Bash ping status script - bash

Question

I've done the following script
HOSTS="ns1.server.com ns2.server.com"
SUBJECT="Host Down"
for myHost in $HOSTS
do
count=$(ping -c 10 $myHost | grep 'received' | awk -F',' '{ print $2 }' | awk '{
print $1 }')
if [ $count -eq 0 ]; then
echo "Host : $myHost is down (ping failed) at $(date)" | sendEmail -f email (email address removed) -u "$SUBJECT" etc etc
fi
done
Run via cron every 5 minutes however when a host is down I will receive and email every 5 minutes reflecting this. What i'd like is to add the function so that it only emails me when the status has changed. ie if it's down I don't want it to send any further updates until it's up.

Answer 1

I think something like this can help:
#!/bin/bash
HOSTS="ns1.server.com ns2.server.com"
HOSTS="123.123.1.1 ns1.server.com"
SUBJECT="Host Down"
ping_attempts=1
down_hosts=down_hosts.txt
for myHost in $HOSTS
do
count=$(ping -c $ping_attempts $myHost | awk -F, '/received/{print $2*1}')
echo $count
if [ $count -eq 0 ]; then
echo "$myHost is down"
if [ $(grep -c "$myHost" "$down_hosts") -eq 0 ]; then
echo "Host : $myHost is down (ping failed) at $(date)"
echo "$myHost" >> $down_hosts
fi
else
echo "$myHost is alive"
if [ $(grep -c "$myHost" "$down_hosts") -eq 1 ]; then
echo "Host : $myHost is up (ping ok) at $(date)"
sed -i "/$myHost/d" "$down_hosts"
fi
fi
done

Answer 2

There is a good point in the comments that you might want to use an infinite loop. But as you have asked for something different, here you go:
HOSTS="ns1.server.com ns2.server.com"
SUBJECT="Host Down"
PATH_STATUS='/yourfolder/hoststatus_' # For example can be located in /tmp.
for myHost in $HOSTS; do
count=$(ping -c 10 "$myHost" | grep 'received' | awk -F',' '{ print $2 }' | awk '{ print $1 }')
[[ -f "$PATH_STATUS$myHost"]] && prevStatus=$(cat "$PATH_STATUS$myHost") || prevStatus='unknown'
[[ $count == 0 ]] && curStatus='down' || curStatus='up'
if [[ $curStatus != $prevStatus ]]; then
echo "$curStatus" > "$PATH_STATUS$myHost"
echo "Host : $myHost is $curStatus at $(date)" | sendEmail
fi
done