Applying diff's from one file to another, similar file?

[Dennis Jones]

Hello,

Is there a way to apply diff's from one file to a similar file in a
different directory?

For example, if I have a file that is duplicated in multiple directories
with the exception of some minor differences, and I make a change to one of
the files, those same changes need to be replicated on all of the other
files.  Replicating the changes by hand is time-consuming and error-prone,
and gets old after awhile.

I thought perhaps there might be a way to use "cvs up -j -j", but that
doesn't really make sense since the source file is not the same as the
destination file (because they are in different directories).

People here often talk about "patching" the CVS sources, and that sounds
like a reasonable solution to the problem, but I am not familiar with how to
create or apply patches.

Can anyone offer some advice on how to do this?

- Dennis