Create Add action

/**
 * Create Add_action
 */

add_action( $hook, $function_to_add, $priority, $accepted_args );

Create Add_action_google_font

/**
 * Create Add_action_google_font
 */
function add_google_font() {

	wp_enqueue_style( 'google_font', 'http://fonts.googleapis.com/css?family=Pacifico' );

}
add_action( 'wp_enqueue_scripts', 'add_google_font' );

Create Add Filter

/**
 * Create Add_filter
 */
add_filter( $tag, $function_to_add, $priority, $accepted_args );

Create Add_admin_menu

/**
 * Create Add_admin_menu
 */
add_action( 'admin_menu' , 'my_plugin_page' );

function my_plugin_page() {

	add_options_page( 'My Page', 'My Page', 'manage_options', 'my_plugin', 'my_plugin_page' );

}

add_action( 'admin_menu', 'register_my_custom_menu_page' );

function register_my_custom_menu_page() {
	add_menu_page( 'custom menu title', 'custom menu', 'manage_options', 'myplugin/myplugin-admin.php', '', 'dashicons-admin-site', 6 );
}

Positions for Core Menu Items

Dashicons

Create Add_apply_filters

/**
 * Create Add_apply_filters
 */
// First create a function and hook it into new example hook
function example_callback( $string ) {
	$new_value = $string . " NEW!";
	return $new_value;
}
add_filter( 'example_filter', 'example_callback' );

// Then use apply_filters in your code when you want the filter to run
echo $value = apply_filters( 'example_filter', 'Default value' );

// From http://wpseek.com/function/apply_filters/

Create Add_body_class

/**
 * Create Add_body_class
 */
function custom_body_classes( $classes ) {

	if ( 'post' == get_post_type() ) {
		$classes[] = "custom-class";
	}	

    return $classes;
}

add_filter( 'body_class', 'custom_body_classes' );

Create Add_init

/**
 * Create Add_body_class
 */
function my_init_function() {

    echo current_filter(); // 'init'
}
add_action( 'init', 'my_init_function' );

Create Add_do_action

/**
 * Create Add_do_action
 */
    do_action( $tag, $arg );

 
    do_action( $tag, $arg_a, $arg_b, $etc );


    do_action_ref_array( $tag, $args );

Create Add_do_action_hooks

/**
 * Create Add_do_action_hooks
 */
    function custom_footer() {
        do_action('my_footer');
    }

    function custom_footer_text() {
        echo "Custom footer text";
    }
    add_action( 'my_footer', 'custom_footer_text' );

Define Your Own WordPress Action Hooks

Create add_filter_excerpt_length

/**
 * Create add_filter_excerpt_length
 */
 add_filter( 'excerpt_length', 'excerpt_length_example' );
 
function excerpt_length_example( $words ) {
    return 15;
}

Create has_action

/**
 * Create has_action
 */
if ( has_action( 'init', 'custom_plugin_code' ) ) {
    remove_action( 'init', 'custom_plugin_code' );
    add_action( 'init', 'my_content_code' );
}

Create has_filter

/**
 * Create has_filter
 */
if ( has_filter( 'custom_plugin_filter' ) ) {
	add_filter( 'custom_plugin_filter', 'my_custom_code' );
}

if ( has_filter( 'the_content', 'custom_plugin_function' ) ) {
	remove_filter( 'the_content', 'custom_plugin_function' );
	add_filter( 'the_content', 'my_content_code' );
}

Create hook_debugging_functions

/**
 * Create has_filter
 */
function list_hooks( $filter = false ){
    global $wp_filter;

    $hooks = $wp_filter;
    ksort( $hooks );

    foreach( $hooks as $tag => $hook )
        if ( false === $filter || false !== strpos( $tag, $filter ) )
            dump_hook($tag, $hook);
}

function list_live_hooks( $hook = false ) {
    if ( false === $hook )
        $hook = 'all';

    add_action( $hook, 'list_hook_details', -1 );
}

function list_hook_details( $input = NULL ) {
    global $wp_filter;

    $tag = current_filter();
    if( isset( $wp_filter[$tag] ) )
        dump_hook( $tag, $wp_filter[$tag] );

    return $input;
}

function dump_hook( $tag, $hook ) {
    ksort($hook);

    echo "<pre>&gt;&gt;&gt;&gt;&gt;\t<strong>$tag</strong><br />";

    foreach( $hook as $priority => $functions ) {

        echo $priority;

        foreach( $functions as $function )
            if( $function['function'] != 'list_hook_details' ) {

                echo "\t";

                if( is_string( $function['function'] ) )
                    echo $function['function'];

                elseif( is_string( $function['function'][0] ) )
                    echo $function['function'][0] . ' -> ' . $function['function'][1];

                elseif( is_object( $function['function'][0] ) )
                    echo "(object) " . get_class( $function['function'][0] ) . ' -> ' . $function['function'][1];

                else
                    print_r($function);

                echo ' (' . $function['accepted_args'] . ') <br />';
            }
    }

    echo '</pre>';
}

Create add_filter_the_content

/**
 * Create add_filter_the_content
 */
function only_run_in_main_loop( $content ) {
    if ( is_main_query() ) {
   
    }
        
}
add_filter( 'the_content', 'only_run_in_main_loop' );

Create list_hooked_functions

/**
 * Create list_hooked_functions
 */
list_hooked_functions();

function list_hooked_functions($tag=false){
    global $wp_filter;
    if ($tag) {
        $hook[$tag]=$wp_filter[$tag];
        if (!is_array($hook[$tag])) {
            trigger_error("Nothing found for '$tag' hook", E_USER_WARNING);
            return;
        }
    }
    else {
        $hook=$wp_filter;
        ksort($hook);
    }
    echo '<pre>';
    foreach($hook as $tag => $priority){
        echo "<br />&gt;&gt;&gt;&gt;&gt;\t<strong>$tag</strong><br />";
        ksort($priority);
        foreach($priority as $priority => $function){
            echo $priority;
            foreach($function as $name => $properties) echo "\t$name<br />";
        }
    }
    echo '</pre>';
    return;
}

Create manage_posts_columns

/**
 * Create manage_posts_columns
 */
function manage_posts_columns_example( $columns ) {

	
	unset( $columns['author'] );    
    unset( $columns['categories'] );
    unset( $columns['tags'] );
    unset( $columns['comments'] );
    return $columns;
    
}

add_filter( 'manage_posts_columns', 'manage_posts_columns_example' );

Create register_menu

/**
 * Create register_menu
 */
function register_my_menus() {
  register_nav_menus(
    array(
      'footer_menu' => __( 'Footer Menu', 'mytheme' )      
    )
  );
}
add_action( 'init', 'register_my_menus' );

Create remove_action

/**
 * Create remove_action
 */
remove_action( $tag, $function_to_remove, $priority );

Create remove_action

/**
 * Create remove_action
 */
remove_action( 'wp_enqueue_scripts', 'add_google_font' );

Create add_filter_bulk_actions-edit-post

/**
 * Create add_filter_bulk_actions-edit-post
 */
function my_custom_bulk_actions($actions){
    var_export( $actions ); 
    unset( $actions['delete'] );
    return $actions;
}
add_filter('bulk_actions-edit-post','__return_empty_array');

Create remove_filter

/**
 * Create remove_filter
 */
remove_filter( $tag, $function_to_remove, $priority );

Create widgets_init

/**
 * Create widgets_init
 */
function create_my_widget() {
 
    register_sidebar(array(
        'name' => __( 'My Sidebar', 'mytheme' ),    
        'id' => 'my_sidebar',
        'description' => __( 'The one and only', 'mytheme' ),
    ));
 
}

add_action( 'widgets_init', 'create_my_widget' ); 

Create wp_enqueue_scripts and wp_enqueue_style

/**
 * Create wp_enqueue_scripts and wp_enqueue_style
 */
function theme_styles() {

	wp_enqueue_style( 'bootstrap_css', get_template_directory_uri() . '/css/bootstrap.min.css' );
	wp_enqueue_style( 'main_css', get_template_directory_uri() . '/style.css' );

}
add_action( 'wp_enqueue_scripts', 'theme_styles' );

function theme_js() {

	wp_enqueue_script( 'bootstrap_js', get_template_directory_uri() . '/js/bootstrap.min.js', array('jquery'), '', true );
	wp_enqueue_script( 'theme_js', get_template_directory_uri() . '/js/theme.js', array('jquery', 'bootstrap_js'), '', true );

}
add_action( 'wp_enqueue_scripts', 'theme_js' ); 

Create add_filter_login_redirect

/**
 * Create add_filter_login_redirect
 */
add_filter( 'login_redirect', 'login_redirect_example', 10, 3 );
 
function login_redirect_example( $redirect_to, $request, $user ) {
    global $user;
    if ( isset( $user->roles ) && is_array( $user->roles ) ) {
        if ( in_array( 'subscriber', $user->roles ) ) {
            return home_url();
        } else {
            return $redirect_to;
            }
    }
    return;
}

Create add_filter_wp_title

/**
 * Create add_filter_wp_title
 */

function custom_wp_title( $title, $sep ) {
	global $page;

		// Add the site name.

	$title .= get_bloginfo( 'name' );

		// Add the site description for the home/front page.

	$site_description = get_bloginfo( 'description', 'display' );
	if ( $site_description && ( is_home() || is_front_page() ) ) {
		$title = "$title $sep $site_description";
	} 

	return $title;

} 
add_filter( 'wp_title', 'custom_wp_title', 20, 2 );

filter-wp-title