Automatically register sidebars for all pages on a WordPress site

functions.php

<?php
/**
 * Per-page areas
 */
 
$pages_args = array(
	'post_type'      => 'page',
	'posts_per_page' => -1,
);

$pages = new WP_Query( $pages_args );

if ( $pages->have_posts() ) {
	while ( $pages->have_posts() ) {
		$pages->the_post();
		global $post;

		$args = array(
			'name' => 'Page Sidebar: ' . get_the_title(),
			'id'   => $post->post_name . '-sidebar',
			'before_widget' => '<aside id="%1$s" class="widget box %2$s">',
			'after_widget'  => '</aside>',
		);
		register_sidebar( $args );
	}
}