my $str = "bea" x 100;
my $re  = qr/(?:be|ea|a)/;

sub atomic {
    use re 'debug';
    say 'Matched $re+\d' if $str =~ m/$re+\d/;
}

sub possessive {
    use re 'debug';
    say 'Matched $re++\d' if $str =~ m/$re++\d/;
}
atomic();
possessive();