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

my %group_map = ();
while (<DATA>) {
    my @list = split;
    
    if ($list[0] =~ /B/) {
        my ($group,$host,$online) = @list[1..3];
        next if $online =~ /OFFLINE/; # filter "OFFLINE"
        push @{$group_map{$group}}, $host;
        next;
    }

    if ($list[0] =~ /G/) {
        my $group = $list[1];
        foreach my $host (@{$group_map{$group}}) {
            print "$group is frozen on $host\n";
        }
        next;
    }
    
}

__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