my %books;
my $twig= new XML::Twig(
    twig_handlers => { book => \&books }
);
$twig->parse($xmlStr);
print Dumper(\%books);
exit;

sub books {
    my ($twig, $book) = @_;
    my $id = $book->att('id');
    $books{$id}{'author'        } = $book->first_child('author'      )->text();
    $books{$id}{'title'         } = $book->first_child('title'       )->text();
    $books{$id}{'genre'         } = $book->first_child('genre'       )->text();
    $books{$id}{'price'         } = $book->first_child('price'       )->text();
    $books{$id}{'publish_date'  } = $book->first_child('publish_date')->text();
}