Have you ever tried netcat? To see if you have it do:
$ man nc
Then you can start a server like this:
$ nc -l 8080 (-l act as a server, listening on port 8080)
(hangs)
If I send a post request with the data 'a=10&b=20' to http://locahost:8080
, netcat outputs:
$ nc -l 8080
POST / HTTP/1.1
Host: localhost:8080
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:23.0) Gecko/20100101 Firefox/23.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: null
Accept-Encoding: gzip, deflate
DNT: 1
Content-Length: 9
Content-Type: text/plain; charset=UTF-8
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
a=10&b=20