my $list = "2-4,10-12";

$list =~ s/\-/../g;
my @array = eval( $list );

# @array is now (2,3,4,10,11,12)

##</code><code>##

my @array = (2,3,4,10,11,12);

my @vlans = ();
my $span = undef;
my $last = undef;
foreach my $vlan (sort @array) {
  if (defined $last && $vlan == $last+1) {
    unless (defined $span) {
      $span = $last;
    }
    $vlans[$#vlans] = $span.'-'.$vlan;
  } else {
    push @vlans, $vlan;
    $span = undef;
  }
  $last = $vlan;
}
my $list = join(',', @vlans);

# $list is now "2-4,10-12" again