use Data::Dumper;

use strict;
use warnings;
my  %foo = ( BAZ => 1 );
sub see_args { };

print Dumper(\%foo);
see_args( @foo{qw(BAR BAZ)} );
print Dumper(\%foo);

##</code><code>##

$VAR1 = {
          'BAZ' => 1
        };
$VAR1 = {
          'BAZ' => 1,
          'BAR' => undef
        };