flock — Manage file locks from shell scripts. It can be used to ensure that only one instance of a command i

Run a command with a file lock as soon as the lock is available

flock {{path/to/lock.lock}} {{command}}

Run a command with a file lock, or exit if the lock is currently being held (with exit code 1)

flock {{path/to/lock.lock}} {{[-n|--nonblock]}} {{command}}

Run a command with a file lock, or exit with a specific error code if the lock is currently being held

flock {{path/to/lock.lock}} {{[-n|--nonblock]}} {{[-E|--conflict-exit-code]}} {{123}} {{command}}

Run a command with a file lock, waiting up to 10 seconds for the lock to be available before giving up

flock {{path/to/lock.lock}} {{[-w|--timeout]}} 10 {{command}}

Backup a bunch of files, waiting for the previous `tar` command to finish if it's still running elsewhere and holding the same lock file (can be used in a `cron` job that runs often)

flock {{path/to/backup.lock}} {{tar -cvf path/to/backup.tar path/to/data/}}