How can I use a nix configuration when not using Nixos?

Question

So I've installed Nix on Arch linux and I'm able to run nix-env -i example, however how can I define a Nix configuration?

As I don't have any /nixos/configuration.nix file present.

Is this possible?

---

My goal here is to be able to define a configuration which I could then use something like nixos-rebuild switch to install and provision all the software.

Answer 1

I use NixOS, but I use /etc/nixos/configuration.nix to describe my system; I keep it fairly minimal and prefer not to install "user" software by editing configuration.nix.

So what I do instead is use my ~/.nixpkgs/config.nix (which I believe you also have an equivalent of even in a non-NixOS nix install? I've never actually used nix separately).

The basic structure I use is this:

{
  packageOverrides = nixpkgs: with nixpkgs; rec {
    mine = with pkgs; buildEnv {
      name = "mine";
      paths = [
        # your packages here
      ];
    };
  };
}

buildEnv is a convenience function from nix that makes an "environment" package out of a bunch of others; installing the package mine depends on (and so installs) all of the things listed in paths, and also makes sure they get included in PATH and things like that.

Then I just use nix-env -riA nixos.mine to deploy changes I've made to my environment description (or to rebuild my environment following channel updates). The -r tells it to remove everything else other than mine from the new generation of my profile, which means I can (ab?)use nix-env -i some-package as a way of "temporarily" installing some-package, and if I don't decide I like it enough to actually record it in my config.nix it'll just get removed anyway next time I deploy.