Think powershell, but built in rust, posix first and better at processing data(xml, csv, json, ...)
As far as i can tell no way to define any function/commands(you have to write plugins in another language, make an executable??). It supports pipeline, has a large amounts of built-in operators/commands(probably enough to be usable as a shell) and built-in parsers for a few formats(how does one write support for another data format?). Maybe in future it will address these questions.
> Looking at Nu today, you can see some common parts of languages like `if` or `open`, but it doesn’t yet feel like there’s enough syntax to build up full programs. You can’t define your own commands, your own variables, and you can’t build out a project across multiple files. We’re working to address all of these limitations so that Nu can function not only for one-liners, but also for much more.