If you use any form of social media, and in particular Twitter, then you have almost certainly come across 'shortlinks' – shortened URLs which act as a label, pointing to a particular page but disguising its lengthier URL. They've been around for over a decade now, but their use really took off with URL shortening services which provided click-through statistics, and character limits on tweets.

WordPress has its own built in 'shortlink' – which, by default, probably isn't very deserving of the name. These are the www.yoursite.com?p=1 links which point to a single post and you can grab them from the 'Get Shortlink' button on your post's edit screen.

There's a good reason for this: WordPress did not want to impose any particular third-party service for URL-shortening, and beneath the default www.yoursite.com?p=1 shortlinks lies an API which allows you to replace it with a more substantially shortened URL from another service – or perhaps even your own.

But WordPress' shortlinks only appear on posts – not pages, or any other post type. In this quick tip I'll be showing you how to rectify this. (And in a similar way you can change the default shortlink entirely by one from a URL shortener service).

Cracking open the source code and locating the wp_get_shortlink() function (see Codex) we find the following:

function wp_get_shortlink($id = 0, $context = 'post', $allow_slugs = true) {

    // Allow plugins to short-circuit this function.
    $shortlink = apply_filters('pre_get_shortlink', false, $id, $context, $allow_slugs);
    if ( false !== $shortlink )
        return $shortlink;

        ...

The hook pre_get_shortlink, therefore, allows us to by-pass WordPress' default handling of shortlinks. To do that our plug-in needs only to hook onto that filter and return anything other than 'false'.

/**
 * A function which adds a shortlinks button for 'portfolio' post type
 */
function wptuts_shortlinks_for_portfolio( $shortlink, $id, $context ) {

	// Context can be post/blog/meta ID or query
	$post_id = 0;

	if ( 'query' == $context && is_singular( 'portfolio' ) ) {

		// If context is query use current queried object for ID
		$post_id = get_queried_object_id();

	}
	elseif ( 'post' == $context ) {

		// If context is post use the passed $id
		$post_id = $id;

	}

	// Only do something if of portfolio post type
	if ( 'portfolio' == get_post_type( $post_id ) ) {
		$shortlink = home_url( '?p=' . $post_id );
	}

	return $shortlink;
}
add_filter( 'pre_get_shortlink', 'wptuts_shortlinks_for_portfolio', 10, 3 );

Note that if you do not want to change the shortlink (for instance, it's the wrong post type) it's important to return $shortlink (the filtered value that was passed to us by the hook) and not 'false' - since other plug-ins may have already changed $shortlink - and by returning false you would be overriding them.