I was also eyeballing the statement $mask=/_(\d\d)_/ . After some investigation with use re 'debugcolor', it turns out that the /_(\d\d)_/ gets compiled but nothing is stored in $mask. In effect, the statement

$_[0] =~ /$mask/ is equal to $_[0] =~ //

In reply to Re^2: Regular expressions and sort by ioannis
in thread Regular expressions and sort by zaro

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