How to get hostname from IP address from file similar to /etc/hosts

Question

I have a file which maps IP Address to hostname. Its format is similar to hosts file and contains a list of ipaddress to hostname mapping.

eg.

10.200.99.1    master1
10.200.99.2    master2
10.200.99.3    master3
10.200.99.4    slave1
10.200.99.5    slave2
10.200.99.6    slave3
...
...
...

I would like to obtain hostname from a given ipaddress using bash script.

How can i do so?

Answer 1

You can try that :

sh script.sh listofip

#!/bin/bash

        echo  "IP ?"
        echo -n "(Value and press Enter) :"
        read ip


while read line
do
#VARIABLES
file1=$line
mip=$(echo $file1 | awk '{print $1}')
name=$(echo $file1 | awk '{print $2}')


    if [ "$mip" = "$ip" ]
        then
        echo "Machine name is " $name
    fi

done < $1

results :

IP ?
(Value and press Enter) :10.200.99.2
Machine name is  master2

Answer 2

In Bash 4, I would use an associative array; see http://mywiki.wooledge.org/BashFAQ/006#Associative_Arrays

For older versions of Bash, maybe use a simple wrapper such as

lookup () {
    echo "$1" |
    awk 'NR==FNR { a[$1] = $2; next }
        $1 in a { print a[$1]; exit 0 }
        END { exit 1 }' input.txt -
}

This is slightly inelegant in that it requires the file to exist in the current directory. You can embed the mapping file in the script itself, though that requires some modest refactoring (the here document will tie up standard input so you cannot pipe your input to the script which reads it).

lookup () {
    awk -v q="$1" '$1 == q { print $2; exit 0 }
            END { exit 1 }' <<'________HERE'
        10.200.99.1    master1
        10.200.99.2    master2
        10.200.99.3    master3
        10.200.99.4    slave1
        10.200.99.5    slave2
        10.200.99.6    slave3
________HERE
}

Answer 3

I got a much simpler solution

#!/bin/bash

### GET IP ADDRESS ###
    echo  "IP Address ?"
    echo -n "(Value and press Enter) :"
    read ip_address

### Find Hostname matching to IPADDRESS ###
    grep  $ip_address /etc/hosts | awk '{print $2}'