#!/usr/bin/env bash

TIMESPAN=1

if [ -z $1 ]; then
    echo "Error: no device specified"
    exit 1
fi
if [ ! -d /sys/class/net/$1 ]; then
    echo "No such device: $1"
    exit 1
fi

BR1=`cat /sys/class/net/$1/statistics/rx_bytes`
BT1=`cat /sys/class/net/$1/statistics/tx_bytes`

sleep $TIMESPAN

BR2=`cat /sys/class/net/$1/statistics/rx_bytes`
BT2=`cat /sys/class/net/$1/statistics/tx_bytes`

DOWNKB=$(((($BR2-$BR1) / $TIMESPAN) /1024))
UPKB=$(((($BT2-$BT1) / $TIMESPAN) /1024))

echo "D ${DOWNKB}KB/s | U ${UPKB}KB/s"

exit 0