nix-shell --run 'echo hi' seems to just give me an interactive shell without running `echo hi`

shell.nix

{ pkgs ? import <nixpkgs> {} }:

(pkgs.buildFHSUserEnv {
  name = "deepspeech-fhs";
  targetPkgs = pkgs: (with pkgs;
    [
      libev
      zlib
      gcc
      readline
    ]);
  multiPkgs = pkgs: (with pkgs;
    [ udev
      alsaLib
    ]);
}).env