use strict;
use warnings;

my @array = (1,2,5,6,4,2,1,2,3,4,6,4,3,2,4,6,6);

my @sorted = sort {$a <=> $b} @array; # numerically

@array = (sort shift @sorted); # overwrite old array

while (my $element = shift @sorted) {
   # if the element differs from the last added, keep it
   # otherwise discard
   if ($element != $array[-1]) { 
      push (@array, $element);
   }
}
# array is now sorted, no duplicate elements