Question: I want to write a script, that would keep checking if any of the devices in network, that should be online all day long, are really online. I tried to use ping, but

```
if [ "`ping -c 1 some_ip_here`" ]
then
  echo 1
else
  echo 0
fi

```

gives `1` no matter if I enter valid or invalid ip address. How can I check if a specific address (or better any of devices from list of ip addresses) went offline?

Answer: 
Ping returns different exit codes depending on the type of error.

```
ping 256.256.256.256 ; echo $?
# 68

ping -c 1 127.0.0.1 ; echo $?
# 0

ping -c 1 192.168.1.5 ; echo $?
# 2

```

0 means host reachable

2 means unreachable
check host every one second and send message when host is reach

```
while :;do ping -c 1 -w 1 -q 8.8.8.8 &>/dev/null && /root/telegram-send.sh "Host reacheble now" && break || sleep 1;done

```