I looks like someone else has done similar work.. In their example, they used:
Prompt => '/'.$switch.'.*?# /',
... where $switch is the name of the switch ... so the text of the prompt would be the switchname and maybe something else, ending in '# '
... but they also had to do extra checking to deal with some other differences between software versions, so this may be a more complex beast to deal with. Odds are, with any piece of networking gear that's out there, someone's already figured out how to interact with in in Perl, even if it means screen scraping HTML GUIs, so it's worth searching for "(hardware name) perl" in your preferred search engine.