mod_rewrite.html.en

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              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>system stuff:</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>''.</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>.