my @keys = qw(foo bar baz);
my %h;

grep '', @h{@keys};              # creates keys
1 for    @h{@keys};              # creates keys
map  '', @h{@keys};              # creates keys

my @a = @h{@keys};               # DOESN'T create keys
sort {$a <=> $b} @h{@keys};      # DOESN'T create keys