Mod Rewrite is a module that can be used with the Apache web server. This module is designed so that a URL can be rewritten, in other words, when you request a web page in a web browser the address in your browser typically maps directly to a file on the web server. But this doesn't have to be the case, with mod rewrite you can change things round a little bit. Take a simple example:

In example (1) you can see which file on the server we are requesting (search.php). The characters following the ? are what we call a query string, all this means is that we are passing this information to the script on the server and we will then process it - in this example that would probably mean getting the price of a granny smith apple. If you look at the second example the URL looks much cleaner but it is not as obvious what is going on any more. Using mod rewrite, example (2) above can be rewritten so that is has exactly the same functionality as example (1), in fact it could even use the same script on the server to do the work (search.php).

There any many powerful ways in which Mod Rewrite can be used, perhaps the most common is when a particular page on your website is moved, perhaps following a bit of a "spring clean" of your website. As a result of moving this web page any links to the old location will now be broken. However, with mod rewrite you can simply forward anyone attempting to view the old page to the new one. A second very common usage of mod rewrite is to enable websites with dynamic content to get their content listed in search engines - historically search engines have struggled to index content on dynamic pages which look like example (1) above, rewriting the URL as example (2) overcomes this problem and can help websites benefit from greater traffic from search engines.

   PHP
   Perl/CGI
   Java
   MySQL
   PostgreSQL
   SQL Server
   HTML
   XML
   XHTML
   JavaScript
   CSS
   AJAX
   .NET
   Regex
   Mod Rewrite