View source for How to fetch Nixpkgs with an empty NIX PATH

The <code>NIX_PATH</code> environment variable is not the only way to fetch a Nixpkgs instance. You can also use a pure, declarative Nixpkgs source by fetching its tarball:

{{file|default.nix|nix|
<nowiki>
let
  nixpkgs = builtins.fetchTarball {
    url    = "https://github.com/NixOS/nixpkgs/archive/4a817d2083d6cd7068dc55511fbf90f84653b301.tar.gz";
    sha256 = "";
  };

  pkgs = import nixpkgs { config = {}; };

in
  ...
</nowiki>
}}

Remember to replace the example git revision (<code>4a817d2</code>...) with the desired revision of Nixpkgs. When building such a file for the very first time, Nix will refuse to evaluate a tarball that has an invalid or missing hash. Fortunately, the error message that will be printed contains the real hash to be used; simply replace <code>sha256 = "";</code> with <code>sha256 = "hash that Nix will give you";</code>, and rebuild the file.

You can also use the <code>nix-prefetch-url</code> utility to obtain the correct SHA256 hash without needing to build a spurious derivation.

{{commands|$ nix-prefetch-url --unpack "https://github.com/NixOS/nixpkgs/archive/4a817d2083d6cd7068dc55511fbf90f84653b301.tar.gz"}}

[[Category:Nix]] [[Category:Nixpkgs]] [[Category:Cookbook]]