You only have one set of capturing parentheses on each side of the alternation, so you're only ever going to get one match. ie. $2 will always be undefined.
Not true.

What is true that you get only one defined capture (if there's a match), but that one can very well be $2.

In reply to Re^2: why such an error happened? by JavaFan
in thread why such an error happened? by lightoverhead

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