#!/usr/bin/perl
use strict;
use warnings;

my %host_contents;
my $host_id;
while (<>) {
    chomp;
    if ($_ =~ /host id="(.*?)"/)
    {
        $host_id = $1;
    }
    if ($_ =~ m{<host-alias>(www.*?)</host-alias>})
    {
        push @{ $host_contents{$host_id} }, $1;
    }
}