Check out our Tutorials section, and especially the tutorial on File Locking.

Update: If this is for some sort of logging, you might wanna check out some of the numerous LOGging modules oncpan.

 
I have a different kind of flex ;)

MJD says you can't just make shit up and expect the computer to know what you mean, retardo! ** The Third rule of perl club is a statement of fact: pod is sexy.