WordPress Duplicate post or page function

/*
 * Function for post duplication. Dups appear as drafts. User is redirected to the edit screen
 */
function rd_duplicate_post_as_draft(){
	global $wpdb;
	if (! ( isset( $_GET['post']) || isset( $_POST['post'])  || ( isset($_REQUEST['action']) && 'rd_duplicate_post_as_draft' == $_REQUEST['action'] ) ) ) {
		wp_die('No post to duplicate has been supplied!');
	}
 
	/*
	 * Nonce verification
	 */
	if ( !isset( $_GET['duplicate_nonce'] ) || !wp_verify_nonce( $_GET['duplicate_nonce'], basename( __FILE__ ) ) )
		return;
 
	/*
	 * get the original post id
	 */
	$post_id = (isset($_GET['post']) ? absint( $_GET['post'] ) : absint( $_POST['post'] ) );
	/*
	 * and all the original post data then
	 */
	$post = get_post( $post_id );
 
	/*
	 * if you don't want current user to be the new post author,
	 * then change next couple of lines to this: $new_post_author = $post->post_author;
	 */
	$current_user = wp_get_current_user();
	$new_post_author = $current_user->ID;
 
	/*
	 * if post data exists, create the post duplicate
	 */
	if (isset( $post ) && $post != null) {
 
		/*
		 * new post data array
		 */
		$args = array(
			'comment_status' => $post->comment_status,
			'ping_status'    => $post->ping_status,
			'post_author'    => $new_post_author,
			'post_content'   => $post->post_content,
			'post_excerpt'   => $post->post_excerpt,
			'post_name'      => $post->post_name,
			'post_parent'    => $post->post_parent,
			'post_password'  => $post->post_password,
			'post_status'    => 'draft',
			'post_title'     => $post->post_title,
			'post_type'      => $post->post_type,
			'to_ping'        => $post->to_ping,
			'menu_order'     => $post->menu_order
		);
 
		/*
		 * insert the post by wp_insert_post() function
		 */
		$new_post_id = wp_insert_post( $args );
 
		/*
		 * get all current post terms ad set them to the new post draft
		 */
		$taxonomies = get_object_taxonomies($post->post_type); // returns array of taxonomy names for post type, ex array("category", "post_tag");
		foreach ($taxonomies as $taxonomy) {
			$post_terms = wp_get_object_terms($post_id, $taxonomy, array('fields' => 'slugs'));
			wp_set_object_terms($new_post_id, $post_terms, $taxonomy, false);
		}
 
		/*
		 * duplicate all post meta just in two SQL queries
		 */
		$post_meta_infos = $wpdb->get_results("SELECT meta_key, meta_value FROM $wpdb->postmeta WHERE post_id=$post_id");
		if (count($post_meta_infos)!=0) {
			$sql_query = "INSERT INTO $wpdb->postmeta (post_id, meta_key, meta_value) ";
			foreach ($post_meta_infos as $meta_info) {
				$meta_key = $meta_info->meta_key;
				if( $meta_key == '_wp_old_slug' ) continue;
				$meta_value = addslashes($meta_info->meta_value);
				$sql_query_sel[]= "SELECT $new_post_id, '$meta_key', '$meta_value'";
			}
			$sql_query.= implode(" UNION ALL ", $sql_query_sel);
			$wpdb->query($sql_query);
		}
 
 
		/*
		 * finally, redirect to the edit post screen for the new draft
		 */
		wp_redirect( admin_url( 'post.php?action=edit&post=' . $new_post_id ) );
		exit;
	} else {
		wp_die('Post creation failed, could not find original post: ' . $post_id);
	}
}
add_action( 'admin_action_rd_duplicate_post_as_draft', 'rd_duplicate_post_as_draft' );
 
/*
 * Add the duplicate link to action list for post_row_actions
 */
function rd_duplicate_post_link( $actions, $post ) {
	if (current_user_can('edit_posts')) {
		$actions['duplicate'] = '<a href="' . wp_nonce_url('admin.php?action=rd_duplicate_post_as_draft&post=' . $post->ID, basename(__FILE__), 'duplicate_nonce' ) . '" title="Duplicate this item" rel="permalink">Duplicate</a>';
	}
	return $actions;
}
 
add_filter( 'post_row_actions', 'rd_duplicate_post_link', 10, 2 );  // While this snippet only works for duplicating posts
/*add_filter('page_row_actions', 'rd_duplicate_post_link', 10, 2);*/  // , you can switch to duplicating WordPress pages by replacing the last line by this:

All you need to do is paste this code in your functions.php file

rd_duplicate_post_as_draft cannot be called twice.

What worked for me, to also do this for pages, is to change all instances of rd_duplicate_post syntax to rd_duplicate_page.

Then the "duplicate" link is seen under all posts or pages listed in WordPress when you hover each one. Plus, it copies all categories, tags, and even all the meta data you entered if you use "All in one SEO" for a page or post. Quite convenient!