trap lockfile

lockdir=/var/lock/somethingcustom.lock
if mkdir "$lockdir"; then
    # directory did not exist, but was created successfully
    echo >&2 "successfully acquired lock: $lockdir"

     # Remove lockdir when the script finishes, or when it receives a signal
     trap 'rm -rf "$lockdir"' 0    # remove directory when script finishes

    # continue script
else
    echo >&2 "cannot acquire lock, giving up on $lockdir"
    exit 0
fi