Instead of counting the well-formed rows when trying to determine the existence of malformed rows, I'd count the malformed ones. In effect, you're using double negation ("no not well-formed rows"), which is less clear than the straightforward approach.

die '@mat malformed'
   if grep { @{$_} != @{$mat[0]} } @mat;

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In reply to Re^2: How to extract the number of cols from a matrix? by ikegami
in thread How to extract the number of cols from a matrix? by parapara

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