use v5.12;
use warnings;

for my $str ("AB","") {
    say "****** str=<$str>";
    for my $re ( qr/../, qr/(.)(.)/, q/XY/, q/(X)Y/, q// ) {
        say "--- re=<$re>";
        my @captures = $str =~ $re;
        if ( defined $& ) {
            say "matched"
        } else {
            say "no match"
        }
        if (defined $1) {
            say "with captures <@captures>";
        } else {
            say "no captures";
        }
    }
}