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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{Emacs Display}, for additional operating system status information pertaining to the terminal and the screen.
1.1 Starting Up Emacs | Customizing Emacs start-up processing. | |
1.2 Getting out of Emacs | How exiting works (permanent or temporary). | |
1.3 Operating System Environment | Distinguish the name and kind of system. | |
1.4 User Identification | Finding the name and user id of the user. | |
1.5 Time of Day | Getting the current time. | |
1.6 Timers | Setting a timer to call a function at a certain time. | |
1.7 Terminal Input | Recording terminal input for debugging. | |
1.8 Terminal Output | Recording terminal output for debugging. | |
1.9 Flow Control | How to turn output flow control on or off. | |
1.10 Batch Mode | Running Emacs without terminal interaction. |
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This section describes what Emacs does when it is started, and how you can customize these actions.
1.1.1 Summary: Sequence of Actions at Start Up | Sequence of actions Emacs performs at start-up. | |
1.1.2 The Init File: ‘.emacs’ | Details on reading the init file (‘.emacs’). | |
1.1.3 Terminal-Specific Initialization | How the terminal-specific Lisp file is read. | |
1.1.4 Command Line Arguments | How command line arguments are processed, and how you can customize them. |
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The order of operations performed (in ‘startup.el’) by Emacs when it is started up is as follows:
before-init-hook
.
inhibit-default-init
is
non-nil
. (This is not done in ‘-batch’ mode or if ‘-q’
was specified on command line.)
after-init-hook
.
term-setup-hook
.
window-setup-hook
. @xref{Window Systems}.
inhibit-startup-message
is non-nil
.
This display is also inhibited in batch mode, and if the current buffer is not ‘*scratch*’.
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.
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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. See Entering Emacs in The GNU Emacs Manual.
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 (@pxref{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 (@pxref{Byte Compilation}), and make your ‘.emacs’
file load the other file using load
(@pxref{Loading}).
See Init File Examples in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your ‘.emacs’ file.
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
.
These two normal hooks are run just before, and just after, loading of the user’s init file or ‘default.el’.
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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. See section 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. @xref{Hooks}.
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)
.
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 @ref{Window Systems}, for a related
feature.
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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 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.
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.
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 Command Line Switches and Arguments in The GNU Emacs Manual.
The value of this variable is the arguments passed by the shell to Emacs, as a list of strings.
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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.
1.2.1 Killing Emacs | Exiting Emacs irreversibly. | |
1.2.2 Suspending Emacs | Exiting Emacs reversibly. |
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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.
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 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.
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.
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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.
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
. @xref{Hooks}.
The next redisplay after resumption will redraw the entire screen,
unless the variable no-redraw-on-reenter
is non-nil
(@pxref{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!
This variable is a normal hook run before suspending.
This variable is a normal hook run after suspending.
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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.
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.
This function returns the name of the machine you are running on.
(system-name) ⇒ "prep.ai.mit.edu"
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
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.
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")
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
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.
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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"
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.
This function returns the full name of the user.
(user-full-name) ⇒ "Bil Lewis"
This function returns the real UID of the user.
(user-real-uid) ⇒ 19
This function returns the effective UID of the user.
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This section explains how to determine the current time and the time zone.
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
(@pxref{File Attributes}).
(current-time-string) ⇒ "Wed Oct 14 22:21:05 1987"
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
. @xref{File Attributes}.
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
(@pxref{File Attributes}).
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You can set up a timer to call a function at a specified future time.
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:
denotes 1 minute from now.
denotes 65 seconds from now.
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.
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.
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This section describes functions and variables for recording or manipulating terminal input. See @ref{Emacs Display}, for related functions.
1.7.1 Input Modes | Options for how input is processed. | |
1.7.2 Translating Input Events | Low level conversion of some characters or events into others. | |
1.7.3 Recording Input | Saving histories of recent or all input events. |
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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. See section 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.
@xref{Quitting}.
The current-input-mode
function returns the input mode settings
Emacs is currently using.
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:
is non-nil
when Emacs is using interrupt-driven input. If
nil
, Emacs is using CBREAK mode.
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
.
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.
is the character Emacs currently uses for quitting, usually C-g.
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.
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This variable lets Lisp programs “press” the modifier keys on the keyboard. The value is a bit mask:
The <SHIFT> key.
The <LOCK> key.
The <CTL> key.
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.
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. (See section 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.
This function modifies keyboard-translate-table
to translate
character code from into character code to. It creates
or enlarges the translate table if necessary.
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. See section Terminal-Specific Initialization.
Emacs versions 18 and earlier used totally different means of detecting the character sequences that represent function keys.
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
.
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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.)
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 (see section Terminal Output).
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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.
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
.
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.
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
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 Terminal Input.
(open-termscript "../junk/termscript") ⇒ nil
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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
.
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
(see section Translating Input Events).
You can use the function enable-flow-control-on
in your
‘.emacs’ file to enable flow control automatically on certain
terminal types.
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:
(set-input-mode nil t)
.
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. See section Terminal Output.
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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.)
This variable is non-nil
when Emacs is running in batch mode.
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