gdiff .. or how to make a patch
How to make a simple patch to source code files ? Something that i make occasionally. Here is the way 
you should also use to make the patch.
Use gdiff and make a copy of the original file. Lets assume the file has the name Makefile.PL, now copy the file
$ cp Makefile.PL Makefile.PL.old
Now make the changes to the Makefile.PL and after that you can make the patch.
$ gdiff -u Makefile.PL.old Makefile.PL > Makefile.patch
Done