use strict;
use warnings;
use Data::Dumper;

sub slice_by_ref {
  my $h = shift;
  my %subset = %$h{'foo', 'bar'};
  print Data::Dumper::Dumper(\%subset);
}

my $h = {blonk => 2, foo => 3, squink => 5, bar => 8};
slice_by_ref($h);

##</code><code>##

$VAR1 = {
          'foo' => 3,
          'bar' => 8
        };