instant traffic monitor

traf.sh

#!/bin/bash
dev=$1
b=0

while :
do
  a=`cat /proc/net/dev | grep $dev | sed "s/\s\{1,\}/ /g" | cut -d" " -f 11`
  #echo $(($a-$b))
  byte=`expr $a - $b`
  echo `expr $byte \* 8`

  b=$a
  sleep 1

done