Use WordPress shortcode to add <meta> tags

Question

I'm writing a simple WordPress plugin that uses shortcode. I want the page that contains the shortcode to have specific <meta> tags. Is this possible? And if so, is there an elegant way to do it?

I know that I can add <meta> tags with the wp_head hook, but I want the meta tag content to match a string produced by the plugin. I could move all the code into the header, but then I'm not sure how to reference it later from the shortcode. In other words, when I declare a variable in the <head> with a filter, it's not available to the class methods that I'm calling with the shortcode.

Any ideas?

UPDATE:

A nice solution was proposed in which the handler function for the shortcode adds the action to the wp_head hook:

add_shortcode('fakeshortcode', 'fakeshortcode_handler');
function fakeshortcode_handler() {

    function add_meta_tags() {
        //echo stuff here that will go in the head
    }
    add_action('wp_head', 'add_meta_tags');
}

This is swell, but the problem is that wp_head happens BEFORE the shortcode gets parsed and adds the action (so nothing gets added to the head with the code above ALONE). To make it work, I borrowed the solution in this post. It's basically a function that "looks ahead" into the post and sees if there is any shortcode coming. If it is, then IT adds the add_action('wp_head'....

EDIT: I removed my follow-up question about how to pass the variable. It's a new question here.

Maxime Maxime · Accepted Answer · 2012-03-04T20:51:15

First attempt (don't use this... see the 'edit' below):

First, you need to set your shortcode with something like this:

add_shortcode( 'metashortcode', 'metashortcode_addshortcode' );

Then, you'll create the function in which you'll have to add a hook to wp_head with something like that:

function metashortcode_addshortcode() {
    add_action( 'wp_head', 'metashortcode_setmeta' );
}

Then, you'll define what you want to do in the wp_head :

function metashortcode_setmeta() {
    echo '<meta name="key" content="value">';
}

Adding the shortcode [metashortcode] should add your meta data as needed. The code was provided only to help you understand how to make it happen. It was not fully tested.

Edit : The previous code was just a concept and cannot work because of the execution order. Here is a working example that will get the expected result:

// Function to hook to "the_posts" (just edit the two variables)
function metashortcode_mycode( $posts ) {
  $shortcode = 'metashortcode';
  $callback_function = 'metashortcode_setmeta';

  return metashortcode_shortcode_to_wphead( $posts, $shortcode, $callback_function );
}

// To execute when shortcode is found
function metashortcode_setmeta() {
    echo '<meta name="key" content="value">';
}

// look for shortcode in the content and apply expected behaviour (don't edit!)
function metashortcode_shortcode_to_wphead( $posts, $shortcode, $callback_function ) {
  if ( empty( $posts ) )
    return $posts;

  $found = false;
  foreach ( $posts as $post ) {
    if ( stripos( $post->post_content, '[' . $shortcode ) !== false ) {
      add_shortcode( $shortcode, '__return_empty_string' );
      $found = true;
      break;
    }
  }

  if ( $found )
    add_action( 'wp_head', $callback_function );

  return $posts;
}

// Instead of creating a shortcode, hook to the_posts
add_action( 'the_posts', 'metashortcode_mycode' );

Enjoy!

Use WordPress shortcode to add <meta> tags

1 Answers