foreach_blog.php

<?php
/**
 * Loops through all the blogs in the network switching blogs and calling the given function with a single site returned from wp_get_sites
 * 
 *
 * @param callable $lambda A function to execute for every single blog on the network
 */
function foreach_blog( $lambda ) {
	$blogs = wp_get_sites( array( 'limit' => false ) );
	foreach ( $blogs as $blog ) {
		switch_to_blog( $blog['blog_id'] );
		$lambda( $blog );
		restore_current_blog();
	}
}

Great for Debugging, fixing, and maintaining multisite networks