defaults = relevant_defaults(names) +defaults["SSHR_PORT"] = 5050 unless defaults["SSHR_PORT"]
This is more simple:
||=
+defaults["SSHR_PORT_BASE"] = 50000 unless defaults["SSHR_PORT_BASE"] +defaults["SSHR_PORT_LEN"]= 2000 unless defaults["SSHR_PORT_LEN"]
Thanks, Fengguang