#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

my ($host, %seen);

while (<DATA>) {
    chomp;

    if (m{^hostname\d\.com}) {
        say $host = $_;
    }   
    else {
        say unless $seen{$host}{$_}++;
    }   
}   

__DATA__
hostname1.com
Gateway FAIL
Gateway FAIL
Gateway FAIL
hostname2.com
Gateway FAIL
Gateway FAIL
Gateway FAIL