Rewrite URLs with mod_rewrite and Apache

Rewrite URLs

In a block (usually found a virtual host file) or .htaccess file, enable mod_rewrite:

Apache Configuration Option

RewriteEngine on

You may create multiple separate rewrite rules. These rules provide a pattern that the server compares against incoming requests. If a request matches a rewrite pattern, the server modifies the request as described by the rule and processes that request. Here is an example of a rewrite rule:

Apache Configuration Option

RewriteRule ^post-id/([0-9]+)$ /posts/$1.html

Let’s explain this rule: The first string is the pattern for matching against incoming requests. The second string specifies the actual files to be served. Rewrite patterns use regular expression syntax. The ^ defines the beginning of the string, and the $ defines the end of the string, meaning that the rewrite engine won’t rewrite strings that match only part of the pattern.

The string rewrites all URLs that specify paths beginning with /post-id/ and contain one or more numbers (eg. [0-9]+), serving a corresponding .html file in the /posts/ directory. The parenthetical term or terms in the pattern specify a variable that is passed to the second string as $1, $2, $3 and so forth, depending on how many parentheticals are given in the first string.

You can create and apply multiple rewrite rules and these rules are applied sequentially. The order in which RewriteRules are stated can affect which rules are matched.

Optionally, you can insert a RewriteBase directive to modify the behavior of the rewrite rules. Let’s assume:

• These directives are specified for the /srv/www/example.com/public_html/ directory.
• Some users make a requests in the form http://example.com/post-id/200, where 200 might be any number longer than one digit.
• Some users make a requests in the form http://example.com/page/title-of-page, where “title of page” might represent any string of characters.
• The files are located on the filesystem at /srv/www/example.com/public_html/objects/ and match requested object in name, but have an .html extension.

Apache Configuration Options

RewriteEngine on
RewriteBase /objects
RewriteRule ^post-id/([0-9]+)$ $1.html
RewriteRule ^page/([^/]+)$ $1.html

The above rewrite rules would take a request for:

• http://example.com/post-id/200/ and serve the file located at /srv/www/example.com/public_html/objects/200.html
• http://example.com/page/free-the-toast/ and serve the file located at /srv/example.com/public_html/objects/free-the-toast.html

This is useful when the locations of files on the file system do not correspond to the URLs as requested by the client. This is also particularly useful when all requests are generated dynamically by a single file, for example index.php.

Rewrite URLs Under Specific ConditionsPermalink

With the RewriteCond parameter, you can set conditions under which a RewriteRule will be used. Let’s take the following example from the default rewrite rules for the WordPress application:

Apache Configuration Option for WordPress

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

In this example, all requests that begin with the top level of the context are affected by the rewrite rules. This is specified by the RewriteBase / directive. The context is determined by where the rewrite rules are specified in the virtual host, directory block, or .htaccess file.

The RewriteCond statements direct Apache to only apply the rule that follows them if their conditions are met. In the above example, the requested file name needs to not match an existing file on the file system (!-f) and not match an existing directory on the file system (!-d).

If both conditions are true and no file or directory exists that matches the request, Apache applies the rewrite rule. For example, if the user requests http://example.com/?post=123 or http://example.com/post/123 the server will return the result for index.php?post=123 or index.php/post/123, respectively.

Multiple RewriteCond are connected with logical AND operators so that all conditions be true in order for a RewriteRule to apply for that request. You may also add an [OR] statement to the end of a RewriteCond directive to join a list of conditions with a logical OR and create several possible conditions where a request would be rewritten by a single RewriteRule. Consult the Apache mod_rewrite documentation for more information about rewrite conditions.

Redirection Codes in mod_rewritePermalink

Finally, there are a number of codes that you may append to a RewriteRule that modify the behavior of the rewrite. In the previous example, RewriteRule . /index.php [L], we used the [L] option which stands for “last rule”. This prevents Apache from applying any additional rewrite rules after that rule. A few common options are:

• F tells the client that the URL is forbidden, responding with HTTP code 403.
• N forces mod_rewrite to begin the rewriting process again, and allows for multi-stage rewriting.
• R tells the client that the requested page has moved, with the HTTP code 302 for temporary redirection. If the page has moved permanently, use “R=301.”

You may also specify multiple options at the end of a RewriteRule separating them with commas: [L,R=301]