check if a MAC device exists on the local network and alerts by sending an email

mac-watchdog.sh

#!/bin/sh
# MAC watchdog, checks if a MAC device exists on the local network and alerts by sending an email
# 2016 by danitool, Tki2000, txutxy
CORREO="mi correo@gmail.com"
MAC="00:11:22:33:44:55"
RANGO_IP=192.168.3.1-254
FLAG=0

while :
do
	MACSTATE=`nmap -v -sP $RANGO_IP|grep $MAC`
	if [ "$MACSTATE" ] && [ $FLAG -eq 0 ]; then
		echo -e "Subject:María está en casa." | sendmail $CORREO
		FLAG=1
	elif [ -z "$MACSTATE" ] && [ $FLAG -eq 1 ]; then
		echo -e "Subject:María se ha ido." | sendmail $CORREO
		FLAG=0
	fi

	sleep 5m
done