def check_boolean_value(option_string):
    """
    Validates that a command line option string represents a boolean value.

    Check if a command line option string represents a valid boolean value.
    Accepted strings for True are "true", "t", "yes", "y" or any cased variants
    thereof. Accepted string for False are "false", "f", "no", "n" or any cased
    variants thereof. Any other values are considered invalid, and supplying
    them will cause an exception to be raised.

    option_string: A command line option string representing a boolean value.
    """
    option_string = option_string.lower()
    if option_string in ["true", "t", "yes", "y"]:
        return True
    elif option_string in ["false", "f", "no", "n"]:
        return False
    else:
        raise Exception("Can't convert '{o}' to bool.".format(o=option_string))