I get the feeling, that you start to think too complicated. When you use the sftp command line client it gives you some feedback about the fact that you have just downloaded a file with name 'x' and stored it somewhere locally with name 'y'. This is the same you want to do in your perl script. So, why don't you just simply print a message after you know you've transfered the file? You can also push the message on an internal message stack for later use.

Regards
McA