detect powernap from the command line I like to plug in my macbook and SSH to it from my Windows machine to take advantage of my 27" monitors, and do work in the shell and in Vim. 

Now i know that supposedly the machine is capable of going into Power Nap mode and still support my SSH session, and I'd like to see this for myself. It does seem like the computer is in some form of sleep mode, as moving my finger over the touchpad does not wake it up; my SSH session is indeed still active. But, the system fan is still on. I guess if it's executing commands, the CPU, RAM, SSD, i guess the whole thing has to be powered on, so that's not surprising. 

What commands can I run to view the system power state? Will I be able to detect a difference between "Power Nap mode" and just plain "having the screen off"?
You will not be able to connect to your Mac without waking it up. Modern Macs can be accessed remotely without needing to power on the display; this behaviour saves energy but is not Power Nap.

Apple's Power Nap technical note describes what the state is and how it affects your Mac.

Power Nap does not leave your Mac in a generally usable state; only specifically designed processes are permitted during the power nap state. The permitted processes do not currently include remote connections via secure shell (ssh).