You need to define "using the files" more fully. If you simply mean that no other user should have read/write access to the files while User A is doing something to the directory through a Perl script, then file locking by means of a semaphore file is the best way to handle this. If you mean that no one else can have access to the files via any means, you will need to set permissions on an OS level. For Win32, this is done with a module: Win32::FileSecurity

For a good example of semaphore file locking have a look at this node

HTH

---- I am what I read