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If you want your script to ignore a kill signal (like Ctrl + C) or run a command before signal is executed, you can use ‘trap’ command.

Usage

You usually place trap command at the beginning of the script:

trap COMMAND SIGNAL_SPEC
  • COMMAND can be any command like echo 'signal detected'. It will run when signal is detected (it does not ignore the signal). An empty string ("") means to ignore the signal.
  • SIGNAL_SPEC can be a signal number (15) o signal name (SIGTERM). You can add several signals (separated by spaces).
  • Type trap -l to print a list of signal names and their corresponding numbers.
  • To restore a signal to default value, just type trap and SIGNAL_SPEC.

Examples

trap "" 2
  • It ignores SIGINT signal (when you press Ctrl + C).
trap "echo 'SIGTSTP signal detected'" 20
  • It runs echo command before triggering SIGTSTP signal (when you press Ctrl + Z).
trap "" 1 2 3 15
  • It ignores several signals.
trap "" 2
# some code
trap 2
  • Second trap command will restore SIGINT signal to its default value (it will not be ignored).

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