One thing you should be aware of, and keep in mind, is that file locking in Perl is advisory only. That is, even if you open a file in locking mode, there is nothing to stop some other script or process from clobbering the file if it isn't observing file locking.

Programming Perl (aka - The Camel, 3rd Edition) has a very good discussion on File Locking in Chapter 16 (beginning on page 419), with plenty of examples. If you have a copy, then I'd thoroughly recommend reviewing this.

Failing that, there is always the flock documentation, as well as some discussion on file locking in the DB_File documentation.

Hope this helps,
Darren