I would look at Linux-Inotify2. You can watch for changes to any file or directory.

I did do some testing with this module on a Linux system, running Active State and I installed it without root permission. My "how to post": Re^3: Linux::Inotify2, adding sub-dirs to watches event-triggered.... From what I could tell, this thing works great although I didn't actually put a program using it into production.