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.
See section Building Emacs, for related information. See also section Emacs Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
The order of operations performed (in `startup.el') by Emacs when it is started up is as follows:
load-path, by running the file
named `subdirs.el' in each directory that is listed.
LANG.
before-init-hook.
inhibit-default-init
is non-nil. (This is not done in `-batch' mode or if
`-q' was specified on the command line.) The library's file name
is usually `default.el'.
after-init-hook.
initial-major-mode, provided
the buffer `*scratch*' is still current and still in Fundamental
mode.
inhibit-startup-echo-area-message.
term-setup-hook.
frame-notice-user-settings, which modifies the
parameters of the selected frame according to whatever the init files
specify.
window-setup-hook. See section Window Systems.
inhibit-startup-message is nil, and the
buffer is still empty.
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.
(setq inhibit-startup-echo-area-message
"your-login-name")
Emacs explicitly checks for an expression as shown above in your
`.emacs' file; your login name must appear in the expression as a
Lisp string constant. Other methods of setting
inhibit-startup-echo-area-message to the same value do not
inhibit the startup message.
This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your `.emacs' file will not inhibit the message for someone else.
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' affect 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 section `Entering Emacs' in The GNU Emacs Manual.
A site may 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 (see section 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 `-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 does not subsequently load the `default.el' file.
Another file for site-customization is `site-start.el'. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option `-no-site-file'.
"site-start". The only
way you can change it with real effect is to do so before dumping
Emacs.
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 (see section Byte Compilation), and make your `.emacs'
file load the other file using load (see section Loading).
See section `Init File Examples' in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your `.emacs' file.
nil,
then the default library is not loaded. The default value is
nil.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. 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. Emacs finds the file
in the normal manner, by searching the load-path directories, and
trying the `.elc' and `.el' suffixes.
The usual function of a terminal-specific library is to enable special
keys to send sequences that Emacs can recognize. It may also need to
set or add to function-key-map if the Termcap entry does not
specify all the terminal's function keys. 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 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. See section Hooks.
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).
You can use term-setup-hook to override the definitions made by a
terminal-specific file.
See window-setup-hook in section Window Systems, for a related
feature.
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.
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.
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 section `Command Line Switches and Arguments' in The GNU Emacs Manual.
nil
value.
These functions are called with no arguments. They can access the
command-line argument under consideration through the variable
argi, which is bound temporarily at this point. The remaining
arguments (not including the current one) are in the variable
command-line-args-left.
When a function recognizes and processes the argument in argi, it
should return a non-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 command-line-args-left.
If all of these functions return nil, then the argument is used
as a file name to visit.
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.
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control. The low-level primitive for
killing Emacs is kill-emacs.
If 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 section Batch Mode.)
If 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.
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
save-buffers-kill-emacs.
save-buffers-kill-emacs
calls the functions in the list kill-emacs-query-functions, in
order of appearance, with no arguments. These functions can ask for
additional confirmation from the user. If any of them returns
nil, Emacs is not killed.
save-buffers-kill-emacs is
finished with all file saving and confirmation, it runs the functions in
this hook.
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, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is using a window system.
suspend-emacs
returns nil to its caller in Lisp.
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.
After the user resumes Emacs, suspend-emacs runs the normal hook
suspend-resume-hook. See section Hooks.
The next redisplay after resumption will redraw the entire screen,
unless the variable no-redraw-on-reenter is non-nil
(see section Refreshing the 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!
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.
string-match.
alpha-vms
aix-v3
berkeley-unix
dgux
gnu
gnu/linux
hpux
irix
ms-dos
next-mach
rtu
unisoft-unix
usg-unix-v
vax-vms
windows-nt
xenix
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
system-configuration to distinguish between different operating
systems.
(system-name)
=> "www.gnu.org"
The symbol system-name is a variable as well as a function. In
fact, the function returns whatever value the variable
system-name currently holds. Thus, you can set the variable
system-name in case Emacs is confused about the name of your
system. The variable is also useful for constructing frame titles
(see section Frame Titles).
nil, it is used instead of
system-name for purposes of generating email addresses. For
example, it is used when constructing the default value of
user-mail-address. See section User Identification. (Since this is
done when Emacs starts up, the value actually used is the one saved when
Emacs was dumped. See section Building Emacs.)
process-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
process-environment; binding that
variable with let is also reasonable practice.
getenv and setenv work by means
of 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")
":" for Unix and GNU systems, and ";" for MS-DOS
and Windows NT.
nil if that directory cannot be determined.
nil, this is a directory within which to look for the
`lib-src' and `etc' subdirectories. This is non-nil
when Emacs can't find those directories in their standard installed
locations, but can find them in a directory related somehow to the one
containing the Emacs executable.
By default, the values are integers that are 100 times the system load
averages, which indicate the average number of processes trying to run.
If use-float is non-nil, then they are returned
as floating point numbers and without multiplying by 100.
(load-average)
=> (169 48 36)
(load-average t)
=> (1.69 0.48 0.36)
lewis@rocky[5] % uptime
11:55am up 1 day, 19:37, 3 users,
load average: 1.69, 0.48, 0.36
t or nil, indicating whether the
privilege is to be turned on or off. Its default is nil. The
function returns t if successful, nil otherwise.
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.
nil if none. The value reflects command line options such as
`-q' or `-u user'.
Lisp packages that load files of customizations, or any other sort of
user profile, should obey this variable in deciding where to find it.
They should load the profile of the user name found in this variable.
If init-file-user is nil, meaning that the `-q'
option was used, then Lisp packages should not load any customization
files or user profile.
LOGNAME
is set, that value is used. Otherwise, if the environment variable
USER is set, that value is used. Otherwise, the value is based
on the effective UID, not the real UID.
If you specify uid, the value is the user name that corresponds to uid (which should be an integer).
(user-login-name)
=> "lewis"
LOGNAME and USER.
NAME, if that is set.
(user-full-name)
=> "Bil Lewis"
If uid is non-nil, then it should be an integer, a user-id,
or a string, a login name. Then user-full-name returns the full
name corresponding to that user-id or login name.
The symbols user-login-name, user-real-login-name and
user-full-name are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to "fake out" Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (see section Frame Titles).
(user-real-uid)
=> 19
This section explains how to determine the current time and the time zone.
substring to extract pieces of it. It is wise to count the
characters from the beginning of the string rather than from the end, as
additional information may some day 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 list whose first
two elements are integers. Thus, you can use times obtained from
current-time (see below) and from file-attributes
(see section Other Information about Files).
(current-time-string)
=> "Wed Oct 14 22:21:05 1987"
(high low microsec). The integers
high and low combine to give the number of seconds since
0:00 January 1, 1970, which is
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. See section Other Information about Files.
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 above) and from file-attributes (see section Other Information about Files).
These functions convert time values (lists of two or three integers)
to strings or to calendrical information. There is also a function to
convert calendrical information to a time value. You can get time
values from the functions current-time (see section Time of Day) and
file-attributes (see section Other Information about Files).
Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future.
Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number -37 represents the Gregorian year 38 B.C.
You can also specify the field width and type of padding for any of
these `%'-sequences. This works as in printf: you write
the field width as digits in the middle of a `%'-sequences. If you
start the field width with `0', it means to pad with zeros. If you
start the field width with `_', it means to pad with spaces.
For example, `%S' specifies the number of seconds since the minute; `%03S' means to pad this with zeros to 3 positions, `%_3S' to pad with spaces to 3 positions. Plain `%3S' pads with zeros, because that is how `%S' normally pads to two positions.
(seconds minutes hour day month year dow dst zone)
Here is what the elements mean:
t if daylight savings time is effect, otherwise nil.
Common Lisp Note: Common Lisp has different meanings for dow and zone.
decode-time. It converts seven
items of calendrical data into a time value. For the meanings of the
arguments, see the table above under decode-time.
Year numbers less than 100 are treated just like other year numbers. If
you want them to stand for years above 1900, you must alter them yourself
before you call encode-time.
The optional argument zone defaults to the current time zone and
its daylight savings time rules. If specified, it can be either a list
(as you would get from current-time-zone), a string as in the
TZ environment variable, or an integer (as you would get from
decode-time). The specified zone is used without any further
alteration for daylight savings time.
If you pass more than seven arguments to encode-time, the first
six are used as seconds through year, the last argument is
used as zone, and the arguments in between are ignored. This
feature makes it possible to use the elements of a list returned by
decode-time as the arguments to encode-time, like this:
(apply 'encode-time (decode-time ...))
You can perform simple date arithmetic by using out-of-range values for the sec, minute, hour, day, and month arguments; for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time values; if you try to encode a time that is out of range, an error results.
You can set up a timer to call a function at a specified future time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
sit-for or read-event which can wait. Therefore, a
timer's execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
Absolute times may be specified in a wide variety of formats; this function tries to accept all the commonly used date formats. Valid formats include these two,
year-month-day hour:min:sec timezone hour:min:sec timezone month/day/year
where in both examples all fields are numbers; the format that
current-time-string returns is also allowed, and many others
as well.
To specify a relative time, use numbers followed by units. For example:
If time is a number (integer or floating point), 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 a number, it
specifies a repetition period measured in seconds.
In most cases, repeat has no effect on when first call
takes place---time alone specifies that. There is one exception:
if time is t, then the timer runs whenever the time is a
multiple of repeat seconds after the epoch. This is useful for
functions like display-time.
The function run-at-time returns a timer value that identifies
the particular scheduled future action. You can use this value to call
cancel-timer (see below).
with-timeout returns
the value of the last form in body. If, however, the execution of
body is cut short by the timeout, then with-timeout
executes all the timeout-forms and returns the value of the last
of them.
This macro works by setting a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a
primitive that can wait, with-timeout cannot stop executing
body while it is in the midst of a computation--only when it
calls one of those primitives. So use with-timeout only with a
body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use
a timer to avoid waiting too long for an answer. See section Yes-or-No Queries.
If repeat is nil, the timer runs just once, the first time
Emacs remains idle for a long enough time. More often repeat is
non-nil, which means to run the timer each time Emacs
remains idle for secs seconds.
The function run-with-idle-timer returns a timer value which you
can use in calling cancel-timer (see below).
Emacs becomes "idle" when it starts waiting for user input, and it remains idle until the user provides some input. If a timer is set for five seconds of idleness, it runs approximately five seconds after Emacs first became idle. Even if its repeat is true, this timer will not run again as long as Emacs remains idle, because the duration of idleness will continue to increase and will not go down to five seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.
run-at-time or run-with-idle-timer.
This cancels the effect of that call to run-at-time; the arrival
of the specified time will not cause anything special to happen.
This section describes functions and variables for recording or manipulating terminal input. See section Emacs Display, for related functions.
nil, then it uses CBREAK mode. The default setting is
system dependent. Some systems always use CBREAK mode regardless
of what is specified.
When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-nil, then Emacs uses XON/XOFF
(C-q, C-s) flow control for output to the terminal. This
has no effect except in CBREAK mode. See section Flow Control.
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
that use 8-bit character sets.
If quit-char is non-nil, it specifies the character to
use for quitting. Normally this character is C-g.
See section Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
set-input-mode,
of the form (interrupt flow meta quit) in
which:
nil when Emacs is using interrupt-driven input. If
nil, Emacs is using CBREAK mode.
nil if Emacs uses XON/XOFF (C-q, C-s)
flow control for output to the terminal. This value is meaningful only
when interrupt is nil.
t if Emacs treats the eighth bit of input characters as
the meta bit; 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.
This section describes features for translating input events into
other input events before they become part of key sequences. These
features apply to each event in the order they are described here: each
event is first modified according to extra-keyboard-modifiers,
then translated through keyboard-translate-table (if applicable),
and finally decoded with the specified keyboard coding system. If it is
being read as part of a key sequence, it is then added to the sequence
being read; then subsequences containing it are checked first with
function-key-map and then with key-translation-map.
Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down.
When using a window system, the program can "press" any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed.
nil.
If keyboard-translate-table is a char-table, then each character
read from the keyboard is looked up in this character. If the value
found there is non-nil, then it is used instead of the
actual input character.
In the example below, we set keyboard-translate-table to a
char-table. 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)
(setq keyboard-translate-table
(make-char-table 'keyboard-translate-table nil))
;; Swap C-s and C-\.
(aset keyboard-translate-table ?\034 ?\^s)
(aset keyboard-translate-table ?\^s ?\034)
;; Swap C-q and C-^.
(aset keyboard-translate-table ?\036 ?\^q)
(aset keyboard-translate-table ?\^q ?\036))
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.
keyboard-translate-table to translate
character code from into character code to. It creates
the keyboard translate table if necessary.
The remaining translation features translate subsequences of key
sequences being read. They are implemented in read-key-sequence
and have no effect on input read with read-event.
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--but if they do, the ordinary
bindings take priority.
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
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.
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. For example,
if C-x f has a binding in key-translation-map, that
translation takes effect even though C-x f also has a key binding
in the global map.
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.
You can use function-key-map or 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 read-key-sequence---or 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 C-c h to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) 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)
Finally, if you have enabled keyboard character set decoding using
set-keyboard-coding-system, decoding is done after the
translations listed above. See section Specifying a Coding System for One Operation. In future
Emacs versions, character set decoding may be done before the other
translations.
You close the dribble file by calling this function with an argument
of 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).
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.
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.
baud-rate.
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
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 open-dribble-file in section Terminal Input.
(open-termscript "../junk/termscript")
=> nil
To define system-specific X11 keysyms, set the variable
system-key-alist.
(code
. symbol), where code is the numeric keysym code (not
including the "vendor specific" bit,
and symbol is the name for the function key.
For example (168 . mute-acute) defines a system-specific key used
by HP X servers whose numeric code is
+ 168.
It is not crucial to exclude from the alist the keysyms of other X servers; those do no harm, as long as they don't conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See section Multiple Displays.
This section attempts to answer the question "Why does Emacs use flow-control characters in its command character set?" For a second view on this issue, read the comments on flow control in the `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 for searching and quoting
was natural and uncontroversial. With so many commands needing key
assignments, of course we assigned meanings to nearly all ASCII
control characters.
Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers ignored them. 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 Emacs users, who can turn flow control off, did not want to switch to less mnemonic key bindings for the sake of flow control.
So which usage is "right"---Emacs's or that of some terminal and concentrator manufacturers? This question 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 (around 1970), C-s and C-q were sent by the computer to turn the punch on and off!
As window systems and PC terminal emulators replace character-only
terminals, the flow control problem is gradually disappearing. For the
mean time, Emacs provides a convenient way of enabling flow control if
you want it: call the function enable-flow-control.
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.
(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. 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.
See section Translating Input Events.
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.
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 error 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.)
nil when Emacs is running in batch mode.
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