Options:
?lookup=example.com
?lookup=1.2.3.4
?lookup=host-or-ip&noredirect
?source

Want to send a raw whois packet? Use tcpsend.php.
Example WHOIS packet:
IP: com.whois-servers.net Port: 43
Data: lucb1e.com\n
(where \n is a new line).
For .de domains (German) you need to use ' -T dn' after the domain and before the newline. Don't ask me why.