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The second line specifies the rewrite rule using the mod_rewrite

RewriteRule

command. You use this

to have mod_rewrite translate

my-super-product.html

to

product.php?product_id=123

. The line

that precedes the

RewriteRule

line is a comment; comments are marked using the pound (character)

at the beginning of the line, and are ignored by the parser:

# Translate my-super.product.html to /product.php?product_id=123

RewriteRule ^my-super-product\.html$ /product.php?product_id=123

You can find the official documentation for

RewriteRule

at

http://www.apacheref.com/

ref/mod_rewrite/RewriteRule.html

.

In its basic form,

RewriteRule

takes two parameters. The first parameter

describes

the original URL that

needs to be rewritten, and the second specifies what it should be rewritten to. The pattern that describes the

original URL is delimited by

^

and

$

, which assert that the string has nothing before or after the matching

text (explained further in the following sections), and its contents are written using

regular expressions

,

which you learn about next.

In case you were wondering why the

.html

extension has been written as

\.html

in the rewrite rule,

we will explain it now. In regular expressions — the programming language used to describe the original

URL that needs to be rewritten — the dot is a character that has a special significance. If you want that

dot to be read as a literal dot, you need to escape it using the backslash character. As you’ll learn, this

is a general rule with regular expressions: when special characters need to be read literally, they need

to be escaped with the backslash character (which is a special character in turn — so if you wanted to

use a backslash, it would be denoted as

\\

).

Introducing Regular Expressions

Many love regular expressions, while others hate them. Many think they’re very hard to work with, while

many (or maybe not so many) think they’re a piece of cake. Either way, they’re one of those topics you can’t

avoid when URL rewriting is involved. We’ll try to serve a gentle introduction to the subject, although

entire books have been written on the subject. You can even find a book dedicated to mod_rewrite, which

Using RewriteBase

The regular expressions and scripts in this book assume that your application runs in

the root folder of their domain. This is the typical scenario. If, however, you host your

application in a subfolder of your domain, such as

http://www.example.com/seophp

, you’d need to make a few changes to accommo-

date the new environment.

The most important change would be to use the

RewriteBase

directive of mod_rewrite

to specify the new location to act as a root of your rewriting rules. This directive is

explained at

http://www.apacheref.com/ref/mod_rewrite/RewriteBase.html

.

Also, the rewritten URL should lose its leading slash, because you’re not rewriting to

root any more. Basically, if you host your first example in a subfolder named

seophp

,

your

.htaccess

file for the previous exercise should look like this:

RewriteEngine On

RewriteBase /seophp

RewriteRule ^my-super-product\.html$ product.php?product_id=123

54

Chapter 3: Provocative SE-Friendly URLs

c03.qxd:c03 10:39 54

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