Security alert: that will run code in (??{ }) / (?p{ }). Maybe something like this instead?

$regex = qr:(??{print "look ma, no rm -rf /\n"}):;
$captures = (() = ""=~/(|$regex)/) - 1;
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Also, note that you have to add a () set and then subtract it from the count to be able to distinguish between 0 captures and 1 capture.