def add_filename_pattern(self, dir_name, pattern):
        """
        Adds a Unix shell-style wildcard pattern underneath the specified directory
        :param dir_name: str: directory that contains the pattern
        :param pattern: str: Unix shell-style wildcard pattern
        """
        full_pattern = '{}{}{}'.format(dir_name, os.sep, pattern)
        filename_regex = fnmatch.translate(full_pattern)
        self.regex_list.append(re.compile(filename_regex))