A total newbie, I've just installed Magento 2.1.2 CE (zip-file with sample data), verified the installation and then attempted to enable a couple of third-party extensions using the following commands:
The upgrade operation appears to fail with the following exceptions:
Area code not set: Area code must be set before starting a session.
Area code is not set
I've seen a multitude of suggested work-arounds on GitHub (resetting the sample data, hacking PHP files, etc.) none of which has worked.