use strict;
use warnings;

my %hash = (
  foo => 'bar',
  42  => 23,
  hello => 'world',
);

my @interesting_keys = qw(foo hello);
my @values = map { $hash{$_} } @interesting_keys;

my @interesting_values = qw(bar 23);
my %reversed_hash = reverse %hash;
my @keys = map { $reversed_hash{$_} } @interesting_values;