# Pastebin 9m8mK5jb
#!/bin/sh -eu
set -o pipefail

main() {
	acquire_lock
	do_stuff
}

acquire_lock() {
	lock="/tmp/lock"
	# open lockfile which will be released when script exits
	exec 9>"${lock}"
	if ! lockf -s -t 5 9; then
		echo "failed to acquire lock"
		exit 1
	fi
}

do_stuff() {
	echo -n "doing..."
	sleep 10
	echo "stuff"
}

main