Well, be it that you are on Unix, you could use the fuser command. fuser returns the pid of any process that has an open file handle to a file. There is a module on CPAN (Linux::Fuser). As the name states, however, it is only for Linux. You could use the command line fuser via backticks and capture the output. Or, if you are the adventurous type you could port the module.

Cheers!
Casey