I could be way off base here (with respect to the question being asked) but here goes...

If your script is running on the machine you are checking the IP of, you could do a 'netstat -i' or a 'ifconfig | grep "inet addr"' to get the list of IPs and parse the list (depending on your Unix variant.)

Obviously, I'm assuming you're using Unix, under Win32 run 'ipconfig /all'

CC