use warnings;
use strict;

my $dataset = 'foo1';
my %site_data;
my $site;

while (<DATA>) {
    chomp;
    next unless length;
    
    if (/^(\w+):$/) {
        $site = $1;
        next;
    }
    
    push @{$site_data{$site}}, $_;
}

die "No site data for $dataset" unless exists $site_data{$dataset};

my @act_bsites = @{$site_data{$dataset}};

print join "\n", @act_bsites;

__DATA__
foo1:
1 - 201 - 229
2 - 201 - 229
3 - 201 - 229
foo2:
1 - 201 - 218
2 - 201 - 218
3 - 201 - 218
4 - 201 - 218
5 - 201 - 218
6 - 201 - 218
7 - 201 - 218