Declaratively manage packages without NixOS or home-manager

example.sh

# add your package set to your existing environment (together with the things you installed imperatively)
$ nix-env -i -f ./packages.nix
# More declarative: _replace_ your environment with _exactly_ what is in ./packages.nix
$ nix-env --set  -f ./packages.nix
# Show previous versions
$ nix-env --list-generations
# Rollback
$ nix-env --rollback

packages.nix

{ pkgs ? import <nixpkgs> {} }:

pkgs.buildEnv {
  name = "user-environment";
  paths = with pkgs; [
    ag
    firefox
    fzf
    git
    gnupg
    htop
    libreoffice
  ];
}