host1
host2
host3
host4
Once you run the for loop you should see something like below:
# for host in `cat hostname.txt`; do ssh -oStrictHostKeyChecking=no $host host $host ; done | awk '{print $1}'
host1.example.com
host2.example.com
host3.example.com
host4.example.com
The output will change based on the domain name your servers are in.
