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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 _pack_cwl(unpacked_cwl):
 """Pack CWL into a single document for submission. """

    out_file = "%s-pack%s" % os.path.splitext(unpacked_cwl)
    cmd = "cwltool --pack {unpacked_cwl} > {out_file}"
    _run_tool(cmd.format(**locals()))
    return out_file