def rot13_app(parser, cmd, args):  # pragma: no cover
    """
    rot13 encrypt a value.
    """

    parser.add_argument('value', help='the value to rot13, read from stdin if omitted', nargs='?')
    args = parser.parse_args(args)
    return rot13(pwnypack.main.string_value_or_stdin(args.value))