While it's possible to determine whether a file is locked, I fail to you why you want to.

Let's look at: unless (-e "./tempads/$i.dat" || <file is locked> )

What is this guard supposed to do? "-e" tests whether the file exists, and if not, you check whether the file is locked. But for a file to be locked, it should exists first. I am not sure what you want to do, do you want to write to the file unless it is locked, or only if it exists and it's not locked?

To check whether a file is locked, open it, and try to acquire a lock. But you have to that non-blocking, or else the command will block till you have a lock. And don't open the file ">", or else you wipe out the content before checking for a lock. Use "+<", and truncate after done writing.

-- Abigail