Bash unix signals

Documentation

man 7 signal	https://man.archlinux.org/man/core/man-pages/signal.7.en
wikipedia: unix signals	https://en.wikipedia.org/wiki/Signal_(IPC)#POSIX_signals

Signal Keybindings

List signal keybindings

stty -a | tr ';' '\n'
# intr = ^C
# quit = ^\
# erase = ^?
# ...

Send Signal

kill -l              # list all signals
kill -9 ${PID}       # send signal 9 (SIGKILL)
kill -SIGINT ${PID}  # send isgnal 2 (SIGINT)

Callback on Signal

# Install callback for SIGINT and SIGTRAP
on_signal() { echo "received SIGINT or SIGTRAP!" }
trap on_signal SIGINT SIGTRAP

# Uninstall a trap
trap - SIGINT SIGTRAP

You can also trap on any process error (and implement behaviour similar to set -e)

on_error() {
    echo "There was an error on line $LINENO"
    exit 1
}

trap on_error ERR

Identifying Trapped Signal

See bin/core/identify-unix-signal.
I wrote a shellscript to identify the signals sent to the process.

print_emitted_signal() {
    echo "SIGNAL IS: $1"
}


trap_all_signals() {
    for i in {1..64} ; do
        trap "print_emitted_signal $i" "$i"
    done
}


mainloop() {
    while true ; do
        echo "type 'q' to exit"
        read input
        if [[ "$input" == "q" ]] ; then
            break
        fi
    done
}


trap_all_signals
mainloop