How do I make sure my bash script isn't already running?

Question

I have a bash script I want to run every 5 minutes from cron... but there\'s a chance the previous run of the script isn\'t done yet... in this case, i want the new run to j

Answer 1

If you use a lockfile, you should make sure that the lockfile is always removed. You can do this with 'trap':

if ( set -o noclobber; echo "locked" > "$lockfile") 2> /dev/null; then
  trap 'rm -f "$lockfile"; exit $?' INT TERM EXIT
  echo "Locking succeeded" >&2
  rm -f "$lockfile"
else
  echo "Lock failed - exit" >&2
  exit 1
fi

The noclobber option makes the creation of lockfile atomic, like using a directory.