How to make lesskey terminal-independent?

Question

In bash scripts we can use tput to set terminal-independent less variables:

export LESS_TERMCAP_me=$(tput sgr0; )

Can we do the same thing with lesskey?

Answer 1

Short answer

• Yes you can put variable LESS_TERMCAP_me in the lesskey file but it requires fixing the source code and building your own less version (I explain that below).

• No the lesskey file cannot contain external commands as tput to become terminal-independent. However, you may use several lesskey files as recommended by the Thomas Dickey's answer.

lesskey file

The command lesskey is used to convert a human-readable text content into a binary configuration file for command less. This configuration file is named lesskey file and is usually the file ~/.less.

This files contains three sections:

1. Command (e.g. :q quit)
2. Line editing (e.g. ^G abort)
3. less environment variables (e.g. LESS_TERMCAP_me = \033(B\033[m)

Put variables LESS_TERMCAP_* in the lesskey file

$ cat > lesskey.txt << EOF
#env
LESS = -iSrsM +Gg
LESS_TERMCAP_md = $(tput bold; tput setaf 6)
LESS_TERMCAP_me = $(tput sgr0)
LESS_TERMCAP_so = $(tput bold; tput setaf 3; tput setab 4)
LESS_TERMCAP_se = $(tput rmso; tput sgr0)
LESS_TERMCAP_us = $(tput smul; tput bold; tput setaf 7)
LESS_TERMCAP_ue = $(tput rmul; tput sgr0)
LESS_TERMCAP_mr = $(tput rev)
LESS_TERMCAP_mh = $(tput dim)
EOF

$ lesskey lesskey.txt  # By default lesskey writes ~/.less

$ man bash             # By default man uses less (pager)

Bug

The command less reads the configuration ~/.less too late:
just after searching for variables LESS_TERMCAP_*.

This bug affects version 487 released on 29 Mar. 2017 (and surely previous versions).

I have just sent a bug report and the corresponding fix to maintainers. I will update this answer when the fix will be applied for the next less release...

Fix it yourself

1. Download source code archive from:

   • upstream: http://www.greenwoodsoftware.com/less/download.html
   • GNU ftp server: http://ftp.gnu.org/gnu/less/?C=M;O=D
   • a mirror server: http://ftpmirror.gnu.org/less/

2. Inverse two lines in file main.c at line 113
   Before:

   /*
    * Process command line arguments and LESS environment arguments.
    * Command line arguments override environment arguments.
    */
   is_tty = isatty(1);
   get_term();
   init_cmds();
   init_charset();
   init_line();
   

   After:

   /*
    * Process command line arguments and LESS environment arguments.
    * Command line arguments override environment arguments.
    */
   is_tty = isatty(1);
   init_cmds();         /* Load lesskey file before */ 
   get_term();          /* getting variables LESS_TERMCAP_* */
   init_charset();
   init_line();
   

3. Install dependencies required for the build

   ./configure
   

   If ./configure fails, identify the missing dependencies.
   In my case I have installed ncurses-devel to get header term.h.

4. Build

   make 
   

5. Keep your own-compiled less somewhere, for example to a personal directory ~/bin

   mkdir -p ~/bin
   cp ./less ~/bin
   PATH="$PATH:~/bin"
   

   Do not forget to set the environment variable PATH in your ~/.profile or if you prefer any other file as ~/.bashrc, ~/.login...

Extra tips

• See the TERMCAPS used in a man-page

  LESS_TERMCAP_DEBUG=1 man bash
  

• Retrieve the man-page with TERMCAPS encoding

  MANPAGER='tee man.txt' man bash
  

• Combine these two tips

  MANPAGER='tee man.txt' man bash
  LESS_TERMCAP_DEBUG=1 less man.txt
  

Answer 2

You can make less read a different lesskey file for each terminal type, e.g., by setting the LESSKEY (or LESSKEY_SYSTEM) environment in your shell initialization. The simple way of doing that would be to use the TERM variable as part of the filename, and making your shell check for the existence of these terminal-dependent files before setting the LESSKEY variable.