---
title: "Flock"
url: https://perrotta.dev/2025/11/flock/
last_updated: 2025-11-20
---


Use [`flock`](https://man.archlinux.org/man/flock.1) to manage file/directory
locks from shell scripts.

## File

Shell #1:

```shell
lockfile=lock
flock "$lockfile" vim foo
```

`vim` will open.

Shell #2:

```shell
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:

```shell
flock . vim foo
```

`vim` will open.

Shell #2:

```shell
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.