mod_rewrite is a popular Apache Module which gives a server administrator the ability to mask a web site's links. Though mod_rewrite has several abilities and can be used in several ways, the only way focused on by this tutorial is to create Search Engine Friendly links.

This tutorial is divided into several sections to help you get started quickly. If you do not have access to your Apache Configuration file or you do not know what an Apache Configuration file is, you should skip the first section. If you encounter any errors at the end of this tutorial, the first section would be a safe bet to review.



Setting up Apache
Browse to your Apache directory and open up the Configuration file, usually named httpd.conf, for both Apache 1.x and Apache 2.x. For Apache 1.x, the file will usually be located inside the base directory of the Apache installation and for Apache 2.x, it will usually be located inside a directory called /conf. If you are using some sort of control panel software, consult your manual.

Scroll down in the Configuration file until you find a line reading:

Basically what this does is make Apache load the mod_rewrite module. It comes bundled automatically with all versions of Apache 1.x and Apache 2.x so there is probably little or no chance you won't find it.

Most web servers do not need the following step, might you might want to follow it to avoid any errors. If you decide to skip this Step and later encounter, errors, you might want to go back to it.

Scroll down in the Configuration file until you find the section reading:

If the last line, the one that says AllowOverride All is set to anything else, change it to read AllowOverride All exactly as shown above. Apache some times has a problem giving access to HTACCESS files on a web server, so this Step ensures that proper access to the HTACCESS file will be given at all times.

We are now done ensuring Apache will work with mod_rewrite. If you have skipped ahead from the start of this tutorial, do not worry about the previous steps. If you do not have access to your Apache Configuration file because you're hosted on a remote server, again do not worry. If your host provider is even half decent, they would have automatically completed the previous Steps for you.



Creating the HTACCESS File
Create a new file named .htaccess. If you are working on a Windows machine, Windows will usually not allow you to create a file with only an extension, such as in our case. The only solution is to login to your web server via FTP and create the file on your web server via the FTP connection and then copy it back to your Windows machine.

Open the created .htaccess file and write the following lines into it. It is preferable to open the file with Notepad if you're working on a Windows machine since Notepad does not add any extra characters to a file when opened:

The first line, RewriteEngine On, is basically the command to Apache to turn on the rewrite engine. We are basically telling Apache that rewrite rules are about to follow.

The second line, RewriteRule ^profile/([0-9]).html$ /viewProfile.php?id=$1 , is our actual rule. Basically what this means is that when Apache encounters a link in the form of say profile/1.html, it should consider it the same as a link in the form of viewProfile.php?id=1.

Confused? Let's narrow down the code just a little:

The bolded part of the code is what we want Apache to expect. In this case, we are saying we want a link in the form of <a href="profile/1.html">. Where did we get 1.html you might be wondering? It is here :

mod_rewrite uses Regular Expressions. A Regular Expression is simply A set of characters, meta characters, and operators that define a string or group of strings in a search pattern. In other words, if we are searching for a string but do not know the exact characters that make it up, we can use Regular Expression to define a pattern, or an idea of what type of characters make it up, so we can find it. This part here:

The bold text is the actual pattern we are looking for. In this case, we know the URL starts with profile/ and even though we do not know the rest, we know it will be any character that makes up a digit between 0 and 9.

We just set up our pattern. Now whenever Apache encounters a link such as <a href="profile/1.html"> or <a href="profile/15.html">, it will translate it.



Translate What!?!
You might be wondering what exactly constitutes a 'translation'. Let's display the previous code and review what translation means for mod_rewrite.

You see the bold text? That is our PHP script. When Apache encounters a link, as stated before, it will translate it to be the same as viewProfile.php. In other words, this link format, <a href="profile/15.html"> is the same as this format, <a href="viewProfile.php?id=15">

We just hid away completely the fact that we are using PHP, and still maintained our benefits. You might be wondering what the $1 at the end means:

Now we are simply telling Apache to provide the result of that pattern as the id for our script. $1 simply means the first pattern. If we had a second pattern, it would be $2, a third would be $3, and so on. Here is a visual example:

Final Testing
Finally, let's test what we have done so far. We already created the .htaccess file, so now let's create a simple PHP script called viewProfile.php to test what we have done.

Paste the following PHP code into a blank file, save it as viewProfile.php, and upload it to your web server in the same directory as the .htaccess file. This will be explained later.

Create another HTML file, call it whatever you want, paste the following HTML in it, and upload it to your web server in the same directory as the PHP script and the .htaccess file.

After you have uploaded all three files, point your browser to the HTML file and try clicking on any of the 3 links. Can you guess which of Yes or No will be displayed for each link. If nothing worked, then you have a problem and should go back to the previous steps and make sure you did everything correctly.



More Regular Expressions
mod_rewrite is powerful and you can bet that the pattern we used in our example is not the only one available. You can use unlimited amount of patterns and define different ones but this is outside the scope of this tutorial. One of the most common patterns that you might use however is this:

The (.*) simply means any combination of characters.

You might be wondering what the ^ and $ at the end of each link means:

These are the characters for line start and line end, respectively. You always start a new pattern with ^. You do not always need to end the line with $ but it is good practice otherwise Apache will always attempt to match characters even after those you specify.

i.e. Without the $, a link like profile/alex.htmllalal or profile/meAhe.htmlalAOlAO103 will always work for the above pattern.

The most and last important to thing to point out is that we have made sure that your web site contains links that will be easier for Search Engines to follow and index. The only problem now is that you have to worry about manually re-coding all your hyperlinks!