A simple Bash script to monitor a remote address and send an email when it goes down.

checknet.sh

#!/bin/bash

# If the file that holds the flag doesn't exist, create it with default of 0

if [ ! -f /tmp/checknet.tmp ]
then
  echo 0 > /tmp/checknet.tmp
fi

target=TARGET_GOES_HERE
email=EMAIL_GOES_HERE
flag=$(cat /tmp/checknet.tmp)
timestamp=$(date "+%d-%b-%Y %H:%M")

ping -c 1 ${target}

# If the ping fails ...

if [ $? -ne 0 ]
then
  if [ "$flag" -eq "0" ]
  then
    echo "Ping to $target failed!" | mail -s "Connection Down ($timestamp)" $email
    echo 1 > /tmp/checknet.tmp
  fi

# If the ping is successful ...

else
  if [ "$flag" -eq "1" ]
  then
    echo "Ping to $target successful!" | mail -s "Connection Up ($timestamp)" $email
    echo 0 > /tmp/checknet.tmp
  fi
fi