check_rdns

#!/bin/bash

## Performs rDNS check using 'host' command

if [[ $# -eq 0 ]] ; then
    echo 'You must provide DNS record as the first argument'
    exit 0
fi

function lookup(){
    OUTPUT=$(host -t A $1); 
    if [ $? == 0 ]
    then
        echo $OUTPUT | cut -d " " -f 4
        return 0
    else 
        #Print output with error and exit
        echo $OUTPUT
        return 1
    fi
}

function rlookup(){
    OUTPUT=$(host -t PTR $1)
    if [ $? == 0 ]
    then
        #sed trims out root domain '.' at the end
        echo $OUTPUT | cut -d " " -f 5 | sed s/\.$//
        return 0
    else 
        #Print output with error and exit
        echo $OUTPUT
        return 1
    fi
}

OUTPUT=$(lookup $1)
if [ $? == 0 ]
then
    OUTPUT=$(rlookup $OUTPUT)
    if [ $? == 0 ]
    then
        if [ $OUTPUT == $1 ];
        then
            echo "PASSED"
            exit 0
        else
            echo "rDNS check FAILED: '$OUTPUT' doesn't match expected '$1'"
            exit 2
        fi
    else
        echo "rDNS check FAILED:" $OUTPUT
        exit 2
    fi
else
    # Print output with error and exit
    echo "rDNS check FAILED:" $OUTPUT
    exit 2
fi