This program seems to do fairly close to what you want.
http://normalize.nongnu.org/
Check the README examples 3 & 4(+2)
EG3. "normalize -bv *.wav" will check all rms value, calculate the mean
deviation, then adjust any files that are more than twice the deviation off.
EG4 will bring all files to the average, then you can use the batch mode (EG2) which will
change all the files the same amount, rather than calculate each one on it's own.
Actually found it trying to find the command you are on about but would find no
information on it...
Hope this at least in some way helps...
Dale.