Can you please take a look at this code and let me know why I am not able to get the Custom Post Meta on publishing the post. I tried thses

function get_cpt_meta($post_ID) {
 $post = get_post($post_ID);
 $meta = get_post_custom(); 
         $mfname = $meta['f_name'][0];
         $mlname = $meta['l_name'][0];
         echo $mfname. " " . $mlname;
}
add_action('publish_book', 'get_cpt_meta');

and

function get_cpt_meta($post_ID) {
 $post = get_post($post_ID);
 $meta = get_post_custom($post); 
         $mfname = $meta['f_name'][0];
         $mlname = $meta['l_name'][0];
         echo $mfname. " " . $mlname;
}
add_action('publish_book', 'get_cpt_meta');