#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;

my %host_add;
my ( $host, $name );

while (<DATA>) {
    s/^\s+|\s+$//;
    if (/^host_name/) {
        ( $host, $name ) = split /\s+/, $_;
        if ( !exists $host_add{$name} ) {
            undef $host_add{$name};
        }
        else { next }
    }
    elsif ( /^address/ or /^hostgroups/ ) {
        my ( $add, $address ) = split /\s+/, $_;
        push @{ $host_add{$name} }, $address;
    }
}

print Dumper \%host_add;

__DATA__
define host{
   use                                  HALF
   host_name                      denlas02
   alias                                denlas02
   address                           146.xxx.xxx.xxx
   hostgroups                      LINUX,DEN,DMZ
}

define host{
        use                             HALF
        host_name                 ppplas11
        alias                            ppplas11
        address                       10.xxx.xxx.xxx
        hostgroups                 LINUX,PPO,ORAPRD
        }

define host{
        use                               ALIVE
        host_name                   ppplas12
        alias                              ppplas12
        address                        10.50.33.26
        hostgroups                   LINUX,GRID,RMAN,CRIT
        }