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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 run_cmd_if_file_missing(cmd, fname, out=os.path.devnull, err=os.path.devnull):
 """Runs an external command if file is absent. :param list cmd: Command to run. :param str fname: Path to the file, which existence is being checked. :param str out: Output file :param str err: Error file :return: True if cmd was executed, False otherwise :rtype: boolean """


    if fname is None or not os.path.exists(fname):
        run_cmd(cmd, out, err)
        return True
    else:
        return False