Filter specific shortcode output?

5 comments

1. There is no filter that I know of that is meant to target individual shortcodes like you want.

   You can filter attributes with shortcode_atts_{$shortcode} though.

   You can hijack another shortcode by creating your own callback and registering it with the original shortcode slug. I think that is what you are probably going to need to do.

   Proof of concept:

   function my_gallery_shortcode($atts) {
     return 'howdy';
   }
   add_shortcode('gallery','my_gallery_shortcode');
   

   Now try to use a gallery 🙂

2. WordPress 4.7 introduced a new filter, do_shortcode_tag, to do exactly this.

3. While there is no hook, there is a small workaround that makes your end-goal possible. You can create a new shortcode that, on a per-instance basis, you always wrap around any other shortcode whose output you want to filter.

   Usage in a post, etc:

   Here is some post text. Blah blah...
   [filter][target_annoying_shortcode size="small" limit="20"][/filter] 
   Here is some more text in my post. More blah blah...
   

   In functions.php:

   function my_shortcode_output_filter( $attr, $content ) {
   
       // Express the shortcode into its output
       $content_translated = do_shortcode(trim($content));
       if($shortcode_to_modify == $content || !$content_translated) {
           // Error handling
           return 'There was an error in filtering shortcode: '.$content;  
       }
   
       // Now modify the output as you like, here...
   
       $content_translated_and_filtered = $content_translated;
   
       return $content_translated_and_filtered;
    }
    add_shortcode('filter', 'my_shortcode_output_filter');
   

4. The only thing that you can filter is the attributes fo the shortcode:

   apply_filters( "shortcode_atts_{$shortcode}", $out, $pairs, $atts );
   

   Point is, that $shortcode is the third argument when registering a shortcode. This argument is pretty new and nearly no shortcode uses it, therefore it will fall back to the default – which is a string of ''.

   This leads to a funny result:

   add_filter( 'shortcode_atts_', 'wpse112294_shortcode_atts_cb' );
   function wpse112294_shortcode_atts_cb( $out, $pairs, $atts )
   {
       // here we need to find a way to uniquely identify a shortcode
       // for which we ain't got a name
   
       // something that makes the shortcode unique:
       $found = isset( $pairs['foo_attribute_key'] );
       if ( $found )
       {
           // Instantly remove this filter to save processing time:
           remove_filter( current_filter(), __FUNCTION__ );
   
           // do something stunning in here!
       }
   
       return $out;
   }
   

   So, yes, with a 90% chance we need to filter the output of every(!) shortcode and try to somehow identify the shortcode by either some default arguments ($pairs) or by input arguments (impossible). Then, finally we’re able to process the output. Are we able to process the string itself? No. This has to be done the way @s_ha_dum showed above.

5. While @s_ha_dum gave a decent answer, you can create a new shortcode for the purpose of filtering an existing shortcode. For example,

   function filter_function($atts, $content) {
       extract(shortcode_atts(array(
               'att1' => 'val1',
               'att2' => 'val2'
       ), $atts));
   
       //save shortcode output in $return
       $return = do_shortcode("[existing_shortcode att1='$att1' att2='$att2'".$content."/existing_shortcode]");
   
       //insert code to modify $return
   
       echo $return;
   }
   add_shortcode('new_shortcode','filter_function');
   

   note that for the [embed] shortcode, you have to use

   global $wp_embed;
   $return = $wp_embed->run_shortcode("[embed ...
   

   instead of do_shortcode

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