Is it possible to automate the configuration of dataguard broker?
Actually, never mind, I've just found the answer ^^

I just had to google the right thing!
http://docs.oracle.com/cd/B19306_01/server.102/b14230/dgmgrl.htm

8.1.1 DGMGRL Optional Parameters

DGMGRL sys/knl_test7@primary "show database 'North_Sales'"