The idiomatic way in perl is to use a hash to mark already inserted data:

my @data;
my %seen;
for (@input) {
  next if $seen{$_}++;
  push @data,$_;
}
[download]

using grep, that would be:

my %seen;
my @data = grep { ! $seen{$_}++ } @input;
[download]

update: s/make/mark/
update2: fixed bug, thanks to Happy-the-monk