lesskey

Compile the default key binding source file

$ lesskey

$ lesskey [path/to/lesskey_file]

$ lesskey -o [path/to/output] [path/to/lesskey_file]

$ lesskey -V

lesskey [-o output] [--] [input]

lesskey is used to specify or customize key bindings for the less pager. It reads a source file containing key binding definitions and compiles it into a binary file that less reads at startup. The default input file is ~/.lesskey and the default output file is ~/.less.
The lesskey source file can contain up to four sections, each introduced by a header line: #command for key bindings, #line-edit for editing behavior at the search prompt, #env for environment variables, and #stop to mark end of file.
In the #command section, each line maps a key sequence to a less action. Keys can be specified as literal characters, control characters (^X), escape sequences (\e), or special keys like arrows (\ku, \kd, \kr, \kl), page up/down (\kU, \kD), home (\kh), end (\ke), and delete (\kx).
The #line-edit section controls behavior at the search and command prompts with actions like forw-complete, back-complete, delete, backspace, home, end, up, down, and abort.
The #env section sets environment variables that less will see at startup, such as LESS for default options and LESSCHARSET for character set configuration.

-o file, --output=file

Specify the output file for the compiled binary key binding file. Defaults to ~/.less

Display the version number of lesskey

Marks the end of options; useful if the input filename begins with a dash

The lesskey source file uses a simple text format. Example ~/.lesskey:

$ #command
j      forw-line
k      back-line
\kd    forw-line
\ku    back-line
gg     goto-line
G      goto-end
q      quit

#line-edit
^A     home
^E     end
^U     abort

#env
LESS = -i -M -R

In less version 583 and later, less reads the ~/.lesskey source file directly without needing to compile it via lesskey. The lesskey binary is considered deprecated in modern versions, though it is still distributed. If both ~/.lesskey (source) and ~/.less (compiled) exist, newer versions of less prefer the source file. The compiled binary format is not portable across architectures or less versions. The #env section can set LESSOPEN and LESSCLOSE which execute external commands, so lesskey files from untrusted sources should be treated with caution.

lesskey was created by Mark Nudelman as a companion utility to the less pager, which he developed starting in 1983 as a replacement for more. Historically, less required a compiled binary key binding file because parsing a text file at startup was considered too slow. Starting with less version 583 (circa 2021), less gained the ability to read the lesskey source file directly, making the lesskey compilation step optional.

less(1), more(1)