Howto measure pps at forwarding plane

Hello,

I'm trying to figure out how much packets are being forwarded on my OpenBSD firewall.
Here a small script i wrote.


#!/bin/sh


VAL1=`netstat -s | grep 'packets forwarded' | head -1 | awk -F ' ' '{print $1}'`

sleep 1

VAL2=`netstat -s | grep 'packets forwarded' | head -1 | awk -F ' ' '{print $1}'`


echo "$(($VAL2-$VAL1))"


But i can not be sure if i am doing the right thing?
Can anyone check it please.
Thanks.