Tracking a file in real-time

[FS]

Hello guys/gals,

I have a need to track changes to a file being made in real-time. So the
entries in this file are MAC addresses of clients that can get
added/deleted, sometimes multiple entries per second. What I want to do is
to see all the changes were from time A to time B.

I thought about tail -f, but that only lists the entries being added. Doing
diff would require copying the file and running diff against it every second
or so, and then again it wouldn't necessarily list all the changes, just the
one between the last changed file and the current one.

I hope I'm explaining this clearly, but basically the question is, is there
a utility in Linux/Unix world which can track any changes being made to a
file in real-time and list/track/put-in-a-file those changes being made?

Many thanks for any help you can provide.

Regards,
Faisal