Physical Layer Monitor

Here's a little script I whipped up to solve an argument as to whether the server was going to sleep or no packets were being routed into the box. The echo line could be tee'd for historical reference:

#/bin/sh
TRUE=1

while [ $TRUE = 1 ]; do
  killall tcpdump 2> /dev/null
  mv /dev/shm/netwatch.txt /dev/shm/netwatch-b.txt
    tcpdump > /dev/shm/netwatch.txt 2> /dev/null &
    IP=`grep -c " IP " /dev/shm/netwatch-b.txt`
    ARP=`grep -c " arp " /dev/shm/netwatch-b.txt`
    echo "`date +%T` packets=$IP arps=$ARP"
  sleep 10
done