emacs/lisp/term/README

Copyright (C) 1993, 2001-2022 Free Software Foundation, Inc.
See the end of the file for license conditions.


   This directory contains files of elisp that customize Emacs for certain
terminal types.

   When Emacs opens a new terminal, it checks the TERM environment variable
to see what type of terminal the user is running on.  (If there is an entry
for TERM in the 'term-file-aliases' variable, Emacs uses the associated value
in place of TERM in the following.)  Emacs searches for an elisp file named
"term/${TERM}.el", and if one exists, loads it.  If Emacs finds no
suitable file, then it strips the last hyphen and what follows it from TERM,
and tries again.  If that still doesn't yield a file, then the previous hyphen
is stripped, and so on until all hyphens are gone.  For example, if the
terminal type is 'aaa-48-foo', Emacs will try first 'term/aaa-48-foo.el', then
'term/aaa-48.el' and finally 'term/aaa.el'.  Emacs stops searching at the
first file found, and will not load more than one file for any terminal.  Note
that it is not an error if Emacs is unable to find a terminal initialization
file; in that case, it will simply proceed with the next step without loading
any files.

   Once the file has been loaded (or the search failed), Emacs tries to call a
function named 'terminal-init-TERMINALNAME' (eg 'terminal-init-aaa-48' for the
'aaa-48' terminal) in order to initialize the terminal.  Once again, if the
function is not found, Emacs strips the last component of the name and tries
again using the shorter name.  This search is independent of the previous file
search, so that you can have terminal initialization functions for a family of
terminals collected in a single file named after the family name, and users
may put terminal initialization functions directly in their .emacs files.

   Note that an individual terminal file is loaded only once in an Emacs
session; if the same terminal type is opened again, Emacs will simply call the
initialization function without reloading the file.  Therefore, all the actual
initialization actions should be collected in terminal-init-* functions; the
file should not contain any top-level form that is not a function or variable
declaration.  Simply loading the file should not have any side effect.

   Similarly, the terminal initialization function is called only once on any
given terminal, when the first frame is created on it.  The function is not
called for subsequent frames on the same terminal.  Therefore, terminal-init-*
functions should only modify terminal-local variables (such as
'local-function-key-map') and terminal parameters.  For example, it is not
correct to modify frame parameters, since the modifications will only be
applied for the first frame opened on the terminal.


   When writing terminal packages, there are some things it is good to keep in
mind.

   First, about keycap names.  Your terminal package can create any keycap
cookies it likes, but there are good reasons to stick to the set recognized by
the X-windows code whenever possible.  The key symbols recognized by Emacs
are listed in src/term.c; look for the string 'keys' in that file.

   For one thing, it means that you'll have the same Emacs key bindings on in
terminal mode as on an X console.  If there are differences, you can bet
they'll frustrate you after you've forgotten about them.

   For another, the X keysyms provide a standard set of names that Emacs knows
about.  It tries to bind many of them to useful things at startup, before your
.emacs is read (so you can override them).  In some ways, the X keysym standard
is an admittedly poor one; it's incomplete, and not well matched to the set of
'virtual keys' that UNIX terminfo(3) provides.  But, trust us, the alternatives
were worse.

   This doesn't mean that if your terminal has a "Cokebottle" key you shouldn't
define a [cokebottle] keycap.  But if you must define cookies that aren't in
that set, try to pattern them on the standard terminfo variable names for
clarity; also, for a fighting chance that your binding may be useful to someone
else someday.

   For example, if your terminal has a 'find' key, observe that terminfo
supports a key_find capability and call your cookie [find].

Here is a complete list, with corresponding X keysyms.

-----------------------------------------------------------------------------
Variable name	cap	X Keysym	Description
--------------	---	------------	-------------------------------------
key_down	kd	down		Sent by terminal down arrow key
key_up		ku	up		Sent by terminal up arrow key
key_left	kl	left		Sent by terminal left arrow key
key_right	kr	right		Sent by terminal right arrow key
key_home	kh	home		Sent by home key.
key_backspace	kb			Sent by backspace key
key_dl		kd	deleteline	Sent by delete line key.
key_il		kA	insertline	Sent by insert line.
key_dc		kD			Sent by delete character key.
key_ic		kI	insertchar (1)	Sent by ins char/enter ins mode key.
key_eic		KM			Sent by rmir or smir in insert mode.
key_clear	kC			Sent by clear screen or erase key.
key_eos		kS			Sent by clear-to-end-of-screen key.
key_eol		kE			Sent by clear-to-end-of-line key.
key_sf		kF			Sent by scroll-forward/down key
key_sr		kR			Sent by scroll-backward/up key
key_npage	kN	next (2)	Sent by next-page key
key_ppage	kP	prior (2)	Sent by previous-page key
key_stab	kT			Sent by set-tab key
key_ctab	kt			Sent by clear-tab key
key_catab	ka			Sent by clear-all-tabs key.
key_enter	@8	kp-enter	Enter/send (unreliable)
key_print	%9	print		print or copy
key_ll		kH			Sent by home-down key
key_a1		K1	kp-1		Upper left of keypad
key_a3		K3	kp-3		Upper right of keypad
key_b2		K2	kp-5		Center of keypad
key_c1		K4	kp-7		Lower left of keypad
key_c3		K5	kp-9		Lower right of keypad
key_btab	kB	backtab		Back tab key
key_beg		@1	begin		beg(inning) key
key_cancel	@2	cancel		cancel key
key_close	@3			close key
key_command	@4	execute (3)	cmd (command) key
key_copy	@5			copy key
key_create	@6			create key
key_end		@7	end		end key
key_exit	@9			exit key
key_find	@0			find key
key_help	%1			help key
key_mark	%2			mark key
key_message	%3			message key
key_move	%4			move key
key_next	%5	next (2)	next object key
key_open	%6			open key
key_options	%7	menu (3)	options key
key_previous	%8	previous (2)	previous object key
key_redo	%0	redo		redo key
key_reference	&1			ref(erence) key
key_refresh	&2			refresh key
key_replace	&3			replace key
key_restart	&4	reset (3)	restart key
key_resume	&5			resume key
key_save	&6			save key
key_sbeg	&9			shifted beginning key
key_select	*6	select		select key
key_suspend	&7			suspend key
key_undo	&8	undo		undo key

key_scancel	&0			shifted cancel key
key_scommand	*1			shifted command key
key_scopy	*2			shifted copy key
key_screate	*3			shifted create key
key_sdc		*4			shifted delete char key
key_sdl		*5			shifted delete line key
key_send	*7			shifted end key
key_seol	*8			shifted clear line key
key_sexit	*9			shifted exit key
key_sf		kF			shifted find key
key_shelp	#1			shifted help key
key_shome	#2			shifted home key
key_sic		#3			shifted input key
key_sleft	#4			shifted left arrow key
key_smessage	%a			shifted message key
key_smove	%b			shifted move key
key_snext	%c			shifted next key
key_soptions	%d			shifted options key
key_sprevious	%e			shifted prev key
key_sprint	%f			shifted print key
key_sredo	%g			shifted redo key
key_sreplace	%h			shifted replace key
key_sright	%i			shifted right arrow
key_sresume	%j			shifted resume key
key_ssave	!1			shifted save key
key_suspend	!2			shifted suspend key
key_sundo	!3			shifted undo key

key_f0		k0	f0 (4)		function key 0
key_f1		k1	f1		function key 1
key_f2		k2	f2		function key 2
key_f3		k3	f3		function key 3
key_f4		k4	f4		function key 4
key_f5		k5	f5		function key 5
key_f6		k6	f6		function key 6
key_f7		k7	f7		function key 7
key_f8		k8	f8		function key 8
key_f9		k9	f9		function key 9
key_f10		k;	f10 (4)		function key 10
key_f11		F1	f11		function key 11
  :		:	   :			:
key_f35		FP	f35		function key 35
key_f36		FQ			function key 36
  :		:	   :			:
key_f64		k1			function key 64

(1) The terminfo documentation says this may be the 'insert character' or
    'enter insert mode' key.  Accordingly, key_ic is mapped to the 'insertchar'
    keysym if there is also a key_dc key; otherwise it's mapped to 'insert'.
    The presumption is that keyboards with 'insert character' keys usually
    have 'delete character' keys paired with them.

(2) If there is no key_next key but there is a key_npage key, key_npage
    will be bound to the 'next' keysym.  If there is no key_previous key but
    there is a key_ppage key, key_ppage will be bound to the 'previous' keysym.

(3) Sorry, these are not exact but they're the best we can do.

(4) The uses of the "k0" capability are inconsistent; sometimes it
    describes F10, whereas othertimes it describes F0 and "k;" describes F10.
    Emacs attempts to politely accommodate both systems by testing for
    "k;", and if it is present, assuming that "k0" denotes F0, otherwise F10.
-----------------------------------------------------------------------------

   The following X keysyms do *not* have terminfo equivalents.   These are
the cookies your terminal package will have to set up itself, if you want them:

	break
	system
	user
	kp-backtab
	kp-space
	kp-tab
	kp-f1
	kp-f2
	kp-f3
	kp-f4
	kp-multiply
	kp-add
	kp-separator
	kp-subtract
	kp-decimal
	kp-divide
	kp-0
	kp-2
	kp-4
	kp-6
	kp-8
	kp-equal

   In general, you should not bind any of the standard keysym names to
functions in a terminal package.  There's code in loaddefs.el that does that;
the less people make exceptions to that, the more consistent an interface Emacs
will have across different keyboards.  Those exceptions should go in your
.emacs file.

   Finally, if you're using a USL UNIX or a Sun box or anything else with the
USL version of curses(3) on it, bear in mind that the original curses(3) had
(and still has) a very much smaller set of keycaps.  In fact, the reliable
ones were just the arrow keys and the first ten function keys.  If you care
about making your package portable to older Berkeley machines, don't count on
the setup code to bind anything else.

   If your terminal's arrow key sequences are so funky that they conflict with
normal Emacs key bindings, the package should set up a function called
(enable-foo-arrow-keys), where 'foo' becomes the terminal name, and leave
it up to the user's .emacs file whether to call it.

   Before writing a terminal-support package, it's a good idea to read the
existing ones and learn the common conventions.


This file is part of GNU Emacs.

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it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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