¬ just serendipity 🍀 (not just serendipity)

Use flock to manage file/directory locks from shell scripts.

File #

Shell #1:

lockfile=lock
flock "$lockfile" vim foo

vim will open.

Shell #2:

lockfile=lock
flock "$lockfile" vim foo

vim will block, waiting until the lock is released.

Once we :q (quit) vim in the first shell, the second vim will immediately open.

lock is a file. It can be anything e.g. lockfile=/tmp/lock or lockfile=$(mktemp) or lockfile=my.lock.

lockfile is just an arbitrary name for the variable. We don’t even need to use a variable, this is just for illustration purposes, and to make it easier to reuse its value in the second shell. Passing the lockfile directly to flock is perfectly acceptable.

Directory #

We can lock entire directories as well.

Shell #1:

flock . vim foo

vim will open.

Shell #2:

flock . vim bar

vim will block, waiting until the lock is released. Same as before.

Once we :q (quit) vim in the first shell, the second vim will immediately open.

When is this handy? For example, when multiple parties need to edit the same file, and we need to ensure they do not overwrite each other’s changes.