SSH usually gives you full access to a shell, thus all the
commands you can use from the command line should
be avialable. Therefore, you can use something
like
ls to look
at all filenames in a directory
and choose the most recent name from them, or search
the output of ls, etc. (with the appropriate options)
to find
the file with the latest timestamp.
Or you might be able to run perl on the machine through
SSH to do this task for you and return the filename
over SSH to your script.
You may want to look at the modules
Net::SSH, Net::SCP, Net::SSH::Perl, IPC::Open2, and/or IPC::Open3.
(The latter two help you open a multidirectional
pipe to a program, the first two are interfaces
to the ssh and scp command line programs, and
Net::SSH::Perl is SSH implemented in perl.)