GNU Radio Raspberry pi

Hello,

I’m trying to get a signal strength value (RSSI) from one specific
frequency through a RTL2832 USB stick.
I’m trying to do all this at an Raspberry pi, with Debian 7.

GNU radio itself is installed and it is showing a moving graph like it
is supposed to do.

I would like GNU radio to give me a specific value of the signal
strength at a centain frequency, which i can use in a python script.

Does anybody know how to do this through GNU radio or another program
that might be more suitable for this?

I’ve allready tried FreqShow(Adafruit) and RTL_power, but I couldn’'t
get those to work…

Many thanks in advance!!

Kind regards,
Stefan