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 <manualpage metafile="rewrite_guide.xml.meta">
   <parentdocument href="./index.html" />

   <title>URL Rewriting Guide</title>

   <summary>

     <p>This document supplements the <module>mod_rewrite</module>
     <a href="../mod/mod_rewrite.html">reference documentation</a>.
     It describes how one can use Apache's <module>mod_rewrite</module>
     to solve typical URL-based problems with which webmasters are
     commonony confronted. We give detailed descriptions on how to
     solve each problem by configuring URL rewriting rulesets.</p>

     <note type="warning">ATTENTION: Depending on your server configuration
     it may be necessary to slightly change the examples for your
     situation, e.g. adding the <code>[PT]</code> flag when
     additionally using <module>mod_alias</module> and
     <module>mod_userdir</module>, etc. Or rewriting a ruleset
     to fit in <code>.htaccess</code> context instead
     of per-server context. Always try to understand what a
     particular ruleset really does before you use it. This
     avoids many problems.</note>

   </summary>
 <seealso><a href="../mod/mod_rewrite.html">Module
 documentation</a></seealso>
 <seealso><a href="rewrite_intro.html">mod_rewrite
 introduction</a></seealso>
 <seealso><a href="rewrite_guide_advanced.html">Practical solutions to
 advanced problems</a></seealso>
 <seealso><a href="rewrite_tech.html">Technical details</a></seealso>


 <section id="canonicalurl">

 <title>Canonical URLs</title>

 <dl>
  <dt>Description:</dt>

    <dd>
      <p>On some webservers there are more than one URL for a
      resource. Usually there are canonical URLs (which should be
      actually used and distributed) and those which are just
      shortcuts, internal ones, etc. Independent of which URL the
      user supplied with the request he should finally see the
      canonical one only.</p>
    </dd>

    <dt>Solution:</dt>

      <dd>
        <p>We do an external HTTP redirect for all non-canonical
        URLs to fix them in the location view of the Browser and
        for all subsequent requests. In the example ruleset below
        we replace <code>/~user</code> by the canonical
        <code>/u/user</code> and fix a missing trailing slash for
        <code>/u/user</code>.</p>

 <example><pre>
 RewriteRule   ^/<strong>~</strong>([^/]+)/?(.*)    /<strong>u</strong>/$1/$2  [<strong>R</strong>]
 RewriteRule   ^/([uge])/(<strong>[^/]+</strong>)$  /$1/$2<strong>/</strong>   [<strong>R</strong>]
 </pre></example>
         </dd>
       </dl>

     </section>

 <section id="canonicalhost"><title>Canonical Hostnames</title>

       <dl>
         <dt>Description:</dt>

         <dd>The goal of this rule is to force the use of a particular
         hostname, in preference to other hostnames which may be used to
         reach the same site. For example, if you wish to force the use
         of <strong>www.example.com</strong> instead of
         <strong>example.com</strong>, you might use a variant of the
         following recipe.</dd>

         <dt>Solution:</dt>

         <dd>
 <p>For sites running on a port other than 80:</p>
 <example><pre>
 RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
 RewriteCond %{HTTP_HOST}   !^$
 RewriteCond %{SERVER_PORT} !^80$
 RewriteRule ^/(.*)         http://fully.qualified.domain.name:%{SERVER_PORT}/$1 [L,R]
 </pre></example>

 <p>And for a site running on port 80</p>
 <example><pre>
 RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
 RewriteCond %{HTTP_HOST}   !^$
 RewriteRule ^/(.*)         http://fully.qualified.domain.name/$1 [L,R]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="moveddocroot">

       <title>Moved <code>DocumentRoot</code></title>

       <dl>
         <dt>Description:</dt>

         <dd>
 <p>Usually the <directive module="core">DocumentRoot</directive>
 of the webserver directly relates to the URL "<code>/</code>".
 But often this data is not really of top-level priority. For example,
 you may wish for visitors, on first entering a site, to go to a
 particular subdirectory <code>/about/</code>. This may be accomplished
 using the following ruleset:</p>
 </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We redirect the URL <code>/</code> to
           <code>/about/</code>:
           </p>

 <example><pre>
 RewriteEngine on
 RewriteRule   <strong>^/$</strong>  /about/  [<strong>R</strong>]
 </pre></example>

     <p>Note that this can also be handled using the <directive
     module="mod_alias">RedirectMatch</directive> directive:</p>

 <example>
 RedirectMatch ^/$ http://example.com/e/www/
 </example>
 </dd>
 </dl>

     </section>

     <section id="trailingslash">

       <title>Trailing Slash Problem</title>

       <dl>
         <dt>Description:</dt>

     <dd><p>The vast majority of "trailing slash" problems can be dealt
     with using the techniques discussed in the <a
     href="http://httpd.apache.org/docs/misc/FAQ-E.html#set-servername">FAQ
     entry</a>. However, occasionally, there is a need to use mod_rewrite
     to handle a case where a missing trailing slash causes a URL to
     fail. This can happen, for example, after a series of complex
     rewrite rules.</p>
     </dd>

         <dt>Solution:</dt>

         <dd>
           <p>The solution to this subtle problem is to let the server
           add the trailing slash automatically. To do this
           correctly we have to use an external redirect, so the
           browser correctly requests subsequent images etc. If we
           only did a internal rewrite, this would only work for the
           directory page, but would go wrong when any images are
           included into this page with relative URLs, because the
           browser would request an in-lined object. For instance, a
           request for <code>image.gif</code> in
           <code>/~quux/foo/index.html</code> would become
           <code>/~quux/image.gif</code> without the external
           redirect!</p>

           <p>So, to do this trick we write:</p>

 <example><pre>
 RewriteEngine  on
 RewriteBase    /~quux/
 RewriteRule    ^foo<strong>$</strong>  foo<strong>/</strong>  [<strong>R</strong>]
 </pre></example>

    <p>Alternately, you can put the following in a
    top-level <code>.htaccess</code> file in the content directory.
    But note that this creates some processing overhead.</p>

 <example><pre>
 RewriteEngine  on
 RewriteBase    /~quux/
 RewriteCond    %{REQUEST_FILENAME}  <strong>-d</strong>
 RewriteRule    ^(.+<strong>[^/]</strong>)$           $1<strong>/</strong>  [R]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="movehomedirs">

       <title>Move Homedirs to Different Webserver</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Many webmasters have asked for a solution to the
           following situation: They wanted to redirect just all
           homedirs on a webserver to another webserver. They usually
           need such things when establishing a newer webserver which
           will replace the old one over time.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>The solution is trivial with <module>mod_rewrite</module>.
           On the old webserver we just redirect all
           <code>/~user/anypath</code> URLs to
           <code>http://newserver/~user/anypath</code>.</p>

 <example><pre>
 RewriteEngine on
 RewriteRule   ^/~(.+)  http://<strong>newserver</strong>/~$1  [R,L]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="multipledirs">

       <title>Search pages in more than one directory</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Sometimes it is necessary to let the webserver search
           for pages in more than one directory. Here MultiViews or
           other techniques cannot help.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We program a explicit ruleset which searches for the
           files in the directories.</p>

 <example><pre>
 RewriteEngine on

 #   first try to find it in custom/...
 #   ...and if found stop and be happy:
 RewriteCond         /your/docroot/<strong>dir1</strong>/%{REQUEST_FILENAME}  -f
 RewriteRule  ^(.+)  /your/docroot/<strong>dir1</strong>/$1  [L]

 #   second try to find it in pub/...
 #   ...and if found stop and be happy:
 RewriteCond         /your/docroot/<strong>dir2</strong>/%{REQUEST_FILENAME}  -f
 RewriteRule  ^(.+)  /your/docroot/<strong>dir2</strong>/$1  [L]

 #   else go on for other Alias or ScriptAlias directives,
 #   etc.
 RewriteRule   ^(.+)  -  [PT]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="setenvvars">

       <title>Set Environment Variables According To URL Parts</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Perhaps you want to keep status information between
           requests and use the URL to encode it. But you don't want
           to use a CGI wrapper for all pages just to strip out this
           information.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We use a rewrite rule to strip out the status information
           and remember it via an environment variable which can be
           later dereferenced from within XSSI or CGI. This way a
           URL <code>/foo/S=java/bar/</code> gets translated to
           <code>/foo/bar/</code> and the environment variable named
           <code>STATUS</code> is set to the value "java".</p>

 <example><pre>
 RewriteEngine on
 RewriteRule   ^(.*)/<strong>S=([^/]+)</strong>/(.*)    $1/$3 [E=<strong>STATUS:$2</strong>]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="uservhosts">

       <title>Virtual User Hosts</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Assume that you want to provide
           <code>www.<strong>username</strong>.host.domain.com</code>
           for the homepage of username via just DNS A records to the
           same machine and without any virtualhosts on this
           machine.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>For HTTP/1.0 requests there is no solution, but for
           HTTP/1.1 requests which contain a Host: HTTP header we
           can use the following ruleset to rewrite
           <code>http://www.username.host.com/anypath</code>
           internally to <code>/home/username/anypath</code>:</p>

 <example><pre>
 RewriteEngine on
 RewriteCond   %{<strong>HTTP_HOST</strong>}                 ^www\.<strong>[^.]+</strong>\.host\.com$
 RewriteRule   ^(.+)                        %{HTTP_HOST}$1          [C]
 RewriteRule   ^www\.<strong>([^.]+)</strong>\.host\.com(.*) /home/<strong>$1</strong>$2
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="redirecthome">

       <title>Redirect Homedirs For Foreigners</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>We want to redirect homedir URLs to another webserver
           <code>www.somewhere.com</code> when the requesting user
           does not stay in the local domain
           <code>ourdomain.com</code>. This is sometimes used in
           virtual host contexts.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>Just a rewrite condition:</p>

 <example><pre>
 RewriteEngine on
 RewriteCond   %{REMOTE_HOST}  <strong>!^.+\.ourdomain\.com$</strong>
 RewriteRule   ^(/~.+)         http://www.somewhere.com/$1 [R,L]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section id="redirectanchors">

       <title>Redirecting Anchors</title>

       <dl>
         <dt>Description:</dt>

         <dd>
         <p>By default, redirecting to an HTML anchor doesn't work,
         because mod_rewrite escapes the <code>#</code> character,
         turning it into <code>%23</code>. This, in turn, breaks the
         redirection.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>Use the <code>[NE]</code> flag on the
           <code>RewriteRule</code>. NE stands for No Escape.
           </p>
         </dd>
       </dl>

     </section>

     <section>

       <title>Time-Dependent Rewriting</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>When tricks like time-dependent content should happen a
           lot of webmasters still use CGI scripts which do for
           instance redirects to specialized pages. How can it be done
           via <module>mod_rewrite</module>?</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>There are a lot of variables named <code>TIME_xxx</code>
           for rewrite conditions. In conjunction with the special
           lexicographic comparison patterns <code>&lt;STRING</code>,
           <code>&gt;STRING</code> and <code>=STRING</code> we can
           do time-dependent redirects:</p>

 <example><pre>
 RewriteEngine on
 RewriteCond   %{TIME_HOUR}%{TIME_MIN} &gt;0700
 RewriteCond   %{TIME_HOUR}%{TIME_MIN} &lt;1900
 RewriteRule   ^foo\.html$             foo.day.html
 RewriteRule   ^foo\.html$             foo.night.html
 </pre></example>

           <p>This provides the content of <code>foo.day.html</code>
           under the URL <code>foo.html</code> from
           <code>07:00-19:00</code> and at the remaining time the
           contents of <code>foo.night.html</code>. Just a nice
           feature for a homepage...</p>
         </dd>
       </dl>

     </section>

     <section>

       <title>Backward Compatibility for YYYY to XXXX migration</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>How can we make URLs backward compatible (still
           existing virtually) after migrating <code>document.YYYY</code>
           to <code>document.XXXX</code>, e.g. after translating a
           bunch of <code>.html</code> files to <code>.phtml</code>?</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We just rewrite the name to its basename and test for
           existence of the new extension. If it exists, we take
           that name, else we rewrite the URL to its original state.</p>


 <example><pre>
 #   backward compatibility ruleset for
 #   rewriting document.html to document.phtml
 #   when and only when document.phtml exists
 #   but no longer document.html
 RewriteEngine on
 RewriteBase   /~quux/
 #   parse out basename, but remember the fact
 RewriteRule   ^(.*)\.html$              $1      [C,E=WasHTML:yes]
 #   rewrite to document.phtml if exists
 RewriteCond   %{REQUEST_FILENAME}.phtml -f
 RewriteRule   ^(.*)$ $1.phtml                   [S=1]
 #   else reverse the previous basename cutout
 RewriteCond   %{ENV:WasHTML}            ^yes$
 RewriteRule   ^(.*)$ $1.html
 </pre></example>
         </dd>
       </dl>

     </section>

   <section id="content">

     <title>Content Handling</title>

     <section>

       <title>From Old to New (intern)</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Assume we have recently renamed the page
           <code>foo.html</code> to <code>bar.html</code> and now want
           to provide the old URL for backward compatibility. Actually
           we want that users of the old URL even not recognize that
           the pages was renamed.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We rewrite the old URL to the new one internally via the
           following rule:</p>

 <example><pre>
 RewriteEngine  on
 RewriteBase    /~quux/
 RewriteRule    ^<strong>foo</strong>\.html$  <strong>bar</strong>.html
 </pre></example>
         </dd>
       </dl>

     </section>

     <section>

       <title>From Old to New (extern)</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Assume again that we have recently renamed the page
           <code>foo.html</code> to <code>bar.html</code> and now want
           to provide the old URL for backward compatibility. But this
           time we want that the users of the old URL get hinted to
           the new one, i.e. their browsers Location field should
           change, too.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We force a HTTP redirect to the new URL which leads to a
           change of the browsers and thus the users view:</p>

 <example><pre>
 RewriteEngine  on
 RewriteBase    /~quux/
 RewriteRule    ^<strong>foo</strong>\.html$  <strong>bar</strong>.html  [<strong>R</strong>]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section>

       <title>From Static to Dynamic</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>How can we transform a static page
           <code>foo.html</code> into a dynamic variant
           <code>foo.cgi</code> in a seamless way, i.e. without notice
           by the browser/user.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We just rewrite the URL to the CGI-script and force the
           correct MIME-type so it gets really run as a CGI-script.
           This way a request to <code>/~quux/foo.html</code>
           internally leads to the invocation of
           <code>/~quux/foo.cgi</code>.</p>

 <example><pre>
 RewriteEngine  on
 RewriteBase    /~quux/
 RewriteRule    ^foo\.<strong>html</strong>$  foo.<strong>cgi</strong>  [T=<strong>application/x-httpd-cgi</strong>]
 </pre></example>
         </dd>
       </dl>

     </section>
 </section>

   <section id="access">

     <title>Access Restriction</title>

     <section>

       <title>Blocking of Robots</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>How can we block a really annoying robot from
           retrieving pages of a specific webarea? A
           <code>/robots.txt</code> file containing entries of the
           "Robot Exclusion Protocol" is typically not enough to get
           rid of such a robot.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We use a ruleset which forbids the URLs of the webarea
           <code>/~quux/foo/arc/</code> (perhaps a very deep
           directory indexed area where the robot traversal would
           create big server load). We have to make sure that we
           forbid access only to the particular robot, i.e. just
           forbidding the host where the robot runs is not enough.
           This would block users from this host, too. We accomplish
           this by also matching the User-Agent HTTP header
           information.</p>

 <example><pre>
 RewriteCond %{HTTP_USER_AGENT}   ^<strong>NameOfBadRobot</strong>.*
 RewriteCond %{REMOTE_ADDR}       ^<strong>123\.45\.67\.[8-9]</strong>$
 RewriteRule ^<strong>/~quux/foo/arc/</strong>.+   -   [<strong>F</strong>]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section>

       <title>Blocked Inline-Images</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>Assume we have under <code>http://www.quux-corp.de/~quux/</code>
           some pages with inlined GIF graphics. These graphics are
           nice, so others directly incorporate them via hyperlinks to
           their pages. We don't like this practice because it adds
           useless traffic to our server.</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>While we cannot 100% protect the images from inclusion,
           we can at least restrict the cases where the browser
           sends a HTTP Referer header.</p>

 <example><pre>
 RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
 RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
 RewriteRule <strong>.*\.gif$</strong>        -                                    [F]
 </pre></example>

 <example><pre>
 RewriteCond %{HTTP_REFERER}         !^$
 RewriteCond %{HTTP_REFERER}         !.*/foo-with-gif\.html$
 RewriteRule <strong>^inlined-in-foo\.gif$</strong>   -                        [F]
 </pre></example>
         </dd>
       </dl>

     </section>

     <section>

       <title>Proxy Deny</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>How can we forbid a certain host or even a user of a
           special host from using the Apache proxy?</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>We first have to make sure <module>mod_rewrite</module>
           is below(!) <module>mod_proxy</module> in the Configuration
           file when compiling the Apache webserver. This way it gets
           called <em>before</em> <module>mod_proxy</module>. Then we
           configure the following for a host-dependent deny...</p>

 <example><pre>
 RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
 RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
 </pre></example>

           <p>...and this one for a user@host-dependent deny:</p>

 <example><pre>
 RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST}  <strong>^badguy@badhost\.mydomain\.com$</strong>
 RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
 </pre></example>
         </dd>
       </dl>

     </section>

   </section>

   <section id="other">

     <title>Other</title>

     <section>

       <title>External Rewriting Engine</title>

       <dl>
         <dt>Description:</dt>

         <dd>
           <p>A FAQ: How can we solve the FOO/BAR/QUUX/etc.
           problem? There seems no solution by the use of
           <module>mod_rewrite</module>...</p>
         </dd>

         <dt>Solution:</dt>

         <dd>
           <p>Use an external <directive module="mod_rewrite"
           >RewriteMap</directive>, i.e. a program which acts
           like a <directive module="mod_rewrite"
           >RewriteMap</directive>. It is run once on startup of Apache
           receives the requested URLs on <code>STDIN</code> and has
           to put the resulting (usually rewritten) URL on
           <code>STDOUT</code> (same order!).</p>

 <example><pre>
 RewriteEngine on
 RewriteMap    quux-map       <strong>prg:</strong>/path/to/map.quux.pl
 RewriteRule   ^/~quux/(.*)$  /~quux/<strong>${quux-map:$1}</strong>
 </pre></example>

 <example><pre>
 #!/path/to/perl

 #   disable buffered I/O which would lead
 #   to deadloops for the Apache server
 $| = 1;

 #   read URLs one per line from stdin and
 #   generate substitution URL on stdout
 while (&lt;&gt;) {
     s|^foo/|bar/|;
     print $_;
 }
 </pre></example>

           <p>This is a demonstration-only example and just rewrites
           all URLs <code>/~quux/foo/...</code> to
           <code>/~quux/bar/...</code>. Actually you can program
           whatever you like. But notice that while such maps can be
           <strong>used</strong> also by an average user, only the
           system administrator can <strong>define</strong> it.</p>
         </dd>
       </dl>

     </section>

   </section>

 </manualpage>
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	<manualpage metafile="rewrite_guide.xml.meta">
	<parentdocument href="./index.html" />

	<title>URL Rewriting Guide</title>

	<summary>

	<p>This document supplements the <module>mod_rewrite</module>
	<a href="../mod/mod_rewrite.html">reference documentation</a>.
	It describes how one can use Apache's <module>mod_rewrite</module>
	to solve typical URL-based problems with which webmasters are
	commonony confronted. We give detailed descriptions on how to
	solve each problem by configuring URL rewriting rulesets.</p>

	<note type="warning">ATTENTION: Depending on your server configuration
	it may be necessary to slightly change the examples for your
	situation, e.g. adding the <code>[PT]</code> flag when
	additionally using <module>mod_alias</module> and
	<module>mod_userdir</module>, etc. Or rewriting a ruleset
	to fit in <code>.htaccess</code> context instead
	of per-server context. Always try to understand what a
	particular ruleset really does before you use it. This
	avoids many problems.</note>

	</summary>
	<seealso><a href="../mod/mod_rewrite.html">Module
	documentation</a></seealso>
	<seealso><a href="rewrite_intro.html">mod_rewrite
	introduction</a></seealso>
	<seealso><a href="rewrite_guide_advanced.html">Practical solutions to
	advanced problems</a></seealso>
	<seealso><a href="rewrite_tech.html">Technical details</a></seealso>


	<section id="canonicalurl">

	<title>Canonical URLs</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>On some webservers there are more than one URL for a
	resource. Usually there are canonical URLs (which should be
	actually used and distributed) and those which are just
	shortcuts, internal ones, etc. Independent of which URL the
	user supplied with the request he should finally see the
	canonical one only.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We do an external HTTP redirect for all non-canonical
	URLs to fix them in the location view of the Browser and
	for all subsequent requests. In the example ruleset below
	we replace <code>/~user</code> by the canonical
	<code>/u/user</code> and fix a missing trailing slash for
	<code>/u/user</code>.</p>

	<example><pre>
	RewriteRule ^/<strong>~</strong>([^/]+)/?(.*) /<strong>u</strong>/$1/$2 [<strong>R</strong>]
	RewriteRule ^/([uge])/(<strong>[^/]+</strong>)$ /$1/$2<strong>/</strong> [<strong>R</strong>]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="canonicalhost"><title>Canonical Hostnames</title>

	<dl>
	<dt>Description:</dt>

	<dd>The goal of this rule is to force the use of a particular
	hostname, in preference to other hostnames which may be used to
	reach the same site. For example, if you wish to force the use
	of <strong>www.example.com</strong> instead of
	<strong>example.com</strong>, you might use a variant of the
	following recipe.</dd>

	<dt>Solution:</dt>

	<dd>
	<p>For sites running on a port other than 80:</p>
	<example><pre>
	RewriteCond %{HTTP_HOST} !^fully\.qualified\.domain\.name [NC]
	RewriteCond %{HTTP_HOST} !^$
	RewriteCond %{SERVER_PORT} !^80$
	RewriteRule ^/(.*) http://fully.qualified.domain.name:%{SERVER_PORT}/$1 [L,R]
	</pre></example>

	<p>And for a site running on port 80</p>
	<example><pre>
	RewriteCond %{HTTP_HOST} !^fully\.qualified\.domain\.name [NC]
	RewriteCond %{HTTP_HOST} !^$
	RewriteRule ^/(.*) http://fully.qualified.domain.name/$1 [L,R]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="moveddocroot">

	<title>Moved <code>DocumentRoot</code></title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Usually the <directive module="core">DocumentRoot</directive>
	of the webserver directly relates to the URL "<code>/</code>".
	But often this data is not really of top-level priority. For example,
	you may wish for visitors, on first entering a site, to go to a
	particular subdirectory <code>/about/</code>. This may be accomplished
	using the following ruleset:</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We redirect the URL <code>/</code> to
	<code>/about/</code>:
	</p>

	<example><pre>
	RewriteEngine on
	RewriteRule <strong>^/$</strong> /about/ [<strong>R</strong>]
	</pre></example>

	<p>Note that this can also be handled using the <directive
	module="mod_alias">RedirectMatch</directive> directive:</p>

	<example>
	RedirectMatch ^/$ http://example.com/e/www/
	</example>
	</dd>
	</dl>

	</section>

	<section id="trailingslash">

	<title>Trailing Slash Problem</title>

	<dl>
	<dt>Description:</dt>

	<dd><p>The vast majority of "trailing slash" problems can be dealt
	with using the techniques discussed in the <a
	href="http://httpd.apache.org/docs/misc/FAQ-E.html#set-servername">FAQ
	entry</a>. However, occasionally, there is a need to use mod_rewrite
	to handle a case where a missing trailing slash causes a URL to
	fail. This can happen, for example, after a series of complex
	rewrite rules.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>The solution to this subtle problem is to let the server
	add the trailing slash automatically. To do this
	correctly we have to use an external redirect, so the
	browser correctly requests subsequent images etc. If we
	only did a internal rewrite, this would only work for the
	directory page, but would go wrong when any images are
	included into this page with relative URLs, because the
	browser would request an in-lined object. For instance, a
	request for <code>image.gif</code> in
	<code>/~quux/foo/index.html</code> would become
	<code>/~quux/image.gif</code> without the external
	redirect!</p>

	<p>So, to do this trick we write:</p>

	<example><pre>
	RewriteEngine on
	RewriteBase /~quux/
	RewriteRule ^foo<strong>$</strong> foo<strong>/</strong> [<strong>R</strong>]
	</pre></example>

	<p>Alternately, you can put the following in a
	top-level <code>.htaccess</code> file in the content directory.
	But note that this creates some processing overhead.</p>

	<example><pre>
	RewriteEngine on
	RewriteBase /~quux/
	RewriteCond %{REQUEST_FILENAME} <strong>-d</strong>
	RewriteRule ^(.+<strong>[^/]</strong>)$ $1<strong>/</strong> [R]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="movehomedirs">

	<title>Move Homedirs to Different Webserver</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Many webmasters have asked for a solution to the
	following situation: They wanted to redirect just all
	homedirs on a webserver to another webserver. They usually
	need such things when establishing a newer webserver which
	will replace the old one over time.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>The solution is trivial with <module>mod_rewrite</module>.
	On the old webserver we just redirect all
	<code>/~user/anypath</code> URLs to
	<code>http://newserver/~user/anypath</code>.</p>

	<example><pre>
	RewriteEngine on
	RewriteRule ^/~(.+) http://<strong>newserver</strong>/~$1 [R,L]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="multipledirs">

	<title>Search pages in more than one directory</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Sometimes it is necessary to let the webserver search
	for pages in more than one directory. Here MultiViews or
	other techniques cannot help.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We program a explicit ruleset which searches for the
	files in the directories.</p>

	<example><pre>
	RewriteEngine on

	# first try to find it in custom/...
	# ...and if found stop and be happy:
	RewriteCond /your/docroot/<strong>dir1</strong>/%{REQUEST_FILENAME} -f
	RewriteRule ^(.+) /your/docroot/<strong>dir1</strong>/$1 [L]

	# second try to find it in pub/...
	# ...and if found stop and be happy:
	RewriteCond /your/docroot/<strong>dir2</strong>/%{REQUEST_FILENAME} -f
	RewriteRule ^(.+) /your/docroot/<strong>dir2</strong>/$1 [L]

	# else go on for other Alias or ScriptAlias directives,
	# etc.
	RewriteRule ^(.+) - [PT]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="setenvvars">

	<title>Set Environment Variables According To URL Parts</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Perhaps you want to keep status information between
	requests and use the URL to encode it. But you don't want
	to use a CGI wrapper for all pages just to strip out this
	information.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We use a rewrite rule to strip out the status information
	and remember it via an environment variable which can be
	later dereferenced from within XSSI or CGI. This way a
	URL <code>/foo/S=java/bar/</code> gets translated to
	<code>/foo/bar/</code> and the environment variable named
	<code>STATUS</code> is set to the value "java".</p>

	<example><pre>
	RewriteEngine on
	RewriteRule ^(.)/<strong>S=([^/]+)</strong>/(.) $1/$3 [E=<strong>STATUS:$2</strong>]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="uservhosts">

	<title>Virtual User Hosts</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Assume that you want to provide
	<code>www.<strong>username</strong>.host.domain.com</code>
	for the homepage of username via just DNS A records to the
	same machine and without any virtualhosts on this
	machine.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>For HTTP/1.0 requests there is no solution, but for
	HTTP/1.1 requests which contain a Host: HTTP header we
	can use the following ruleset to rewrite
	<code>http://www.username.host.com/anypath</code>
	internally to <code>/home/username/anypath</code>:</p>

	<example><pre>
	RewriteEngine on
	RewriteCond %{<strong>HTTP_HOST</strong>} ^www\.<strong>[^.]+</strong>\.host\.com$
	RewriteRule ^(.+) %{HTTP_HOST}$1 [C]
	RewriteRule ^www\.<strong>([^.]+)</strong>\.host\.com(.*) /home/<strong>$1</strong>$2
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="redirecthome">

	<title>Redirect Homedirs For Foreigners</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>We want to redirect homedir URLs to another webserver
	<code>www.somewhere.com</code> when the requesting user
	does not stay in the local domain
	<code>ourdomain.com</code>. This is sometimes used in
	virtual host contexts.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>Just a rewrite condition:</p>

	<example><pre>
	RewriteEngine on
	RewriteCond %{REMOTE_HOST} <strong>!^.+\.ourdomain\.com$</strong>
	RewriteRule ^(/~.+) http://www.somewhere.com/$1 [R,L]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="redirectanchors">

	<title>Redirecting Anchors</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>By default, redirecting to an HTML anchor doesn't work,
	because mod_rewrite escapes the <code>#</code> character,
	turning it into <code>%23</code>. This, in turn, breaks the
	redirection.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>Use the <code>[NE]</code> flag on the
	<code>RewriteRule</code>. NE stands for No Escape.
	</p>
	</dd>
	</dl>

	</section>

	<section>

	<title>Time-Dependent Rewriting</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>When tricks like time-dependent content should happen a
	lot of webmasters still use CGI scripts which do for
	instance redirects to specialized pages. How can it be done
	via <module>mod_rewrite</module>?</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>There are a lot of variables named <code>TIME_xxx</code>
	for rewrite conditions. In conjunction with the special
	lexicographic comparison patterns <code><STRING</code>,
	<code>>STRING</code> and <code>=STRING</code> we can
	do time-dependent redirects:</p>

	<example><pre>
	RewriteEngine on
	RewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
	RewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
	RewriteRule ^foo\.html$ foo.day.html
	RewriteRule ^foo\.html$ foo.night.html
	</pre></example>

	<p>This provides the content of <code>foo.day.html</code>
	under the URL <code>foo.html</code> from
	<code>07:00-19:00</code> and at the remaining time the
	contents of <code>foo.night.html</code>. Just a nice
	feature for a homepage...</p>
	</dd>
	</dl>

	</section>

	<section>

	<title>Backward Compatibility for YYYY to XXXX migration</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>How can we make URLs backward compatible (still
	existing virtually) after migrating <code>document.YYYY</code>
	to <code>document.XXXX</code>, e.g. after translating a
	bunch of <code>.html</code> files to <code>.phtml</code>?</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We just rewrite the name to its basename and test for
	existence of the new extension. If it exists, we take
	that name, else we rewrite the URL to its original state.</p>


	<example><pre>
	# backward compatibility ruleset for
	# rewriting document.html to document.phtml
	# when and only when document.phtml exists
	# but no longer document.html
	RewriteEngine on
	RewriteBase /~quux/
	# parse out basename, but remember the fact
	RewriteRule ^(.*)\.html$ $1 [C,E=WasHTML:yes]
	# rewrite to document.phtml if exists
	RewriteCond %{REQUEST_FILENAME}.phtml -f
	RewriteRule ^(.*)$ $1.phtml [S=1]
	# else reverse the previous basename cutout
	RewriteCond %{ENV:WasHTML} ^yes$
	RewriteRule ^(.*)$ $1.html
	</pre></example>
	</dd>
	</dl>

	</section>

	<section id="content">

	<title>Content Handling</title>

	<section>

	<title>From Old to New (intern)</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Assume we have recently renamed the page
	<code>foo.html</code> to <code>bar.html</code> and now want
	to provide the old URL for backward compatibility. Actually
	we want that users of the old URL even not recognize that
	the pages was renamed.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We rewrite the old URL to the new one internally via the
	following rule:</p>

	<example><pre>
	RewriteEngine on
	RewriteBase /~quux/
	RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html
	</pre></example>
	</dd>
	</dl>

	</section>

	<section>

	<title>From Old to New (extern)</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Assume again that we have recently renamed the page
	<code>foo.html</code> to <code>bar.html</code> and now want
	to provide the old URL for backward compatibility. But this
	time we want that the users of the old URL get hinted to
	the new one, i.e. their browsers Location field should
	change, too.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We force a HTTP redirect to the new URL which leads to a
	change of the browsers and thus the users view:</p>

	<example><pre>
	RewriteEngine on
	RewriteBase /~quux/
	RewriteRule ^<strong>foo</strong>\.html$ <strong>bar</strong>.html [<strong>R</strong>]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section>

	<title>From Static to Dynamic</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>How can we transform a static page
	<code>foo.html</code> into a dynamic variant
	<code>foo.cgi</code> in a seamless way, i.e. without notice
	by the browser/user.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We just rewrite the URL to the CGI-script and force the
	correct MIME-type so it gets really run as a CGI-script.
	This way a request to <code>/~quux/foo.html</code>
	internally leads to the invocation of
	<code>/~quux/foo.cgi</code>.</p>

	<example><pre>
	RewriteEngine on
	RewriteBase /~quux/
	RewriteRule ^foo\.<strong>html</strong>$ foo.<strong>cgi</strong> [T=<strong>application/x-httpd-cgi</strong>]
	</pre></example>
	</dd>
	</dl>

	</section>
	</section>

	<section id="access">

	<title>Access Restriction</title>

	<section>

	<title>Blocking of Robots</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>How can we block a really annoying robot from
	retrieving pages of a specific webarea? A
	<code>/robots.txt</code> file containing entries of the
	"Robot Exclusion Protocol" is typically not enough to get
	rid of such a robot.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We use a ruleset which forbids the URLs of the webarea
	<code>/~quux/foo/arc/</code> (perhaps a very deep
	directory indexed area where the robot traversal would
	create big server load). We have to make sure that we
	forbid access only to the particular robot, i.e. just
	forbidding the host where the robot runs is not enough.
	This would block users from this host, too. We accomplish
	this by also matching the User-Agent HTTP header
	information.</p>

	<example><pre>
	RewriteCond %{HTTP_USER_AGENT} ^<strong>NameOfBadRobot</strong>.*
	RewriteCond %{REMOTE_ADDR} ^<strong>123\.45\.67\.[8-9]</strong>$
	RewriteRule ^<strong>/~quux/foo/arc/</strong>.+ - [<strong>F</strong>]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section>

	<title>Blocked Inline-Images</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>Assume we have under <code>http://www.quux-corp.de/~quux/</code>
	some pages with inlined GIF graphics. These graphics are
	nice, so others directly incorporate them via hyperlinks to
	their pages. We don't like this practice because it adds
	useless traffic to our server.</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>While we cannot 100% protect the images from inclusion,
	we can at least restrict the cases where the browser
	sends a HTTP Referer header.</p>

	<example><pre>
	RewriteCond %{HTTP_REFERER} <strong>!^$</strong>
	RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
	RewriteRule <strong>.*\.gif$</strong> - [F]
	</pre></example>

	<example><pre>
	RewriteCond %{HTTP_REFERER} !^$
	RewriteCond %{HTTP_REFERER} !.*/foo-with-gif\.html$
	RewriteRule <strong>^inlined-in-foo\.gif$</strong> - [F]
	</pre></example>
	</dd>
	</dl>

	</section>

	<section>

	<title>Proxy Deny</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>How can we forbid a certain host or even a user of a
	special host from using the Apache proxy?</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>We first have to make sure <module>mod_rewrite</module>
	is below(!) <module>mod_proxy</module> in the Configuration
	file when compiling the Apache webserver. This way it gets
	called <em>before</em> <module>mod_proxy</module>. Then we
	configure the following for a host-dependent deny...</p>

	<example><pre>
	RewriteCond %{REMOTE_HOST} <strong>^badhost\.mydomain\.com$</strong>
	RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
	</pre></example>

	<p>...and this one for a user@host-dependent deny:</p>

	<example><pre>
	RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST} <strong>^badguy@badhost\.mydomain\.com$</strong>
	RewriteRule !^http://[^/.]\.mydomain.com.* - [F]
	</pre></example>
	</dd>
	</dl>

	</section>

	</section>

	<section id="other">

	<title>Other</title>

	<section>

	<title>External Rewriting Engine</title>

	<dl>
	<dt>Description:</dt>

	<dd>
	<p>A FAQ: How can we solve the FOO/BAR/QUUX/etc.
	problem? There seems no solution by the use of
	<module>mod_rewrite</module>...</p>
	</dd>

	<dt>Solution:</dt>

	<dd>
	<p>Use an external <directive module="mod_rewrite"
	>RewriteMap</directive>, i.e. a program which acts
	like a <directive module="mod_rewrite"
	>RewriteMap</directive>. It is run once on startup of Apache
	receives the requested URLs on <code>STDIN</code> and has
	to put the resulting (usually rewritten) URL on
	<code>STDOUT</code> (same order!).</p>

	<example><pre>
	RewriteEngine on
	RewriteMap quux-map <strong>prg:</strong>/path/to/map.quux.pl
	RewriteRule ^/~quux/(.*)$ /~quux/<strong>${quux-map:$1}</strong>
	</pre></example>

	<example><pre>
	#!/path/to/perl

	# disable buffered I/O which would lead
	# to deadloops for the Apache server
	$\| = 1;

	# read URLs one per line from stdin and
	# generate substitution URL on stdout
	while (<>) {
	s\|^foo/\|bar/\|;
	print $_;
	}
	</pre></example>

	<p>This is a demonstration-only example and just rewrites
	all URLs <code>/~quux/foo/...</code> to
	<code>/~quux/bar/...</code>. Actually you can program
	whatever you like. But notice that while such maps can be
	<strong>used</strong> also by an average user, only the
	system administrator can <strong>define</strong> it.</p>
	</dd>
	</dl>

	</section>

	</section>

	</manualpage>