use strict;
use warnings;

my @strings = qw( 12-12 12-12-12 12-13-12-13 12-12-13-13 12-13-13-14 );
 
for (@strings) {
    my $prev = -1; # numbers being separated by dashes, I assume that a negative value is not possible
    print join "-", grep {$prev != $_ and $prev = $_} sort {$a <=> $b} split /-/, $_;
    print "\n";
}