While on Linux, you would use Linux::Inotify, on Win32, you need to use Win32::ChangeNotify. Hope this helps.

I wrote something recently that does this. It is not the best way but it works for me. click

Well you are describing a "broken" interface (to call it something). You cannot guarantee the copy will be ok. Imagine the other side writes to the file in chunks of 10k every twenty minutes for ...

On the pragmatic side, the idea is simple, check the length of the file every x seconds, copy when it hasn't changed in the last n checks (y = n * x); choose n wisely ;)

Actually on my to_do list is to check File::Monitor; might be useful to you.

While writing this it occurs to me a variation: have the previous check of the size done by a child process, and have the child change the name to *.ok. In the main program just copy the *ok.

Make certain that you open it in append mode, though, or you will overwrite the data you are trying to process.

--MidLifeXis

UPDATE: I have no control over the file name and I cannot ask them to send an md5 or other file size/md5sum info.
If the sender can/will not tell you when the file is complete, you can only *assume* the state based on the lack of updates over a certain time period. If the sender is concerned that the information is complete when processed, they will provide a mechanism to do so.