Module Rewrite - URL Rewriting Guide

• Module Rewrite
• RewriteCond
• RewriteRule
• Regular expressions
• Condition pattern

• Protecting your images and files from linking
• Redirect visitor by domain name
• Redirect domains to other directory
• Redirect visitor by user agent

This document describes how one can use Apache's mod_rewrite to solve typical URL based problems webmasters are usually confronted with in practice. The Apache module mod_rewrite is a module which provides a powerful way to do URL manipulations. With it you can nearly do all types of URL manipulations you ever dreamed about. The price you have to pay is to accept complexity, because mod_rewrite is not easy to understand and use for the beginner.

NOTE: Depending on your server configuration it can be necessary to change the examples for your situation. Always try to understand what it really does before you use it. Bad use would lead to deadloops and will hang the server.

The most example's can be used in the .htaccess file while other ones only in the Apache htppd.conf file.

The RewriteCond directive defines a rule condition. Preserve a RewriteRule with one or more RewriteCond directives. The following rewriting rule is only used if its pattern matches the current state of the URI and if these additional conditions apply too.

You can set special flags for condition pattern by appending a third argument to the RewriteCond directive. Flags is a comma-separated list of the following flags:

The RewriteRule directive is the real rewriting.

You can set special flags for condition pattern by appending a third argument to the RewriteCond directive. Flags is a comma-separated list of the following flags:

Text:
  . Any single character
  [chars] One  of chars
  [^chars] None of chars
  text1|text2 text1 or text2

Quantifiers:
  ? 0 or 1 of the preceding text
  * 0 or N of the preceding text (N > 0)
  + 1 or N of the preceding text (N > 1)

Grouping:
  (text) Grouping of text

Anchors:
  ^ Start of line anchor
  $ End of line anchor

Escaping:
  \ char escape that particular char

There are some special variants of CondPatterns. Instead of real regular expression strings you can also use one of the following:

NOTE: You can prefix the pattern string with a '!' character (exclamation mark) to specify a non-matching pattern.

DESCRIPTION: In some cases other webmasters are linking to your download files or using images, hosted on your server as inline-images on their pages.

RewriteEngine On
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteCond %{HTTP_REFERER} !^http://domain.com [NC]
RewriteCond %{HTTP_REFERER} !^http://www.domain.com [NC]
RewriteCond %{HTTP_REFERER} !^http://212.204.218.80 [NC]
RewriteRule ^.*$ http://www.domain.com/ [R,L]

EXPLAIN: In this case are the visitors redirect to http://www.domain.com/ if the hyperlink has not arrived from http://domain.com, http://www.domain.com or http://212.204.218.80.

DESCRIPTION: In some cases the same web site is accessible by different addresses, like domain.com, www.domain.com, www.domain2.com and we want to redirect it to one address.

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

EXPLAIN: In this case the requested URL http://domain.com/foo.html would redirected to the URL http://www.domain.com/foo.html.

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.domain.com$
RewriteCond %{REQUEST_URI} !^/HTML2/
RewriteRule ^(.*)$ /HTML2/$1

DESCRIPTION: For important top level pages it is sometimes necesarry to provide pages dependend on the browser. One has to provide a version for the latest Netscape, a version for the latest Internet Explorer, a version for the Lynx or old browsers and a average feature version for all others.

# MS Internet Explorer - Mozilla v4
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/4(.*)MSIE
RewriteRule ^index\.html$ /index.IE.html [L]

# Netscape v6.+ - Mozilla v5
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/5(.*)Gecko
RewriteRule ^index\.html$ /index.NS5.html [L]

# Lynx or Mozilla v1/2
RewriteCond %{HTTP_USER_AGENT} ^Lynx/ [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/[12]
RewriteRule ^index\.html$ /index.20.html [L]

# All other browsers
RewriteRule ^index\.html$ /index.32.html [L]

EXPLAIN: In this case we have to act on the HTTP header User-Agent. If the User-Agent begins with Mozilla/4 and is MS Internet Explorer (MSIE), the page index.html is rewritten to index.IE.html and the rewriting stops. If the User-Agent begins with Mozilla/5 and is Netscape (Gecko), the page index.html is rewritten to index.NS5.html. If the User-Agent begins with Lynx/ or Mozilla/1,2, the page index.html is rewritten to index.20.html. All other browsers receive page index.32.html