How do I kill background processes / jobs when my shell script exits?

To clean up some mess, trap can be used. It can provide a list of stuff executed when a specific signal arrives:

trap "echo hello" SIGINT

but can also be used to execute something if the shell exits:

trap "killall background" EXIT

It's a builtin, so help trap will give you information (works with bash). If you only want to kill background jobs, you can do

trap 'kill $(jobs -p)' EXIT

Watch out to use single ', to prevent the shell from substituting the $() immediately.

This works for me (improved thanks to the commenters):

trap "trap - SIGTERM && kill -- -$$" SIGINT SIGTERM EXIT

kill -- -$$ sends a SIGTERM to the whole process group, thus killing also descendants.
Specifying signal EXIT is useful when using set -e (more details here).

Update: https://stackoverflow.com/a/53714583/302079 improves this by adding exit status and a cleanup function.

trap "exit" INT TERM
trap "kill 0" EXIT

Why convert INT and TERM to exit? Because both should trigger the kill 0 without entering an infinite loop.

Why trigger kill 0 on EXIT? Because normal script exits should trigger kill 0, too.

Why kill 0? Because nested subshells need to be killed as well. This will take down the whole process tree.

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