74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
|
---
|
||
|
|
date: 2025-07-08
|
||
|
|
title: Writing robust bash scripts with Nix
|
||
|
|
permalink: /daily/2025/07/08/writing-robust-bash-scripts-nix
|
||
|
|
---
|
||
|
|
|
||
|
|
I have a lot of custom Bash scripts I use - some to perform simple commands like `git log` with some additional arguments, to more complex ones that mount and unmount USB devices plugged into my laptop.
|
||
|
|
|
||
|
|
A lot of people will post their scripts online along with their dotfiles for others to read and take inspiration from.
|
||
|
|
|
||
|
|
Mine are in my [nix config][0] directory and each script is added as a custom package I can install.
|
||
|
|
|
||
|
|
Here's an example of a script written as a Nix package:
|
||
|
|
|
||
|
|
```nix
|
||
|
|
{ pkgs }:
|
||
|
|
|
||
|
|
pkgs.writeShellApplication {
|
||
|
|
name = "get-tags";
|
||
|
|
|
||
|
|
runtimeInputs = with pkgs; [ git ];
|
||
|
|
|
||
|
|
text = ''
|
||
|
|
if [[ "$#" -gt 0 ]]; then
|
||
|
|
git tag | grep "$*"
|
||
|
|
exit 0
|
||
|
|
fi
|
||
|
|
|
||
|
|
git tag
|
||
|
|
'';
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
It gets a filtered list of Git tags within a repository using the `git tag` and `grep` commands.
|
||
|
|
|
||
|
|
Nix automatically adds the shebang line and sets some default shell options, so those aren't included within the script text.
|
||
|
|
|
||
|
|
It also automatically runs `shellcheck` to ensure the script is correct.
|
||
|
|
|
||
|
|
## Injecting Dependencies
|
||
|
|
|
||
|
|
This script depends on `git`. Without it, it would not run successfully.
|
||
|
|
|
||
|
|
Instead of assuming it is installed, `runtimeInputs` ensures any dependencies are present and the script can be executed, even if the dependencies aren't enabled globally.
|
||
|
|
|
||
|
|
Scripts can also rely on other scripts.
|
||
|
|
|
||
|
|
`get-tags` has a corresponding `count-tags` script that counts the returned tags:
|
||
|
|
|
||
|
|
```nix
|
||
|
|
pkgs.writeShellApplication {
|
||
|
|
name = "count-tags";
|
||
|
|
|
||
|
|
runtimeInputs = with pkgs; [
|
||
|
|
coreutils
|
||
|
|
get-tags
|
||
|
|
];
|
||
|
|
|
||
|
|
text = ''
|
||
|
|
get-tags "''${1:-}" | wc -l
|
||
|
|
'';
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
`get-tags` is declared as a dependency, as well as `coreutils` to add the `wc` command that counts the lines.
|
||
|
|
|
||
|
|
## Here's the thing
|
||
|
|
|
||
|
|
Using this approach gives me more robust scripts that are checked and verified, and will always have the required dependencies.
|
||
|
|
|
||
|
|
And, because they are added as custom Nix packages in my configuration, I am able to decide which scripts to install on which computer, giving me the most flexibility.
|
||
|
|
|
||
|
|
[0]: https://code.oliverdavies.uk/opdavies/nix-config
|