foreach (@data) {
   push(@$pos{$_},$i++);
}
foreach (keys %pos) {
   if ($#{$pos{$_}) {
      print join(" and ",map("\$data[$_]",@$pos{$_}))," have the same 
+value: $_\n";
   }
}
[download]

First create a HoA, keys of the hash are the values from the array @data, and the arrays contain the indices in @data where each data can be found.

Then just print those keys where the size of the list of indices is more than 1.

Due to the nature of the way we fill the HoA, there won't be any empty lists (Otherwise I'd have to be carefull of the $#==-1 case.)