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I have a shortcode that outputs null ("").

What I'm trying to accomplish is to output a default message if the shortcode outputs null. I don't want to extend my shortcode because there may be multiple instances of the shortcode and I don't want to output the message multiple times.

So my function is as follows:

function av_standalone_doc_404($content) {
    if(has_term('standalone-document', 'formats')){
        $filtered_content = apply_filters('the_content', $content);
            // Display 404 message
            $output .= '<div id="404_message">Error:
                Please check this page later.</div>';
            $output .= '';
        return $output . $content;
add_filter('the_content', 'av_standalone_doc_404', 12);

The problem is that apply_filters is causing a fatal error - obviously because you can't apply a filter to the content and call apply_filters within that filter.

The '12' load order doesn't appear to help either.

How can I apply the filter after the subsequent filters which apply the shortcode to the_content?

share|improve this question
up vote 1 down vote accepted

if you want to keep the current setup, try to hook in early and use do_shortcode():

function av_standalone_doc_404($content) 
    remove_filter( current_filter(), __FUNCTION__ );

    if ( has_term( 'standalone-document', 'formats' ) )
        $filtered_content = do_shortcode( $content );
        // …

If you want to avoid repeating shortcode outputs use a static variable in the shortcode handler:

function shortode_handler()
    static $done = FALSE;

    if ( $done )

    $done = TRUE;

    // create the shortcode output; this will happen only once.

    return $output;
share|improve this answer
What is the hook here? Also, it's not that I want to limit the output of my shortcodes, it's that I want to assess the_content after the shortcodes are applied. I may have some shortcodes that output content. The 'null' is a conditional, not a static output. – AlxVallejo Nov 12 '12 at 18:03
@AlxVallejo See my update. – toscho Nov 12 '12 at 18:09
Hm, remove_filter/do_shortcode did not work – AlxVallejo Nov 12 '12 at 19:27
Just tried 'remove_shortcode' and it worked! The shortcode is in tact in the content but replaced with my 404 error message! – AlxVallejo Nov 12 '12 at 20:30

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