sudo apt-get install powershell
Ah crap, it says it can't find that in the repository.
Well, I'm relieved... Debian/Ubuntu replaced bash with dash as standard shell (/bin/sh links to dash) for the sake of speed and memory footprint. Using a shell that has dependencies on .Net is just the opposite, and looks like a very bad idea!
Also, I want my scripts as "Posix" as possible so that I can run them on my Synology too (default script engine is ash), or when they are published, people can run them with bash if they see fit, or any other reasonably Posix script engine. And I'm not sure PS has any level of compliance to Posix: any idea about that M$ fanboys?