Network interface usage in kb/s in format down,up every 3 seconds. usage: ./netuse.sh <interface>

netuse.sh

#!/bin/bash
delay=3
while true; do

mon_total_down_old=$(cat /proc/net/dev | grep $1 | awk '{print $2}')
mon_total_up_old=$(cat /proc/net/dev | grep $1 | awk '{print $10}')
sleep 1
mon_total_down=$(cat /proc/net/dev | grep $1 | awk '{print $2}')
mon_total_up=$(cat /proc/net/dev | grep $1 | awk '{print $10}')

mon_speed_down=$(echo | awk -v mon_total_old=$mon_total_down_old -v mon_total=$mon_total_down '{printf "%d", (mon_total - mon_total_old) / 1000}')
mon_speed_up=$(echo | awk -v mon_total_old=$mon_total_up_old -v mon_total=$mon_total_up '{printf "%d", (mon_total - mon_total_old) / 1000}')
echo $mon_speed_down,$mon_speed_up

sleep $delay
done