With what hook can I address all posts from all custom post types when they are published?

Question

I want that when every Custom Post Type is published, a hook is called (where I send an email notification to the administrator). I know I can use:

add_action('publish_{custom_post_type_name}', 'function_to_call');

but I don't know the custom_post_type_names (every site has different Custom Post Types registered). In addition, I can't take for granted that the Custom Post Types will always remain the same (because at any time other plugins or themes may register/deregister Custom Post Types).

Any hint?

Answer 1

What about using save_post or wp_insert_post hook, both have

@param     int               $post_ID     Post ID.
@param     WP_Post     $post          Post object.
@param     bool            $update     Whether this is an existing post being updated or not.

as parameters. It is pretty self-explaining that the $update can be used to determine, if it is a new post or not. Additionally you will need to check for is it a custom post type, I use the is_custom_post_type() function by @toscho.

So here we go:

function wpse135423_function_to_call( $post_id, $post, $update ) {
    if ( wp_is_post_autosave( $post_id ) ) {
        return 'do nothing, because it is an autosave';
    }
    if ( wp_is_post_revision( $post_id ) ) {
        return 'do nothing, because it is a revision';
    }
    // if it is an update 
    if ( $update == TRUE ) {
        return 'do nothing, because it is an update';
    }
    // if it is a custom post type 
    if ( is_custom_post_type() == TRUE ) {
        // code to do whatever you want
    }
}
// Do NOT use both hooks!
add_action( 'save_post', 'wpse135423_function_to_call', 10, 3 );
add_action( 'wp_insert_post', 'wpse135423_function_to_call', 10, 3 );

Shortly, only newly created custom post type posts are addressed, while there is no need to know the custom post types name.

Answer 2

There isn't one hook that will fire when all custom post types are published. But we can accomplish the same thing using a combination of hooks and conditionals. There are at least two ways to do it, in addition to the other answer. The first is to hook into register_post_type and conditionally add a hook to publish_$post_type if the post type isn't a WordPress default. Below is a sample plugin that will do that.

namespace = StackExchange\WordPress;
class plugin {
  protected $defaultPostTypes = [
    'post', 'page', 'attachment', 'revision',
    'nav_menu_item', 'custom_css', 'customize_changeset',
  ];
  public function plugins_loaded() {
    \add_action( 'registered_post_type', [ $this, 'registered_post_type' ], 10, 2 );
  }
  public function registered_post_type( string $post_type, \WP_Post_Type $post_type_object ) {
    if( in_array( $post_type, $this->defaultPostTypes ) ) return;
    \add_action( "publish_$post_type", [ $this, 'publish_post_type' ], 10, 3 );
  }
  public function publish_post_type( int $post_ID, \WP_Post $post, bool $update ) {
    //* This method will execute whenever a custom post type is published.
  }
}
\add_action( 'plugins_loaded', [ new plugin(), 'plugins_loaded' ] );

Or, we can use the transition_post_status hook

function wpse_135423_transition_post_status( $new_status, $old_status, $post ) {
  //* Make sure the new status is published
  if( 'publish' !== $new_status ) return;

  //* And that the post_type isn't one of the WordPress defaults
  $default = array(
    'post', 
    'page', 
    'attachment', 
    'revision',
    'nav_menu_item', 
    'custom_css', 
    'customize_changeset',
  );
  if( in_array( $post->post_type, $default ) ) return;

  //* A custom post type just got published.
}
add_action( 'transition_post_status', 'wpse_135423_transition_post_status', 10, 3 );