Sometimes, you want to be notified if a host goes up or down. Usually Nagios is perfect for this, but in this case I had an internet circuit, and all I cared about was knowing when the ISP deactivated it. Use ping in a loop, make 1 request every second, if ping doesn’t get a response, then send a text message (Verizon number) and stop the loop.

while true; do ping -nc 1 -W 1 5.6.7.8 | grep -q icmp; if [ "$?" == "1" ]; then echo "circuit is down" | mail <10-digit phone number no spaces>@vtext.com; break; fi; sleep 1s; done;

I also use the converse of this method when I want to know when a new circuit comes up.