How to check in a bash script if something is running and exit if it is

Question

I have a script that runs every 15 minutes but sometimes if the box is busy it hangs and the next process will start before the first one is finished creating a snowball effect.

Answer 1

In lieu of pidfiles, as long as your script has a uniquely identifiable name you can do something like this:

#!/bin/bash
COMMAND=$0
# exit if I am already running
RUNNING=`ps --no-headers -C${COMMAND} | wc -l`
if [ ${RUNNING} -gt 1 ]; then
  echo "Previous ${COMMAND} is still running."
  exit 1
fi
... rest of script ...