<?php
/**
Plugin Name: Change Permalink or Slug Helper
Plugin URI: http://www.techytalk.info/
Description: Redirect and send "301 Moved Permanently" when permalink structure or slug has been changed WordPress plugin
Version: 1.0
Author: Marko Martinović
Author URI: http://www.techytalk.info/ 
 
Copyright 2012.  Marko Martinović  (email : marko AT techytalk.info)
 
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2, as
published by the Free Software Foundation.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
if ( !function_exists('add_action') ) {
	header('Status: 403 Forbidden');
	header('HTTP/1.1 403 Forbidden');
	exit;
}
 
if ( !class_exists('ChangePermalinkHelper') ) {
    class ChangePermalinkHelper {
        private $slugRedirect = array('old-slug' => 'new-slug');
 
        function ChangePermalinkHelper() {
 
            add_action( 'plugins_loaded', array( &$this, 'onLoad' ) );
        }
 
 
        function onLoad() {
            if ( is_admin() )
                    return;
 
            add_action( 'template_redirect', array( &$this, 'is404Permalink' ) );
            add_action( 'template_redirect', array( &$this, 'is404Slug' ) );
        }
 
        function is404Permalink() {
            global $wpdb;
 
            if ( !is_404() )
                    return;
 
            $slug = htmlspecialchars( basename( $_SERVER['REQUEST_URI'] ) );
            $id = $wpdb->get_var( 
                            $wpdb->prepare( "
                                    SELECT ID 
                                    FROM $wpdb->posts
                                    WHERE post_name = '%s'
                                    AND post_status = 'publish'
                            ", $slug )
                    );
 
            if ($id) {
                    wp_redirect(get_permalink($id), 301);
                    exit;
            } else {
                    return true;
            }
 
        }
 
        function is404Slug() {
            global $wpdb;
 
            if (!is_404())
                    return;
 
            $slug = htmlspecialchars(basename($_SERVER['REQUEST_URI']));                    
 
            if(!array_key_exists($slug, $this->slugRedirect))
                return;
 
            $id = $wpdb->get_var( 
                            $wpdb->prepare( "
                                    SELECT ID 
                                    FROM $wpdb->posts
                                    WHERE post_name = '%s'
                                    AND post_status = 'publish'
                            ", $this->slugRedirect[$slug] )
                    );
 
            if ($id) {
                wp_redirect(get_permalink($id), 301);
                exit;
            } else {
                return true;
            }
 
        }                
 
    }
 
    $ChangePermalinkHelper = new ChangePermalinkHelper();
}
?>

private $slugRedirect = array('old-slug' => 'new-slug', 'second-old-slug' => 'second-new-slug');