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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_cert_serial(cert_file):
    '''
    Get the serial number of a certificate file

    cert_file
        The certificate file to find the serial for

    CLI Example:

    .. code-block:: bash

        salt '*' certutil.get_cert_serial <certificate name>
    '''
    cmd = "certutil.exe -silent -verify {0}".format(cert_file)
    out = __salt__['cmd.run'](cmd)
    # match serial number by paragraph to work with multiple languages
    matches = re.search(r":\s*(\w*)\r\n\r\n", out)
    if matches is not None:
        return matches.groups()[0].strip()
    else:
        return None