Redirects with mod_rewrite

Overview

A redirect automatically changes the browser’s URL from one address to another. Different redirect codes can be used to control how the browser or search engine spider interprets the redirect. In this guide, we'll cover how to set up redirects using mod_rewrite in the .htaccess file.

Usage

All redirects are configured within the .htaccess file located in the document root of your target domain or subdomain. Below is a simple example that redirects www.example.com to example.com:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule ^(.*)$ http://example.com/$1 [R,L]

To reverse the process and redirect example.com to www.example.com, you only need to slightly modify the RewriteCond and RewriteRule:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^example\.com$
RewriteRule ^(.*)$ http://www.example.com/$1 [R,L]

How It Works

• RewriteCond: Stands for "rewrite condition." This directive checks if the specified condition is met.
• RewriteRule: Stands for "rewrite rule." If the condition is met, this rule is applied to the current URL, using regular expression substitution.

The mod_rewrite module uses Perl-compatible regular expressions (PCRE) to match and manipulate URLs.

Required Components

For a redirect to function correctly, two key components must be included:

• RewriteEngine On: Enables the URL rewriting engine.
• RewriteBase /: Anchors all rules to the current directory. This directive is crucial when working with addon domains and subdomains.

These lines are essential, though they are omitted in the following examples for brevity.

Examples

Redirect to SSL

The following example redirects all HTTP traffic to HTTPS:

RewriteCond %{HTTPS} !^on$
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R,L]

Explanation:

• The server checks for the HTTPS environment variable. If SSL is not active (!^on$), it assumes the request is using HTTP.
• The RewriteRule then redirects the request to the same hostname and URL path but using HTTPS.

Redirect Codes

You can specify a redirect code by appending a number to the R flag in the RewriteRule. By default, a 302 Found redirect is used, but you can change this by specifying one of the following codes:

Code	Name	Description
301	Moved Permanently	Resource is no longer accessible under the original URL; use the new URL
302	Found	URL is temporarily under a new resource; continue using the original URL
303	See Other	Response resides elsewhere and should be retrieved using a GET request
307	Temporary Redirect	URL temporarily resides elsewhere; use the original URL in future requests
308	Permanent Redirect	Similar to 301 but preserves the request method (e.g., POST); experimental

See Also

• Introduction to regular expressions and mod_rewrite
• URL rewriting with mod_rewrite

By following these guidelines, you can effectively manage URL redirects using mod_rewrite in your .htaccess file, ensuring smooth transitions and better control over your website's URLs.