Add 'trap'

[b-long]

What is it?

It allows you to run commands, "when the shell receives signal sigspec" (source the GNU manual).

It's complex, hence I don't recommend using Shell programming:

• https://www.gnu.org/software/bash/manual/html_node/Bourne-Shell-Builtins.html#index-trap
• https://unix.stackexchange.com/questions/79648/how-to-trigger-error-using-trap-command
• https://unix.stackexchange.com/questions/282722/is-trap-inherited-by-a-subshell
• https://unix.stackexchange.com/questions/57940/trap-int-term-exit-really-necessary
• https://stackoverflow.com/questions/54613527/how-to-trap-ctrlz-in-linux-posix-shell-script-possible-or-not
• https://stackoverflow.com/questions/8122779/is-it-necessary-to-specify-traps-other-than-exit

Platform / Compatibility

• It seems to be a part of POSIX shells (citation needed)
• Other shells have it, e.g. fish *Note, fish does not recommend using it: https://fishshell.com/docs/current/cmds/trap.html

Patterns you may see

trap cmd 0 1 2 3 13 15