'\" t
.TH LESSKEY 1 "29 Jan 2026" "less 692"
.\" Define a string for the caret ("hat") as portably as possible.
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.\" Define a string for the neutral apostrophe as portably as possible.
.ie \n(.g .ds ' \(aq
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.SH NAME
lesskey \- customize key bindings for less
.SH "SYNOPSIS (deprecated)"
.B lesskey
.RB [ \-o
.IR output ]
.B \-\-
.I input
.br
.B lesskey
.RB [ \-\-output=\c
.IR output ]
.B \-\-
.I input
.PP
.B "lesskey \-V"
.br
.B "lesskey \-\-version"
.SH SCOPE
This document describes the format of the 
.B lesskey
source file, which is used by
.B less
version 582 and later.
In previous versions of 
.BR less ,
a separate program called
.B lesskey
was used to compile the 
.B lesskey 
source file into a format understood by
.BR less .
This compilation step is no longer required and the
.B lesskey
program is therefore deprecated, although the file format remains supported by
.B less
itself.
.PP
.SH DESCRIPTION
A
.B lesskey
file specifies a set of key bindings and environment variables
to be used by subsequent invocations of
.BR less .
.SH FILE FORMAT
The input file consists of one or more
.IR sections .
Each section starts with a line that identifies the type of section.
Possible sections are:
.IP #command
Customizes command key bindings.
.IP #line\-edit
Customizes line-editing key bindings.
.IP #env
Defines environment variables.
.PP
Blank lines are ignored.
Any text that follows an unescaped hash mark (#) in a line is ignored,
except as noted below.
.
.SH "COMMAND SECTION"
The command section begins with the line
.PP
#command
.PP
If the command section is the first section in the file,
this line may be omitted.
The command section consists of lines of the form:
.PP
	\fIstring\fP <whitespace> \fIaction\fP <whitespace> [extra-string] <newline>
.PP
Whitespace is any sequence of one or more spaces and/or tabs.
The \fIstring\fP is the command key(s) which invoke the action.
The \fIstring\fP may be a single command key, or a sequence of up to 15 keys.
The \fIaction\fP is the name of the less action, 
from the lists in the EXAMPLE sections below.
The characters in the \fIstring\fP may appear literally, or be
prefixed by a caret to indicate a control key.
A backslash followed by one to three octal digits may be used to
specify a character by its octal value.
A backslash followed by certain characters specifies input
characters as follows:
.RS 5m
.TS
l l l.
\eb	BACKSPACE	(0x08)
\ee	ESCAPE	(0x1B)
\en	NEWLINE	(0x0A)
\er	RETURN	(0x0D)
\et	TAB	(0x09)
.TE
.RE
.PP
\ek followed by one or two characters represents the char(s) produced
when one of these keys is pressed:
.RS 5m
.TS
l l.
\ekb	BACKSPACE (the BACKSPACE key; may be different than \eb)
\ekB	ctrl-BACKSPACE
\ekd	DOWN ARROW
\ekD	PAGE DOWN
\eke	END
\ekE	ctrl-END
\ekF	shift-END
\ekh	HOME
\ekH	ctrl-HOME
\ekI	shift-HOME
\eki	INSERT
\ekl	LEFT ARROW
\ekL	ctrl-LEFT ARROW
\ekM	shift-LEFT ARROW
\ekr	RIGHT ARROW
\ekR	ctrl-RIGHT ARROW
\ekS	shift-RIGHT ARROW
\ekt	BACKTAB
\eku	UP ARROW
\ekU	PAGE UP
\ekx	DELETE
\ekX	ctrl-DELETE
\ek1	F1
\ekp1	lower left key on the numeric keypad
\ekp2	lower center key on the numeric keypad
\ekp3	lower right key on the numeric keypad
\ekp4	center left key on the numeric keypad
\ekp5	center key on the numeric keypad
\ekp6	center right key on the numeric keypad
\ekp7	upper left key on the numeric keypad
\ekp8	upper center key on the numeric keypad
\ekp9	upper right key on the numeric keypad
\ekp0	0 on the numeric keypad
\ekp*	* on the numeric keypad
\ekp/	/ on the numeric keypad
\ekp\-	\- on the numeric keypad
\ekp+	+ on the numeric keypad
\ekp.	. on the numeric keypad
\ekp,	, on the numeric keypad
.TE
.RE
.PP
A backslash followed by any other character indicates that character is
to be taken literally.
Characters which must be preceded by backslash include
caret, space, tab, hash mark and the backslash itself.
.PP
An action may be followed by an "extra" string.
When such a command is entered while running
.BR less ,
the action is performed, and then the extra
string is parsed, just as if it were typed in to
.BR less .
This feature can be used in certain cases to extend
the functionality of a command.
For example, see the "{" and ":t" commands in the example below.
It can also be used to execute more than one command when a key is pressed.
For example, if this line were in a lesskey file, pressing the "B" key
would first set the "b" mark and then search for the string "next":
.PP
.EX
.nf
    B set\-mark b/next\en
.fi
.EE
.PP
The extra string has a special meaning for the "quit" action:
when
.B less
quits, the ASCII value of the first character of the extra string 
is used as its exit status.
.
.SH EXAMPLE
The following input file describes the set of
default command keys used by 
.BR less .
Documentation on each command can be found in the
.B less
man page, under the key sequence which invokes the command.
.PP
.RS 5m
.TS
l l.
#command
\er	forw\-line
\en	forw\-line
e	forw\-line
j	forw\-line
\ekd	forw\-line
\*^E	forw\-line
\*^N	forw\-line
k	back\-line
y	back\-line
\*^Y	back\-line
\*^K	back\-line
\*^P	back\-line
\eku	back\-line
J	forw\-line\-force
K	back\-line\-force
Y	back\-line\-force
d	forw\-scroll
\*^D	forw\-scroll
u	back\-scroll
\*^U	back\-scroll
\e40	forw\-screen
f	forw\-screen
\*^F	forw\-screen
\*^V	forw\-screen
\ekD	forw\-screen
b	back\-screen
\*^B	back\-screen
\eev	back\-screen
\ekU	back\-screen
z	forw\-window
w	back\-window
\ee\e40	forw\-screen\-force
\eeb	back\-screen\-force
\eej	forw\-newline
\eek	back\-newline
F	forw\-forever
\eeF	forw\-until\-hilite
\eef	forw\-bell\-hilite
R	repaint\-flush
r	repaint
\*^R	repaint
\*^L	repaint
\eeu	undo\-hilite
\eeU	clear\-search
g	goto\-line
\ekh	goto\-line
\ekH	goto\-line \ee{
\ekI	goto\-line \ee{
\eke	goto\-end
\ekE	goto\-end \ee}
\ekF	goto\-end \ee}
<	goto\-line
\ee<	goto\-line
p	percent
%	percent
\ee(	left\-scroll
\ee)	right\-scroll
\ee{	no\-scroll
\ee}	end\-scroll
\ekl	left\-scroll
\ekr	right\-scroll
\ekL	no\-scroll
\ekM	no\-scroll
\ekR	end\-scroll
\ekS	end\-scroll
{	forw\-bracket {}
}	back\-bracket {}
(	forw\-bracket ()
)	back\-bracket ()
[	forw\-bracket []
]	back\-bracket []
\ee\*^F	forw\-bracket
\ee\*^B	back\-bracket
G	goto\-end
\ee>	goto\-end
>	goto\-end
P	goto\-pos
\eeG	goto\-end\-buffered
\&=	status
\*^G	status
:f	status
/	forw\-search
?	back\-search
\ee/	forw\-search *
\ee?	back\-search *
n	repeat\-search
\een	repeat\-search\-all
N	reverse\-search
\eeN	reverse\-search\-all
&	filter
m	set\-mark
M	set\-mark\-bottom
\eem	clear\-mark
\&\*'	goto\-mark
\*^X\*^X	goto\-mark
E	examine
:e	examine
\*^X\*^V	examine
:n	next\-file
:p	prev\-file
\*^O\*^N	osc8\-forw\-search
\*^On	osc8\-forw\-search
\*^O\*^P	osc8\-back\-search
\*^Op	osc8\-back\-search
\*^O\*^O	osc8\-open
\*^Oo	osc8\-open
\*^O\*^L	osc8\-jump
\*^Ol	osc8\-jump
t	next\-tag
T	prev\-tag
:x	index\-file
:d	remove\-file
\-	toggle\-option
:t	toggle\-option t
s	toggle\-option o
	## Use a long option name by starting the 
	## extra string with ONE dash; eg:
	##   s toggle\-option \-log\-file\en
\&_	display\-option
|	pipe
v	visual
!	shell
#	pshell
+	firstcmd
\ee[M	mouse
\ee[<	mouse6
\ekp1	goto\-end
\ekp2	forw\-line
\ekp3	forw\-screen
\ekp4	left\-scroll
\ekp6	right\-scroll
\ekp7	goto\-line
\ekp8	back\-line
\ekp9	back\-screen
\ekp0	noaction 0
\ekp*	noaction *
\ekp/	noaction /
\ekp\-	noaction \-
\ekp+	noaction +
\ekp.	noaction .
\ekp,	noaction ,
H	help
h	help
\ek1	help
V	version
0	digit
1	digit
2	digit
3	digit
4	digit
5	digit
6	digit
7	digit
8	digit
9	digit
q	quit
Q	quit
:q	quit
:Q	quit
ZZ	quit
.TE
.RE
.SH PRECEDENCE
Commands specified by
.B lesskey
take precedence over the default commands.
A default command key may be disabled by including it in the
input file with the action "invalid".
Alternatively, a key may be defined
to do nothing by using the action "noaction".
"noaction" is similar to "invalid", but
.B less
will give an error beep for an "invalid" command,
but not for a "noaction" command.
In addition, ALL default commands may be disabled by
adding this control line to the input file:
.PP
#stop
.PP
This will cause all default commands to be ignored.
The #stop line should be the last line in that section of the file.
.PP
Be aware that #stop can be dangerous.
Since all default commands are disabled,
you must provide sufficient commands before the #stop line
to enable all necessary actions.
For example, failure to provide a "quit" command can lead to frustration.
.
.SH "LINE EDITING SECTION"
The line-editing section begins with the line:
.PP
.EX
#line\-edit
.EE
.PP
This section specifies new key bindings for the line editing commands,
in a manner similar to the way key bindings for
ordinary commands are specified in the #command section.
The line-editing section consists of a list of keys and actions,
one per line as in the example below.
.
.SH EXAMPLE
The following input file describes the set of
default line-editing keys used by
.BR less :
.PP
.RS 5m
.TS
l l.
#line\-edit
\et	forw\-complete
\e17	back\-complete
\eekt	back\-complete
\ee\et	back\-complete
^L	expand
^V	literal
^A	literal
\eel	right
\ekr	right
\eeh	left
\ekl	left
\eeb	word\-left
\ee\ekl	word\-left
\ee\ekL	word\-left
\eew	word\-right
\ee\ekr	word\-right
\ee\ekR	word\-right
\eei	insert
\eki	insert
\eex	delete
\ekx	delete
\eeX	word\-delete
\eekx	word\-delete
\ekX	word\-delete
\ee\eb	word\-backspace
\ekB	word\-backspace
\ee0	home
\ekh	home
\ee$	end
\eke	end
\eek	up
\eku	up
\eej	down
\ekd	down
^G	abort
\ekp1	end
\ekp2	down
\ekp4	left
\ekp6	right
\ekp7	home
\ekp8	up
\ekp0	noaction 0
\ekp*	noaction *
\ekp/	noaction /
\ekp\-	noaction \-
\ekp+	noaction +
\ekp.	noaction .
\ekp,	noaction ,
\ee[M	mouse
\ee[<	mouse6
.TE
.RE
.
.SH "LESS ENVIRONMENT VARIABLES"
The environment variable section begins with the line
.PP
#env
.PP
Following this line is a list of environment variable assignments.
Each line consists of an environment variable name, an equals sign (=)
and the value to be assigned to the environment variable.
White space before and after the equals sign is ignored.
Variables assigned in this way are visible only to
.BR less .
If a variable is specified in the system environment and also in a
lesskey file, the value in the lesskey file takes precedence.
.
.PP
If the variable name is followed by += rather than =,
the string is appended to the variable's existing value.
This currently works only if any += lines immediately follow
the same variable's original definition (with an = line),
without any intervening definitions of other variables.
It can append only to a variable defined earlier in the file;
it cannot append to a variable in the system environment.
The string is appended literally, without any extra whitespace added,
so if whitespace is desired,
it should be appended to the end of the preceding line.
(It cannot be added to the beginning of the += string because space after
the equals sign is ignored, as noted above.)
.
.PP
In the string after the = sign, a substring of the form ${NAME}
is replaced with the value of the environment variable "NAME".
The value of the variable may come from either the system environment,
an earlier lesskey file, or an earlier definition in the current lesskey file.
Simple text replacements can be performed by using 
the syntax ${NAME/STRING/REPL}.
This replaces all instances of "STRING" in the named 
environment variable with the text "REPL".
STRING is matched using a simple text comparison;
no metacharacters are supported.
An instance of slash or right curly bracket in STRING or REPL
must be escaped by preceding it with \fItwo\fP backslashes.
If REPL is an empty string, all instances of STRING are removed.
A slash immediately before the right curly bracket may be omitted.
Multiple replacements may be performed by using
the syntax ${NAME/STRING1/REPL1/STRING2/REPL2} and so on.
.
.SH CONDITIONAL CONFIGURATION
If a line begins with #version followed by a relational operator and a version number,
the remainder of the line is parsed if and only if the running version of
.B less
(or
.BR lesskey )
matches the operator.
This can be helpful if a lesskey file is used by different versions of
.BR less .
.PP
For example, suppose that a new command named 'sideways\-search' is added in
.B less
version 777.
Then the following line would assign the command to the Q key, but only in versions of
.B less
which support it. The line would be ignored by versions earlier than 777.
.PP
.EX
.nf
	#version >= 777  Q sideways\-search
.fi
.EE
.PP
These six operators are supported:
.RS 5m
.TS
l l.
 >	Greater than
 <	Less than
 >=	Greater than or equal to
 <=	Less than or equal to
 =	Equal to
 !=	Not equal to
.TE
.RE
.PP
The #version feature is not supported in
.B less
and
.B lesskey
before version 594.
In those older versions, all #version lines are ignored.
.
.SH EXAMPLE
The following input file sets the \-i and \-S options when
.B less
is run and, on version 595 and higher, adds a \-\-color option.
.PP
.EX
.nf
	#env
	## (Note that there must be a space at the end of the next line,
	##  to separate the \-\-color option from the \-S option.)
	LESS = \-i\ \-S\ 
	#version\ >=\ 595\ \ LESS\ +=\ \-\-color=Hkc
.fi
.EE
.
.SH "SEE ALSO"
.BR less (1)
.
.SH WARNINGS
On MS-DOS and OS/2 systems, certain keys send a sequence of characters
which start with a NUL character (0).
This NUL character should be represented as \e340 in a lesskey file.
.
.SH COPYRIGHT
Copyright (C) 1984-2026  Mark Nudelman
.PP
less is part of the GNU project and is free software.
You can redistribute it and/or modify it
under the terms of either
(1) the GNU General Public License as published by
the Free Software Foundation; or (2) the Less License.
See the file README in the less distribution for more details
regarding redistribution.
You should have received a copy of the GNU General Public License
along with the source for less; see the file COPYING.
If not, write to the Free Software Foundation, 59 Temple Place,
Suite 330, Boston, MA  02111-1307, USA.
You should also have received a copy of the Less License;
see the file LICENSE.
.PP
less is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.
.
.SH AUTHOR
.
Mark Nudelman
.br
Report bugs at
.nh
https://\*:github\*:.com/\*:gwsw/\*:less/\*:issues.
.hy
