Nmap a target periodically and be updated on any changes

nmap-scan-diff.sh

#!/bin/sh
#
# Taken from https://nmap.org/book/ndiff-man-periodic.html
#
# Add the following to your crontab to run the scan at 1PM each day:
#
# 0 13 * * * /home/YOUR_HOME_DIR/bin/nmap-scan-diff.sh
#

TARGETS="192.168.1.1"
OPTIONS="-v -T4 -F -sV"
date=`date +%F`
cd $HOME/nmap_scans
nmap $OPTIONS $TARGETS -oA scan-$date > /dev/null
if [ -e scan-prev.xml ]; then
        ndiff scan-prev.xml scan-$date.xml > diff-$date
        echo "*** NDIFF RESULTS ***"
        cat diff-$date
        echo
fi
echo "*** NMAP RESULTS ***"
cat scan-$date.nmap
ln -sf scan-$date.xml scan-prev.xml