Filter and Hook WordPress example

Action

function add_single_background(){
	$id = get_the_id();
	$bg = get_post_meta($id, 'background', true);

	if($bg){
	?>
	<style>
	body{
		background-image: url(<?php echo $bg; ?>);
	}
	</style>
	<?php
	}
}

add_action('wp_enqueue_scripts', 'add_single_background');

Filter

/$content contiene el contenido que está guardado en el artículo
function append_author($content){
	$author = get_the_author();
	$content .= '<div class="by_author">' . __('Wrote the dedication by: ') . $author . '</div>';

	return $content;
}
add_filter('the_content', 'append_author');