script for checking IP's hostname from file

Question

I used for to file one contain the IP with hostname like the /ec/hosts and the other contain the IP and counter try to print the ip if hostname not found and if is found print the hostname.

Script:

for i in `cat ip | awk '{print $2}'` ;do
   var=`grep "$i" Server_ip` |
   awk ' {if($var == "") print $i  else print $1}';
done

File 1

localhost 127.0.0.1
test 10.0.0.1
test1 10.0.0.2

File 2

3 127.0.0.1
2 10.0.0.1
1 10.0.0.2
4 10.0.0.3
5 10.0.0.4

Desired output

localhost
test
test1
10.0.0.3
10.0.0.4

Answer 1

You can try this;

#!/bin/bash
for i in `cat ip | awk '{print $2}'` ;do
var=`awk -v ip=${i} '$2 == ip {print $1}' Server_ip`

 if [ -z "$var" ]; then
  echo $i
 else 
  echo "$var"
 fi

done

Eg;

user@host:/tmp/test$ cat Server_ip
localhost 127.0.0.1
test 10.0.0.1
test1 10.0.0.2

user@host:/tmp/test$ cat ip
3 127.0.0.1
2 10.0.0.1
1 10.0.0.2
4 10.0.0.3
5 10.0.0.4

user@host:/tmp/test$ ./test.sh
localhost
test
test1
10.0.0.3
10.0.0.4