and we can specify it

What's "it"? Specify that the file can't be read and/or opened by another application? That would be file locking, which can be done using flock. If you flock a file in Perl script, it will prevent other applications (whether their Perl scripts or not) from also using that file. Caveat: The other applications also have to use flock. This is called an advisory locking scheme, since the lock can be ignored.