Example:
Look for an user-agent that gives a response length different from 131 bytes at URL https://10.211.55.14/test/
$ ./fake_ua.py https://10.211.55.14/test/ 131
User-Agent: Mozilla/4.0 (compatible; MSIE 4.01; Windows CE; PPC; MDA Pro/1.0 Profile/MIDP-2.0 Configuration/CLDC-1.1) [1475]