def pub_filename(filetype):
    """
    Regex pattern to search for the public use CPS filename.

    Parameters:
        filetype (character): The type of file you want to search for (.txt, .zip, ect.)

    Returns (character): The regex pattern required to find the desired filetype
    """
    if filetype == '.txt':
        return r'(?<=[/])[\w\d_.-]+(.txt)$'

    if filetype == '.zip':
        return r'(?<=[/])[\w\d_.-]+(pub)(.zip)$'

    message = 'Filetype not supported'
    return message