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How to Safely Interrupt a Sleeping Script

Bátori István, December 2006

Sometimes, instead of using the cron daemon, you write a script that enters a sleep cycle. For example:

while :
do
    doAction
    sleep $sleepTime
done

This method can make it difficult to interrupt the script and restart it while it is sleeping -- particularly if the script has left processes running or if it's important to have only one instance of the script running. You can get around this problem by starting the sleep process in the background, enabling the script to catch the stop signal immediately. Here's an example:

trapAction() {
    echo "exit signal has received, exiting..."

    # you can kill the sleep process here if you like
    [[ -f $TMP_FILE ]] && rm $TMP_FILE
    exit 2
}


trap trapAction INT TERM

while :
do
    doAction
    sleep $sleepTime &
    wait $!
done

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