The unwisdom of your beguilement with package globals may be demonstrated by the following code. Can you explain the difference between the outputs of the two loops?

c:\@Work\Perl\monks>perl -wMstrict -e
"for ($loop::i = 0;  $loop::i < 3;  $loop::i++) {
   clust($loop::i)
   }
 print qq{\n};
 ;;
 for (my $i = 0;  $i < 3;  $i++) {
   clust2($i);
   }
 ;;
 ;;
 sub clust {
   my ($n) = @_;
   ;;
   for ($loop::i = 0;  $loop::i < 3;  $loop::i++) {
     my $m = $n * $loop::i;
     print qq{= $m };
     }
   print qq{\n};
   }
 ;;
 sub clust2 {
   my ($n) = @_;
   ;;
   for (my $i = 0;  $i < 3;  $i++) {
     my $m = $n * $i;
     print qq{- $m };
     }
   print qq{\n};
   }
"
= 0 = 0 = 0

- 0 - 0 - 0
- 0 - 1 - 2
- 0 - 2 - 4
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Global data is, IMHO, always problematic. If you are looking for up-to-date on-line general introductory tutorials, I would suggest perlintro, perhaps followed by chromatic's freely downloadable Modern Perl.