mod_rewrite.html.en

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      </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>

          <p>External rewriting programs are not started if they're defined in a
          context that does not have <code class="directive">RewriteEngine</code> set to
          <code>on</code></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>For some hints on <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular
      expressions</a>, see
      the <a href="../rewrite/rewrite_intro.html#regex">mod_rewrite
      Introduction</a>.</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>