add_action( string $hook_name, callable $callback, int $priority = 10, int $accepted_args = 1 )

Adds a callback function to an action hook.

Description

Actions are the hooks that the WordPress core launches at specific points during execution, or when specific events occur. Plugins can specify that one or more of its PHP functions are executed at these points, using the Action API.

Parameters

$hook_name

(string) (Required) The name of the action to add the callback to.

$callback

(callable) (Required) The callback to be run when the action is called.

$priority

(int) (Optional) Used to specify the order in which the functions associated with a particular action are executed. Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.

Default value: 10

$accepted_args

(int) (Optional) The number of arguments the function accepts.

Default value: 1

Return

(true) Always returns true.

More Information

Usage 

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

To find out the number and name of arguments for an action, simply search the code base for the matching do_action() call. For example, if you are hooking into ‘save_post’, you would find it in post.php:

do_action( 'save_post', $post_ID, $post, $update );

Your add_action call would look like:

add_action( 'save_post', 'wpdocs_my_save_post', 10, 3 );

And your function would be:

function wpdocs_my_save_post( $post_ID, $post, $update ) {
   // do stuff here
}

Source

File: wp-includes/plugin.php 

function add_action( $hook_name, $callback, $priority = 10, $accepted_args = 1 ) {
	return add_filter( $hook_name, $callback, $priority, $accepted_args );
}

Uses

Uses Description
wp-includes/plugin.php: add_filter()

Adds a callback function to a filter hook.

Used By

Used By Description
wp-includes/block-template.php: locate_block_template()

Find a block template with equal or higher specificity than a given PHP template file.
wp-includes/sitemaps/class-wp-sitemaps.php: WP_Sitemaps::init()

Initiates all sitemap functionality.
wp-includes/class-wp-recovery-mode.php: WP_Recovery_Mode::initialize()

Initialize recovery mode for the current request.
wp-admin/includes/class-wp-site-health.php: WP_Site_Health::__construct()

WP_Site_Health constructor.
wp-includes/ms-site.php: wp_is_site_initialized()

Checks whether a site is initialized.
wp-admin/includes/meta-boxes.php: register_and_do_post_meta_boxes()

Registers the default post meta boxes, and runs the do_meta_boxes actions.
wp-admin/includes/class-wp-privacy-policy-content.php: WP_Privacy_Policy_Content::text_change_check()

Quick check if any privacy info has changed.
wp-includes/class-wp-roles.php: WP_Roles::get_roles_data()

Gets the available roles data.
wp-includes/widgets/class-wp-widget-text.php: WP_Widget_Text::_register_one()

Add hooks for enqueueing assets when registering all widget instances of this widget class.
wp-includes/widgets/class-wp-widget-custom-html.php: WP_Widget_Custom_HTML::_register_one()

Add hooks for enqueueing assets when registering all widget instances of this widget class.
wp-includes/widgets/class-wp-widget-media.php: WP_Widget_Media::_register_one()

Add hooks while registering all widget instances of this widget class.
wp-includes/class-wp-editor.php: _WP_Editors::enqueue_default_editor()

Enqueue all editor scripts.
wp-includes/nav-menu.php: _wp_delete_customize_changeset_dependent_auto_drafts()

Delete auto-draft posts associated with the supplied changeset.
wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::import_theme_starter_content()

Import theme starter content into the customized state.
wp-includes/class-wp-post-type.php: WP_Post_Type::register_meta_boxes()

Registers the post type meta box if a custom callback was specified.
wp-includes/class-wp-post-type.php: WP_Post_Type::add_hooks()

Adds the future post hook action for the post type.
wp-includes/class-wp-customize-widgets.php: WP_Customize_Widgets::selective_refresh_init()

Adds hooks for selective refresh.
wp-includes/customize/class-wp-customize-selective-refresh.php: WP_Customize_Selective_Refresh::init_preview()

Initializes the Customizer preview.
wp-includes/customize/class-wp-customize-selective-refresh.php: WP_Customize_Selective_Refresh::enqueue_preview_scripts()

Enqueues preview scripts.
wp-includes/customize/class-wp-customize-selective-refresh.php: WP_Customize_Selective_Refresh::__construct()

Plugin bootstrap for Partial Refresh functionality.
wp-includes/rest-api.php: rest_api_default_filters()

Registers the default REST API filters.
wp-includes/class-wp-customize-setting.php: WP_Customize_Setting::aggregate_multidimensional()

Set up the setting for aggregated multidimensional values.
wp-includes/admin-bar.php: wp_admin_bar_customize_menu()

Adds the “Customize” link to the Toolbar.
wp-includes/class-wp-widget-factory.php: WP_Widget_Factory::__construct()

PHP5 constructor.
wp-includes/customize/class-wp-customize-site-icon-control.php: WP_Customize_Site_Icon_Control::__construct()

Constructor.
wp-includes/customize/class-wp-customize-nav-menu-item-setting.php: WP_Customize_Nav_Menu_Item_Setting::__construct()

Constructor.
wp-includes/class-wp-customize-nav-menus.php: WP_Customize_Nav_Menus::customize_preview_init()

Add hooks for the Customizer preview.
wp-includes/class-wp-customize-nav-menus.php: WP_Customize_Nav_Menus::__construct()

Constructor.
wp-admin/includes/class-wp-site-icon.php: WP_Site_Icon::__construct()

Registers actions and filters.
wp-login.php: login_header()

Output the login page header.
wp-admin/includes/class-language-pack-upgrader.php: Language_Pack_Upgrader::bulk_upgrade()

Bulk upgrade language packs.
wp-admin/includes/class-theme-upgrader.php: Theme_Upgrader::install()

Install a theme package.
wp-admin/includes/class-theme-upgrader.php: Theme_Upgrader::upgrade()

Upgrade a theme.
wp-admin/includes/class-plugin-upgrader.php: Plugin_Upgrader::install()

Install a plugin package.
wp-admin/includes/class-plugin-upgrader.php: Plugin_Upgrader::upgrade()

Upgrade a plugin.
wp-admin/includes/class-wp-list-table.php: WP_List_Table::__construct()

Constructor.
wp-admin/includes/class-wp-theme-install-list-table.php: WP_Theme_Install_List_Table::prepare_items()
wp-admin/includes/update.php: wp_plugin_update_rows()
wp-admin/includes/update.php: wp_theme_update_rows()
wp-admin/includes/plugin.php: uninstall_plugin()

Uninstall a single plugin.
wp-admin/includes/plugin.php: add_menu_page()

Add a top-level menu page.
wp-admin/includes/plugin.php: add_submenu_page()

Add a submenu page.
wp-admin/includes/class-wp-plugin-install-list-table.php: WP_Plugin_Install_List_Table::prepare_items()
wp-admin/includes/class-wp-internal-pointers.php: WP_Internal_Pointers::enqueue_scripts()

Initializes the new feature pointers.
wp-admin/includes/class-custom-image-header.php: Custom_Image_Header::__construct()

Constructor – Register administration header callback.
wp-admin/includes/class-custom-image-header.php: Custom_Image_Header::init()

Set up the hooks for the Custom Header admin page.
wp-admin/includes/class-custom-background.php: Custom_Background::__construct()

Constructor – Register administration header callback.
wp-admin/includes/class-custom-background.php: Custom_Background::init()

Set up the hooks for the Custom Background admin page.
wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::customize_preview_init()

Print JavaScript settings.
wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::setup_theme()

Start preview and customize theme.
wp-includes/class-wp-customize-manager.php: WP_Customize_Manager::__construct()

Constructor.
wp-includes/cron.php: wp_cron()

Register _wp_cron() to run on the {@see ‘wp_loaded’} action.
wp-includes/theme.php: _custom_header_background_just_in_time()

Registers the internal custom header and background routines.
wp-includes/general-template.php: add_thickbox()

Enqueues the default ThickBox js and css.
wp-includes/functions.php: wp_auth_check_load()

Load the auth check for monitoring whether the user is still logged in.
wp-includes/functions.php: wp_maybe_load_widgets()

Determines if Widgets library should be loaded.
wp-includes/widgets/class-wp-widget-recent-comments.php: WP_Widget_Recent_Comments::__construct()

Sets up a new Recent Comments widget instance.
wp-includes/class-wp-embed.php: WP_Embed::__construct()

Constructor
wp-includes/class-wp-admin-bar.php: WP_Admin_Bar::add_menus()
wp-includes/class-wp-admin-bar.php: WP_Admin_Bar::initialize()
wp-includes/plugin.php: register_activation_hook()

Set the activation hook for a plugin.
wp-includes/plugin.php: register_deactivation_hook()

Sets the deactivation hook for a plugin.
wp-includes/class-wp-customize-setting.php: WP_Customize_Setting::preview()

Add filters to supply the setting’s value when accessed.
wp-includes/media.php: wp_enqueue_media()

Enqueues all scripts, styles, settings, and templates necessary to use all media JS APIs.
wp-includes/media.php: wp_playlist_scripts()

Outputs and enqueue default scripts and styles for playlists.
wp-includes/class-wp-rewrite.php: WP_Rewrite::wp_rewrite_rules()

Retrieves the rewrite rules.
wp-includes/class-wp-rewrite.php: WP_Rewrite::flush_rules()

Removes rewrite rules and then recreate rewrite rules.
wp-includes/rewrite.php: add_feed()

Add a new feed type like /atom1/.
wp-includes/class.wp-scripts.php: WP_Scripts::__construct()

Constructor.
wp-includes/customize/class-wp-customize-header-image-control.php: WP_Customize_Header_Image_Control::prepare_control()
wp-includes/class-wp-customize-widgets.php: WP_Customize_Widgets::customize_preview_init()

Adds hooks for the Customizer preview.
wp-includes/class-wp-customize-widgets.php: WP_Customize_Widgets::__construct()

Initial loader.
wp-includes/class-wp-customize-widgets.php: WP_Customize_Widgets::schedule_customize_register()

Ensures widgets are available for all types of previews.
wp-includes/comment.php: wp_set_comment_status()

Sets the status of a comment.
wp-includes/class-wp-editor.php: _WP_Editors::editor_settings()
wp-includes/media-template.php: wp_print_media_templates()

Prints the templates used in the media manager.

Changelog

Version Description
1.2.0 Introduced.

© 2003–2021 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/functions/add_action