WordPress: How do I get all the registered functions for ‘the_content’ filter

3 comments

1. Simple function to print from the filter array?

   function print_filters_for( $hook = '' ) {
       global $wp_filter;
       if( empty( $hook ) || !isset( $wp_filter[$hook] ) )
           return;
   
       print '<pre>';
       print_r( $wp_filter[$hook] );
       print '</pre>';
   }
   

   Call it where you need it.

   print_filters_for( 'the_content' );
   

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2. This is a bit more advanced example, that will, in addition to data from $wp_filter array, show the path of the file where the hook is attached, as well as the line in code where the function is defined.

   To get a basic list of functions hooked on a specific action ( or filter ) it is enough to fetch the items from the filter array, but since the functions can be attached in various ways ( as a class method or closure ) that list will contain a ton of irelevant data that includes objects presented as string. This example will display only the relevant data, in order of priority:

   • function name ( depending on callbacks syntax ):
     • function callback: 'function_name'
     • object method: array( $object, 'function_name' )
     • static class method: array( 'class_name', 'function_name' ) and 'class_name::function_name'
     • closure: function() {}
     • relative static class method: array( 'class_name', 'parent::function_name' )
   • accepted args
   • file name
   • start line
   • id
   • priority

   ---

   function list_hooks( $hook = '' ) {
       global $wp_filter;
   
       if ( isset( $wp_filter[$hook]->callbacks ) ) {      
           array_walk( $wp_filter[$hook]->callbacks, function( $callbacks, $priority ) use ( &$hooks ) {           
               foreach ( $callbacks as $id => $callback )
                   $hooks[] = array_merge( [ 'id' => $id, 'priority' => $priority ], $callback );
           });         
       } else {
           return [];
       }
   
       foreach( $hooks as &$item ) {
           // skip if callback does not exist
           if ( !is_callable( $item['function'] ) ) continue;
   
           // function name as string or static class method eg. 'Foo::Bar'
           if ( is_string( $item['function'] ) ) {
               $ref = strpos( $item['function'], '::' ) ? new ReflectionClass( strstr( $item['function'], '::', true ) ) : new ReflectionFunction( $item['function'] );
               $item['file'] = $ref->getFileName();
               $item['line'] = get_class( $ref ) == 'ReflectionFunction' 
                   ? $ref->getStartLine() 
                   : $ref->getMethod( substr( $item['function'], strpos( $item['function'], '::' ) + 2 ) )->getStartLine();
   
           // array( object, method ), array( string object, method ), array( string object, string 'parent::method' )
           } elseif ( is_array( $item['function'] ) ) {
   
               $ref = new ReflectionClass( $item['function'][0] );
   
               // $item['function'][0] is a reference to existing object
               $item['function'] = array(
                   is_object( $item['function'][0] ) ? get_class( $item['function'][0] ) : $item['function'][0],
                   $item['function'][1]
               );
               $item['file'] = $ref->getFileName();
               $item['line'] = strpos( $item['function'][1], '::' )
                   ? $ref->getParentClass()->getMethod( substr( $item['function'][1], strpos( $item['function'][1], '::' ) + 2 ) )->getStartLine()
                   : $ref->getMethod( $item['function'][1] )->getStartLine();
   
           // closures
           } elseif ( is_callable( $item['function'] ) ) {     
               $ref = new ReflectionFunction( $item['function'] );         
               $item['function'] = get_class( $item['function'] );
               $item['file'] = $ref->getFileName();
               $item['line'] = $ref->getStartLine();
   
           }       
       }
   
       return $hooks;
   }
   

   Since hooks can be added and removed throughout the entire runtime, the output depends on at what point the function is called ( wp_footer action is a good place to get the complete list )

   print_r example for the_content filter:

   Array
   (
       [0] => Array
           (
               [id] => 000000004c8a4a660000000011808a14run_shortcode
               [priority] => 8
               [function] => Array
                   (
                       [0] => WP_Embed
                       [1] => run_shortcode
                   )
   
               [accepted_args] => 1
               [file] => C:xampphtdocswordpresswp-includesclass-wp-embed.php
               [line] => 58
           )
   
       [1] => Array
           (
               [id] => wptexturize
               [priority] => 10
               [function] => wptexturize
               [accepted_args] => 1
               [file] => C:xampphtdocswordpresswp-includesformatting.php
               [line] => 41
           )
   
       [2] => Array
           (
               [id] => 0000000006c5dc6d0000000064b1bc8e
               [priority] => 10
               [function] => Closure
               [accepted_args] => 1
               [file] => C:xampphtdocswordpresswp-contentpluginspluginplugin.php
               [line] => 16
           )
   
       .....
   

   ---

   Edit: 2017-05-05

   • adapted for WP_Hook class
   • added priority
   • fixed: error raised if callback does not exists, although WordPress also raises a warning for that
   • fixed: hook with the same id but different priority overwrites the previous one

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3. Based on the same idea of print_filters_for, an extended function for those who need not only print but return as well:

   function filters_for( $hook = '', $return = FALSE ) {
       global $wp_filter;
       if( empty( $hook ) || !isset( $wp_filter[$hook] ) )
           return;
   
       if( $return ) {
           ob_start();
       }
   
       print '<pre>';
       print_r( $wp_filter[$hook] );
       print '</pre>';
   
       if( $return ) {
           return ob_get_flush();
       }
   }
   

   Output:

   filters_for( 'the_content' );
   

   Get and output:

   $output = filters_for( 'the_content', true );
   echo $output;
   

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