How to install a shell script with Nix

Note

Let's say you're a Nix user and you've found some piece of software that consists of a shell script ( there are a lot of those ). Unfortunately, your trusty friend nixpkgs doesn't yield any result for it, and you want your system to be fully reproducible, so naturally, you choose Nix. Now, how would we add this package to our system with Nix without it being in nixpkgs? We'll build a derivation for it and install it ourselves.

We'll fetch the package from GitHub (tmux-up, i'll do a post about that some time), then use the install command to move it to the bin folder of the derivation and set the permissions so we will be able to call it. We specify dontBuild = true as we don't require any building here.

It looks like this (in a tmux-up.nix file):

{ stdenv, fetchFromGitHub }:

stdenv.mkDerivation rec {
  name = "tmux-up";
  version = "87a89989ad4a588eb5f02cc2cda50335d26d8435";

  src = fetchFromGitHub {
    owner = "jamesottaway";
    repo = "tmux-up";
    rev = version;
    sha256 = "1ykxqayz7qh7c7xzz01wkcvw4hmxg1nr50a6lpr0w0w99qcz0y8x";
  };

  dontBuild = true;

  installPhase = ''
    install -Dm755 -t $out/bin tmux-up
  '';
}

To fetch the information needed for fetchFromGitHub, we can use the nix-prefetch-git utility:

nix-prefetch-git --url https://github.com/jamesottaway/tmux-up

The result at the time of writing is:

{
  "url": "https://github.com/jamesottaway/tmux-up",
  "rev": "87a89989ad4a588eb5f02cc2cda50335d26d8435",
  "date": "...",
  "path": "...",
  "sha256": "1ykxqayz7qh7c7xzz01wkcvw4hmxg1nr50a6lpr0w0w99qcz0y8x",
  "fetchSubmodules": false,
  "deepClone": false,
  "leaveDotGit": false
}

To use this, we use the callPackage function (which does things like passing the stdenv and fetchFromGitHub arguments automatically) in a default.nix file:

let
  pkgs = import <nixpkgs> {};
in
pkgs.callPackage ./tmux-up.nix {}

Now, we can call nix-build and execute with result/bin/tmux-up.

Easy as that! (Well, Nix does have a bit of a learning curve, but once you get used to it it's not that bad. Just be ready to read nixpkgs code and copy paste from other people's configs a lot until it works!)

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