in reply to How to use this subroutine

>  my($seq, $colno) = shift @_;

This looks non sensical.

Remove the shift, otherwise $colno is never set.

update

BTW: IMHO you should have got a "is not initialized" warning.

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

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Re^2: How to use this subroutine
by bisimen (Acolyte) on Oct 16, 2017 at 15:48 UTC

    Removed shift.

    And yeah, I did get that warning. But was confused by it... I see now that, I didn't declare a number how long each line should be.