11–20 of 159 posts
I asked on the mailing list if this was expected behavior, and it turns out that POSIX only requires EXIT to run on a clean shutdown; to catch interruptions, add more signals.
trap 'eval $(ssh-agent -k)' EXIT INT ABRT KILL TERM[flagged]
An annoying thing about bash is that EXIT will also run on SIGINT (^C), which most other shells won't (in my reading it's also not POSIX compliant, although the document is a bit vague). Some might argue this is a feature, but IMHO it's a bug – sometimes you really don't want cleanup to happen so people can inspect the contents of temporary files for debugging. Because trap doesn't pass the signal information to the…
My opinion is that LLM pair programming is most or maybe only beneficial to already skilled programmers. ChatGPT can open the door for you, but it can’t show you where the door is. I needed the experience to ask it for a Bash script that handles exit codes gracefully, which is not a question all junior programmers would be able to ask.
Glossing over some complexity, but roughly:
add_cleanup(){
event on cleanup "$@"
}
trap "event emit 'cleanup'" HUP EXIT
start_postgres(){
add_cleanup stop_postgres
# actually start pg
}
start_apache(){
add_cleanup stop_apache
# actually start apache
}
I used an exit trap to kill an SSH agent that I am running, and I noticed that dash did not kill if the script was interrupted, but only if it ran to successful completion. I asked on the mailing list if this was expected behavior, and it turns out that POSIX only requires EXIT to run on a clean shutdown; to catch interruptions, add more signals. trap 'eval $(ssh-agent -k)' EXIT INT ABRT KILL TERM
Otherwise a good article. I use the following code to enable passing the signal name to the trap handler, so that I can kill the Bash process with the correct signal name, which is best practice for Unix signal handling (EXIT would have to be handled specially in `sig_rekill`):
# Set trap for several signals and pass signal name to trap function.
# https://stackoverflow.com/a/2183063/207384
trap_with_arg() {
func="$1" ; shift
for sig ; do
trap "$func $sig" "$sig"
done
}
sig_rekill() {
# Kill whole process group.
trap "$1"; kill -"$1" -$$
}
# Catch signal and kill whole process group.
trap_with_arg sig_rekill HUP INT QUIT PIPE TERMI used an exit trap to kill an SSH agent that I am running, and I noticed that dash did not kill if the script was interrupted, but only if it ran to successful completion. I asked on the mailing list if this was expected behavior, and it turns out that POSIX only requires EXIT to run on a clean shutdown; to catch interruptions, add more signals. trap 'eval $(ssh-agent -k)' EXIT INT ABRT KILL TERM
Harsh lesson, those five signal names are identical if one squints real good. Would have never known.
I used an exit trap to kill an SSH agent that I am running, and I noticed that dash did not kill if the script was interrupted, but only if it ran to successful completion. I asked on the mailing list if this was expected behavior, and it turns out that POSIX only requires EXIT to run on a clean shutdown; to catch interruptions, add more signals. trap 'eval $(ssh-agent -k)' EXIT INT ABRT KILL TERM