use warnings;
use strict;


my $file =<<END;
object-group network HOSTNAME-1A_1ST
 network-object host 10.1.1.1

object-group network HOSTNAME-1B_2ND
 network-object host 10.1.1.2

object-group network HOSTNAME-2A_1ST
 network-object host 10.3.1.1

object-group network HOSTNAME-2B_2ND
 network-object host 10.3.1.2

object-group service WEB_TCP tcp
 port-object eq 80
END

my $hostname;

open my $fh, '<', \$file or die "unable to open read file $!";
while (my $line = <$fh>)
{
  if (my ($name) = $line =~ /^object-group network (\w+)/)
  {
     $hostname = $name; # "last seen hostname"
  }

  my ($ip) = $line =~ /(\d+\.\d+\.\d+\.\d+)/;

  if (defined ($ip))
  {
     print "ip $ip goes with host name $hostname\n";
  }
}

##</code><code>##

ip 10.1.1.1 goes with host name HOSTNAME
ip 10.1.1.2 goes with host name HOSTNAME
ip 10.3.1.1 goes with host name HOSTNAME
ip 10.3.1.2 goes with host name HOSTNAME