While running Ubuntu 14.04, my laptop has both its Wifi turned on with a saved wireless network in range, and an ethernet cable plugged in (which leads to a Devolo homeplug from the same network). If I click the "Up/Down" button at the top right of the main screen, both have a "Disconnect" option below them, so that I can't tell which one the computer is using to connect to the internet.
Short of disabling the wifi or disconnecting the ethernet cable, is there any 'programmatic' method to determine how the computer is connected to the internet?