qq about clap: I have

let untar_opts = &App::new("tar_api")
    .subcommand(
      SubCommand::with_name("untar")
    ).get_matches();

  let tar_file = untar_opts
    .value_of("file")
    .map(PathBuf::from)
    .unwrap();

  let dest = untar_opts
    .value_of("dest")
    .map(PathBuf::from)
    .unwrap();