apache web server history

URL Rewriting is the process of manipulating an URL or a link, which is send to a web server in such a way that the link is dynamically modified at the server to include additional parameters and information along with a server initiated redirection. The web server performs all these manipulations on the fly so that the browser is kept out of the loop regarding the change made in URL and the redirection.

URL Rewriting can benefit your websites and web based applications by providing better security, better visibility or friendliness with Search Engines and helps in keeping the structure of the website more easy to maintain for future changes.

In this article we will be taking a look at how we can implement URL Rewriting on an Apache based web server environment using the mod_rewrite module for Apache.

What is mod_rewrite?

Mod_rewrite is one of the most favored modules for the Apache web server and there are many web developers and administrators who will vote this module as the best thing to happen on Apache. This module has a lot of tricks up its sleeve so that it can be called the Swiss Army Knife of all Apache Modules. Apart from providing simple URL Rewriting functionality for an Apache based website, this module arms the website with better URL protection, better search engine visibility, protection against bandwidth thieves by stopping hot linking, hassle free restructuring possibilities and options to provide friendliest of URLs for the website users. This module due to its versatility and functionality can at times feel a bit daunting to master, but getting a through understanding of the basics can make you a master of the craft of URL Rewriting.

Lets Begin! – A look at all the stuff you need to have on your test environment to get mod-rewrite alive and kicking.

First and foremost you should have a properly configured Apache Web Server on your test machine. Mod_rewrite is usually installed along with the Apache server, but in case it is missing – this can be the case on a Linux machine where the mod_rewrite module was not compiled along with the installation – you will have to get it installed. For using mod_rewrite on your Apache box you will have to configure this module to load dynamically on demand made by Apache. On a shared server you will have to contact your web hosting company to get this module installed and loaded on Apache.

On your local machine you can find if the module is installed along with Apache by having a look at the modules directory of Apache. Check for a file named mod_rewrite.so and if it is there then the module can be made to load in to the Apache server dynamically. By default this module is not loaded when Apache starts and you need to tell Apache to enable this module for dynamic loading by making changes in the web servers configuration file, which is explained below.

How to Enable mod_rewrite on Apache?

You can make the mod_rewrite module load dynamically in to the Apache web server environment using the LoadModuleDirective in the httpd.conf file. Load this file in a text editor and find a line similar to the one given below.

#LoadModule rewrite_module modules/mod_rewrite.so

Uncomment this line by removing the # and save the httpd.conf file. Restart your Apache server and if all went well mod_rewrite module will now be enabled on your web server.

Lets Rewrite our first URL using mod_rewrite Ok, now the mod_rewrite module is enabled on your server. Lets have a look at how to make this module load itself and to make it work for us.

In order to load the module dynamically you have to add a single line to your .htaccess file. The .htaccess files are configuration files with Apache directives defined in them and they provide distributed directory level configuration for a website. Create a .htaccess file in your web servers test directory – or any other directory on which you want to make URL Rewriting active – and add the below given line to it.

RewriteEngine on

Now we have the rewrite engine turned on and Apache is ready to rewrite URLs for you. Lets look at a sample rewrite instruction for making a request to our server for first.html redirected to second.html at server level. Add the below given line to your .htaccess file along with the RewriteEngine directive that we have added before.

RewriteRule ^first.html$ second.html

I will explain what we have done here at the next section, but if all went well then any requests for first.html made on your server will be transferred to second.html. This is one of the simplest forms of URL Rewritting.

A point to note here is that the redirect is kept totally hidden from client and this differs from the classic HTTP Redirects. The client or the browser is given the impression that the content of the second.html is being fetched from first.html. This enables websites to generate on the fly URLs with out the clients awareness and is what makes URL Rewriting very powerful.

Basics of mod_rewrite module

Now we know that mod_rewrite can be enabled for an entire website or a specific directory by using .htaccess file and have done a basic rewrite directive in the previous example. Here I will explain what exactly have we done in the first sample rewrite.

Mod_rewrite module provides a set of configuration directive statements for URL Rewriting and the RewriteRule directive – that we saw in the previous sample – is the most important one. The mod_rewrite engine uses pattern-matching substitutions for making the translations and this means a good grasp of Regular Expressions can help you a lot.

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