I would like to know what it is about my pattern that creates all those undefs

Your pattern   (\d+) | (?:"(.+?)") has two groups of capturing parentheses so when one group matches the other returns undef and vice-versa.

In reply to Re: Understanding regular expressions: why do I have to use map to clear up undefs in regex output? by jwkrahn
in thread Understanding regular expressions: why do I have to use map to clear up undefs in regex output? by corenth

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