Apache mod_rewrite Dave Ross The West Suburban Chicago PHP Meetup April 3, 2008

mod_rewrite is an Apache module that takes what the browser requests and “rewrites” it into something else before the other Apache modules see it

Request Apache Request mod_rewrite Apache directives Other modules

mod_rewrite directives can go in the Apache config file (httpd.conf)‏ or in an .htaccess file if I have to put them in httpd.conf, I usually make a separate file and include it Include rewrite_rules.conf

RewriteEngine on|off RewriteCond RewriteRule The main mod_rewrite directives: They're all you need to get started.

RewriteEngine on|off

RewriteCond

RewriteRule

RewriteCond {string} {pattern} [{flags}] {string} is a mod_rewrite variable. Usually, you'll use %{REQUEST_URI}. {pattern} is: An extended regular expression (ereg)‏ A lexical test (>, <, or =)‏ -d (is directory?)‏ -f (is regular file?)‏ -l (is symlink?)‏ other lesser-used values {flags} are NC (“no case”) or OR (“this condition or the next one”)‏

An extended regular expression (ereg)‏

A lexical test (>, <, or =)‏

-d (is directory?)‏

-f (is regular file?)‏

-l (is symlink?)‏

other lesser-used values

RewriteRule {pattern} {substitution} [{flags}] {pattern} is regular expression to match {substitution} is a string to replace that URL with. It can contain variables, reference parts of the {pattern}, or it can be the special “no substitution” string: - {flags} let you define behavior, like making the browser [R]edirect to the rewritten URL, telling the browser the page is [G]one, or returning a certain MIME [T]ype.

For a full list of RewriteCond and RewriteRule options, read the docs at: Get really nice “cheat sheets” you can print at:

mod_rewrite is mostly used to implement “friendly” URLs. They go by many names: Friendly URLs Search Engine Friendly URLs Rational URLs Permalinks

Friendly URLs

Search Engine Friendly URLs

Rational URLs

Permalinks

Search engines like “friendly” URLs. How else are they supposed to know index.php?postid=6 is a different page than index.php?postid=7 ?

Programs like WordPress and Drupal have support built-in. They'll even write the .htaccess for you. How sweet is that?

Another common use of mod_rewrite is to map old URLs to new URLs

Say you change your CMS... Search engines have links, and users have bookmarks to pages in your old CMS. You don't want 404 Not Found errors when they visit those URLs again. So you use mod_rewrite to convert URLs in one format to another

Need More Info? There's a mod_rewrite tutorial at: This site not only has a tutorial, it has an active message board just about mod_rewrite: