From the command line, how do I tell if a particular VPN connection is up? Suppose that I have multiple VPN connections configured in System Preferences/Network.

How do I tell if a particular one (identified by the service name in System Preferences/Network) is up, on the command line in OS X Mavericks?
If you know the network address range, you could use "ifconfig" and parse the output to see if an interface is up and running with an IP in the appropriate range.