growl-pianobar should never be invoked directly. But should instead be referenced in pianobar's configuration file.
Simply run the installation script with this command:
Now when you run pianobar and the song changes, you should be notified via growl of the current song.
growl-pianobar is compatible with Mac OS X. You need to have growlnotify installed.
Pandora icon CC BY-SA 2.0 by rossr