{ pkgs ? import <nixpkgs> {} }:

let

  inherit (pkgs) lib;

  instances = {
    foo = "/etc/foo.yaml";
    bar = "/etc/lol/xyz.yaml";
    baz = "/etc/baz.yaml";
  };

  script = pkgs.writers.writeBashBin "get-config" ''
    case "$1" in
    ${lib.concatStrings (lib.mapAttrsToList (name: value: ''
        ${name})
          echo ${lib.escapeShellArg value}
          ;;
      '') instances)}
      *)
      echo error: invalid instance >&2
      exit 1
      ;;
    esac
  '';

in script