Maybe I'm missing something, but what's wrong with saying: 
  &numbers($b);

[download]
in the main script and 
sub numbers {
     my $b=shift @_;
        print "$b";
     }

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in your external_subs.txt? That way, it will work with my, and use strict and all the rest of the stuff that will save you from having your brain fried once your script gets a bit more complex.

In reply to Re: Passing Variables to External Subroutines (Perl/Tk) by matija
in thread Passing Variables to External Subroutines (Perl/Tk) by antioch

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