current_filter() │ WP 2.5.0

An interesting example that shows how you can dynamically change the header of an email (who the email is from), depending on which filter the same function (filter_system_from_mail) is triggered from.

add_filter( 'wp_mail_from',      'filter_system_from_mail' );
add_filter( 'wp_mail_from_name', 'filter_system_from_mail' );

function filter_system_from_mail(){

	$opt = 'wp_mail_from' == current_filter() ? 'admin_email' : 'blogname';

	return get_option( $opt );
}

Get the current filter name:

add_filter( 'the_content', 'wpdocs_my_filter' );

function wpdocs_my_filter() {
	echo current_filter(); // 'the_content'
}

Get the current action name:

add_action( 'init', 'wpdocs_my_init_function' );

function wpdocs_my_init_function() {
	echo current_filter(); // 'init'
}

In this example the mechanism of WordPress filters is demonstrated: the example illustrates that inside a callback you can determine which filter is currently executing using current_filter().

function my_filter_callback() {
	my_filter_callback_child();
}

function my_filter_callback_child(){
	echo current_filter();
}

add_filter( 'my_filter', 'my_filter_callback' );

apply_filters( 'my_filter', null ); //> my_filter

• add_filter( 'my_filter', 'my_filter_callback' ); — registers the function my_filter_callback as a handler for the my_filter filter.
• apply_filters( 'my_filter', null ); — runs the my_filter filter. WordPress calls all functions attached to it.

The call proceeds as follows:

1. apply_filters() calls my_filter_callback().
2. Inside my_filter_callback() my_filter_callback_child() is called.
3. my_filter_callback_child() echoes the result of current_filter().
4. current_filter() returns the name of the currently executing filter — here it's 'my_filter'.