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Some of these flags are used in later chapters as well.

RewriteRule

commands are processed in sequential order as they are written in the configuration file.

If you want to make sure that a rule is the last one processed in case a match is found for it, you need to

use the

[L]

flag as listed in the preceding table:

RewriteRule ^Products/P([0-9]*)\.html$ ./product.php?product_id=$1

[L]

This is particularly useful if you have a long list of

RewriteRule

commands, because using

[L]

improves

performance and prevents mod_rewrite from processing all the

RewriteRule

commands that follow once

a match is found. This is usually what you want regardless.

URL Rewriting and PHP

Regular expressions are also supported by PHP. Whenever you need to do string manipulation that is

too hard to implement using the typical PHP string functions (

http://www.php.net/strings

), the

regular expression functions can come in handy, as soon as you get accustomed to working with regular

expressions.

PHP has many regular expression functions, the most common of which are listed in Table 3-5 for your

convenience. The examples in this book use only

preg_match

and

preg_replace

, which are the most

frequently used, but it’s good to know there are others. For more information, visit

http://www.php

.net/pcre

.

Table 3-5

PHP Function

Description

preg_grep

Receives as parameters a regular expression, and an array of input

strings. The function returns an array containing the elements of the

input that match the pattern. More details at

http://www.php.net/

preg_grep

.

preg_match

Receives as parameters a regular expression and a string. If a match

is found, the function returns 1. Otherwise, it returns 0. The function

doesn’t search for more matches: after one match is found, the execu-

tion stops. More details at

http://www.php.net/preg_match

.

One detail worth keeping in mind is that the regular PHP string manipulation

functions execute much faster than regular expressions, so you should use them

only when necessary. For example, if you simply want to check whether one string

literal is included in another, using

strpos()

or

strstr()

would be much more

efficient than using

preg_match()

.

60

Chapter 3: Provocative SE-Friendly URLs

c03.qxd:c03 10:39 60

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