Find gateway address and netmask?
Solution 1:
With ifconfig on OS X you can find netmask :
inet 192.168.1.2 netmask 0xffffff00 broadcast 192.168.1.255
netmask 0xffffff00 means 255.255.255.0
And for finding gateway address use arp -a or as geekosaur said use netstat -nr | grep '^default'.
Solution 2:
On most Unix-like systems, including OSX, that information comes from netstat -r (r for "route").