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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 main(argv=None):
 """ben-sh entry point"""

    arguments = cli_common(__doc__, argv=argv)
    campaign_file = arguments['CAMPAIGN_FILE']
    if arguments['-g']:
        if osp.exists(campaign_file):
            raise Exception('Campaign file already exists')
        with open(campaign_file, 'w') as ostr:
            Generator().write(ostr)
    else:
        node = arguments.get('-n')
        output_dir = arguments.get('--output-dir')
        exclude_nodes = arguments.get('--exclude-nodes')
        srun_tag = arguments.get('--srun')
        driver = CampaignDriver(
            campaign_file,
            node=node,
            output_dir=output_dir,
            srun=srun_tag,
            exclude_nodes=exclude_nodes,
        )
        driver()
        if argv is not None:
            return driver
        campaign_fd = int(arguments.get('--campaign-path-fd') or 1)
        message = (osp.abspath(driver.campaign_path) + '\n').encode()
        os.write(campaign_fd, message)