Wrappers vs. Dotfiles

Usually user applications (like editors, etc.) get configured through dotfiles in the user's home directory. An alternative, declarative approach is to create wrappers for application on a per-user basis, like this:

{
  users.users.root.packages = [
    (pkgs.writeScriptBin "htop" ''
      #! ${pkgs.bash}/bin/bash
      export HTOPRC=${pkgs.writeText "htoprc" ...}
      exec ${pkgs.htop}/bin/htop "$@"
    '')
  ];
}

The disadvantage of this way is that it doesn't propagate man pages and other paths from the old derivation. Please refer to Nix_Cookbook#Wrapping_packages to possible solutions to retain all outputs.

You can use this simple function which takes care of wrapping the script & symlinking

 writeShellScriptBinAndSymlink = name: text: super.symlinkJoin {
    name = name;
    paths = [
      (super.writeShellScriptBin name text)
      super."${name}"
    ];
  };

Downside of the Wrapper Approach

• There might be applications that don't provide means to specify configuration. One could override $HOME, but then there might be applications that require $HOME for other stuff than configuration.
• Applications cannot write their configuration anymore, e.g. htop will just terminate without error and nothing changed.

Alternatives

• Home Manager manages dotfiles in the user's home directory