#!/bin/bash
#
# Script prints packets per second passing through default interface
#

time="1"     # one second
# Finding out default interface:
def=`ip route | grep default`
found=0
for i in $def; do
  if [ $found -eq 1 ]; then int=$i; break; fi;
  if [ "$i" == "dev" ]; then found=1; fi ;
done

while true
do
        txpkts_old="`cat /sys/class/net/$int/statistics/tx_packets`" # sent packets
        rxpkts_old="`cat /sys/class/net/$int/statistics/rx_packets`" # recv packets
        sleep $time
        txpkts_new="`cat /sys/class/net/$int/statistics/tx_packets`" # sent packets
        rxpkts_new="`cat /sys/class/net/$int/statistics/rx_packets`" # recv packets
        txpkts="`expr $txpkts_new - $txpkts_old`"                    # evaluate expressions for sent packets
        rxpkts="`expr $rxpkts_new - $rxpkts_old`"                    # evaluate expressions for recv packets
        echo "tx $txpkts pkts/s - rx $rxpkts pkts/ on interface $int"
done