you could cron your script up to run every so often? I don't know that port listening was the intended use of
Net::SSH::Perl Have a look at what the author says the module does/can do. Then decide if the module is what you need.
with a socket connection your port 22 is not someone else's port 22, so being able to listen to a port, would just be between the client and the server.
I wrote a multi-threaded client server chat app in java. Whenever you send a msg from a client to server on the same port as other clients are connected, only the server and not all the clients receive that msg (if i'm not mistaken)that's why port listening is more the job of a server than a script. ie the post made below about writing your own SSH server. My chat server wrote a connect log, which I could use to parse who logged in. basically you want to parse logfiles via Net::SSH::Perl and not listen on a port.