#!/bin/bash

if [ -z "$1" ]; then
        echo
        echo usage: $0 network-interface
        echo
        echo e.g. $0 eth0
        echo
        exit
fi

interface=$1

while true
do
        r1=`cat /sys/class/net/$interface/statistics/rx_bytes`
        t1=`cat /sys/class/net/$interface/statistics/tx_bytes`
        sleep 1
        r2=`cat /sys/class/net/$interface/statistics/rx_bytes`
        t2=`cat /sys/class/net/$interface/statistics/tx_bytes`
        tbps=`expr $T2 - $T1`
        rbps=`expr $R2 - $R1`
        tkbps=`expr $tbps / 1024`
        rkbps=`expr $rbps / 1024`
        echo "tx $interface: $tkbps kb/s rx $interface: $rkbps kb/s"
done