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<div id="preamble"><h1>Apache Module mod_rewrite</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_rewrite.html" title="English">&nbsp;en&nbsp;</a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Provides a rule-based rewriting engine to rewrite requested
URLs on the fly</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>rewrite_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_rewrite.c</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 1.3 and later</td></tr></table>
<h3>Summary</h3>

      <p>This module uses a rule-based rewriting engine (based on a
      regular-expression parser) to rewrite requested URLs on the
      fly. It supports an unlimited number of rules and an
      unlimited number of attached rule conditions for each rule, to
      provide a really flexible and powerful URL manipulation
      mechanism. The URL manipulations can depend on various tests,
      of server variables, environment variables, HTTP
      headers, or time stamps. Even external database lookups in
      various formats can be used to achieve highly granular URL
      matching.</p>

      <p>This module operates on the full URLs (including the
      path-info part) both in per-server context
      (<code>httpd.conf</code>) and per-directory context
      (<code>.htaccess</code>) and can generate query-string
      parts on result. The rewritten result can lead to internal
      sub-processing, external request redirection or even to an
      internal proxy throughput.</p>

      <p>Further details, discussion, and examples, are provided in the
      <a href="../rewrite/">detailed mod_rewrite documentation</a>.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#rewritebase">RewriteBase</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewritecond">RewriteCond</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewriteengine">RewriteEngine</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewritelock">RewriteLock</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewritelog">RewriteLog</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewriteloglevel">RewriteLogLevel</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewritemap">RewriteMap</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewriteoptions">RewriteOptions</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#rewriterule">RewriteRule</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#quoting">Quoting Special Characters</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#EnvVar">Environment Variables</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#vhosts">Rewriting in Virtual Hosts</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#Solutions">Practical Solutions</a></li>
</ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="quoting" id="quoting">Quoting Special Characters</a></h2>

      <p>As of Apache 1.3.20, special characters in
      <em>TestString</em> and <em>Substitution</em> strings can be
      escaped (that is, treated as normal characters without their
      usual special meaning) by prefixing them with a slash ('\')
      character. In other words, you can include an actual
      dollar-sign character in a <em>Substitution</em> string by
      using '<code>\$</code>'; this keeps mod_rewrite from trying
      to treat it as a backreference.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="EnvVar" id="EnvVar">Environment Variables</a></h2>

      <p>This module keeps track of two additional (non-standard)
      CGI/SSI environment variables named <code>SCRIPT_URL</code>
      and <code>SCRIPT_URI</code>. These contain the
      <em>logical</em> Web-view to the current resource, while the
      standard CGI/SSI variables <code>SCRIPT_NAME</code> and
      <code>SCRIPT_FILENAME</code> contain the <em>physical</em>
      System-view. </p>

      <p>Notice: These variables hold the URI/URL <em>as they were
      initially requested</em>, that is, <em>before</em> any
      rewriting. This is important to note because the rewriting process is
      primarily used to rewrite logical URLs to physical
      pathnames.</p>

<div class="example"><h3>Example</h3><pre>
SCRIPT_NAME=/sw/lib/w3s/tree/global/u/rse/.www/index.html
SCRIPT_FILENAME=/u/rse/.www/index.html
SCRIPT_URL=/u/rse/
SCRIPT_URI=http://en1.engelschall.com/u/rse/
</pre></div>

</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="vhosts" id="vhosts">Rewriting in Virtual Hosts</a></h2>

     <p>By default, <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> configuration
     settings from the main server context are not inherited by
     virtual hosts. To make the main server settings apply to virtual
     hosts, you must place the following directives in each <code class="directive"><a href="../mod/core.html#virtualhost">&lt;VirtualHost&gt;</a></code> section:</p>

     <div class="example"><p><code>
     RewriteEngine On<br />
     RewriteOptions Inherit
     </code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="Solutions" id="Solutions">Practical Solutions</a></h2>

    <p>For numerous examples of common, and not-so-common, uses for
    mod_rewrite, see the <a href="../rewrite/rewrite_guide.html">Rewrite
    Guide</a>, and the <a href="../rewrite/rewrite_guide_advanced.html">Advanced Rewrite
    Guide</a> documents.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteBase" id="RewriteBase">RewriteBase</a> <a name="rewritebase" id="rewritebase">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the base URL for per-directory rewrites</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteBase <em>URL-path</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>See usage for information.</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>The <code class="directive">RewriteBase</code> directive explicitly
      sets the base URL for per-directory rewrites. As you will see
      below, <code class="directive"><a href="#rewriterule">RewriteRule</a></code>
      can be used in per-directory config files
      (<code>.htaccess</code>). In such a case, it will act locally,
      stripping the local directory prefix before processing, and applying
      rewrite rules only to the remainder. When processing is complete, the 
      prefix is automatically added back to the
      path. The default setting is; <code class="directive">RewriteBase</code> <em>physical-directory-path</em></p>

      <p>When a substitution occurs for a new URL, this module has
      to re-inject the URL into the server processing. To be able
      to do this it needs to know what the corresponding URL-prefix
      or URL-base is. By default this prefix is the corresponding
      filepath itself. <strong>However, for most websites, URLs are NOT
      directly related to physical filename paths, so this
      assumption will often be wrong!</strong> Therefore, you can 
      use the <code>RewriteBase</code> directive to specify the
      correct URL-prefix.</p>

<div class="note"> If your webserver's URLs are <strong>not</strong> directly
related to physical file paths, you will need to use
<code class="directive">RewriteBase</code> in every <code>.htaccess</code>
file where you want to use <code class="directive"><a href="#rewriterule">RewriteRule</a></code> directives.
</div>

        <p> For example, assume the following per-directory config file:</p>

<div class="example"><pre>
#
#  /abc/def/.htaccess -- per-dir config file for directory /abc/def
#  Remember: /abc/def is the physical path of /xyz, <em>i.e.</em>, the server
#            has a 'Alias /xyz /abc/def' directive <em>e.g.</em>
#

RewriteEngine On

#  let the server know that we were reached via /xyz and not
#  via the physical path prefix /abc/def
RewriteBase   /xyz

#  now the rewriting rules
RewriteRule   ^oldstuff\.html$  newstuff.html
</pre></div>

        <p>In the above example, a request to
        <code>/xyz/oldstuff.html</code> gets correctly rewritten to
        the physical file <code>/abc/def/newstuff.html</code>.</p>

<div class="note"><h3>For Apache Hackers</h3>
<p>The following list gives detailed information about
              the internal processing steps:</p>
<pre>
Request:
  /xyz/oldstuff.html

Internal Processing:
  /xyz/oldstuff.html     -&gt; /abc/def/oldstuff.html  (per-server Alias)
  /abc/def/oldstuff.html -&gt; /abc/def/newstuff.html  (per-dir    RewriteRule)
  /abc/def/newstuff.html -&gt; /xyz/newstuff.html      (per-dir    RewriteBase)
  /xyz/newstuff.html     -&gt; /abc/def/newstuff.html  (per-server Alias)

Result:
  /abc/def/newstuff.html
</pre>
              <p>This seems very complicated, but is in fact
              correct Apache internal processing. Because the
              per-directory rewriting comes late in the
              process, the rewritten request
              has to be re-injected into the Apache kernel. 
              This is not the serious overhead it may seem to be - 
              this re-injection is completely internal to the 
	      Apache server (and the same procedure is used by 
	      many other operations within Apache).</p> 
</div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteCond" id="RewriteCond">RewriteCond</a> <a name="rewritecond" id="rewritecond">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Defines a condition under which rewriting will take place
</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code> RewriteCond
      <em>TestString</em> <em>CondPattern</em></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>The <code class="directive">RewriteCond</code> directive defines a
      rule condition. One or more <code class="directive">RewriteCond</code>
      can precede a <code class="directive"><a href="#rewriterule">RewriteRule</a></code> 
      directive. The following rule is then only used if both
      the current state of the URI matches its pattern, <strong>and</strong> if these conditions are met.</p>

      <p><em>TestString</em> is a string which can contain the
      following expanded constructs in addition to plain text:</p>

      <ul>
        <li>
          <strong>RewriteRule backreferences</strong>: These are
          backreferences of the form <strong><code>$N</code></strong>
          (0 &lt;= N &lt;= 9), which provide access to the grouped
          parts (in parentheses) of the pattern, from the
          <code>RewriteRule</code> which is subject to the current 
	  set of <code>RewriteCond</code> conditions..
        </li>
        <li>
          <strong>RewriteCond backreferences</strong>: These are
          backreferences of the form <strong><code>%N</code></strong>
          (1 &lt;= N &lt;= 9), which provide access to the grouped
          parts (again, in parentheses) of the pattern, from the last matched
          <code>RewriteCond</code> in the current set
          of conditions.
        </li>
        <li>
          <strong>RewriteMap expansions</strong>: These are
          expansions of the form <strong><code>${mapname:key|default}</code></strong>.
          See <a href="#mapfunc">the documentation for
          RewriteMap</a> for more details.
        </li>
        <li>
          <strong>Server-Variables</strong>: These are variables of
          the form 
            <strong><code>%{</code> <em>NAME_OF_VARIABLE</em>
            <code>}</code></strong>
          where <em>NAME_OF_VARIABLE</em> can be a string taken
          from the following list: 

          <table>
          
            <tr>
              <th>HTTP headers:</th> <th>connection &amp; request:</th> <th />
	    </tr>

            <tr>
	      <td>
		 HTTP_USER_AGENT<br />
                 HTTP_REFERER<br />
                 HTTP_COOKIE<br />
                 HTTP_FORWARDED<br />
                 HTTP_HOST<br />
                 HTTP_PROXY_CONNECTION<br />
                 HTTP_ACCEPT<br />
              </td>

              <td>
                 REMOTE_ADDR<br />
                 REMOTE_HOST<br />
                 REMOTE_PORT<br />
                 REMOTE_USER<br />
                 REMOTE_IDENT<br />
                 REQUEST_METHOD<br />
                 SCRIPT_FILENAME<br />
                 PATH_INFO<br />
                 QUERY_STRING<br />
                 AUTH_TYPE<br />
              </td>
	      
	      <td />
            </tr>

            <tr>
              <th>server internals:</th> <th>date and time:</th> <th>specials:</th>
	    </tr>

            <tr>
	      <td>
	         DOCUMENT_ROOT<br />
                 SERVER_ADMIN<br />
                 SERVER_NAME<br />
                 SERVER_ADDR<br />
                 SERVER_PORT<br />
                 SERVER_PROTOCOL<br />
                 SERVER_SOFTWARE<br />
              </td>

              <td>
                 TIME_YEAR<br />
                 TIME_MON<br />
                 TIME_DAY<br />
                 TIME_HOUR<br />
                 TIME_MIN<br />
                 TIME_SEC<br />
                 TIME_WDAY<br />
                 TIME<br />
              </td>

              <td>
                 API_VERSION<br />
                 THE_REQUEST<br />
                 REQUEST_URI<br />
                 REQUEST_FILENAME<br />
                 IS_SUBREQ<br />
                 HTTPS<br />
              </td>
            </tr>
          </table>

                <p>These variables all
                correspond to the similarly named HTTP
                MIME-headers, C variables of the Apache server or
                <code>struct tm</code> fields of the Unix system.
                Most are documented elsewhere in the Manual or in
                the CGI specification. Those that are special to
                mod_rewrite include those below.</p>
	<div class="note">
                <dl>
                  <dt><code>IS_SUBREQ</code></dt>

                  <dd>Will contain the text "true" if the request
                  currently being processed is a sub-request,
                  "false" otherwise. Sub-requests may be generated
                  by modules that need to resolve additional files
                  or URIs in order to complete their tasks.</dd>

                  <dt><code>API_VERSION</code></dt>

                  <dd>This is the version of the Apache module API
                  (the internal interface between server and
                  module) in the current httpd build, as defined in
                  include/ap_mmn.h. The module API version
                  corresponds to the version of Apache in use (in
                  the release version of Apache 1.3.14, for
                  instance, it is 19990320:10), but is mainly of
                  interest to module authors.</dd>

                  <dt><code>THE_REQUEST</code></dt>

                  <dd>The full HTTP request line sent by the
                  browser to the server (e.g., "<code>GET
                  /index.html HTTP/1.1</code>"). This does not
                  include any additional headers sent by the
                  browser.</dd>

                  <dt><code>REQUEST_URI</code></dt>

                  <dd>The resource requested in the HTTP request
                  line. (In the example above, this would be
                  "/index.html".)</dd>

                  <dt><code>REQUEST_FILENAME</code></dt>

                  <dd>The full local filesystem path to the file or
                  script matching the request.</dd>

                  <dt><code>HTTPS</code></dt>

                  <dd>Will contain the text "on" if the connection is
                  using SSL/TLS, or "off" otherwise.  (This variable
                  can be safely used regardless of whether or not
                  <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is loaded).</dd>

                </dl>
</div>
        </li>
      </ul>

      <p>Other things you should be aware of:</p>

      <ol>
        <li>The variables SCRIPT_FILENAME and REQUEST_FILENAME
        contain the same value - the value of the
        <code>filename</code> field of the internal
        <code>request_rec</code> structure of the Apache server.
        The first name is the commonly known CGI variable name
        while the second is the appropriate counterpart of
        REQUEST_URI (which contains the value of the
        <code>uri</code> field of <code>request_rec</code>).</li>

        <li>
        <code>%{ENV:variable}</code>, where <em>variable</em> can be
	any environment variable, is also available. 
	This is looked-up via internal
        Apache structures and (if not found there) via
        <code>getenv()</code> from the Apache server process.</li>

        <li>
        <code>%{SSL:variable}</code>, where <em>variable</em> is the
        name of an <a href="mod_ssl.html#envvars">SSL environment
        variable</a>, can be used whether or not
        <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is loaded, but will always expand to
        the empty string if it is not.  Example:
        <code>%{SSL:SSL_CIPHER_USEKEYSIZE}</code> may expand to
        <code>128</code>.</li>

        <li>
        <code>%{HTTP:header}</code>, where <em>header</em> can be
	any HTTP MIME-header name, can always be used to obtain the
	value of a header sent in the HTTP request.
        Example: <code>%{HTTP:Proxy-Connection}</code> is
        the value of the HTTP header
        ``<code>Proxy-Connection:</code>''.
        <p>If a HTTP header is used in a condition this header is added to
        the Vary header of the response in case the condition evaluates to
        to true for the request. It is <strong>not</strong> added if the
        condition evaluates to false for the request. Adding the HTTP header
        to the Vary header of the response is needed for proper caching.</p>
        <p>It has to be kept in mind that conditions follow a short circuit
        logic in the case of the '<strong><code>ornext|OR</code></strong>' flag
        so that certain conditions might not be evaluated at all.</p></li>

        <li>
        <code>%{LA-U:variable}</code> can be used for look-aheads which perform
        an internal (URL-based) sub-request to determine the final
	value of <em>variable</em>. This can be used to access
        variable for rewriting which is not available at the current 
	stage, but will be set in a later phase.
	<p>For instance, to rewrite according to the
        <code>REMOTE_USER</code> variable from within the
        per-server context (<code>httpd.conf</code> file) you must
        use <code>%{LA-U:REMOTE_USER}</code> - this
        variable is set by the authorization phases, which come
	<em>after</em> the URL translation phase (during which mod_rewrite
	operates).</p>
	<p>On the other hand, because mod_rewrite implements
        its per-directory context (<code>.htaccess</code> file) via
        the Fixup phase of the API and because the authorization
        phases come <em>before</em> this phase, you just can use
	<code>%{REMOTE_USER}</code> in that context.</p></li>

        <li>
        <code>%{LA-F:variable}</code> can be used to perform an internal
        (filename-based) sub-request, to determine the final value
        of <em>variable</em>. Most of the time, this is the same as
        LA-U above.</li>
      </ol>

      <p><em>CondPattern</em> is the condition pattern,
       a regular expression which is applied to the
      current instance of the <em>TestString</em>.
      <em>TestString</em> is first evaluated, before being matched against
      <em>CondPattern</em>.</p>

      <p><strong>Remember:</strong> <em>CondPattern</em> is a
      <em>perl compatible regular expression</em> with some
      additions:</p>

      <ol>
        <li>You can prefix the pattern string with a
        '<code>!</code>' character (exclamation mark) to specify a
        <strong>non</strong>-matching pattern.</li>

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

          <ul>
            <li>'<strong>&lt;CondPattern</strong>' (lexicographically 
	    precedes)<br />
            Treats the <em>CondPattern</em> as a plain string and
            compares it lexicographically to <em>TestString</em>. True if
            <em>TestString</em> lexicographically precedes
            <em>CondPattern</em>.</li>

            <li>'<strong>&gt;CondPattern</strong>' (lexicographically
            follows)<br />
            Treats the <em>CondPattern</em> as a plain string and
            compares it lexicographically to <em>TestString</em>. True if
            <em>TestString</em> lexicographically follows
            <em>CondPattern</em>.</li>

            <li>'<strong>=CondPattern</strong>' (lexicographically
            equal)<br />
            Treats the <em>CondPattern</em> as a plain string and
            compares it lexicographically to <em>TestString</em>. True if
            <em>TestString</em> is lexicographically equal to
            <em>CondPattern</em> (the two strings are exactly
            equal, character for character). If <em>CondPattern</em>
            is <code>""</code> (two quotation marks) this
            compares <em>TestString</em> to the empty string.</li>

            <li>'<strong>-d</strong>' (is
            <strong>d</strong>irectory)<br />
             Treats the <em>TestString</em> as a pathname and tests
            whether or not it exists, and is a directory.</li>

            <li>'<strong>-f</strong>' (is regular
            <strong>f</strong>ile)<br />
             Treats the <em>TestString</em> as a pathname and tests
            whether or not it exists, and is a regular file.</li>

            <li>'<strong>-s</strong>' (is regular file, with
            <strong>s</strong>ize)<br />
            Treats the <em>TestString</em> as a pathname and tests
            whether or not it exists, and is a regular file with size greater
            than zero.</li>

            <li>'<strong>-l</strong>' (is symbolic
            <strong>l</strong>ink)<br />
            Treats the <em>TestString</em> as a pathname and tests
            whether or not it exists, and is a symbolic link.</li>

            <li>'<strong>-x</strong>' (has e<strong>x</strong>ecutable
            permissions)<br />
            Treats the <em>TestString</em> as a pathname and tests
	    whether or not it exists, and has executable permissions. 
	    These permissions are determined according to 
	    the underlying OS.</li>

            <li>'<strong>-F</strong>' (is existing file, via
            subrequest)<br />
            Checks whether or not <em>TestString</em> is a valid file,
            accessible via all the server's currently-configured
            access controls for that path. This uses an internal
            subrequest to do the check, so use it with care -
            it can impact your server's performance!</li>

            <li>'<strong>-U</strong>' (is existing URL, via
            subrequest)<br />
            Checks whether or not <em>TestString</em> is a valid URL,
            accessible via all the server's currently-configured
            access controls for that path. This uses an internal
            subrequest to do the check, so use it with care - 
            it can impact your server's performance!</li>
          </ul>

<div class="note"><h3>Note:</h3>
              All of these tests can
              also be prefixed by an exclamation mark ('!') to
              negate their meaning.
</div>
        </li>

	<li>You can also set special flags for
      <em>CondPattern</em> by appending
        <strong><code>[</code><em>flags</em><code>]</code></strong>
      as the third argument to the <code>RewriteCond</code>
      directive, where <em>flags</em> is a comma-separated list of any of the
      following flags:

      <ul>
        <li>'<strong><code>nocase|NC</code></strong>'
        (<strong>n</strong>o <strong>c</strong>ase)<br />
        This makes the test case-insensitive - differences 
	between 'A-Z' and 'a-z' are ignored, both in the
        expanded <em>TestString</em> and the <em>CondPattern</em>.
        This flag is effective only for comparisons between
        <em>TestString</em> and <em>CondPattern</em>. It has no
        effect on filesystem and subrequest checks.</li>

        <li>
          '<strong><code>ornext|OR</code></strong>'
          (<strong>or</strong> next condition)<br />
          Use this to combine rule conditions with a local OR
          instead of the implicit AND. Typical example: 

<div class="example"><pre>
RewriteCond %{REMOTE_HOST}  ^host1.*  [OR]
RewriteCond %{REMOTE_HOST}  ^host2.*  [OR]
RewriteCond %{REMOTE_HOST}  ^host3.*
RewriteRule ...some special stuff for any of these hosts...
</pre></div>

          Without this flag you would have to write the condition/rule
          pair three times.
        </li>

        <li>'<strong><code>novary|NV</code></strong>'
        (<strong>n</strong>o <strong>v</strong>ary)<br />
        If a HTTP header is used in the condition, this flag prevents
        this header from being added to the Vary header of the response. <br />
        Using this flag might break proper caching of the response if
        the representation of this response varies on the value of this header.
        So this flag should be only used if the meaning of the Vary header
        is well understood.
        </li>
      </ul>
      </li>
     </ol>

      <p><strong>Example:</strong></p>

       <p>To rewrite the Homepage of a site according to the
        ``<code>User-Agent:</code>'' header of the request, you can
        use the following: </p>

<div class="example"><pre>
RewriteCond  %{HTTP_USER_AGENT}  ^Mozilla.*
RewriteRule  ^/$                 /homepage.max.html  [L]

RewriteCond  %{HTTP_USER_AGENT}  ^Lynx.*
RewriteRule  ^/$                 /homepage.min.html  [L]

RewriteRule  ^/$                 /homepage.std.html  [L]
</pre></div>

        <p>Explanation: If you use a browser which identifies itself 
	as 'Mozilla' (including Netscape Navigator, Mozilla etc), then you
        get the max homepage (which could include frames, or other special
	features).
        If you use the Lynx browser (which is terminal-based), then
	you get the min homepage (which could be a version designed for 
	easy, text-only browsing).
	If neither of these conditions apply (you use any other browser,
	or your browser identifies itself as something non-standard), you get
        the std (standard) homepage.</p>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteEngine" id="RewriteEngine">RewriteEngine</a> <a name="rewriteengine" id="rewriteengine">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enables or disables runtime rewriting engine</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteEngine on|off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>RewriteEngine off</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>       

      <p>The <code class="directive">RewriteEngine</code> directive enables or
      disables the runtime rewriting engine. If it is set to
      <code>off</code> this module does no runtime processing at
      all. It does not even update the <code>SCRIPT_URx</code>
      environment variables.</p>

      <p>Use this directive to disable the module instead of
      commenting out all the <code class="directive"><a href="#rewriterule">RewriteRule</a></code> directives!</p>

      <p>Note that rewrite configurations are not
      inherited by virtual hosts. This means that you need to have a
      <code>RewriteEngine on</code> directive for each virtual host
      in which you wish to use rewrite rules.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteLock" id="RewriteLock">RewriteLock</a> <a name="rewritelock" id="rewritelock">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the name of the lock file used for <code class="directive"><a href="#rewritemap">RewriteMap</a></code>
synchronization</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteLock <em>file-path</em></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>This directive sets the filename for a synchronization
      lockfile which mod_rewrite needs to communicate with <code class="directive"><a href="#rewritemap">RewriteMap</a></code>
      <em>programs</em>. Set this lockfile to a local path (not on a
      NFS-mounted device) when you want to use a rewriting
      map-program. It is not required for other types of rewriting
      maps.</p>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteLog" id="RewriteLog">RewriteLog</a> <a name="rewritelog" id="rewritelog">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the name of the file used for logging rewrite engine
processing</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteLog <em>file-path</em></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>The <code class="directive">RewriteLog</code> directive sets the name
      of the file to which the server logs any rewriting actions it
      performs. If the name does not begin with a slash
      ('<code>/</code>') then it is assumed to be relative to the
      <em>Server Root</em>. The directive should occur only once per
      server config.</p>

<div class="note">    To disable the logging of
          rewriting actions it is not recommended to set
          <em>Filename</em> to <code>/dev/null</code>, because
          although the rewriting engine does not then output to a
          logfile it still creates the logfile output internally.
          <strong>This will slow down the server with no advantage
          to the administrator!</strong> To disable logging either
          remove or comment out the <code class="directive">RewriteLog</code>
          directive or use <code>RewriteLogLevel 0</code>!
</div>

<div class="note"><h3>Security</h3>

See the <a href="../misc/security_tips.html">Apache Security Tips</a>
document for details on how your security could be compromised if the
directory where logfiles are stored is writable by anyone other than
the user that starts the server.
</div>

<div class="example"><h3>Example</h3><p><code>
RewriteLog "/usr/local/var/apache/logs/rewrite.log"
</code></p></div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteLogLevel" id="RewriteLogLevel">RewriteLogLevel</a> <a name="rewriteloglevel" id="rewriteloglevel">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets the verbosity of the log file used by the rewrite
engine</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteLogLevel <em>Level</em></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>RewriteLogLevel 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>The <code class="directive">RewriteLogLevel</code> directive sets the
      verbosity level of the rewriting logfile. The default level 0
      means no logging, while 9 or more means that practically all
      actions are logged.</p>

      <p>To disable the logging of rewriting actions simply set
      <em>Level</em> to 0. This disables all rewrite action
      logs.</p>

<div class="note"> Using a high value for
          <em>Level</em> will slow down your Apache server
          dramatically! Use the rewriting logfile at a
          <em>Level</em> greater than 2 only for debugging!
</div>

<div class="example"><h3>Example</h3><p><code>
RewriteLogLevel 3
</code></p></div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteMap" id="RewriteMap">RewriteMap</a> <a name="rewritemap" id="rewritemap">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Defines a mapping function for key-lookup</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>The choice of different dbm types is available in
Apache 2.0.41 and later</td></tr>
</table>
      <p>The <code class="directive">RewriteMap</code> directive defines a
      <em>Rewriting Map</em> which can be used inside rule
      substitution strings by the mapping-functions to
      insert/substitute fields through a key lookup. The source of
      this lookup can be of various types.</p>

      <p>The <a id="mapfunc" name="mapfunc"><em>MapName</em></a> is
      the name of the map and will be used to specify a
      mapping-function for the substitution strings of a rewriting
      rule via one of the following constructs:</p>

      <p class="indent">
        <strong><code>${</code> <em>MapName</em> <code>:</code>
        <em>LookupKey</em> <code>}</code><br />
         <code>${</code> <em>MapName</em> <code>:</code>
        <em>LookupKey</em> <code>|</code> <em>DefaultValue</em>
        <code>}</code></strong>
      </p>

      <p>When such a construct occurs, the map <em>MapName</em> is
      consulted and the key <em>LookupKey</em> is looked-up. If the
      key is found, the map-function construct is substituted by
      <em>SubstValue</em>. If the key is not found then it is
      substituted by <em>DefaultValue</em> or by the empty string
      if no <em>DefaultValue</em> was specified.</p>

      <p>For example, you might define a
      <code class="directive">RewriteMap</code> as:</p>

      <div class="example"><p><code>
      RewriteMap examplemap txt:/path/to/file/map.txt
      </code></p></div>

      <p>You would then be able to use this map in a
      <code class="directive">RewriteRule</code> as follows:</p>

      <div class="example"><p><code>
      RewriteRule ^/ex/(.*) ${examplemap:$1}
      </code></p></div>

      <p>The following combinations for <em>MapType</em> and
      <em>MapSource</em> can be used:</p>

      <ul>
        <li>
          <strong>Standard Plain Text</strong><br />
           MapType: <code>txt</code>, MapSource: Unix filesystem
          path to valid regular file 

          <p>This is the standard rewriting map feature where the
          <em>MapSource</em> is a plain ASCII file containing
          either blank lines, comment lines (starting with a '#'
          character) or pairs like the following - one per
          line.</p>

          <p class="indent">
            <strong><em>MatchingKey</em>
            <em>SubstValue</em></strong>
          </p>

<div class="example"><h3>Example</h3><pre>
##
##  map.txt -- rewriting map
##

Ralf.S.Engelschall    rse   # Bastard Operator From Hell
Mr.Joe.Average        joe   # Mr. Average
</pre></div>

<div class="example"><p><code>
RewriteMap real-to-user txt:/path/to/file/map.txt
</code></p></div>
        </li>

        <li>
          <strong>Randomized Plain Text</strong><br />
           MapType: <code>rnd</code>, MapSource: Unix filesystem
          path to valid regular file 

          <p>This is identical to the Standard Plain Text variant
          above but with a special post-processing feature: After
          looking up a value it is parsed according to contained
          ``<code>|</code>'' characters which have the meaning of
          ``or''. In other words they indicate a set of
          alternatives from which the actual returned value is
          chosen randomly. For example, you might use the following map
          file and directives to provide a random load balancing between
          several back-end server, via a reverse-proxy. Images are sent
          to one of the servers in the 'static' pool, while everything
          else is sent to one of the 'dynamic' pool.</p>
          <p>Example:</p>

<div class="example"><h3>Rewrite map file</h3><pre>
##
##  map.txt -- rewriting map
##

static   www1|www2|www3|www4
dynamic  www5|www6
</pre></div>

<div class="example"><h3>Configuration directives</h3><p><code>
RewriteMap servers rnd:/path/to/file/map.txt<br />
<br />
RewriteRule ^/(.*\.(png|gif|jpg)) http://${servers:static}/$1
[NC,P,L]<br />
RewriteRule ^/(.*) http://${servers:dynamic}/$1 [P,L]
</code></p></div>
        </li>

        <li>
          <strong>Hash File</strong><br /> MapType:
          <code>dbm[=<em>type</em>]</code>, MapSource: Unix filesystem
          path to valid regular file

          <p>Here the source is a binary format DBM file containing
          the same contents as a <em>Plain Text</em> format file, but
          in a special representation which is optimized for really
          fast lookups. The <em>type</em> can be sdbm, gdbm, ndbm, or
          db depending on <a href="../install.html#dbm">compile-time
          settings</a>.  If the <em>type</em> is omitted, the
          compile-time default will be chosen.</p>

          <p>To create a dbm file from a source text file, use the <a href="../programs/httxt2dbm.html">httxt2dbm</a> utility.</p>

<div class="example"><p><code>
$ httxt2dbm -i mapfile.txt -o mapfile.map
</code></p></div>
        </li>

        <li>
          <strong>Internal Function</strong><br />
           MapType: <code>int</code>, MapSource: Internal Apache
          function 

          <p>Here, the source is an internal Apache function.
          Currently you cannot create your own, but the following
          functions already exist:</p>

          <ul>
            <li><strong>toupper</strong>:<br />
             Converts the key to all upper case.</li>

            <li><strong>tolower</strong>:<br />
             Converts the key to all lower case.</li>

            <li><strong>escape</strong>:<br />
             Translates special characters in the key to
            hex-encodings.</li>

            <li><strong>unescape</strong>:<br />
             Translates hex-encodings in the key back to
            special characters.</li>
          </ul>
        </li>

        <li>
          <strong>External Rewriting Program</strong><br />
           MapType: <code>prg</code>, MapSource: Unix filesystem
          path to valid regular file 

          <p>Here the source is a program, not a map file. To
          create it you can use a language of your choice, but
          the result has to be an executable program (either
          object-code or a script with the magic cookie trick
          '<code>#!/path/to/interpreter</code>' as the first
          line).</p>

         <p>This program is started once, when the Apache server
          is started, and then communicates with the rewriting engine
          via its <code>stdin</code> and <code>stdout</code>
          file-handles. For each map-function lookup it will
          receive the key to lookup as a newline-terminated string
          on <code>stdin</code>. It then has to give back the
          looked-up value as a newline-terminated string on
          <code>stdout</code> or the four-character string
          ``<code>NULL</code>'' if it fails (<em>i.e.</em>, there
          is no corresponding value for the given key). A trivial
          program which will implement a 1:1 map (<em>i.e.</em>,
          key == value) could be:</p>

<div class="example"><pre>
#!/usr/bin/perl
$| = 1;
while (&lt;STDIN&gt;) {
    # ...put here any transformations or lookups...
    print $_;
}
</pre></div>

          <p>But be very careful:</p>

          <ol>
            <li>``<em>Keep it simple, stupid</em>'' (KISS).
	    If this program hangs, it will cause Apache to hang 
	    when trying to use the relevant rewrite rule.</li>

            <li>A common mistake is to use buffered I/O on
            <code>stdout</code>. Avoid this, as it will cause a deadloop!
            ``<code>$|=1</code>'' is used above, to prevent this.</li>

            <li>The <code class="directive"><a href="#rewritelock">RewriteLock</a></code> directive can 
	    be used to define a lockfile which mod_rewrite can use to synchronize 
            communication with the mapping program. By default no such
            synchronization takes place.</li>
          </ol>
        </li>
      </ul>
      <p>The <code class="directive">RewriteMap</code> directive can occur more than
      once. For each mapping-function use one
      <code class="directive">RewriteMap</code> directive to declare its rewriting
      mapfile. While you cannot <strong>declare</strong> a map in
      per-directory context it is of course possible to
      <strong>use</strong> this map in per-directory context. </p>

<div class="note"><h3>Note</h3> For plain text and DBM format files the
looked-up keys are cached in-core until the <code>mtime</code> of the
mapfile changes or the server does a restart. This way you can have
map-functions in rules which are used for <strong>every</strong>
request.  This is no problem, because the external lookup only happens
once!
</div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteOptions" id="RewriteOptions">RewriteOptions</a> <a name="rewriteoptions" id="rewriteoptions">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Sets some special options for the rewrite engine</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteOptions <var>Options</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td><code>MaxRedirects</code> is no longer available in version 2.1 and
later</td></tr>
</table>

      <p>The <code class="directive">RewriteOptions</code> directive sets some
      special options for the current per-server or per-directory
      configuration. The <em>Option</em> string can currently 
      only be one of the following:</p>

      <dl>
      <dt><code>inherit</code></dt>
      <dd>This forces the current configuration to inherit the
      configuration of the parent. In per-virtual-server context,
      this means that the maps, conditions and rules of the main
      server are inherited. In per-directory context this means
      that conditions and rules of the parent directory's
      <code>.htaccess</code> configuration are inherited.</dd>
      </dl>

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="RewriteRule" id="RewriteRule">RewriteRule</a> <a name="rewriterule" id="rewriterule">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Defines rules for the rewriting engine</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RewriteRule
      <em>Pattern</em> <em>Substitution</em> [<em>flags</em>]</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_rewrite</td></tr>
</table>
      <p>The <code class="directive">RewriteRule</code> directive is the real
      rewriting workhorse. The directive can occur more than once, 
      with each instance defining a single rewrite rule. The
      order in which these rules are defined is important - this is the order
      in which they will be applied at run-time.</p>

      <p><a id="patterns" name="patterns"><em>Pattern</em></a> is
      a perl compatible <a id="regexp" name="regexp">regular
      expression</a>. On the first RewriteRule it is applied to the
      <a href="./directive-dict.html#Syntax">URL-path</a> of the request;
      subsequent patterns are applied to the output of the last matched
      RewriteRule.</p>

<div class="note"><h3>What is matched?</h3>
      <p>The <em>Pattern</em> will initially be matched against the part of the
      URL after the hostname and port, and before the query string. If you wish
      to match against the hostname, port, or query string, use a
      <code class="directive"><a href="#rewritecond">RewriteCond</a></code> with the
      <code>%{HTTP_HOST}</code>, <code>%{SERVER_PORT}</code>, or
      <code>%{QUERY_STRING}</code> variables respectively.</p>
</div>



      <p>Some hints on the syntax of <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular 
      expressions</a>:</p>

<div class="note"><pre>
<strong>Text:</strong>
  <strong><code>.</code></strong>           Any single character
  <strong><code>[</code></strong>chars<strong><code>]</code></strong>     Character class: Any character of the class ``chars''
  <strong><code>[^</code></strong>chars<strong><code>]</code></strong>    Character class: Not a character of the class ``chars''
  text1<strong><code>|</code></strong>text2 Alternative: text1 or text2

<strong>Quantifiers:</strong>
  <strong><code>?</code></strong>           0 or 1 occurrences of the preceding text
  <strong><code>*</code></strong>           0 or N occurrences of the preceding text (N &gt; 0)
  <strong><code>+</code></strong>           1 or N occurrences of the preceding text (N &gt; 1)

<strong>Grouping:</strong>
  <strong><code>(</code></strong>text<strong><code>)</code></strong>      Grouping of text
              (used either to set the borders of an alternative as above, or
              to make backreferences, where the <strong>N</strong>th group can 
              be referred to on the RHS of a RewriteRule as <code>$</code><strong>N</strong>)

<strong>Anchors:</strong>
  <strong><code>^</code></strong>           Start-of-line anchor
  <strong><code>$</code></strong>           End-of-line anchor

<strong>Escaping:</strong>
  <strong><code>\</code></strong>char       escape the given char
              (for instance, to specify the chars "<code>.[]()</code>" <em>etc.</em>)
</pre></div>

      <p>For more information about regular expressions, have a look at the
      perl regular expression manpage ("<a href="http://perldoc.perl.org/perlre.html">perldoc
      perlre</a>"). If you are interested in more detailed
      information about regular expressions and their variants
      (POSIX regex etc.) the following book is dedicated to this topic:</p>

      <p class="indent">
        <em>Mastering Regular Expressions, 2nd Edition</em><br />
         Jeffrey E.F. Friedl<br />
         O'Reilly &amp; Associates, Inc. 2002<br />
         ISBN 0-596-00289-0<br />
      </p>

      <p>In mod_rewrite, the NOT character	
       ('<code>!</code>') is also available as a possible pattern 
      prefix. This enables you to negate a pattern; to say, for instance:
      ``<em>if the current URL does <strong>NOT</strong> match this
      pattern</em>''. This can be used for exceptional cases, where
      it is easier to match the negative pattern, or as a last
      default rule.</p>

<div class="note"><h3>Note</h3>
When using the NOT character to negate a pattern, you cannot include 
grouped wildcard parts in that pattern. This is because, when the 
pattern does NOT match (ie, the negation matches), there are no 
contents for the groups. Thus, if negated patterns are used, you
cannot use <code>$N</code> in the substitution string!
</div>

      <p>The <a id="rhs" name="rhs"><em>Substitution</em></a> of a
      rewrite rule is the string that replaces the original URL-path that
      was matched by <em>Pattern</em>.  The <em>Substitution</em> may
      be a:</p>

      <dl>

        <dt>file-system path</dt>

        <dd>Designates the location on the file-system of the resource
        to be delivered to the client.</dd>

        <dt>URL-path</dt> 

        <dd>A <code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code>-relative path to the
        resource to be served. Note that <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
        tries to guess whether you have specified a file-system path
        or a URL-path by checking to see if the first segment of the
        path exists at the root of the file-system. For example, if
        you specify a <em>Substitution</em> string of
        <code>/www/file.html</code>, then this will be treated as a
        URL-path <em>unless</em> a directory named <code>www</code>
        exists at the root or your file-system, in which case it will
        be treated as a file-system path. If you wish other
        URL-mapping directives (such as <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code>) to be applied to the
        resulting URL-path, use the <code>[PT]</code> flag as
        described below.</dd>

        <dt>Absolute URL</dt>

        <dd>If an absolute URL is specified,
        <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code> checks to see whether the
        hostname matches the current host. If it does, the scheme and
        hostname are stripped out and the resulting path is treated as
        a URL-path. Otherwise, an external redirect is performed for
        the given URL. To force an external redirect back to the
        current host, see the <code>[R]</code> flag below.</dd>

        <dt><code>-</code> (dash)</dt>

        <dd>A dash indicates that no substitution should be performed
        (the existing path is passed through untouched). This is used
        when a flag (see below) needs to be applied without changing
        the path.</dd>

      </dl>

      <p>In addition to plain text, the <em>Substition</em> string can include</p>

      <ol>
        <li>back-references (<code>$N</code>) to the RewriteRule
        pattern</li>

        <li>back-references (<code>%N</code>) to the last matched
        RewriteCond pattern</li>

        <li>server-variables as in rule condition test-strings
        (<code>%{VARNAME}</code>)</li>

        <li><a href="#mapfunc">mapping-function</a> calls
        (<code>${mapname:key|default}</code>)</li>
      </ol>

      <p>Back-references are identifiers of the form 
	      <code>$</code><strong>N</strong>
      (<strong>N</strong>=0..9), which will be replaced
      by the contents of the <strong>N</strong>th group of the
      matched <em>Pattern</em>. The server-variables are the same
      as for the <em>TestString</em> of a <code>RewriteCond</code>
      directive. The mapping-functions come from the
      <code>RewriteMap</code> directive and are explained there.
      These three types of variables are expanded in the order above.</p>

      <p>As already mentioned, all rewrite rules are
      applied to the <em>Substitution</em> (in the order in which 
      they are defined
      in the config file). The URL is <strong>completely
      replaced</strong> by the <em>Substitution</em> and the
      rewriting process continues until all rules have been applied,
      or it is explicitly terminated by a
      <code><strong>L</strong></code> flag.</p>

     <div class="note"><h3>Modifying the Query String</h3>
      <p>By default, the query string is passed through unchanged. You
      can, however, create URLs in the substitution string containing
      a query string part. Simply use a question mark inside the
      substitution string to indicate that the following text should
      be re-injected into the query string. When you want to erase an
      existing query string, end the substitution string with just a
      question mark. To combine new and old query strings, use the
      <code>[QSA]</code> flag.</p> 
     </div>


      <p>Additionally you can set special <a name="rewriteflags" id="rewriteflags">actions</a> to be performed by 
      appending <strong><code>[</code><em>flags</em><code>]</code></strong>
      as the third argument to the <code>RewriteRule</code>
      directive. <em>Flags</em> is a comma-separated list, surround by square 
      brackets, of any of the following flags: </p>

      <dl>
        <dt>'<code>B</code>' (escape backreferences)</dt>
        <dd><p>Apache has to unescape URLs before mapping them,
        so backreferences will be unescaped at the time they are applied.
        Using the B flag, non-alphanumeric characters in backreferences
        will be escaped.  For example, consider the rule:</p>
        <pre><code> RewriteRule ^(.*)$ index.php?show=$1 </code></pre>
        <p>This will map <code>/C++</code> to <code>index.php?show=C++</code>.
        But it will also map <code>/C%2b%2b</code> to
        <code>index.php?show=C++</code>, because the <code>%2b</code>
        has been unescaped.  With the B flag, it will instead map to
        <code>index.php?show=&gt;/C%2b%2b</code>.</p>
        <p>This escaping is particularly necessary in a proxy situation,
        when the backend may break if presented with an unescaped URL.</p>
        </dd>

        <dt>'<code>chain|C</code>'
        (chained with next rule)</dt><dd>
         This flag chains the current rule with the next rule
        (which itself can be chained with the following rule,
        and so on). This has the following effect: if a rule
        matches, then processing continues as usual - 
        the flag has no effect. If the rule does
        <strong>not</strong> match, then all following chained
        rules are skipped. For instance, it can be used to remove the
        ``<code>.www</code>'' part, inside a per-directory rule set,
        when you let an external redirect happen (where the
        ``<code>.www</code>'' part should not occur!).</dd>

        <dt>'<code>cookie|CO=</code><em>NAME</em>:<em>VAL</em>:<em>domain</em>[:<em>lifetime</em>[:<em>path</em>]]'
        (set cookie)</dt><dd>
        This sets a cookie in the client's browser.  The cookie's name
        is specified by <em>NAME</em> and the value is
        <em>VAL</em>. The <em>domain</em> field is the domain of the
        cookie, such as '.apache.org', the optional <em>lifetime</em>
	is the lifetime of the cookie in minutes, and the optional 
	<em>path</em> is the path of the cookie</dd>

        <dt>
        '<code>env|E=</code><em>VAR</em>:<em>VAL</em>'
        (set environment variable)</dt><dd>
        This forces an environment variable named <em>VAR</em> to
        be set to the value <em>VAL</em>, where <em>VAL</em> can
        contain regexp backreferences (<code>$N</code> and
        <code>%N</code>) which will be expanded. You can use this
        flag more than once, to set more than one variable. The
        variables can later be dereferenced in many situations, most commonly
	from within XSSI (via <code>&lt;!--#echo
        var="VAR"--&gt;</code>) or CGI (<code>$ENV{'VAR'}</code>). 
	You can also dereference the variable in a later RewriteCond pattern, using
        <code>%{ENV:VAR}</code>. Use this to strip 
        information from URLs, while maintaining a record of that information.</dd>

        <dt>'<code>forbidden|F</code>' (force URL
        to be forbidden)</dt><dd>
        This forces the current URL to be forbidden - it immediately 
	sends back a HTTP response of 403 (FORBIDDEN). 
	Use this flag in conjunction with
        appropriate RewriteConds to conditionally block some
        URLs.</dd>

        <dt>'<code>gone|G</code>' (force URL to be
        gone)</dt><dd>
        This forces the current URL to be gone - it
        immediately sends back a HTTP response of 410 (GONE). Use
        this flag to mark pages which no longer exist as gone.</dd>

        <dt>
        '<code>handler|H</code>=<em>Content-handler</em>'
        (force Content handler)</dt><dd>
         Force the Content-handler of the target file to be
        <em>Content-handler</em>. For instance, this can be used to
        simulate the <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> directive
	<code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>, 
	which internally forces all files
        inside the mapped directory to have a handler of
        ``<code>cgi-script</code>''.</dd>

        <dt>'<code>last|L</code>'
        (last rule)</dt><dd> Stop the rewriting process
        here and don't apply any more rewrite rules. This corresponds
        to the Perl <code>last</code> command or the
        <code>break</code> command in C. Use this flag to prevent the
        currently rewritten URL from being rewritten further by
        following rules. Remember, however, that if the
        <code class="directive">RewriteRule</code> generates an internal
        redirect (which frequently occurs when rewriting in a
        per-directory context), this will reinject the request and
        will cause processing to be repeated starting from the first
        <code class="directive">RewriteRule</code>.</dd>

        <dt>'<code>next|N</code>'
        (next round)</dt><dd>
        Re-run the rewriting process (starting again with the
        first rewriting rule). This time, the URL to match is no longer
        the original URL, but rather the URL returned by the last rewriting rule.
        This corresponds to the Perl <code>next</code> command or
        the <code>continue</code> command in C. Use
        this flag to restart the rewriting process -
        to immediately go to the top of the loop.
         <strong>Be careful not to create an infinite
        loop!</strong></dd>

        <dt>'<code>nocase|NC</code>'
        (no case)</dt><dd>
        This makes the <em>Pattern</em> case-insensitive,
        ignoring difference between 'A-Z' and
        'a-z' when <em>Pattern</em> is matched against the current
        URL.</dd>

        <dt>
          '<code>noescape|NE</code>'
          (no URI escaping of
          output)</dt><dd>
          This flag prevents mod_rewrite from applying the usual URI
          escaping rules to the result of a rewrite. Ordinarily,
          special characters (such as '%', '$', ';', and so on)
          will be escaped into their hexcode equivalents ('%25',
          '%24', and '%3B', respectively); this flag prevents this
          from happening. This allows percent symbols to appear in
          the output, as in 
<div class="example"><p><code>
    RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]
</code></p></div>
          which would turn '<code>/foo/zed</code>' into a safe
          request for '<code>/bar?arg=P1=zed</code>'. 
        </dd>

        <dt>
          '<code>nosubreq|NS</code>'
          (not for internal
          sub-requests)</dt><dd>
          <p>This flag forces the rewriting engine to skip a
          rewriting rule if the current request is an internal
          sub-request. For instance, sub-requests occur internally
          in Apache when <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> tries to find out
          information about possible directory default files
          (<code>index.xxx</code> files). On sub-requests it is not
          always useful, and can even cause errors, if
          the complete set of rules are applied. Use this flag to
          exclude some rules.</p>
          <p>To decide whether or not to use this rule: if you
          prefix URLs with CGI-scripts, to force them to be
	  processed by the CGI-script, it's likely that you 
          will run into problems (or significant overhead) on
          sub-requests. In these cases, use this flag.</p>
        </dd>

        <dt>
          '<code>proxy|P</code>' (force
          proxy)</dt><dd>
          This flag forces the substitution part to be internally
	  sent as a proxy request and immediately (rewrite 
	  processing stops here) put through the <a href="mod_proxy.html">proxy module</a>. You must make
          sure that the substitution string is a valid URI
          (typically starting with
          <code>http://</code><em>hostname</em>) which can be
          handled by the Apache proxy module. If not, you will get an
          error from the proxy module. Use this flag to achieve a
          more powerful implementation of the <a href="mod_proxy.html#proxypass">ProxyPass</a> directive,
          to map remote content into the namespace of the local
          server. 

          <p>Note: <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> must be enabled in order
          to use this flag.</p>
        </dd>

        <dt>
          '<code>passthrough|PT</code>'
          (pass through to next
          handler)</dt><dd>
           This flag forces the rewrite engine to set the
          <code>uri</code> field of the internal
          <code>request_rec</code> structure to the value of the
          <code>filename</code> field. This flag is just a hack to
          enable post-processing of the output of
          <code>RewriteRule</code> directives, using
          <code>Alias</code>, <code>ScriptAlias</code>,
          <code>Redirect</code>, and other directives from
          various URI-to-filename translators. For example, to rewrite
          <code>/abc</code> to <code>/def</code> using
          <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>, and then
          <code>/def</code> to <code>/ghi</code> using
          <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code>: 
<div class="example"><p><code>
    RewriteRule ^/abc(.*)  /def$1 [PT]<br />
    Alias       /def       /ghi
</code></p></div>
          If you omit the <code>PT</code> flag,
          <code>mod_rewrite</code> will rewrite 
	  <code>uri=/abc/...</code> to
          <code>filename=/def/...</code> as a full API-compliant
          URI-to-filename translator should do. Then
          <code>mod_alias</code> will try to do a
          URI-to-filename transition, which will fail. 

          <p>Note: <strong>You must use this flag if you want to
          mix directives from different modules which allow
          URL-to-filename translators</strong>. The typical example
          is the use of <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> and
          <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>

          <p>The <code>PT</code> flag implies the <code>L</code> flag:
          rewriting will be stopped in order to pass the request to
          the next phase of processing.</p>
        </dd>

        <dt>'<code>qsappend|QSA</code>'
        (query string
        append)</dt><dd>
        This flag forces the rewrite engine to append a query
        string part of the substitution string to the existing string,
        instead of replacing it. Use this when you want to add more
        data to the query string via a rewrite rule.</dd>

        <dt>'<code>redirect|R</code>
          [=<em>code</em>]' (force <a id="redirect" name="redirect">redirect</a>)</dt><dd>
        <p>Prefix <em>Substitution</em> with
          <code>http://thishost[:thisport]/</code> (which makes the
          new URL a URI) to force a external redirection. If no
          <em>code</em> is given, a HTTP response of 302 (MOVED
          TEMPORARILY) will be returned. If you want to use other
          response codes, simply specify the appropriate number or use
          one of the following symbolic names: <code>temp</code>
          (default), <code>permanent</code>,
          <code>seeother</code>. Use this for rules to canonicalize
          the URL and return it to the client - to translate
          ``<code>/~</code>'' into ``<code>/u/</code>'', or to always
          append a slash to <code>/u/</code><em>user</em>, etc.<br />
          <strong>Note:</strong> When you use this flag, make sure
          that the substitution field is a valid URL! Otherwise, you
          will be redirecting to an invalid location. Remember that
          this flag on its own will only prepend
          <code>http://thishost[:thisport]/</code> to the URL, and
          rewriting will continue. Usually, you will want to stop
          rewriting at this point, and redirect immediately. To stop
          rewriting, you should add the 'L' flag.</p>
          <p>While this is typically used for redirects, any valid status
          code can be given here. If the status code is outside the redirect
          range (300-399), then the <em>Substitution</em> string is dropped
          and rewriting is stopped as if the <code>L</code> flag was
          used.</p>
        </dd>

        <dt>'<code>skip|S</code>=<em>num</em>'
        (skip next rule(s))</dt><dd>
        This flag forces the rewriting engine to skip the next
        <em>num</em> rules in sequence, if the current rule
        matches. Use this to make pseudo if-then-else constructs:
        The last rule of the then-clause becomes
        <code>skip=N</code>, where N is the number of rules in the
        else-clause. (This is <strong>not</strong> the same as the
        'chain|C' flag!)</dd>

        <dt>
        '<code>type|T</code>=<em>MIME-type</em>'
        (force MIME type)</dt><dd>
         Force the <a class="glossarylink" href="../glossary.html#mime-type" title="see glossary">MIME-type</a> of the target file to be
        <em>MIME-type</em>. This can be used to
        set up the content-type based on some conditions.
        For example, the following snippet allows <code>.php</code> files to
        be <em>displayed</em> by <code>mod_php</code> if they are called with
        the <code>.phps</code> extension:
        <div class="example"><p><code>
            RewriteRule ^(.+\.php)s$ $1 [T=application/x-httpd-php-source]
        </code></p></div>
        </dd>
      </dl>

<div class="note"><h3>Home directory expansion</h3>
<p> When the substitution string begins with a string
resembling "/~user" (via explicit text or backreferences), mod_rewrite performs
home directory expansion independent of the presence or configuration
of <code class="module"><a href="../mod/mod_userdir.html">mod_userdir</a></code>.</p>

<p> This expansion does not occur when the <em>PT</em>
flag is used on the <code class="directive"><a href="#rewriterule">RewriteRule</a></code>
directive.</p>
</div>

<div class="note"><h3>Per-directory Rewrites</h3>
 
<p>The rewrite engine may be used in <a href="../howto/htaccess.html">.htaccess</a> files.  To enable the
rewrite engine for these files you need to set
"<code>RewriteEngine On</code>" <strong>and</strong>
"<code>Options FollowSymLinks</code>" must be enabled. If your
administrator has disabled override of <code>FollowSymLinks</code> for
a user's directory, then you cannot use the rewrite engine. This
restriction is required for security reasons.</p>

<p>When using the rewrite engine in <code>.htaccess</code> files the
per-directory prefix (which always is the same for a specific
directory) is automatically <em>removed</em> for the pattern matching
and automatically <em>added</em> after the substitution has been
done. This feature is essential for many sorts of rewriting; without
this, you would always have to match the parent directory, which is
not always possible.  There is one exception: If a substitution string
starts with <code>http://</code>, then the directory prefix will
<strong>not</strong> be added, and an external redirect (or proxy
throughput, if using flag <strong>P</strong>) is forced.  See the
<code class="directive"><a href="#rewritebase">RewriteBase</a></code> directive for
more information.</p>

<p>The rewrite engine may also be used in <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code> sections with the same
prefix-matching rules as would be applied to <code>.htaccess</code>
files.  It is usually simpler, however, to avoid the prefix substitution
complication by putting the rewrite rules in the main server or
virtual host context, rather than in a <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code> section.</p>

<p>Although rewrite rules are syntactically permitted in <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> sections, this
should never be necessary and is unsupported.</p>

</div>

     <p>Here are all possible substitution combinations and their
      meanings:</p>

      <p><strong>Inside per-server configuration
      (<code>httpd.conf</code>)<br />
       for request ``<code>GET
      /somepath/pathinfo</code>'':</strong><br />
      </p>

<div class="note"><pre>
<strong>Given Rule</strong>                                      <strong>Resulting Substitution</strong>
----------------------------------------------  ----------------------------------
^/somepath(.*) otherpath$1                      invalid, not supported

^/somepath(.*) otherpath$1  [R]                 invalid, not supported

^/somepath(.*) otherpath$1  [P]                 invalid, not supported
----------------------------------------------  ----------------------------------
^/somepath(.*) /otherpath$1                     /otherpath/pathinfo

^/somepath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                via external redirection

^/somepath(.*) /otherpath$1 [P]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^/somepath(.*) http://thishost/otherpath$1      /otherpath/pathinfo

^/somepath(.*) http://thishost/otherpath$1 [R]  http://thishost/otherpath/pathinfo
                                                via external redirection

^/somepath(.*) http://thishost/otherpath$1 [P]  doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^/somepath(.*) http://otherhost/otherpath$1     http://otherhost/otherpath/pathinfo
                                                via external redirection

^/somepath(.*) http://otherhost/otherpath$1 [R] http://otherhost/otherpath/pathinfo
                                                via external redirection
                                                (the [R] flag is redundant)

^/somepath(.*) http://otherhost/otherpath$1 [P] http://otherhost/otherpath/pathinfo
                                                via internal proxy
</pre></div>

      <p><strong>Inside per-directory configuration for
      <code>/somepath</code><br />
       (<code>/physical/path/to/somepath/.htacccess</code>, with
      <code>RewriteBase /somepath</code>)<br />
       for request ``<code>GET
      /somepath/localpath/pathinfo</code>'':</strong><br /> 
     </p>

<div class="note"><pre>
<strong>Given Rule</strong>                                      <strong>Resulting Substitution</strong>
----------------------------------------------  ----------------------------------
^localpath(.*) otherpath$1                      /somepath/otherpath/pathinfo

^localpath(.*) otherpath$1  [R]                 http://thishost/somepath/otherpath/pathinfo
                                                via external redirection

^localpath(.*) otherpath$1  [P]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^localpath(.*) /otherpath$1                     /otherpath/pathinfo

^localpath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                via external redirection

^localpath(.*) /otherpath$1 [P]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^localpath(.*) http://thishost/otherpath$1      /otherpath/pathinfo

^localpath(.*) http://thishost/otherpath$1 [R]  http://thishost/otherpath/pathinfo
                                                via external redirection

^localpath(.*) http://thishost/otherpath$1 [P]  doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^localpath(.*) http://otherhost/otherpath$1     http://otherhost/otherpath/pathinfo
                                                via external redirection

^localpath(.*) http://otherhost/otherpath$1 [R] http://otherhost/otherpath/pathinfo
                                                via external redirection
                                                (the [R] flag is redundant)

^localpath(.*) http://otherhost/otherpath$1 [P] http://otherhost/otherpath/pathinfo
                                                via internal proxy
</pre></div>
  
</div>
</div>
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