Script to check bytes usage on a specific network card using system files

bandwidth.sh

#!/bin/bash

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

INICIO=$(cat /sys/class/net/$1/statistics/tx_bytes)
ANTERIOR=-1
while true
do
    MEH=$(cat /sys/class/net/$1/statistics/tx_bytes)
    ACTUAL=$(($MEH - $INICIO))
    if [ $ACTUAL -ne $ANTERIOR ]; then
        echo $ACTUAL
        date
    fi
    ANTERIOR=$ACTUAL
done