ruby -we '@s = File.open("/proc/net/dev"); @pq = (); while sleep 20; @s.rewind; cq = @s.readlines.find{|l|l=~/^\s*eth0/}.scan(/[^\W:]+/)[9].to_i; ct = Time.now; @pq and printf "%.2f byte/sec\n", (cq-@pq)/Float(ct-@pt); @pq, @pt = cq, ct; end;'