five-minute monitoring

A system independent of my mail server will text my phone if any of the ports on the mail server are not accessible. It checks every 5 minutes, which is about how long it took to whip this thing up.

me@workstation:~$ crontab -l
*/5 * * * * /bin/sh /home/me/code/shell/monitor.sh > /dev/null 2>&1
me@workstation:~$ cat /home/me/code/shell/monitor.sh
#!/bin/sh

EMAIL="my_number@cell_phone_company.com";
HOST="mailserver.domain.tld";
PORTS="25,80,110,143,443,587,993,995";
CMD=`/usr/bin/nmap -p $PORTS $HOST | grep tcp | grep -v open`;

if [ -n "$CMD" ] # if output of command has non-zero length
then
    echo $CMD | /bin/mail $EMAIL;
else
    echo "$PORTS are open on $HOST";
fi
me@workstation:~$