Examples

Package an applicaton

{
  description = "Flake utils demo";

  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system}; in
      {
        packages = rec {
          hello = pkgs.hello;
          default = hello;
        };
        apps = rec {
          hello = flake-utils.lib.mkApp { drv = self.packages.${system}.hello; };
          default = hello;
        };
      }
    );
}

a more complete example

{
  description = "Flake utils demo";

  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.simpleFlake {
      inherit self nixpkgs;
      name = "simple-flake";
      overlay = ./overlay.nix;
      shell = ./shell.nix;
    };
}

Explanation

{
  # pass an instance of self
  self
, # pass an instance of the nixpkgs flake
  nixpkgs
, # we assume that the name maps to the project name, and also that the
  # overlay has an attribute with the `name` prefix that contains all of the
  # project's packages.
  name
, # nixpkgs config
  config ? { }
, # pass either a function or a file
  overlay ? null
, # use this to load other flakes overlays to supplement nixpkgs
  preOverlays ? [ ]
, # maps to the devShell output. Pass in a shell.nix file or function.
  shell ? null
, # pass the list of supported systems
  systems ? [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ]
}: null

Source

flake-utils - MyNixOS