8

I would like to define rc-files of my software via Nix. Therefore I define a new package in config.nix which will contain a config file:

{ pkgs, ... }:
{
packageOverrides = pkgs : with pkgs; {
  custom-config = import ./custom-config {
    inherit (pkgs) stdenv;
  };
};
}

Then in custom-config/default.nix the file is defined inline:

{ stdenv }:

stdenv.mkDerivation rec {
  name = "custom-config";
  stdenv.mkDerivation {
    name = "CustomConfig";
    src = builtins.toFile "customrc" ''
      # content
      '';
  };
}

The last part missing is: Add a specific environment variable to the users default shell, like CUSTOM_CONFIG_RC, which is honored by to relevant program.

Can anybody give me a hint? I am just starting to grasp the language.

Chris Martin
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lksdfjöalksdjf
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1 Answers1

11

The typical Nix way is to do this without modifying the user's shell, and instead use makeWrapper to wrap the program that uses the RC file. That way your environment doesn't need to get polluted with variables that only one program needs.

buildInputs = [ makeWrapper ];

postInstall = ''
  wrapProgram "$out/bin/my-program" --set CUSTOM_CONFIG_RC "$rcFile"
'';

See more examples of makeWrapper use in the Nixpkgs repo.

If you really do want that variable available in your environment, your derivation could do something like

postInstall = ''
  mkdir -p $out/share
  echo "export CUSTOM_CONFIG_RC=$rcFile" > $out/share/your-rc-setup-script.sh
'';

When the package is installed, this will end up symlinked from ~/.nix-profile/share/your-rc-setup-script.sh, and then in your .bashrc, you can load it with

source $HOME/.nix-profile/share/your-rc-setup-script.sh
Chris Martin
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  • Ok, I see. But using 'makeWrapper' leads to recompilation from source of the whole packet -- while the only change I need is a runtime environment variable and an added file? The second tip: Yeah, had it like this... didn't taste right ;-) Would like to have all specifications in a single place. Is it right that: The 'config.nix' cannot influence the 'environment' variable present in the 'configuration.nix'? – lksdfjöalksdjf Sep 27 '16 at 08:35
  • 1. Instead of altering the package, you could make the wrapped program be a separate derivation to avoid the need for recompilation. 2. The "one place" could be a directory of these scripts e.g. `~/.nix-profile/share/rc-scripts/...` and your `.bashrc` could iterate through that directory and source them all. 3. I don't exactly follow, but I think what you're saying is right. There is no direct mechanism for setting your base environment from packages as far as I know, and in my opinion that would break with Nix philosophy. – Chris Martin Sep 27 '16 at 15:23
  • I was wondering that if you had a Python package that had multiple scripts, and all expected some environment variable to be used when you call it, is the expected idiom to use makeWrapper on each of the scripts? Or is there a way to wrap all scripts in one go? – CMCDragonkai Jul 18 '18 at 06:17