Adds a list of posts in a 404 page using Posts in Sidebar

404-with-posts-in-sidebar.php

<?php
$request_uri = $_SERVER['REQUEST_URI']; // Returns for example /blog/loremipsum
// Remove trailing slash and take only the word after the last slash
preg_match( '/[^\/]+$/', rtrim( $request_uri, '/' ), $search );
$search = implode( '', $search ); // Returns for example loremipsum
echo do_shortcode('[pissc search="' . $search . '" orderby=title number=5 debug_query="true"]');