#!/bin/bash
function usage
{
  echo "Usage: $0 "
  echo "e.g. $0 eth0 2"
  exit 1
}

if [ $# -lt 2 ];then
   usage
fi

eth=$1
interval=$2

in_old=$(cat /proc/net/dev | grep -w $eth | sed -e "s/\(.*\)\:\(.*\)/\2/g" | awk '{ print $1 }' )
out_old=$(cat /proc/net/dev | grep -w $eth | sed -e "s/\(.*\)\:\(.*\)/\2/g" | awk '{ print $9 }' )

while true
do
   sleep ${interval}
   in=$(cat /proc/net/dev | grep -w $eth | sed -e "s/\(.*\)\:\(.*\)/\2/g" | awk '{ print $1 }' )
   out=$(cat /proc/net/dev | grep -w $eth | sed -e "s/\(.*\)\:\(.*\)/\2/g" | awk '{ print $9 }')
   sub_in=$(( ($in-$in_old)/$interval ))
   sub_out=$(( ($out-$out_old)/$interval ))
   echo "Recv rate: $((${sub_in}/1024)) KB/s   Sent rate:  $((${sub_out}/1024)) KB/s "
   in_old=${in}
   out_old=${out}
done
exit 0