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-vmsaix-v3berkeley-unixdguxgnugnu/linuxhpuxirixms-dosnext-machrtuunisoft-unixusg-unix-vvax-vmswindows-ntxenixWe 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.