> take a look at the varous slider.c in /contrib (fgb did one for me time ago)
slider is at /n/sources/contrib/fgb/cmd/slider.c it uses control(2)
and accepts -c col1 col2 col2, the idea was to have several slider's
one per mixer opt, volume, etc. hence the colors opts
% slider | while(v=`{read}){echo volume $v > /dev/volume}
