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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_primary_command_usage(message=''):
 # type: (str) -> str """Return the usage string for the primary command."""

    if not settings.merge_primary_command and None in settings.subcommands:
        return format_usage(settings.subcommands[None].__doc__)
    if not message:
        message = '\n{}\n'.format(settings.message) if settings.message else ''
    doc = _DEFAULT_DOC.format(message=message)
    if None in settings.subcommands:
        return _merge_doc(doc, settings.subcommands[None].__doc__)
    return format_usage(doc)