How to map function keys in less?

Question

Is it possible to map function keys (F1-F12) in less with lesskey?

This doesn't seem to work:

#command
F1    forw-line

Answer 1

Historically, terminals use escaped sequences for functions keys, cursor keys and more. The termcap and terminfo facilities help to deal with the variations across terminals.

First you need to determine what your terminal sends when you hit F1, in bash you can do:

printf "%q\n" "CtrlV F1"

Within the second pair of quotes you type Ctrl+V to cause the next keystroke to be treated literally (verbatim), and then F1. On my terminal (rxvt) I see

$'\E[11~'

so my F1 sequence is escape [ 11 ~, so into .lesskey should go

#command
\e[11~  forw-line

run lesskey to update, and now F1 will invoke that command.

infocmp is another way to see how your terminal is set up, e.g.

infocmp -L1 rxvt | grep key_f1=

See Stéphane Chazelas answer here for more details on that, though less doesn't use readline, configuring readline requires a similar understanding.