nmap network monitor

#! /bin/sh
# Automated network monitor using nmap
# source: https://www.mariusv.com/automate-your-nmap-scans

DIR="/opt/nmap/scans"
NETWORKS="192.168.1.0-255"
TODAY=`date +%Y%m%d`
YESTERDAY=`date -d yesterday +%Y%m%d`


for network in $NETWORKS
do
      nmap -n -sS $network -oG $DIR/$network.$TODAY.nmap
done


for network in $NETWORKS
do
      diff -I "^#" $DIR/$network.$TODAY.nmap $DIR/$network.$YESTERDAY.nmap  > $DIR/$network.$TODAY.diff
done

for network in $NETWORKS
do
      SIZE=`find $DIR/$network.$TODAY.diff -size +0b`
      if [ "$SIZE" = "$DIR/$network.$TODAY.diff" ]
      then
              cat $DIR/$network.$TODAY.diff | mail -s "Change Detected for $network"  user@host.com
      fi
done