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This is Info file elisp, produced by Makeinfo-1.55 from the input file
elisp.texi.
This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for
Emacs Version 19.
Published by the Free Software Foundation, 675 Massachusetts Avenue,
Cambridge, MA 02139 USA
Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
File: elisp, Node: Sentinels, Next: Transaction Queues, Prev: Output from Processes, Up: Processes
Sentinels: Detecting Process Status Changes
===========================================
A "process sentinel" is a function that is called whenever the
associated process changes status for any reason, including signals
(whether sent by Emacs or caused by the process's own actions) that
terminate, stop, or continue the process. The process sentinel is also
called if the process exits. The sentinel receives two arguments: the
process for which the event occurred, and a string describing the type
of event.
The string describing the event looks like one of the following:
* `"finished\n"'.
* `"exited abnormally with code EXITCODE\n"'.
* `"NAME-OF-SIGNAL\n"'.
* `"NAME-OF-SIGNAL (core dumped)\n"'.
A sentinel runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output). This avoids the
timing errors that could result from running them at random places in
the middle of other Lisp programs. You may explicitly cause Emacs to
wait, so that sentinels will run, by calling `sit-for', `sleep-for' or
`accept-process-output' (*note Accepting Output::.). Emacs is also
waiting when the command loop is reading input.
Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing `C-g' at command level or to quit a user command would
be unpredictable. If you want to permit quitting inside a sentinel,
bind `inhibit-quit' to `nil'. *Note Quitting::.
All sentinels that do regexp searching or matching should save and
restore the match data. Otherwise, a sentinel that runs during a call
to `sit-for' might clobber the match data of the program that called
`sit-for'. *Note Match Data::.
- Function: set-process-sentinel PROCESS SENTINEL
This function associates SENTINEL with PROCESS. If SENTINEL is
`nil', then the process will have no sentinel. The default
behavior when there is no sentinel is to insert a message in the
process's buffer when the process status changes.
(defun msg-me (process event)
(princ
(format "Process: %s had the event `%s'" process event)))
(set-process-sentinel (get-process "shell") 'msg-me)
=> msg-me
(kill-process (get-process "shell"))
-| Process: #<process shell> had the event `killed'
=> #<process shell>
- Function: process-sentinel PROCESS
This function returns the sentinel of PROCESS, or `nil' if it has
none.
- Function: waiting-for-user-input-p
While a sentinel or filter function is running, this function
returns non-`nil' if Emacs was waiting for keyboard input from the
user at the time the sentinel or filter function was called, `nil'
if it was not.
File: elisp, Node: Transaction Queues, Next: TCP, Prev: Sentinels, Up: Processes
Transaction Queues
==================
You can use a "transaction queue" for more convenient communication
with subprocesses using transactions. First use `tq-create' to create
a transaction queue communicating with a specified process. Then you
can call `tq-enqueue' to send a transaction.
- Function: tq-create PROCESS
This function creates and returns a transaction queue
communicating with PROCESS. The argument PROCESS should be a
subprocess capable of sending and receiving streams of bytes. It
may be a child process, or it may be a TCP connection to a server
possibly on another machine.
- Function: tq-enqueue QUEUE QUESTION REGEXP CLOSURE FN
This function sends a transaction to queue QUEUE. Specifying the
queue has the effect of specifying the subprocess to talk to.
The argument QUESTION is the outgoing message which starts the
transaction. The argument FN is the function to call when the
corresponding answer comes back; it is called with two arguments:
CLOSURE, and the answer received.
The argument REGEXP is a regular expression to match the entire
answer; that's how `tq-enqueue' tells where the answer ends.
The return value of `tq-enqueue' itself is not meaningful.
- Function: tq-close QUEUE
Shut down transaction queue QUEUE, waiting for all pending
transactions to complete, and then terminate the connection or
child process.
Transaction queues are implemented by means of a filter function.
*Note Filter Functions::.
File: elisp, Node: TCP, Prev: Transaction Queues, Up: Processes
Emacs Lisp programs can open TCP connections to other processes on
the same machine or other machines. A network connection is handled by
Lisp much like a subprocess, and is represented by a process object.
However, the process you are communicating with is not a child of the
Emacs process, so you can't kill it or send it signals. All you can do
is send and receive data. `delete-process' closes the connection, but
does not kill the process at the other end; that process must decide
what to do about closure of the connection.
You can distinguish process objects representing network connections
from those representing subprocesses with the `process-status'
function. *Note Process Information::.
- Function: open-network-stream NAME BUFFER-OR-NAME HOST SERVICE
This function opens a TCP connection for a service to a host. It
returns a process object to represent the connection.
The NAME argument specifies the name for the process object. It
is modified as necessary to make it unique.
The BUFFER-OR-NAME argument is the buffer to associate with the
connection. Output from the connection is inserted in the buffer,
unless you specify a filter function to handle the output. If
BUFFER-OR-NAME is `nil', it means that the connection is not
associated with any buffer.
The arguments HOST and SERVICE specify where to connect to; HOST
is the host name (a string), and SERVICE is the name of a defined
network service (a string) or a port number (an integer).
File: elisp, Node: System Interface, Next: Emacs Display, Prev: Processes, Up: Top
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.
*Note Building Emacs::, for related information. See also *Note
Emacs 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.
* Flow Control:: How to turn output flow control on or off.
* Batch Mode:: Running Emacs without terminal interaction.
File: elisp, Node: Starting Up, Next: Getting Out, Up: System Interface
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 (`.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.
File: elisp, Node: Start-up Summary, Next: Init File, Up: Starting Up
Summary: Sequence of Actions at Start Up
----------------------------------------
The order of operations performed (in `startup.el') by Emacs when it
is started up is as follows:
1. It runs the normal hook `before-init-hook'.
2. It loads `.emacs' unless `-q' was specified on command line.
(This is not done in `-batch' mode.) `.emacs' is found in the
user's home directory; the `-u' option can specify the user name
whose home directory should be used.
3. It loads `default.el' unless `inhibit-default-init' is non-`nil'.
(This is not done in `-batch' mode or if `-q' was specified on
command line.)
4. It runs the normal hook `after-init-hook'.
5. It loads the terminal-specific Lisp file, if any, except when in
batch mode.
6. It runs `term-setup-hook'.
7. It runs `window-setup-hook'. *Note Window Systems::.
8. It displays copyleft and nonwarranty, plus basic use information,
unless the value of the variable `inhibit-startup-message' is
non-`nil'.
This display is also inhibited in batch mode, and if the current
buffer is not `*scratch*'.
9. It processes any remaining command line arguments.
- User Option: inhibit-startup-message
This variable inhibits the initial startup messages (the
nonwarranty, etc.). If it is non-`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.
File: elisp, Node: Init File, Next: Terminal-Specific, Prev: Start-up Summary, Up: Starting Up
The Init File: `.emacs'
-----------------------
When you start Emacs, it normally attempts to load the file `.emacs'
from your home directory. This file, if it exists, must contain Lisp
code. It is called your "init file". The command line switches `-q'
and `-u' can be used to control the use of the init file; `-q' says not
to load an init file, and `-u' says to load a specified user's init
file instead of yours. *Note Entering Emacs: (emacs)Entering Emacs.
Emacs may also have a "default init file", which is the library
named `default.el'. Emacs finds the `default.el' file through the
standard search path for libraries (*note How Programs Do Loading::.).
The Emacs distribution does not have any such file; you may create one
at your site for local customizations. If the default init file
exists, it is loaded whenever you start Emacs, except in batch mode or
if `-q' is specified. But your own personal init file, if any, is
loaded first; if it sets `inhibit-default-init' to a non-`nil' value,
then Emacs will not subsequently load the `default.el' file.
If there is a great deal of code in your `.emacs' file, you should
move it into another file named `SOMETHING.el', byte-compile it (*note
Byte Compilation::.), and make your `.emacs' file load the other file
using `load' (*note Loading::.).
*Note Init File Examples: (emacs)Init File Examples, for examples of
how to make various commonly desired customizations in your `.emacs'
file.
- User Option: inhibit-default-init
This variable prevents Emacs from loading the default
initialization library file for your session of Emacs. If its
value is non-`nil', then the default library is not loaded. The
default value is `nil'.
- Variable: before-init-hook
- Variable: after-init-hook
These two normal hooks are run just before, and just after,
loading of the user's init file or `default.el'.
File: elisp, Node: Terminal-Specific, Next: Command Line Arguments, Prev: Init File, Up: Starting Up
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 TERMTYPE,
the library is called `term/TERMTYPE'. Emacs finds the file by
searching the `load-path' directories as it does for other files, and
trying the `.elc' and `.el' suffixes. Normally, terminal-specific Lisp
library is located in `emacs/lisp/term', a subdirectory of the
`emacs/lisp' directory in which most Emacs Lisp libraries are kept.
The library's name is constructed by concatenating the value of the
variable `term-file-prefix' and the terminal type. Normally,
`term-file-prefix' has the value `"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 `function-key-map' if the Termcap entry does not
fully explain what should go in it. *Note Terminal Input::.
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 `aaa-48' and `aaa-30-rv' both use
the `term/aaa' library. If necessary, the library can evaluate
`(getenv "TERM")' to find the full name of the terminal type.
Your `.emacs' file can prevent the loading of the terminal-specific
library by setting the variable `term-file-prefix' to `nil'. This
feature is very 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 `term-setup-hook'.
This is a normal hook which Emacs runs using `run-hooks' at the end of
Emacs initialization, after loading both your `.emacs' file and any
terminal-specific libraries. You can use this variable to define
initializations for terminals that do not have their own libraries.
*Note Hooks::.
- Variable: term-file-prefix
If the `term-file-prefix' variable is non-`nil', Emacs loads a
terminal-specific initialization file as follows:
(load (concat term-file-prefix (getenv "TERM")))
You may set the `term-file-prefix' variable to `nil' in your
`.emacs' file if you do not wish to load the
terminal-initialization file. To do this, put the following in
your `.emacs' file: `(setq term-file-prefix nil)'.
- Variable: term-setup-hook
This variable is a normal hook which Emacs runs after loading your
`.emacs' file, the default initialization file (if any) and after
loading terminal-specific Lisp files. arguments.
You can use `term-setup-hook' to override the definitions made by
a terminal-specific file.
See `window-setup-hook' in *Note Window Systems::, for a related
feature.
File: elisp, Node: Command Line Arguments, Prev: Terminal-Specific, Up: Starting Up
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.
- Function: command-line
This function parses the command line which Emacs was called with,
processes it, loads the user's `.emacs' file and displays the
initial nonwarranty information, etc.
- Variable: command-line-processed
The value of this variable is `t' once the command line has been
processed.
If you redump Emacs by calling `dump-emacs', you may wish to set
this variable to `nil' first in order to cause the new dumped Emacs
to process its new command line arguments.
- Variable: command-switch-alist
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 "command line option" is an argument on the command line of the
form:
-OPTION
The elements of the `command-switch-alist' look like this:
(OPTION . HANDLER-FUNCTION)
The HANDLER-FUNCTION is called to handle 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 HANDLER-FUNCTION can find all the
remaining command-line arguments in the variable
`command-line-args-left'. (The entire list of command-line
arguments is in `command-line-args'.)
The command line arguments are parsed by the `command-line-1'
function in the `startup.el' file. See also *Note Command Line
Switches and Arguments: (emacs)Command Switches.
- Variable: command-line-args
The value of this variable is the arguments passed by the shell to
Emacs, as a list of strings.
File: elisp, Node: Getting Out, Next: System Environment, Prev: Starting Up, Up: System Interface
Getting out of 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.
File: elisp, Node: Killing Emacs, Next: Suspending Emacs, Up: Getting Out
Killing Emacs
-------------
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control.
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.
- Function: kill-emacs &optional NO-QUERY
This function exits the Emacs process and kills it.
Normally, if there are modified files or if there are running
processes, `kill-emacs' asks the user for confirmation before
exiting. However, if NO-QUERY is supplied and non-`nil', then
Emacs exits without confirmation.
If NO-QUERY is an integer, then it is used as the exit status of
the Emacs process. (This is useful primarily in batch operation;
see *Note Batch Mode::.)
If NO-QUERY 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.
- Variable: kill-emacs-hook
This variable is a normal hook (a list of functions); the first
thing `kill-emacs' does is to run this hook with `run-hooks'. That
calls each of the functions in the list, with no arguments.
File: elisp, Node: Suspending Emacs, Prev: Killing Emacs, Up: Getting Out
Suspending Emacs
----------------
"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 `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.
- Function: suspend-emacs STRING
This function stops Emacs and returns to the superior process. It
returns `nil'.
If STRING is non-`nil', its characters are sent to be read as
terminal input by Emacs's superior shell. The characters in
STRING are not echoed by the superior shell; only the results
appear.
Before suspending, `suspend-emacs' runs the normal hook
`suspend-hook'. In Emacs version 18, `suspend-hook' was not a
normal hook; its value was a single function, and if its value was
non-`nil', then `suspend-emacs' returned immediately without
actually suspending anything.
After the user resumes Emacs, it runs the normal hook
`suspend-resume-hook' using `run-hooks'. *Note Hooks::.
The next redisplay after resumption will redraw the entire screen,
unless the variable `no-redraw-on-reenter' is non-`nil' (*note
Refresh Screen::.).
In the following example, note that `pwd' is not echoed after
Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs)
=> nil
(add-hook 'suspend-hook
(function (lambda ()
(or (y-or-n-p
"Really suspend? ")
(error "Suspend cancelled")))))
=> (lambda nil
(or (y-or-n-p "Really suspend? ")
(error "Suspend cancelled")))
(add-hook 'suspend-resume-hook
(function (lambda () (message "Resumed!"))))
=> (lambda nil (message "Resumed!"))
(suspend-emacs "pwd")
=> nil
---------- Buffer: Minibuffer ----------
Really suspend? `y'
---------- Buffer: Minibuffer ----------
---------- Parent Shell ----------
lewis@slug[23] % /user/lewis/manual
lewis@slug[24] % fg
---------- Echo Area ----------
Resumed!
- Variable: suspend-hook
This variable is a normal hook run before suspending.
- Variable: suspend-resume-hook
This variable is a normal hook run after suspending.
File: elisp, Node: System Environment, Next: User Identification, Prev: Getting Out, Up: System Interface
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 UID, and so on.
- Variable: 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.
`aix-v3'
AIX version 3.
`berkeley-unix'
Berkeley BSD 4.1, 4.2, or 4.3.
`hpux'
Hewlett-Packard operating system, version 5, 6, or 7.
`irix'
Silicon Graphics Irix system.
`rtu'
RTU 3.0, UCB universe.
`unisoft-unix'
UniSoft's UniPlus 5.0 or 5.2.
`usg-unix-v'
AT&T's System V.0, System V Release 2.0, 2.2, or 3.
`vax-vms'
VAX VMS version 4 or 5.
`xenix'
SCO Xenix 386 Release 2.2.
We do not wish to add new symbols to make finer distinctions
unless it is absolutely necessary! In fact, it would be nice to
eliminate some of these alternatives in the future.
- Function: system-name
This function returns the name of the machine you are running on.
(system-name)
=> "prep.ai.mit.edu"
- Function: getenv VAR
This function returns the value of the environment variable VAR,
as a string. If the variable `process-environment' specifies a
value for VAR, that overrides the actual environment.
(getenv "USER")
=> "lewis"
lewis@slug[10] % printenv
PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
USER=lewis
TERM=ibmapa16
SHELL=/bin/csh
HOME=/user/lewis
- Command: setenv VARIABLE VALUE
This command sets the value of the environment variable named
VARIABLE to VALUE. Both arguments should be strings. This works
by modifying `process-environment'; binding that variable with
`let' is also reasonable practice.
- Variable: process-environment
This variable is a list of strings to append to the environment of
processes as they are created. Each string assigns a value to a
shell environment variable. (This applies both to asynchronous and
synchronous processes.) The function `getenv' also looks at this
variable.
process-environment
=> ("l=/usr/stanford/lib/gnuemacs/lisp"
"PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
"USER=lewis"
"TERM=ibmapa16"
"SHELL=/bin/csh"
"HOME=/user/lewis")
- Function: 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.)
(load-average)
=> (169 48 36)
lewis@rocky[5] % uptime
11:55am up 1 day, 19:37, 3 users,
load average: 1.69, 0.48, 0.36
- Function: 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, SETP, is `t' or `nil', indicating whether the
privilege is to be turned on or off. Its default is `nil'. The
function returns `t' if success, `nil' if not.
If the third argument, GETPRV, is non-`nil', `setprv' does not
change the privilege, but returns `t' or `nil' indicating whether
the privilege is currently enabled.
File: elisp, Node: User Identification, Next: Time of Day, Prev: System Environment, Up: System Interface
User Identification
===================
- Function: user-login-name
This function returns the name under which the user is logged in.
This is based on the effective UID, not the real UID.
(user-login-name)
=> "lewis"
- Function: user-real-login-name
This function returns the name under which the user logged in.
This is based on the real UID, not the effective UID. This
differs from `user-login-name' only when running with the setuid
bit.
- Function: user-full-name
This function returns the full name of the user.
(user-full-name)
=> "Bil Lewis"
- Function: user-real-uid
This function returns the real UID of the user.
(user-real-uid)
=> 19
- Function: user-uid
This function returns the effective UID of the user.
File: elisp, Node: Time of Day, Next: Timers, Prev: User Identification, Up: System Interface
Time of Day
===========
This section explains how to determine the current time and the time
zone.
- Function: 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 `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.
The argument 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 `current-time'
(see below) and from `file-attributes' (*note File Attributes::.).
(current-time-string)
=> "Wed Oct 14 22:21:05 1987"
- Function: current-time
This function returns the system's time value as a list of three
integers: `(HIGH LOW MICROSEC)'. The integers HIGH and LOW
combine to give the number of seconds since 0:00 January 1, 1970,
which is HIGH * 2**16 + LOW.
The third element, 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 `file-attributes'. *Note File
Attributes::.
- Function: 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 `(OFFSET NAME)'. Here 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, 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
`nil'.
The argument 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 `current-time'
(see below) and from `file-attributes' (*note File Attributes::.).
File: elisp, Node: Timers, Next: Terminal Input, Prev: Time of Day, Up: System Interface
Timers
======
You can set up a timer to call a function at a specified future time.
- Function: run-at-time TIME REPEAT FUNCTION &rest ARGS
This function arranges to call FUNCTION with arguments ARGS at
time TIME. The argument FUNCTION is a function to call later, and
ARGS are the arguments to give it when it is called. The time
TIME is specified as a string.
Absolute times may be specified in a wide variety of formats; The
form `HOUR:MIN:SEC TIMEZONE MONTH/DAY/YEAR', where all fields are
numbers, works; the format that `current-time-string' returns is
also allowed.
To specify a relative time, use numbers followed by units. For
example:
`1 min'
denotes 1 minute from now.
`1 min 5 sec'
denotes 65 seconds from now.
`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.
If TIME is an integer, that specifies a relative time measured in
seconds.
The argument REPEAT specifies how often to repeat the call. If
REPEAT is `nil', there are no repetitions; FUNCTION is called just
once, at TIME. If REPEAT is an integer, it specifies a repetition
period measured in seconds.
- Function: cancel-timer TIMER
Cancel the requested action for TIMER, which should be a value
previously returned by `run-at-time'. This cancels the effect of
that call to `run-at-time'; the arrival of the specified time will
not cause anything special to happen.
File: elisp, Node: Terminal Input, Next: Terminal Output, Prev: Timers, Up: System Interface
Terminal Input
==============
This section describes functions and variables for recording or
manipulating terminal input. See *Note Emacs 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.
File: elisp, Node: Input Modes, Next: Translating Input, Up: Terminal Input
Input Modes
-----------
- Function: set-input-mode INTERRUPT FLOW META QUIT-CHAR
This function sets the mode for reading keyboard input. If
INTERRUPT is non-null, then Emacs uses input interrupts. If it is
`nil', then it uses CBREAK mode.
If FLOW is non-`nil', then Emacs uses XON/XOFF (`C-q', `C-s') flow
control for output to terminal. This has no effect except in
CBREAK mode. *Note Flow Control::.
The normal setting is system dependent. Some systems always use
CBREAK mode regardless of what is specified.
The argument META controls support for input character codes above
127. If META is `t', Emacs converts characters with the 8th bit
set into Meta characters. If META is `nil', Emacs disregards the
8th bit; this is necessary when the terminal uses it as a parity
bit. If META is neither `t' nor `nil', Emacs uses all 8 bits of
input unchanged. This is good for terminals using European 8-bit
character sets.
If QUIT-CHAR is non-`nil', it specifies the character to use for
quitting. Normally this character is `C-g'. *Note Quitting::.
The `current-input-mode' function returns the input mode settings
Emacs is currently using.
- Function: current-input-mode
This function returns current mode for reading keyboard input. It
returns a list, corresponding to the arguments of `set-input-mode',
of the form `(INTERRUPT FLOW META QUIT)' in which:
INTERRUPT
is non-`nil' when Emacs is using interrupt-driven input. If
`nil', Emacs is using CBREAK mode.
FLOW
is non-`nil' if Emacs uses XON/XOFF (`C-q', `C-s') flow
control for output to the terminal. This value has no effect
unless INTERRUPT is non-`nil'.
META
is non-`nil' if Emacs is paying attention to the eighth bit of
input characters; if nil, Emacs clears the eighth bit of
every input character.
QUIT
is the character Emacs currently uses for quitting, usually
`C-g'.
- Variable: meta-flag
This variable used to control whether to treat the 0200 bit in
keyboard input as the Meta bit. `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 `set-input-mode' instead.
File: elisp, Node: Translating Input, Next: Recording Input, Prev: Input Modes, Up: Terminal Input
Translating Input Events
------------------------
- Variable: extra-keyboard-modifiers
This variable lets Lisp programs "press" the modifier keys on the
keyboard. The value is a bit mask:
1
The SHIFT key.
2
The LOCK key.
4
The CTL key.
8
The META key.
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 CTL and META keys can be
virtually pressed.
- Variable: 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 `nil'.
If `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 N,
character codes N and up are untranslated.
In the example below, we set `keyboard-translate-table' to a
string of 128 characters. Then we fill it in to swap the
characters `C-s' and `C-\' and the characters `C-q' and `C-^'.
Subsequently, typing `C-\' has all the usual effects of typing
`C-s', and vice versa. (*Note Flow Control:: for more information
on this subject.)
(defun evade-flow-control ()
"Replace C-s with C-\ and C-q with C-^."
(interactive)
(let ((the-table (make-string 128 0)))
(let ((i 0))
(while (< i 128)
(aset the-table i i)
(setq i (1+ i))))
;; Swap `C-s' and `C-\'.
(aset the-table ?\034 ?\^s)
(aset the-table ?\^s ?\034)
;; Swap `C-q' and `C-^'.
(aset the-table ?\036 ?\^q)
(aset the-table ?\^q ?\036)
(setq keyboard-translate-table the-table)))
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 `recent-keys' and dribble files record the
characters after translation.
- Function: keyboard-translate FROM TO
This function modifies `keyboard-translate-table' to translate
character code FROM into character code TO. It creates or
enlarges the translate table if necessary.
- Variable: 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 `function-key-map' "binds" a key sequence K to a vector V, then
when K appears as a subsequence *anywhere* in a key sequence, it
is replaced with the events in V.
For example, VT100 terminals send `ESC O P' when the keypad PF1
key is pressed. Therefore, we want Emacs to translate that
sequence of events into the single event `pf1'. We accomplish
this by "binding" `ESC O P' to `[pf1]' in `function-key-map', when
using a VT100.
Thus, typing `C-c PF1' sends the character sequence `C-c ESC O P';
later the function `read-key-sequence' translates this back into
`C-c PF1', which it returns as the vector `[?\C-c pf1]'.
Entries in `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 `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 a number of terminal-specific files for many
common terminals; their main purpose is to make entries in
`function-key-map' beyond those that can be deduced from Termcap
and Terminfo. *Note Terminal-Specific::.
Emacs versions 18 and earlier used totally different means of
detecting the character sequences that represent function keys.
- Variable: key-translation-map
This variable is another keymap used just like `function-key-map'
to translate input events into other events. It differs from
`function-key-map' in two ways:
* `key-translation-map' goes to work after `function-key-map' is
finished; it receives the results of translation by
`function-key-map'.
* `key-translation-map' overrides actual key bindings.
The intent of `key-translation-map' is for users to map one
character set to another, including ordinary characters normally
bound to `self-insert-command'.
File: elisp, Node: Recording Input, Prev: Translating Input, Up: Terminal Input
Recording Input
---------------
- Function: 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.)
- Command: open-dribble-file FILENAME
This function opens a "dribble file" named FILENAME. When a
dribble file is open, each input event from the keyboard or mouse
(but not those from keyboard macros) are written in that file. A
non-character event is expressed using its printed representation
surrounded by `<...>'.
You close the dribble file by calling this function with an
argument of `nil'. The function always returns `nil'.
This function is normally used to record the input necessary to
trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble")
=> nil
See also the `open-termscript' function (*note Terminal Output::.).
File: elisp, Node: Terminal Output, Next: Flow Control, Prev: Terminal Input, Up: System Interface
Terminal Output
===============
The terminal output functions send output to the terminal or keep
track of output sent to the terminal. The variable `baud-rate' tells
you what Emacs thinks is the output speed of the terminal.
- Variable: 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.
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 `baud-rate'.
- Function: baud-rate
This function returns the value of the variable `baud-rate'. In
Emacs versions 18 and earlier, this was the only way to find out
the terminal speed.
- Function: send-string-to-terminal STRING
This function sends STRING to the terminal without alteration.
Control characters in 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 `C-u C-f'
to the computer):
(send-string-to-terminal "\eF4\^U\^F")
=> nil
- Command: open-termscript FILENAME
This function is used to open a "termscript file" that will record
all the characters sent by Emacs to the terminal. It returns
`nil'. Termscript files are useful for investigating problems
where Emacs garbles the screen, problems which are due to incorrect
Termcap entries or to undesirable settings of terminal options more
often than 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 `open-dribble-file' in *Note Terminal Input::.
(open-termscript "../junk/termscript")
=> nil
File: elisp, Node: Flow Control, Next: Batch Mode, Prev: Terminal Output, Up: System Interface
Flow Control
============
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
`emacs/INSTALL' file from the distribution; for help with Termcap
entries and DEC terminal concentrators, see `emacs/etc/TERMS'.
At one time, most terminals did not need flow control, and none used
`C-s' and `C-q' for flow control. Therefore, the choice of `C-s' and
`C-q' as command characters was unobjectionable. Emacs, for economy of
keystrokes and portability, used nearly all the ASCII control
characters, with mnemonic meanings when possible; thus, `C-s' for
search and `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 `C-s' and `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 is a rhetorical (or religious)
question; it has no simple answer.
One reason why we are reluctant to cater to the problems caused by
`C-s' and `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), `C-s'
and `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 `enable-flow-control'.
- Function: enable-flow-control
This function enables use of `C-s' and `C-q' for output flow
control, and provides the characters `C-\' and `C-^' as aliases
for them using `keyboard-translate-table' (*note Translating
Input::.).
You can use the function `enable-flow-control-on' in your `.emacs'
file to enable flow control automatically on certain terminal types.
- Function: enable-flow-control-on &rest TERMTYPES
This function enables flow control, and the aliases `C-\' and
`C-^', if the terminal type is one of TERMTYPES. For example:
(enable-flow-control-on "vt200" "vt300" "vt101" "vt131")
Here is how `enable-flow-control' does its job:
1. It sets CBREAK mode for terminal input, and tells the kernel to
handle flow control, with `(set-input-mode nil t)'.
2. It sets up `keyboard-translate-table' to translate `C-\' and `C-^'
into `C-s' and `C-q' were typed. Except at its very lowest level,
Emacs never knows that the characters typed were anything but
`C-s' and `C-q', so you can in effect type them as `C-\' and `C-^'
even when they are input for other commands. For example:
(setq keyboard-translate-table (make-string 128 0))
(let ((i 0))
;; Map most characters into themselves.
(while (< i 128)
(aset keyboard-translate-table i i)
(setq i (1+ i))))
;; Map `C-\' to `C-s'.
(aset the-table ?\034 ?\^s)
;; Map `C-^' to `C-q'.
(aset the-table ?\036 ?\^q)))
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 `baud-rate' to a smaller value so that Emacs uses
a smaller speed when calculating the padding needed. *Note Terminal
Output::.
File: elisp, Node: Batch Mode, Prev: Flow Control, Up: System Interface
Batch Mode
==========
The command line option `-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 `-l FILE', which loads the
library named FILE, and `-f FUNCTION', which calls FUNCTION with no
arguments.
Any Lisp program output that would normally go to the echo area,
either using `message' or using `prin1', etc., with `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.)
- Variable: noninteractive
This variable is non-`nil' when Emacs is running in batch mode.