Shell Script needed

[Zack Gardner]

Hello all. This question should be a breeze for all you unix experts
out there.

I need a shell script to do the following: I have a bunch of files all
named fort.11, fort.12, fort.13, etc. (not necessarily in an unbroken
sequence), and I want a command where I can say something like:

rename cn90

which will rename fort.11 to cn90.11, fort.12 to cn90.12 etc.
In other words all the fort.* files get renamed to cn90.*.

This seems tremendously simple, but I can't figure out how to do
it. Any ideas?

Thanks in advance,
Zack