my $data_file = "ActiveItems2.txt";
open(DAT, $data_file) || die("Could not open file: $!");
my %seen;

$seen{$_}++ while <DAT>;
print for sort keys %seen;

close(DAT);

##</code><code>##

@seen{<DAT>} = (); # Hash slice assignement
print for sort keys %seen;