BASH Script measuring PPS by BFP filter

max_pps.sh

#!/bin/bash
# USAGE: max_pps.sh eth0 'portrange 5060-5090' 2>&1 | tee -a output.log
if [ -z "$1" ]
  then
    echo "No capture interface supplied!"
fi
if [ -z "$2" ]
  then
    echo "No FILTER supplied!"
fi

# Output statistics
tcpdump -i $1 -l -e -n $2 | \
perl -e '$max=0;$avg=0;$cnt=0;$tot=0; while (<>) {$l++;if (time > $e) {$e=time;if($l > $max){ $max=$l}; $cnt++;$tot+=$l;$avg=$tot/$cnt;print STDERR "{ \"timestamp\":\"",scalar localtime (),"\", \"pps_peak\":$max, \"pps_avg\":$avg }\n";$l=0 }}'