
+TERM=ibmapa16
+SHELL=/bin/csh
+HOME=/user/lewis
+@end group
+@end example
+@end defun
+
+@c Emacs 19 feature
+@deffn Command setenv variable 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.
+@end deffn
+
+@defvar process-environment
+This variable is a list of strings, each describing one environment
+variable.  The functions @code{getenv} and @code{setenv} work by means
+of this variable.
+
+@smallexample
+@group
+process-environment
+@result{} ("l=/usr/stanford/lib/gnuemacs/lisp"
+    "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
+    "USER=lewis" 
+@end group
+@group
+    "TERM=ibmapa16" 
+    "SHELL=/bin/csh"
+    "HOME=/user/lewis")
+@end group
+@end smallexample
+@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.)
+
+@example
+@group
+(load-average)
+     @result{} (169 48 36)
+@end group
+
+@group
+lewis@@rocky[5] % uptime
+ 11:55am  up 1 day, 19:37,  3 users,
+ load average: 1.69, 0.48, 0.36
+@end group
+@end example
+@end defun
+
+@defun emacs-pid
+This function returns the process @sc{id} of the Emacs process.
+@end defun
+
+@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.
+
+  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
+
+@defun user-login-name
+This function returns the name under 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}.
+
+@example
+@group
+(user-login-name)
+     @result{} "lewis"
+@end group
+@end example
+@end defun
+
+@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
+environment variables @code{LOGNAME} and @code{USER}.
+@end defun
+
+@defun user-full-name
+This function returns the full name of the user.
+
+@example
+@group
+(user-full-name)
+     @result{} "Bil Lewis"
+@end group
+@end example
+@end defun
+
+@defun user-real-uid
+This function returns the real @sc{uid} of the user.
+
+@example
+@group
+(user-real-uid)
+     @result{} 19
+@end group
+@end example
+@end defun
+
+@defun user-uid
+This function returns the effective @sc{uid} of the user.  
+@end defun
+
+@node Time of Day
+@section Time of Day
+
+  This section explains how to determine the current time and the time
+zone.
+
+@defun current-time-string &optional time-value
+This function returns the current time and date as a humanly-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.  However, it would be 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.
+
+@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 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 below) and from @code{file-attributes} (@pxref{File Attributes}).
+
+@example
+@group
+(current-time-string)
+     @result{} "Wed Oct 14 22:21:05 1987"
+@end group
+@end example
+@end defun
+
+@c Emacs 19 feature
+@defun current-time
+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
+@var{high} * 2**16 + @var{low}.
+@end ifinfo
+@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).
+
+The first two elements can be compared with file time values such as you
+get with the function @code{file-attributes}.  @xref{File Attributes}.
+@end defun
+
+@c Emacs 19 feature
+@defun current-time-zone &optional time-value
+This function returns a list describing the time zone that the user is
+in.
+
+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;
+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}.
+
+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 below) and from @code{file-attributes} (@pxref{File Attributes}).
+@end defun
+
+@node Timers
+@section Timers
+
+You can set up a timer to call a function at a specified future time.
+
+@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.
+
+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.
+
+To specify a relative time, use numbers followed by units.
+For example:
+
+@table @samp
+@item 1 min
+denotes 1 minute from now.
+@item 1 min 5 sec
+denotes 65 seconds from now.
+@item 1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year
+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.
+
+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.
+@end defun
+
+@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.
+@end defun
+
+@node Terminal Input
+@section Terminal Input
+@cindex terminal input
+
+  This section describes functions and variables for recording or
+manipulating terminal input.  See @ref{Display}, for related
+functions.
+
+@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
+
+@node Input Modes
+@subsection Input Modes
+@cindex input modes
+@cindex terminal input modes
+
+@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.
+
+If @var{flow} is non-@code{nil}, then Emacs uses @sc{xon/xoff} (@kbd{C-q},
+@kbd{C-s}) flow control for output to terminal.  This has no effect except
+in @sc{cbreak} mode.  @xref{Flow Control}.
+
+The default setting is system dependent.  Some systems always use
+@sc{cbreak} mode regardless of what is specified.
+
+@c Emacs 19 feature
+The argument @var{meta} controls support for input character codes
+above 127.  If @var{meta} is @code{t}, Emacs converts characters with
+the 8th bit set into Meta characters.  If @var{meta} is @code{nil},
+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.
+
+@c Emacs 19 feature
+If @var{quit-char} is non-@code{nil}, it specifies the character to
+use for quitting.  Normally this character is @kbd{C-g}.
+@xref{Quitting}.
+@end defun
+
+The @code{current-input-mode} function returns the input mode settings
+Emacs is currently using.
+
+@c Emacs 19 feature
+@defun current-input-mode
+This function returns 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:
+@table @var
+@item interrupt
+is non-@code{nil} when Emacs is using interrupt-driven input.  If
+@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}.
+@item meta
+is non-@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
+input character; any other value means Emacs uses all eight bits as the
+basic character code.
+@item quit
+is the character Emacs currently uses for quitting, usually @kbd{C-g}.
+@end table
+@end defun
+
+@defvar meta-flag
+This variable used to control whether to treat the eight bit in keyboard
+input characters as the @key{Meta} bit.  @code{nil} meant no, and
+anything else meant yes.  This variable existed in Emacs versions 18 and
+earlier but no longer exists in Emacs 19; use @code{set-input-mode}
+instead.
+@end defvar
+
+@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 you use 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 which describes the character sequences
+sent by function keys on an ordinary character terminal.  This keymap
+uses the 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
+(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))))
+    (if (symbolp e)
+        symbol
+      (cons symbol (cdr e)))))
+
+(define-key function-key-map "\C-ch" 'hyperify)
+@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
+
+@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
+should be enough to see the events which invoked the macros.)
+@end defun
+
+@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
+not those from keyboard macros) is written in that file.  A
+non-character event is expressed using its printed representation
+surrounded by @samp{<@dots{}>}.
+
+You close the dribble file by calling this function with an argument
+of @code{nil}.
+
+This function is normally used to record the input necessary to
+trigger an Emacs bug, for the sake of a bug report.
+
+@example
+@group
+(open-dribble-file "~/dribble")
+     @result{} nil
+@end group
+@end example
+@end deffn
+
+  See also the @code{open-termscript} function (@pxref{Terminal Output}).
+
+@node Terminal Output
+@section Terminal Output
+@cindex terminal output
+
+  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.
+
+@defvar baud-rate
+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.)
+
+The value is measured in baud.
+@end defvar
+
+  If you are running across a network, and different parts of the
+network work at different baud rates, the value returned by Emacs may be
+different from the value used by your local terminal.  Some network
+protocols communicate the local terminal speed to the remote machine, so
+that Emacs and other programs can get the proper value, but others do
+not.  If Emacs has the wrong value, it makes decisions that are less
+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.
+@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.
+
+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
+characters (by transmitting the characters @kbd{C-u C-f} to the
+computer):
+
+@example
+@group
+(send-string-to-terminal "\eF4\^U\^F")
+     @result{} nil
+@end group
+@end example
+@end defun
+
+@deffn Command open-termscript filename
+@cindex termscript file
+This function is used to open a @dfn{termscript file} that will record
+all the characters sent by Emacs to the terminal.  It returns
+@code{nil}.  Termscript files are useful for investigating problems
+where Emacs garbles the screen, problems that are due to incorrect
+Termcap entries or to undesirable settings of terminal options more
+often than to actual Emacs bugs.  Once you are certain which characters
+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}.
+
+@example
+@group
+(open-termscript "../junk/termscript")
+     @result{} nil
+@end group
+@end example
+@end deffn
+
+@node Special Keysyms
+@section System-Specific X11 Keysyms
+
+To define system-specific X11 keysyms, set the variable
+@code{system-key-alist}.
+
+@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.
+
+For example @code{(168 . mute-acute)} defines a system-specific key used
+by HP X servers whose numeric code is (1 << 28) + 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.
+@end defvar
+
+@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!
+
+  GNU Emacs version 19 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}).
+@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.
+
+@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:
+
+@smallexample
+(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
+@end smallexample
+@end defun
+
+  Here is how @code{enable-flow-control} does its job:
+
+@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)}.
+
+@item
+It sets up @code{keyboard-translate-table} to translate @kbd{C-\} and
+@kbd{C-^} into @kbd{C-s} and @kbd{C-q} were typed.  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}.
+
+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}.
+
+@node Batch Mode
+@section Batch Mode
+@cindex batch mode
+@cindex noninteractive use
+
+  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.
+
+  Any Lisp program output that would normally go to the echo area,
+either using @code{message} or using @code{prin1}, etc., with @code{t}
+as the stream, goes instead to Emacs's standard output descriptor when
+in batch mode.  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