%Valid_Pets = ( 'dog' => 1, 'cat' => 1, 'parakeet' => 1, 'lemur' => 1 ); # $pet_type should contain 'dog', 'cat', 'lemur' etc... # but might not.. we die if it doesn't exists $Valid_Pets{$pet_type} or die "I'm sorry, '$pet_type' is not a valid pet\n";