use strict;
use warnings;

my (%tags_to_match, @extracted_tags);
my  $in_matching =  0;
my  $tag_prefix  = 'bbc_';
my  $tag_regex   =  qr{ ( $tag_prefix \w+ _ \d+ ) }x;

while (my $line = <DATA>)
{
    if ($in_matching)
    {
        if ($line =~ / ^ \s* \[ end \] \s* $ /x)
        {
            $in_matching = 0;
        }
        elsif ($line =~ $tag_regex)
        {
            $tags_to_match{ $1 }++;
        }
    }
    elsif ($line =~ / ^ \s* \[ start \] \s* $ /x)
    {
        $in_matching = 1;
    }
    elsif ($line =~ $tag_regex)
    {
        my $tag = $1;

        foreach (keys %tags_to_match)
        {
            if ($tag eq $_)
            {
                push @extracted_tags, $tag;
                last;
            }
        }
    }
}

say "\@extracted_tags = ", join(', ', @extracted_tags);

__DATA__
[start]
bbc_arc_001
bbc_arc_002
abc_arc_001
[end]

bbc_arc_001
bbc_arc_002
bbc_arc_003
bbc_arc_004