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Congratulations! You’ve taken your first step into the world of mod_rewrite! The example is indeed

very simplistic and without much practical value — at least compared with what you’ll learn next! But

you need to fully understand the basics of URL rewriting first.

You started by creating a very simple PHP script that takes a numeric parameter through the query

string. You could imagine this is a more involved page that displays lots of details about the product

with the ID mentioned by the

product_id

query string parameter, but in your case you’re simply

displaying a text message that confirms the ID has been correctly read from the query string. The

product.php

script is indeed very simple! Here’s its code again:

<?php

// display product details

echo ‘You have selected product #‘ . $_GET[‘product_id’];

?>

This script is easy to understand even if you’re relatively new to PHP. The

echo

command is used to

output text, and

$_GET[‘product_id’]

tells PHP to access the value of

product_id

contained by

the query string.

For a visual example of how the predefined server variables are interpreted, see Figure 3-6.

After testing that

product.php

script works, you moved on to access this same script, but through a

URL that doesn’t physically exist on your server. This is done through URL rewriting, and you imple-

mented this by adding a rule to be processed by the mod_rewrite module.

The

.htaccess

file you’ve created in the

phpseo

folder contains two lines. The first enables the URL

rewriting engine:

RewriteEngine On

URL Rewriting and PHP

As Figure 3-3 describes, the PHP script is accessed

after

the original URL has been

rewritten. This explains why

$_GET[‘product_id’]

reads the value of

product_id

from the

rewritten

version of the URL. This is helpful, because the script works fine

no matter whether you accessed

product.php

directly, or the initial request was for

another URL that was rewritten to

product.php

.

The

$_GET

predefined variable, as well as almost all the other predefined PHP variables,

work with the rewritten URL. The PHP documentation pages for the predefined variables

are

http://www.php.net/reserved.variables

and

http://www.php.net”/

variables.predefined

.

PHP, however, also allows you retrieve the originally requested URL through

$_SERVER

[‘REQUEST_URI’]

, which returns the path (excluding the domain name) of the origi-

nal request. This is helpful whenever you need to know what was the original request

initiated by the client.

Table 3-1 describes the most commonly used server variables.

52

Chapter 3: Provocative SE-Friendly URLs

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