Bash script file-based lock

script.sh

#!/bin/bash

LOCK='path/to/file.lock'

[ -f "$LOCK" ] && { echo 'locked' >&2; exit 1; } || { touch "$LOCK" && trap 'rm -f "$LOCK"; exit $?' INT TERM EXIT;  } || { echo 'unable to lock' >&2; exit 2; }

# processing