def _filename_in_headerblock(relative_path, contents, linter_options):
    """Check for a filename in a header block.

    like such:
    # /path/to/filename
    """
    del linter_options
    check_index = 0

    if len(contents) > 0:
        if _line_is_shebang(contents[0]):
            check_index = 1

    if len(contents) < check_index + 1:
        description = ("""Document cannot have less than """
                       """{0} lines""").format(check_index + 1)
        return LinterFailure(description, 1, replacement=None)

    header_path = relative_path.replace("\\", "/")
    regex = re.compile(r"^{0} \/{1}$".format(_HDR_COMMENT,
                                             re.escape(header_path)))
    if not regex.match(contents[check_index]):
        description = ("""The filename /{0} must be the """
                       """first line of the header""")
        return LinterFailure(description.format(header_path),
                             check_index + 1,
                             _comment_type_from_line(contents[check_index]) +
                             "/{0}\n".format(header_path))
Check for a filename in a header block.

    like such:
    # /path/to/filename