Re^3: if ($2) behaves differently than if (defined $2)

[repellent]

Apparently, in Lisp, this is referred to as a semi-predicate problem.

The very fact that you are using

    if ($2)

followed by

    $price = $1 . "." . $2

shows that you are using $2 as a semi-predicate, i.e. to show validity and to hold value.

Next time, whenever you use if ($var), you should consider if $var needs to be a full-predicate, i.e. strictly a boolean to only show true-or-false.