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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_variable_name_from_bird(bird_conf):
 """Return the variable name set in Bird configuration. The variable name in Bird configuration is set with the keyword 'define', here is an example: define ACAST_PS_ADVERTISE = and we exract the string between the word 'define' and the equals sign. Arguments: bird_conf (str):
 The absolute file name path of Bird configuration. Returns: The variable name as a string or None if it isn't found. """

    bird_variable_pattern = re.compile(
        r'''
        ^\s*
        define\s+
        (?P<name>\S+\b)
        \s+
        =
        ''', re.VERBOSE
    )

    with open(bird_conf, 'r') as content:
        for line in content.readlines():
            variable_match = bird_variable_pattern.search(line)
            if variable_match:
                return variable_match.group('name')

    return None