xavierarmadillo: I see that in your latest posting the substitution
    s/nodata/$secondary/gi
has become
    s/0;nodata/1;$secondary/gi
adding '0;' and '1;' to the mix. Maybe this is intentional, but I just thought I'd mention it.

Another point is that you are now defining the  addSecondary function with an empty prototype, meaning that the function takes no arguments — and then you pass it two arguments! This suggests to me that you are calling the function in a way that causes Perl (not PERL) to ignore prototypes. If prototypes do nothing in your program, or you don't fully understand them, or both, why bother to use them?

The final and perhaps most important point is that it is wise always to enable warnings and strictures at the beginning of a program, and as you are a newcomer to Perl, to enable diagnostics. So your program would begin with the following lines:
    use warnings;
    use strict;
    use diagnostics;  # for good measure
See warnings, strict and diagnostics.