Espruino command-line and NPM module

I mean "serialport" as in the npm module :)

Yes, sorry - typo on my part. That's the lib it uses.

automatically find my espruino if I just plugged it in

No, if there are >0 ports, it'll pick the first one. It isn't able to test to see if an Espruino is on that port - although if it were possible (reported back by the OS?) that'd be really cool.