Nix-shell shebang: Difference between revisions

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Created page with "You can use <code>nix-shell</code> as a script interpreter to * run scripts in arbitrary languages * provide dependencies with Nix To do this, start the script with multiple..."
 
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add links: Speeding up nix-shell shebang, cached-nix-shell
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* [https://gist.github.com/travisbhartwell/f972aab227306edfcfea nix-shell and Shebang Lines]
* [https://gist.github.com/travisbhartwell/f972aab227306edfcfea nix-shell and Shebang Lines]
* [https://notes.yukiisbo.red/posts/2021/07/Spice_up_with_Nix_Scripts.html Spice up with Nix: Scripts with magical dependencies]
* [https://notes.yukiisbo.red/posts/2021/07/Spice_up_with_Nix_Scripts.html Spice up with Nix: Scripts with magical dependencies]
* [https://discourse.nixos.org/t/speeding-up-nix-shell-shebang/4048 Speeding up nix-shell shebang]
* [https://github.com/xzfc/cached-nix-shell cached-nix-shell] - Instant startup time for nix-shell

Revision as of 19:25, 2 April 2022

You can use nix-shell as a script interpreter to

  • run scripts in arbitrary languages
  • provide dependencies with Nix

To do this, start the script with multiple shebang (#!) lines.
The first shebang line is always #! /usr/bin/env nix-shell.
The second shebang line declares the script language and the script dependencies.

Examples

Bash

To run bash scripts, set the interpreter with -i bash

#! /usr/bin/env nix-shell
#! nix-shell -i bash

echo hello world

You can use nix-shell -p ... to add dependencies:

#! /usr/bin/env nix-shell
#! nix-shell -i bash -p imagemagick cowsay

# scale image by 50%
convert "$1" -scale 50% "$1.s50.jpg" &&
cowsay "done $1.q50.jpg"

Python

#! /usr/bin/env nix-shell
#! nix-shell -i python3

print("hello world")
#! /usr/bin/env nix-shell
#! nix-shell -i python3 -p python3Packages.pillow python3Packages.ansicolor

# scale image by 50%
import sys, PIL.Image, ansicolor
path = sys.argv[1]
image = PIL.Image.open(path)
factor = 0.5
image = image.resize((round(image.width * factor), round(image.height * factor)))
path = path + ".s50.jpg"
image.save(path)
print(ansicolor.green(f"done {path}"))

Pinning nixpkgs

To pin nixpkgs to a specific version, add a third shebang line:

#! /usr/bin/env nix-shell
#! nix-shell -i bash
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.03.tar.gz

echo hello world

See also