getting CGI output

[Drew Fisher]

I'm pretty sure this question has been asked before, but I seem to be
unable to find the answer.

Does anybody know how to display output from a CGI program to the
webpage as the program is running? 

For example, I want to be able to write a CGI that accepts an IP address
from the user and then runs traceroute on that IP.

As each hop is discovered, the CGI script would print just that line to
the screen.

If I remember right, you had to copy sys.stdout and modify it somehow.

Please tell me if you know how to do it!

Thanks!
Drew Fisher