How can I tell when another process has stopped writing to a file in Perl? -

I have a system that is writing files in a folder using FTP. I need to copy those files, but how can I tell when the FTP system is finished when the first process is ending.

There is another possibility that the uploading process uploads files under temporary name and then Their name changes.

The name changes, because atomically there will be no such case, where the file was incomplete under the last name.

Ignore the transcript process temporary named files.