Скриптик.

~ $ curl http://www.linux.org.ru/fdfgddfg --fail
curl: (22) The requested URL returned error: 404

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import httplib

netloc = 'example.com'
path = '/' 
method = "GET"

connect = httplib.HTTPConnection(netloc)
connect.request(method, path)
response = connect.getresponse()
connect.close()

print response.status if response.status == 502 else 0

echo -ne 'HEAD / HTTP/1.0\r\n\r\n' | ncat example.net 80 | head -1 | cut -d' ' -f2