Exercise

Determining Host Status Exercise

Task

The finance application runs across several addresses and you have been asked which of them are actually answering. Write a script that checks each address and reports it as up or down.

Host: servera
Script location: ~/scripts/pinger.sh

Create a basic script file

Create the scripts directory, move into it, and open a new file.
```
mkdir -p ~/scripts
cd ~/scripts
vim pinger.sh
```
Start with the hashbang and a line that proves the script ran.
```
#!/bin/bash
echo "Starting $0"
```
Make it executable
```
chmod a+x pinger.sh
./pinger.sh
```
Write a basic for loop

Store the addresses in a variable and loop over them. Three of these are on the lab network and two are not, which is what makes the report worth producing.
```
vim pinger.sh
```
```
#!/bin/bash
echo "Starting $0"
finance_app_ips="172.25.250.9 19.19.19.18 172.25.250.10 19.19.19.19 172.25.250.11"
for host in $finance_app_ips; do
    echo "Checking $host..."
done
```
```
./pinger.sh
```
Branch on the result of ping

ping returns 0 when the host answers and 1 when it does not. That number is exactly what if reads.
```
vim pinger.sh
```
```
for host in $finance_app_ips; do
    echo "Checking $host..."
    if ping -c1 -W1 "$host"; then
        echo "$host is UP"
    else
        echo "$host is DOWN"
    fi
done
```
```
./pinger.sh
```
What the options do -c1 sends a single packet instead of pinging forever, and -W1 waits at most one second for a reply. Without both, an unreachable host would stall the script.
Silence the ping output

Your report is buried in ping's own output. Send that output to /dev/null so only your report remains. The exit code is unaffected.
```
vim pinger.sh
```
```
    if ping -c1 -W1 "$host" > /dev/null; then
```
Read the finished script back, then run it.
```
cat pinger.sh
./pinger.sh
```
The output is now a clean status report:
```
Starting ./pinger.sh
Checking 172.25.250.9...
172.25.250.9 is UP
Checking 19.19.19.18...
19.19.19.18 is DOWN
Checking 172.25.250.10...
172.25.250.10 is UP
Checking 19.19.19.19...
19.19.19.19 is DOWN
Checking 172.25.250.11...
172.25.250.11 is UP
```
/dev/null A special file that discards everything written to it. Redirecting to it is the standard way to throw output away without hiding errors, which travel on a separate channel.
Clean up

Remove the script.
```
rm ~/scripts/pinger.sh
cd ~
```

Task

Create a basic script file

Make it executable

Write a basic for loop

Branch on the result of ping

Silence the ping output

Clean up