Unrelated to the error but:

(1) This is probably wrong as you're ||-ing "$np[$a] eq $np[$b]" with itself:

34: if($np[$a] eq $np[$b] || $np[$a] eq $np[$b] || $np[$b] eq $np[$c])
       ^^^^^^^^^^^^^^^^^^    ^^^^^^^^^^^^^^^^^^
           once                  and again
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Maybe you meant:

                                             v
                                             v
34: if($np[$a] eq $np[$b] || $np[$a] eq $np[$c] || $np[$b] eq $np[$c])
                                             ^
                                             ^
[download]

(2) Also your rexexps m/^\d.+/ can be simplified very slightly to m/^\d./ ie remove the +.
(I only mention this incase your rexexps are wrong.)