Thanks Corion. The exact problem is about finding all the combinations. I find Math:Combinatorics useful as well. Here is what i did to gather all 2-item combinations from N item array. I wasn't sure how i would do it for any M items.

@a=(1..5);
my @comb="";
for(my $i=0;$i<=$#a;$i++) {
  for(my $j=0;$j<=$#a;$j++) {
      next if $i==$j;
      if ($a[$i] < $a[$j]) { push @comb, "$a[$i] , $a[$j]" ; }
      else                 { push @comb, "$a[$j] , $a[$i]" ; }
}
}
shift @comb;
use List::MoreUtils qw(uniq);
@comb = uniq(@comb);
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