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Bash Bits are small examples and tips for Bash Scripts. This bash bit shows you how to capture a Control C signal in a bash script, for example, to clean up any temp or pid files when your script is killed or closed.

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Exit signals are sent when for example you use pkill or killall. If you do not specify a number, a SIGTERM is sent. If you for example do a pkill -9 firefox, it sents a SIGKILL. If you have a bash script which places a temp file, or a pid file, you might want to clean that up before you exit.

We create a function to catch the exit signals first, then we bind this function to the exit signals.

This is the control_c function:

function control_c {
    echo -en "\n## Caught SIGINT; Clean up and Exit \n"
    rm /var/run/myscript.pid
    exit $?
}

Then we use the trap command to bind the function to an exit signal. Here I bind it to both SIGINT and SIGTERM:

trap control_c SIGINT
trap control_c SIGTERM

Now when the script gets killed or you do a control c, the script will remove it's pid file. You can put anything in the control_c function, I mostly use it for cleanup.

Read more about Signals here on The Linux Documentation Project

Tags: bash , bash-bits , control-c , exit-signals , shell , sigterm , snippets