Showing a blog post excerpt that isn't the current post in a sidebar using Perch CMS. Use this on your post page.

sidebarcode.php

<?php 
     perch_blog_custom(array(
         'filter' => 'postSlug',
         'match' => 'neq',
         'value' => perch_get('s'),
         'sort'=>'postDateTime',
         'sort-order'=>'DESC',
         'count'=>1,
         'template'=>'blog/post_in_list_sidebar.html'
        ));
?>