for (my $q =1; $q < 10000; $q++){
    my @x = ( 'A' x $q, 'B' x $q );
    my $glob = '{' . join(',', @x) . '}';

    my $g = join(',', glob($glob));
    if (length $g == 0){
        print "fail silently, q=$q\n";
        last;
    }
}