How to debug the Networkmanager-dispatcher-variables

I want to debug a script that contains Networkmanager-dispacher-variables like DEVICE_IFACE, IP4_GATEWAY. The Networkmanager-manual describes these variables but doesn't mention how to debug them. I searched a lot but i am unable to figure out how to get the value of these variables. When i echo on the command line like echo ${DEVICE_IFACE} i get no value.