I'm assuming that the '\n' in DATA are actually new lines.

Maybe something like this is what you want:

my $re = qr/\[\s*([-a-zA-Z0-9_.*\s]+)\s*\]/;
my ($last);
while (<DATA>)
{
    chomp;
    $_ = $last.$_ if($last);
    if (/$re/){
        print "yep\n";
        $last = '';
    }elsif(substr($_, -1, 1) ne ']'){
        $last = $_;
    }else{
        $last = '';
    }
}

__DATA__
[TEST 
DATA]
[ TEST DATA ]
[download]