my @list = qw/a b c d d a e b a b d e f/;
my @uniq = keys %{{ map {$_ => 1} @list }};

print "@list\n@uniq\n";

__output__

a b c d d a e b a b d e f
e f a b c d

##</code><code>##

map { $_ => 1 } @list

##</code><code>##

{ map { $_ => 1 } @list }

##</code><code>##

keys %{ { map { $_ => 1 } @list } }