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:
before-init-hook.
inhibit-default-init
is non-nil. (This is not done in `-batch' mode or if
`-q' was specified on 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.
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")
Simply setting inhibit-startup-echo-area-message to your login
name is not sufficient to inhibit the message; Emacs explicitly checks
whether `.emacs' contains an expression as shown above. Your login
name must appear in the expression as a Lisp string constant.
This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your `.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'.
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. 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
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. 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-buffer-query-functions, in
order of appearance, with no arguments. These functions can ask for
additional confirmation from the user. If any of them returns
non-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 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.
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. 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. 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.
aix-v3
berkeley-unix
hpux
irix
linux
rtu
unisoft-unix
usg-unix-v
vax-vms
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.
string-match.
(system-name)
=> "prep.ai.mit.edu"
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")
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 near where the Emacs executable was found.
(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
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.
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.
(user-login-name)
=> "lewis"
LOGNAME and USER.
(user-full-name)
=> "Bil Lewis"
(user-real-uid)
=> 19
This section explains how to determine the current time and the time zone.
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 (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 below) and from file-attributes (see section Other Information about Files).
You can set up a timer to call a function at a specified future time.
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:
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.
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.
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.
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 default 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.
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 has no effect
unless interrupt is non-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.
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.
This section describes features for translating input events into other input events before they become part of key sequences.
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.
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.
keyboard-translate-table to translate
character code from into character code to. It creates
or enlarges the translate table if necessary.
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
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.
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.
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 20) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key function-key-map "\C-ch" 'hyperify)
The `iso-transl' library uses this feature to provide a way of inputting non-ASCII Latin-1 characters.
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. In
Emacs versions 18 and earlier, this was the only way to find out the
terminal speed.
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, 1 << 28), 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 (1 << 28) + 168.
It is not a problem if the alist defines keysyms for other X servers, as long as they don't conflict with the ones used by the X server actually in use.
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 uncontroversial.
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 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 (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.
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 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.
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 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.)
nil when Emacs is running in batch mode.