@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);