def add_arg(cmd, arg):
    """
    Add an argument to a command string. Concat the two.

    Args:
        cmd (str): The base command
        arg (str): An argument

    Returns:
        str
    """
    if not isinstance(arg, str):
        arg = str(arg)
    if len(cmd.split()) != 1:
        cmd = cmd + ',' + arg
    else:
        cmd = cmd + ' ' + arg
    return cmd
