use warnings;
use strict;
use Data::Dumper qw/Dumper/;

my %data = ();
while (<DATA>){
  chomp( my $line = $_ );
  my @stuff = split /\s+/, $line;
  ## separate the classes
  if ( $stuff[0] eq 'B'){
    $data{$stuff[0]}{$stuff[1]}{$stuff[2]} = $stuff[3];
  }
  else{
    $data{$stuff[0]}{$stuff[1]} = 1;
  }
}
print Dumper \%data;

for my $group ( keys %{ $data{'G'} } ){
  if ( !exists$data{'B'}{ $group } ){
    print "Frozen Group \'$group\' is not defined for \'B\' Section.\n";
  }
  else{
    for ( keys %{ $data{'B'}{ $group } } ){
      if ( $data{'B'}{ $group }{$_} eq 'ONLINE' ){
        print "Group \'$group\' is frozen on host \'$_\'.\n";
      }
    }
  }
}

__DATA__
B  group1      host1       ONLINE
B  group1      host2       OFFLINE
B  group2      host2       ONLINE
B  group2      host3       OFFLINE
B  group3      host3       ONLINE
B  group4      host1       ONLINE
B  group5      host3       ONLINE
G group2
G group3