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From sl...@apache.org
Subject cvs commit: httpd-2.0/docs/manual/mod mod_access.xml mod_actions.xml mod_rewrite.xml
Date Fri, 15 Feb 2002 18:02:19 GMT
slive       02/02/15 10:02:19

  Added:       docs/manual/mod mod_access.xml mod_actions.xml
                        mod_rewrite.xml
  Log:
  Convert three more modules to the xml format.
  
  Revision  Changes    Path
  1.1                  httpd-2.0/docs/manual/mod/mod_access.xml
  
  Index: mod_access.xml
  ===================================================================
  <?xml version="1.0"?>
  <!DOCTYPE xml:manual [ <!ENTITY nbsp "&#160;"> ]>
  <?xml-stylesheet type="text/xsl" href="../style/manual.xsl"?>
  <modulesynopsis>
  
  <name>mod_access</name> 
  
  <description>Provides access control based on client hostname, IP
  address, or other characteristics of the client request.</description>
  
  <status>Base</status>
  <sourcefile>mod_access.c</sourcefile>
  <identifier>access_module</identifier>
  
  <summary>
      <p>The directives provided by mod_access are used in <directive
      module="core">&lt;Directory&gt;</directive>, <directive
      module="core">&lt;Files&gt;</directive>, and <directive
      module="core">&lt;Location&gt;</directive> sections as well as
      <code><a href="core.html#accessfilename">.htaccess</a></code>
      files to control access to particular parts of the server. Access
      can be controlled based on the client hostname, IP address, or
      other characteristics of the client request, as captured in <a
      href="../env.html">environment variables</a>. The <directive
      module="mod_access">Allow</directive> and <directive
      module="mod_access">Deny</directive> directives are used to
      specify which clients are or are not allowed access to the server,
      while the <directive module="mod_access">Order</directive>
      directive sets the default access state, and configures how the
      <directive module="mod_access">Allow</directive> and <directive
      module="mod_access">Deny</directive> directives interact with each
      other.</p>
  
      <p>Both host-based access restrictions and password-based
      authentication may be implemented simultaneously. In that case,
      the <directive module="core">Satisfy</directive> directive is used
      to determine how the two sets of restrictions interact.</p>
  
      <p>In general, access restriction directives apply to all
      access methods (<code>GET</code>, <code>PUT</code>,
      <code>POST</code>, etc). This is the desired behavior in most
      cases. However, it is possible to restrict some methods, while
      leaving other methods unrestricted, by enclosing the directives
      in a <directive module="core">&lt;Limit&gt;</directive> section.</p>
  </summary>
  
  <seealso><directive module="core">Satisfy</directive></seealso>
  <seealso><directive module="core">Require</directive></seealso>
  
  <directivesynopsis>
  <name>Allow</name>
  
  <description>Controls which hosts can access an area of the
  server</description>
  <syntax> Allow from
      all|<em>host</em>|env=<em>env-variable</em>
      [<em>host</em>|env=<em>env-variable</em>] ...</syntax>
  <contextlist><context>directory</context><context>.htaccess</context>
  </contextlist>
  <override>Limit</override>
  
  <usage>
  
      <p>The <directive>Allow</directive> directive affects which hosts can
      access an area of the server. Access can be controlled by
      hostname, IP Address, IP Address range, or by other
      characteristics of the client request captured in environment
      variables.</p>
  
      <p>The first argument to this directive is always
      <code>from</code>. The subsequent arguments can take three
      different forms. If <code>Allow from all</code> is specified, then
      all hosts are allowed access, subject to the configuration of the
      <directive module="mod_access">Deny</directive> and <directive
      module="mod_access">Order</directive> directives as discussed
      below. To allow only particular hosts or groups of hosts to access
      the server, the <em>host</em> can be specified in any of the
      following formats:</p>
  
      <dl>
        <dt>A (partial) domain-name</dt>
  
        <dd>Example: <code>Allow from apache.org</code><br />
         Hosts whose names match, or end in, this string are allowed
        access. Only complete components are matched, so the above
        example will match <code>foo.apache.org</code> but it will
        not match <code>fooapache.org</code>. This configuration will
        cause the server to perform a reverse DNS lookup on the
        client IP address, regardless of the setting of the <directive
        module="core">HostnameLookups</directive>
        directive.</dd>
  
        <dt>A full IP address</dt>
  
        <dd>Example: <code>Allow from 10.1.2.3</code><br />
         An IP address of a host allowed access</dd>
  
        <dt>A partial IP address</dt>
  
        <dd>Example: <code>Allow from 10.1</code><br />
         The first 1 to 3 bytes of an IP address, for subnet
        restriction.</dd>
  
        <dt>A network/netmask pair</dt>
  
        <dd>Example: <code>Allow from
        10.1.0.0/255.255.0.0</code><br />
         A network a.b.c.d, and a netmask w.x.y.z. For more
        fine-grained subnet restriction.</dd>
  
        <dt>A network/nnn CIDR specification</dt>
  
        <dd>Example: <code>Allow from 10.1.0.0/16</code><br />
         Similar to the previous case, except the netmask consists of
        nnn high-order 1 bits.</dd>
      </dl>
  
      <p>Note that the last three examples above match exactly the
      same set of hosts.</p>
  
      <p>The third format of the arguments to the
      <directive>Allow</directive> directive allows access to the server
      to be controlled based on the existence of an <a
      href="../env.html">environment variable</a>. When <code>Allow from
      env=</code><em>env-variable</em> is specified, then the request is
      allowed access if the environment variable <em>env-variable</em>
      exists. The server provides the ability to set environment
      variables in a flexible way based on characteristics of the client
      request using the directives provided by
      <module>mod_setenvif</module>.  Therefore, this directive can be
      used to allow access based on such factors as the clients
      <code>User-Agent</code> (browser type), <code>Referer</code>, or
      other HTTP request header fields.</p>
  
  <example>
  <title>Example:</title>
  SetEnvIf User-Agent ^KnockKnock/2.0 let_me_in<br />
  &lt;Directory /docroot&gt;<br />
  &nbsp;&nbsp;    Order Deny,Allow<br />
  &nbsp;&nbsp;    Deny from all<br />
  &nbsp;&nbsp;    Allow from env=let_me_in<br />
  &lt;/Directory&gt;
  </example>
  
      <p>In this case, browsers with a user-agent string beginning
      with <code>KnockKnock/2.0</code> will be allowed access, and all
      others will be denied.</p>
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  
  <name>Deny</name>
  
  <description>Controls which hosts are denied access to the
  server</description>
  
  <syntax> Deny from
      all|<em>host</em>|env=<em>env-variable</em>
      [<em>host</em>|env=<em>env-variable</em>] ...</syntax>
  <contextlist><context>directory</context><context>.htaccess</context>
  </contextlist>
  <override>Limit</override>
  
  <usage>
      <p>This directive allows access to the server to be restricted
      based on hostname, IP address, or environment variables. The
      arguments for the <directive>Deny</directive> directive are
      identical to the arguments for the <directive
      module="mod_access">Allow</directive> directive.</p>
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  
  <name>Order</name>
  
  <description>Controls the default access state and the order in which
  <directive>Allow</directive> and <directive>Deny</directive> are
  evaluated.</description>
  
  <syntax> Order <em>ordering</em></syntax>
  <default>Order Deny,Allow</default>
  <contextlist><context>directory</context><context>.htaccess</context>
  </contextlist>
  <override>Limit</override>
  
  <usage>
  
      <p>The <directive>Order</directive> directive controls the default
      access state and the order in which <directive
      module="mod_access">Allow</directive> and <directive
      module="mod_access">Deny</directive> directives are evaluated.
      <em>Ordering</em> is one of</p>
  
      <dl>
        <dt>Deny,Allow</dt>
  
        <dd>The <directive module="mod_access">Deny</directive> directives
        are evaluated before the <directive
        module="mod_access">Allow</directive> directives. Access is
        allowed by default.  Any client which does not match a
        <directive module="mod_access">Deny</directive> directive or does
        match an <directive module="mod_access">Allow</directive>
        directive will be allowed access to the server.</dd>
  
        <dt>Allow,Deny</dt>
  
        <dd>The <directive module="mod_access">Allow</directive>
        directives are evaluated before the <directive
        module="mod_access">Deny</directive> directives. Access is denied
        by default. Any client which does not match an <directive
        module="mod_access">Allow</directive> directive or does match a
        <directive module="mod_access">Deny</directive> directive will be
        denied access to the server.</dd>
  
        <dt>Mutual-failure</dt>
  
        <dd>Only those hosts which appear on the <directive
        module="mod_access">Allow</directive> list and do not appear on
        the <directive module="mod_access">Deny</directive> list are
        granted access. This ordering has the same effect as <code>Order
        Allow,Deny</code> and is deprecated in favor of that
        configuration.</dd>
      </dl>
  
      <p>Keywords may only be separated by a comma; no whitespace is
      allowed between them. Note that in all cases every <directive
      module="mod_access">Allow</directive> and <directive
      module="mod_access">Deny</directive> statement is evaluated.</p>
  
      <p>In the following example, all hosts in the apache.org domain
      are allowed access; all other hosts are denied access.</p>
  
  <example>
        Order Deny,Allow<br />
        Deny from all<br />
        Allow from apache.org<br />
  </example>
  
      <p>In the next example, all hosts in the apache.org domain are
      allowed access, except for the hosts which are in the
      foo.apache.org subdomain, who are denied access. All hosts not
      in the apache.org domain are denied access because the default
      state is to deny access to the server.</p>
  
  <example>
         Order Allow,Deny<br />
         Allow from apache.org<br />
         Deny from foo.apache.org<br />
  </example>
  
      <p>On the other hand, if the <code>Order</code> in the last
      example is changed to <code>Deny,Allow</code>, all hosts will
      be allowed access. This happens because, regardless of the
      actual ordering of the directives in the configuration file,
      the <code>Allow from apache.org</code> will be evaluated last
      and will override the <code>Deny from foo.apache.org</code>.
      All hosts not in the <code>apache.org</code> domain will also
      be allowed access because the default state will change to
      <em>allow</em>.</p>
  
      <p>The presence of an <code>Order</code> directive can affect
      access to a part of the server even in the absence of accompanying
      <directive module="mod_access">Allow</directive> and <directive
      module="mod_access">Deny</directive> directives because of its effect
      on the default access state.  For example,</p>
  
  <example>
        &lt;Directory /www&gt;<br />
        &nbsp;&nbsp;Order Allow,Deny<br />
        &lt;/Directory&gt;
  </example>
  
      <p>will deny all access to the <code>/www</code> directory
      because the default access state will be set to
      <em>deny</em>.</p>
  
      <p>The <directive>Order</directive> directive controls the order of access
      directive processing only within each phase of the server's
      configuration processing. This implies, for example, that an
      <directive module="mod_access">Allow</directive> or <directive
      module="mod_access">Deny</directive> directive occurring in a
      <directive module="core">&lt;Location&gt;</directive> section will
      always be evaluated after an <directive
      module="mod_access">Allow</directive> or <directive
      module="mod_access">Deny</directive> directive occurring in a
      <directive module="core">&lt;Directory&gt;</directive> section or
      <code>.htaccess</code> file, regardless of the setting of the
      <directive>Order</directive> directive. For details on the merging
      of configuration sections, see the documentation on <a
      href="../sections.html">How Directory, Location and Files sections
      work</a>.</p>
  </usage>
  
  </directivesynopsis>
  
  </modulesynopsis>
  
  
  
  1.1                  httpd-2.0/docs/manual/mod/mod_actions.xml
  
  Index: mod_actions.xml
  ===================================================================
  <?xml version="1.0"?>
  <!DOCTYPE xml:manual [ <!ENTITY nbsp "&#160;"> ]>
  <?xml-stylesheet type="text/xsl" href="../style/manual.xsl"?>
  <modulesynopsis>
  
  <name>mod_actions</name> 
  
  <description>This module provides for executing CGI scripts based on
  media type or request method.</description>
  
  <status>Base</status>
  <sourcefile>mod_actions.c</sourcefile>
  <identifier>actions_module</identifier>
  
  <summary>
      <p>This module has two directives. The <directive
      module="mod_actions">Action</directive> directive lets you run CGI
      scripts whenever a file of a certain type is requested. The
      <directive module="mod_actions">Script</directive> directive lets
      you run CGI scripts whenever a particular method is used in a
      request. This makes it much easier to execute scripts that process
      files.</p>
  </summary>
  
  <directivesynopsis>
  
  <name>Action</name>
  
  <description>Activates a CGI script for a particular handler or
  content-type</description>
  
  <syntax>Action <em>action-type cgi-script</em></syntax>
  <contextlist>
  <context>server config</context><context>virtual host</context>
  <context>directory</context><context>.htaccess</context>
  </contextlist>
  <override>FileInfo</override>
  
  <usage>
      <p>This directive adds an action, which will activate
      <em>cgi-script</em> when <em>action-type</em> is triggered by
      the request. The <em>action-type</em> can be either a <a
      href="../handler.html">handler</a> or a MIME content type. It
      sends the URL and file path of the requested document using the
      standard CGI PATH_INFO and PATH_TRANSLATED environment
      variables.</p>
  
  <example>
  <title>Examples</title>
  
      # Requests for files of a particular type:<br />
      Action image/gif /cgi-bin/images.cgi<br />
  <br />
      # Files of a particular file extension<br />
      AddHandler my-file-type .xyz<br />
      Action my-file-type /cgi-bin/program.cgi<br />
  </example>
  
      <p>In the first example, requests for files with a MIME content
      type of <code>image/gif</code> will instead be handled by the
      specified cgi script <code>/cgi-bin/images.cgi</code>.</p>
  
      <p>In the second example, requests for files with a file extension of
      <code>.xyz</code> are handled instead by the specified cgi script 
      <code>/cgi-bin/program.cgi</code>.</p>
  </usage>
  
  <seealso><directive module="mod_mime">AddHandler</directive></seealso>
  
  </directivesynopsis>
  
  <directivesynopsis>
  
  <name>Script</name>
  
  <description>Activates a CGI script for a particular request
  method.</description>
  <syntax> Script <em>method cgi-script</em></syntax>
  <contextlist>
  <context>server config</context><context>virtual host</context>
  <context>directory</context></contextlist>
  <usage>
      <p>This directive adds an action, which will activate
      <em>cgi-script</em> when a file is requested using the method of
      <em>method</em>. It sends the URL and file path of the requested
      document using the standard CGI PATH_INFO and PATH_TRANSLATED
      environment variables.</p>
  
  <note>
        Any arbitrary method name may be used. <strong>Method names are
        case-sensitive</strong>, so <code>Script&nbsp;PUT</code> and
        <code>Script&nbsp;put</code> have two entirely different
        effects.
  </note>
  
      <p>Note that the Script command defines default actions only.
      If a CGI script is called, or some other resource that is
      capable of handling the requested method internally, it will do
      so. Also note that Script with a method of <code>GET</code>
      will only be called if there are query arguments present
      (<em>e.g.</em>, foo.html?hi). Otherwise, the request will
      proceed normally.</p>
  
  <example>
  <title>Examples</title>
      # For &lt;ISINDEX&gt;-style searching<br />
      Script GET /cgi-bin/search<br />
      # A CGI PUT handler<br />
      Script PUT /~bob/put.cgi<br />
  </example>
  </usage>
  
  </directivesynopsis>
  
  </modulesynopsis>
  
  
  1.1                  httpd-2.0/docs/manual/mod/mod_rewrite.xml
  
  Index: mod_rewrite.xml
  ===================================================================
  <?xml version="1.0"?>
  <!DOCTYPE xml:manual [ <!ENTITY nbsp "&#160;"> ]>
  <?xml-stylesheet type="text/xsl" href="../style/manual.xsl"?>
  <modulesynopsis>
  
  <name>mod_rewrite</name> 
  
  <description>Provides a rule-based rewriting engine to rewrite requested
  URLs on the fly</description>
  
  <status>Extension</status>
  <sourcefile>mod_rewrite.c</sourcefile>
  <identifier>rewrite_module</identifier>
  <compatibility>Available in Apache 1.3 and later</compatibility>
  
  <summary>
        <blockquote>
              <em>``The great thing about mod_rewrite is it gives you
              all the configurability and flexibility of Sendmail.
              The downside to mod_rewrite is that it gives you all
              the configurability and flexibility of Sendmail.''</em>
              
  
              <div align="RIGHT">
                -- Brian Behlendorf<br />
                 Apache Group
              </div>
        </blockquote>
  
        <blockquote>
              <em>`` Despite the tons of examples and docs,
              mod_rewrite is voodoo. Damned cool voodoo, but still
              voodoo. ''</em> 
  
              <div align="RIGHT">
                -- Brian Moore<br />
                 bem@news.cmc.net
              </div>
            </blockquote>
  
  
        <p>Welcome to mod_rewrite, the Swiss Army Knife of URL
        manipulation!</p>
  
        <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,
        for instance server variables, environment variables, HTTP
        headers, time stamps and even external database lookups in
        various formats can be used to achieve a really 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 even 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>But all this functionality and flexibility has its
        drawback: complexity. So don't expect to understand this
        entire module in just one day.</p>
  
        <p>This module was invented and originally written in April
        1996 and gifted exclusively to the The Apache Group in July 1997
        by</p>
  
        <blockquote>
          <a href="http://www.engelschall.com/"><code>Ralf S.
          Engelschall</code></a><br />
           <a
          href="mailto:rse@engelschall.com"><code>rse@engelschall.com</code></a><br />
           <a
          href="http://www.engelschall.com/"><code>www.engelschall.com</code></a>
        </blockquote>
  </summary>
  
  <section id="Internal"><title>Interal Processing</title>
  
        <p>The internal processing of this module is very complex but
        needs to be explained once even to the average user to avoid
        common mistakes and to let you exploit its full
        functionality.</p>
  
  <section id="InternalAPI"><title>API Phases</title>
  
        <p>First you have to understand that when Apache processes a
        HTTP request it does this in phases. A hook for each of these
        phases is provided by the Apache API. Mod_rewrite uses two of
        these hooks: the URL-to-filename translation hook which is
        used after the HTTP request has been read but before any
        authorization starts and the Fixup hook which is triggered
        after the authorization phases and after the per-directory
        config files (<code>.htaccess</code>) have been read, but
        before the content handler is activated.</p>
  
        <p>So, after a request comes in and Apache has determined the
        corresponding server (or virtual server) the rewriting engine
        starts processing of all mod_rewrite directives from the
        per-server configuration in the URL-to-filename phase. A few
        steps later when the final data directories are found, the
        per-directory configuration directives of mod_rewrite are
        triggered in the Fixup phase. In both situations mod_rewrite
        rewrites URLs either to new URLs or to filenames, although
        there is no obvious distinction between them. This is a usage
        of the API which was not intended to be this way when the API
        was designed, but as of Apache 1.x this is the only way
        mod_rewrite can operate. To make this point more clear
        remember the following two points:</p>
  
        <ol>
          <li>Although mod_rewrite rewrites URLs to URLs, URLs to
          filenames and even filenames to filenames, the API
          currently provides only a URL-to-filename hook. In Apache
          2.0 the two missing hooks will be added to make the
          processing more clear. But this point has no drawbacks for
          the user, it is just a fact which should be remembered:
          Apache does more in the URL-to-filename hook than the API
          intends for it.</li>
  
          <li>
            Unbelievably mod_rewrite provides URL manipulations in
            per-directory context, <em>i.e.</em>, within
            <code>.htaccess</code> files, although these are reached
            a very long time after the URLs have been translated to
            filenames. It has to be this way because
            <code>.htaccess</code> files live in the filesystem, so
            processing has already reached this stage. In other
            words: According to the API phases at this time it is too
            late for any URL manipulations. To overcome this chicken
            and egg problem mod_rewrite uses a trick: When you
            manipulate a URL/filename in per-directory context
            mod_rewrite first rewrites the filename back to its
            corresponding URL (which is usually impossible, but see
            the <code>RewriteBase</code> directive below for the
            trick to achieve this) and then initiates a new internal
            sub-request with the new URL. This restarts processing of
            the API phases. 
  
            <p>Again mod_rewrite tries hard to make this complicated
            step totally transparent to the user, but you should
            remember here: While URL manipulations in per-server
            context are really fast and efficient, per-directory
            rewrites are slow and inefficient due to this chicken and
            egg problem. But on the other hand this is the only way
            mod_rewrite can provide (locally restricted) URL
            manipulations to the average user.</p>
          </li>
        </ol>
  
        <p>Don't forget these two points!</p>
  </section>
  
  <section id="InternalRuleset"><title>Ruleset Processing</title>
   
        <p>Now when mod_rewrite is triggered in these two API phases, it
        reads the configured rulesets from its configuration
        structure (which itself was either created on startup for
        per-server context or during the directory walk of the Apache
        kernel for per-directory context). Then the URL rewriting
        engine is started with the contained ruleset (one or more
        rules together with their conditions). The operation of the
        URL rewriting engine itself is exactly the same for both
        configuration contexts. Only the final result processing is
        different. </p>
  
        <p>The order of rules in the ruleset is important because the
        rewriting engine processes them in a special (and not very
        obvious) order. The rule is this: The rewriting engine loops
        through the ruleset rule by rule (<directive
        module="mod_rewrite">RewriteRule</directive> directives) and
        when a particular rule matches it optionally loops through
        existing corresponding conditions (<code>RewriteCond</code>
        directives). For historical reasons the conditions are given
        first, and so the control flow is a little bit long-winded. See
        Figure 1 for more details.</p>
  
        <div align="CENTER">
          <table cellspacing="0" cellpadding="2" border="0">
            <tr>
              <td bgcolor="#CCCCCC"><img
              src="../images/mod_rewrite_fig1.gif" width="428"
              height="385"
              alt="[Needs graphics capability to display]" /></td>
            </tr>
  
            <tr>
              <td align="CENTER"><strong>Figure 1:</strong> The
              control flow through the rewriting ruleset</td>
            </tr>
          </table>
        </div>
  
        <p>As you can see, first the URL is matched against the
        <em>Pattern</em> of each rule. When it fails mod_rewrite
        immediately stops processing this rule and continues with the
        next rule. If the <em>Pattern</em> matches, mod_rewrite looks
        for corresponding rule conditions. If none are present, it
        just substitutes the URL with a new value which is
        constructed from the string <em>Substitution</em> and goes on
        with its rule-looping. But if conditions exist, it starts an
        inner loop for processing them in the order that they are
        listed. For conditions the logic is different: we don't match
        a pattern against the current URL. Instead we first create a
        string <em>TestString</em> by expanding variables,
        back-references, map lookups, <em>etc.</em> and then we try
        to match <em>CondPattern</em> against it. If the pattern
        doesn't match, the complete set of conditions and the
        corresponding rule fails. If the pattern matches, then the
        next condition is processed until no more conditions are
        available. If all conditions match, processing is continued
        with the substitution of the URL with
        <em>Substitution</em>.</p>
  
  </section>
  
  <section id="quoting"><title>Quoting Special Characters</title>
  
        <p>As of Apache 1.3.20, special characters in
        <i>TestString</i> and <i>Substitution</i> strings can be
        escaped (that is, treated as normal characters without their
        usual special meaning) by prefixing them with a slosh ('\')
        character. In other words, you can include an actual
        dollar-sign character in a <i>Substitution</i> string by
        using '<code>\$</code>'; this keeps mod_rewrite from trying
        to treat it as a backreference.</p>
  </section>
  
  <section id="InternalBackRefs"><title>Regex Back-Reference Availability</title>
  
        <p>One important thing here has to be remembered: Whenever you
        use parentheses in <em>Pattern</em> or in one of the
        <em>CondPattern</em>, back-references are internally created
        which can be used with the strings <code>$N</code> and
        <code>%N</code> (see below). These are available for creating
        the strings <em>Substitution</em> and <em>TestString</em>.
        Figure 2 shows to which locations the back-references are
        transfered for expansion.</p>
  
        <div align="CENTER">
          <table cellspacing="0" cellpadding="2" border="0">
            <tr>
              <td bgcolor="#CCCCCC"><img
              src="../images/mod_rewrite_fig2.gif" width="381"
              height="179"
              alt="[Needs graphics capability to display]" /></td>
            </tr>
  
            <tr>
              <td align="CENTER"><strong>Figure 2:</strong> The
              back-reference flow through a rule</td>
            </tr>
          </table>
        </div>
  
        <p>We know this was a crash course on mod_rewrite's internal
        processing. But you will benefit from this knowledge when
        reading the following documentation of the available
        directives.</p>
  
  </section>
  </section>
  
  <section id="EnvVar"><title>Environment Variables</title>
  
        <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>, <em>i.e.</em>, <em>before</em> any
        rewriting. This is important because the rewriting process is
        primarily used to rewrite logical URLs to physical
        pathnames.</p>
  
        <p><strong>Example:</strong></p>
  
  <example>
  <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>
  </example>
  
  </section>
  
  <section id="Solutions"><title>Practical Solutions</title>
  
        <p>We also have an <a href="../misc/rewriteguide.html">URL
        Rewriting Guide</a> available, which provides a collection of
        practical solutions for URL-based problems. There you can
        find real-life rulesets and additional information about
        mod_rewrite.</p>
  </section>
  
  
  <directivesynopsis>
  
  <name>RewriteEngine</name>
  
  <summary>Enables or disables runtime rewriting engine</summary>
  
  <syntax>RewriteEngine on|off</syntax>
  <default>RewriteEngine off</default>
  <contextlist><context>server config</context><context>virtual host</context>
  <context>directory</context><context>.htaccess</context></contextlist>
  <override>FileInfo</override>
  
  <usage>       
  
        <p>The <directive>RewriteEngine</directive> 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 <directive
        module="mod_rewrite">RewriteRule</directive> directives!</p>
  
        <p>Note that, by default, rewrite configurations are not
        inherited. This means that you need to have a
        <code>RewriteEngine on</code> directive for each virtual host
        in which you wish to use it.</p>
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteOptions</name>
  <description>Sets some special options for the rewrite engine</description>
  <syntax>RewriteOptions <em>Options</em></syntax>
  <default>None</default>
  <contextlist><context>server config</context><context>virtual host</context>
  <context>directory</context><context>.htaccess</context></contextlist>
  
  <usage>
  
        <p>The <directive>RewriteOptions</directive> directive sets some
        special options for the current per-server or per-directory
        configuration. The <em>Option</em> strings can be one of the
        following:</p>
  
        <ul>
          <li>'<strong><code>inherit</code></strong>'<br />
           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.</li>
        </ul>
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteLog</name>
  <description>Sets the name of the file used for logging rewrite engine
  processing</description>
  <syntax>RewriteLog <em>file-path</em></syntax>
  <contextlist><context>server config</context><context>virtual host</context>
  </contextlist>
  
  <usage>
        <p>The <directive>RewriteLog</directive> 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>
  
  <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 <directive>RewriteLog</directive>
            directive or use <code>RewriteLogLevel 0</code>!
  </note>
  
  <note><title>Security</title>
  
  See the <a href="../misc/security_tips.html">Apache Security Tips</a>
  document for details on why your security could be compromised if the
  directory where logfiles are stored is writable by anyone other than
  the user that starts the server.
  </note>
  
  <example><title>Example</title>
  RewriteLog "/usr/local/var/apache/logs/rewrite.log"
  </example>
  
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteLogLevel</name>
  <description>Sets the verbosity of the log file used by the rewrite
  engine</description>
  <syntax>RewriteLogLevel <em>Level</em></syntax>
  <default>RerwiteLogLevel 0</default>
  <contextlist><context>server config</context><context>virtual host</context>
  </contextlist>
  
  <usage>
        <p>The <directive>RewriteLogLevel</directive> 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>
  
  <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!
  </note>
  
  <example><title>Example</title>
  RewriteLogLevel 3
  </example>
  
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteLock</name>
  <description>Sets the name of the lock file used for <directive
  module="mod_rewrite">RewriteMap</directive>
  synchronization</description>
  <syntax>RewriteLock <em>file-path</em></syntax>
  <default>None</default>
  <contextlist><context>server config</context></contextlist>
  
  <usage>
        <p>This directive sets the filename for a synchronization
        lockfile which mod_rewrite needs to communicate with <directive
        module="mod_rewrite">RewriteMap</directive>
        <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>
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteMap</name>
  <description>Defines a mapping function for key-lookup</description>
  <syntax>RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>
  </syntax>
  <default>None</default>
  <contextlist><context>server config</context><context>virtual host</context>
  </contextlist>
  
  <usage>
        <p>The <directive>RewriteMap</directive> 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>
  
        <blockquote>
          <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>
        </blockquote>
  
        <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>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>
  
            <blockquote>
              <strong><em>MatchingKey</em>
              <em>SubstValue</em></strong>
            </blockquote>
  
  <example><title>Example</title>
  <pre>
  ##
  ##  map.txt -- rewriting map
  ##
  
  Ralf.S.Engelschall    rse   # Bastard Operator From Hell
  Mr.Joe.Average        joe   # Mr. Average
  </pre>
  </example>
  
  <example>
  RewriteMap real-to-user txt:/path/to/file/map.txt
  </example>
          </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. Although this sounds crazy and useless,
            it was actually designed for load balancing in a reverse
            proxy situation where the looked up values are server
            names. Example:</p>
  
  <example>
  <pre>
  ##
  ##  map.txt -- rewriting map
  ##
  
  static   www1|www2|www3|www4
  dynamic  www5|www6
  </pre>
  </example>
  
  <example>
  RewriteMap servers rnd:/path/to/file/map.txt
  </example>
          </li>
  
          <li>
            <strong>Hash File</strong><br />
             MapType: <code>dbm</code>, MapSource: Unix filesystem
            path to valid regular file 
  
            <p>Here the source is a binary NDBM format 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. You can create such a
            file with any NDBM tool or with the following Perl
            script:</p>
  
  <example>
  <pre>
  #!/path/to/bin/perl
  ##
  ##  txt2dbm -- convert txt map to dbm format
  ##
  
  use NDBM_File;
  use Fcntl;
  
  ($txtmap, $dbmmap) = @ARGV;
  
  open(TXT, "&lt;$txtmap") or die "Couldn't open $txtmap!\n";
  tie (%DB, 'NDBM_File', $dbmmap,O_RDWR|O_TRUNC|O_CREAT, 0644) or die "Couldn't create $dbmmap!\n";
  
  while (&lt;TXT&gt;) {
    next if (/^\s*#/ or /^\s*$/);
    $DB{$1} = $2 if (/^\s*(\S+)\s+(\S+)/);
  }
  
  untie %DB;
  close(TXT);
  </pre>
  </example>
  
  <example>
  $ txt2dbm map.txt map.db
  </example>
          </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 exists:</p>
  
            <ul>
              <li><strong>toupper</strong>:<br />
               Converts the looked up key to all upper case.</li>
  
              <li><strong>tolower</strong>:<br />
               Converts the looked up key to all lower case.</li>
  
              <li><strong>escape</strong>:<br />
               Translates special characters in the looked up key to
              hex-encodings.</li>
  
              <li><strong>unescape</strong>:<br />
               Translates hex-encodings in the looked up 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 the language of your choice, but
            the result has to be a executable (<em>i.e.</em>, 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 at startup of the Apache
            servers and then communicates with the rewriting engine
            over 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>
  
  <example>
  <pre>
  #!/usr/bin/perl
  $| = 1;
  while (&lt;STDIN&gt;) {
      # ...put here any transformations or lookups...
      print $_;
  }
  </pre>
  </example>
  
            <p>But be very careful:</p>
  
            <ol>
              <li>``<em>Keep it simple, stupid</em>'' (KISS), because
              if this program hangs it will hang the Apache server
              when the rule occurs.</li>
  
              <li>Avoid one common mistake: never do buffered I/O on
              <code>stdout</code>! This will cause a deadloop! Hence
              the ``<code>$|=1</code>'' in the above example...</li>
  
              <li>Use the <directive
              module="mod_rewrite">RewriteLock</directive> directive to
              define a lockfile mod_rewrite can use to synchronize the
              communication to the program. By default no such
              synchronization takes place.</li>
            </ol>
          </li>
        </ul>
        The <directive>RewriteMap</directive> directive can occur more than
        once. For each mapping-function use one
        <directive>RewriteMap</directive> 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. 
  
  <note><title>Note</title> 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!
  </note>
  
  </usage>
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteBase</name>
  <description>Sets the base URL for per-directory rewrites</description>
  <syntax>RewriteBase <em>URL-path</em></syntax>
  <default>RewriteBase <em>physical-directory-path</em></default>
  <contextlist><context>directory</context><context>.htaccess</context>
  </contextlist>
  <override>FileInfo</override>
  
  <usage>
        <p>The <directive>RewriteBase</directive> directive explicitly
        sets the base URL for per-directory rewrites. As you will see
        below, <directive module="mod_rewrite">RewriteRule</directive>
        can be used in per-directory config files
        (<code>.htaccess</code>). There it will act locally,
        <em>i.e.</em>, the local directory prefix is stripped at this
        stage of processing and your rewriting rules act only on the
        remainder. At the end it is automatically added back to the
        path.</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>But at most websites URLs are NOT
        directly related to physical filename paths, so this
        assumption will usually be wrong!</strong> There you have to
        use the <code>RewriteBase</code> directive to specify the
        correct URL-prefix.</p>
  
  <note> If your webserver's URLs are <strong>not</strong> directly
  related to physical file paths, you have to use
  <directive>RewriteBase</directive> in every <code>.htaccess</code>
  files where you want to use <directive
  module="mod_rewrite">RewriteRule</directive> directives.
  </note>
  
          <p> For example, assume the following per-directory config file:</p>
  
  <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>
  </example>
  
          <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>
  
  <note><title>For Apache Hackers</title>
  <p>The following list gives detailed information about
                the internal processing steps:</p>
  <pre>
  <font size="-1">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
  </font>
  </pre>
                <p><font size="-1">This seems very complicated but is
                the correct Apache internal processing, because the
                per-directory rewriting comes too late in the
                process. So, when it occurs the (rewritten) request
                has to be re-injected into the Apache kernel! BUT:
                While this seems like a serious overhead, it really
                isn't, because this re-injection happens fully
                internally to the Apache server and the same
                procedure is used by many other operations inside
                Apache. So, you can be sure the design and
                implementation is correct.</font></p>
  </note>
  
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteCond</name>
  <description>Defines a condition under which rewriting will take place
  </description>
  <syntax> RewriteCond
        <em>TestString</em> <em>CondPattern</em></syntax>
  <default>None</default>
  <contextlist><context>server config</context><context>virtual host</context>
  <context>directory</context><context>.htaccess</context></contextlist>
  <override>FileInfo</override>
  
  <usage>
        <p>The <directive>RewriteCond</directive> directive defines a
        rule condition. Precede a <directive
        module="mod_rewrite">RewriteRule</directive> directive with one
        or more <directive>RewriteCond</directive> directives. The following
        rewriting rule is only used if its pattern matches the current
        state of the URI <strong>and</strong> if these additional
        conditions apply too.</p>
  
        <p><em>TestString</em> is a string which can contains the
        following expanded constructs in addition to plain text:</p>
  
        <ul>
          <li>
            <strong>RewriteRule backreferences</strong>: These are
            backreferences of the form 
  
            <blockquote>
              <strong><code>$N</code></strong>
            </blockquote>
            (0 &lt;= N &lt;= 9) which provide access to the grouped
            parts (parenthesis!) of the pattern from the
            corresponding <code>RewriteRule</code> directive (the one
            following the current bunch of <code>RewriteCond</code>
            directives).
          </li>
  
          <li>
            <strong>RewriteCond backreferences</strong>: These are
            backreferences of the form 
  
            <blockquote>
              <strong><code>%N</code></strong>
            </blockquote>
            (1 &lt;= N &lt;= 9) which provide access to the grouped
            parts (parentheses!) of the pattern from the last matched
            <code>RewriteCond</code> directive in the current bunch
            of conditions.
          </li>
  
          <li>
            <strong>RewriteMap expansions</strong>: These are
            expansions of the form 
  
            <blockquote>
              <strong><code>${mapname:key|default}</code></strong>
            </blockquote>
            See <a href="#mapfunc">the documentation for
            RewriteMap</a> for more details.
          </li>
  
          <li>
            <strong>Server-Variables</strong>: These are variables of
            the form 
  
            <blockquote>
              <strong><code>%{</code> <em>NAME_OF_VARIABLE</em>
              <code>}</code></strong>
            </blockquote>
            where <em>NAME_OF_VARIABLE</em> can be a string taken
            from the following list: 
  
            <table bgcolor="#F0F0F0" cellspacing="0" cellpadding="5">
              <tr>
                <td valign="TOP">
                  <strong>HTTP headers:</strong> 
  
                  <p><font size="-1">HTTP_USER_AGENT<br />
                   HTTP_REFERER<br />
                   HTTP_COOKIE<br />
                   HTTP_FORWARDED<br />
                   HTTP_HOST<br />
                   HTTP_PROXY_CONNECTION<br />
                   HTTP_ACCEPT<br />
                  </font></p>
                </td>
  
                <td valign="TOP">
                  <strong>connection &amp; request:</strong> 
  
                  <p><font size="-1">REMOTE_ADDR<br />
                   REMOTE_HOST<br />
                   REMOTE_USER<br />
                   REMOTE_IDENT<br />
                   REQUEST_METHOD<br />
                   SCRIPT_FILENAME<br />
                   PATH_INFO<br />
                   QUERY_STRING<br />
                   AUTH_TYPE<br />
                  </font></p>
                </td>
              </tr>
  
              <tr>
                <td valign="TOP">
                  <strong>server internals:</strong> 
  
                  <p><font size="-1">DOCUMENT_ROOT<br />
                   SERVER_ADMIN<br />
                   SERVER_NAME<br />
                   SERVER_ADDR<br />
                   SERVER_PORT<br />
                   SERVER_PROTOCOL<br />
                   SERVER_SOFTWARE<br />
                  </font></p>
                </td>
  
                <td valign="TOP">
                  <strong>system stuff:</strong> 
  
                  <p><font size="-1">TIME_YEAR<br />
                   TIME_MON<br />
                   TIME_DAY<br />
                   TIME_HOUR<br />
                   TIME_MIN<br />
                   TIME_SEC<br />
                   TIME_WDAY<br />
                   TIME<br />
                  </font></p>
                </td>
  
                <td valign="TOP">
                  <strong>specials:</strong> 
  
                  <p><font size="-1">API_VERSION<br />
                   THE_REQUEST<br />
                   REQUEST_URI<br />
                   REQUEST_FILENAME<br />
                   IS_SUBREQ<br />
                  </font></p>
                </td>
              </tr>
            </table>
  
  <note>
                  <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:</p>
  
                  <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>
                  </dl>
  </note>
          </li>
        </ul>
  
        <p>Special Notes:</p>
  
        <ol>
          <li>The variables SCRIPT_FILENAME and REQUEST_FILENAME
          contain the same value, <em>i.e.</em>, the value of the
          <code>filename</code> field of the internal
          <code>request_rec</code> structure of the Apache server.
          The first name is just the commonly known CGI variable name
          while the second is the consistent counterpart to
          REQUEST_URI (which contains the value of the
          <code>uri</code> field of <code>request_rec</code>).</li>
  
          <li>There is the special format:
          <code>%{ENV:variable}</code> where <em>variable</em> can be
          any environment variable. This is looked-up via internal
          Apache structures and (if not found there) via
          <code>getenv()</code> from the Apache server process.</li>
  
          <li>There is the special format:
          <code>%{HTTP:header}</code> where <em>header</em> can be
          any HTTP MIME-header name. This is looked-up from the HTTP
          request. Example: <code>%{HTTP:Proxy-Connection}</code> is
          the value of the HTTP header
          ``<code>Proxy-Connection:</code>''.</li>
  
          <li>There is the special format
          <code>%{LA-U:variable}</code> for look-aheads which perform
          an internal (URL-based) sub-request to determine the final
          value of <em>variable</em>. Use this when you want to use a
          variable for rewriting which is actually set later in an
          API phase and thus is not available at the current stage.
          For instance when you want to rewrite according to the
          <code>REMOTE_USER</code> variable from within the
          per-server context (<code>httpd.conf</code> file) you have
          to use <code>%{LA-U:REMOTE_USER}</code> because this
          variable is set by the authorization phases which come
          <em>after</em> the URL translation phase where mod_rewrite
          operates. 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> there.</li>
  
          <li>There is the special format:
          <code>%{LA-F:variable}</code> which performs 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,
        <em>i.e.</em>, a regular expression which is applied to the
        current instance of the <em>TestString</em>, <em>i.e.</em>,
        <em>TestString</em> is evaluated and then matched against
        <em>CondPattern</em>.</p>
  
        <p><strong>Remember:</strong> <em>CondPattern</em> is a
        standard <em>Extended 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>' (is lexically
              lower)<br />
               Treats the <em>CondPattern</em> as a plain string and
              compares it lexically to <em>TestString</em>. True if
              <em>TestString</em> is lexically lower than
              <em>CondPattern</em>.</li>
  
              <li>'<strong>&gt;CondPattern</strong>' (is lexically
              greater)<br />
               Treats the <em>CondPattern</em> as a plain string and
              compares it lexically to <em>TestString</em>. True if
              <em>TestString</em> is lexically greater than
              <em>CondPattern</em>.</li>
  
              <li>'<strong>=CondPattern</strong>' (is lexically
              equal)<br />
               Treats the <em>CondPattern</em> as a plain string and
              compares it lexically to <em>TestString</em>. True if
              <em>TestString</em> is lexically equal to
              <em>CondPattern</em>, i.e the two strings are exactly
              equal (character by character). If <em>CondPattern</em>
              is just <samp>""</samp> (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
              if 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
              if 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
              if 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
              if it exists and is a symbolic link.</li>
  
              <li>'<strong>-F</strong>' (is existing file via
              subrequest)<br />
               Checks if <em>TestString</em> is a valid file and
              accessible via all the server's currently-configured
              access controls for that path. This uses an internal
              subrequest to determine the check, so use it with care
              because it decreases your servers performance!</li>
  
              <li>'<strong>-U</strong>' (is existing URL via
              subrequest)<br />
               Checks if <em>TestString</em> is a valid URL and
              accessible via all the server's currently-configured
              access controls for that path. This uses an internal
              subrequest to determine the check, so use it with care
              because it decreases your server's performance!</li>
            </ul>
  
  <note><title>Notice</title>
                All of these tests can
                also be prefixed by an exclamation mark ('!') to
                negate their meaning.
  </note>
          </li>
        </ol>
  
        <p>Additionally you can set special flags for
        <em>CondPattern</em> by appending</p>
  
        <blockquote>
          <strong><code>[</code><em>flags</em><code>]</code></strong>
        </blockquote>
        as the third argument to the <code>RewriteCond</code>
        directive. <em>Flags</em> is a comma-separated list 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, <em>i.e.</em>, there
          is no difference between 'A-Z' and 'a-z' 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: 
  
  <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>
  </example>
  
            Without this flag you would have to write the cond/rule
            three times.
          </li>
        </ul>
  
        <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>
  
  <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>
  </example>
  
          <p>Interpretation: If you use Netscape Navigator as your
          browser (which identifies itself as 'Mozilla'), then you
          get the max homepage, which includes Frames, <em>etc.</em>
          If you use the Lynx browser (which is Terminal-based), then
          you get the min homepage, which contains no images, no
          tables, <em>etc.</em> If you use any other browser you get
          the standard homepage.</p>
  
  </usage>
  
  </directivesynopsis>
  
  <directivesynopsis>
  <name>RewriteRule</name>
  <description>Defines rules for the rewriting engine</description>
  <syntax>RewriteRule
        <em>Pattern</em> <em>Substitution</em></syntax>
  <default>None</default>
  <contextlist><context>server config</context><context>virtual host</context>
  <context>directory</context><context>.htaccess</context></contextlist>
  <override>FileInfo</override>
  
  <usage>
        <p>The <directive>RewriteRule</directive> directive is the real
        rewriting workhorse. The directive can occur more than once.
        Each directive then defines one single rewriting rule. The
        <strong>definition order</strong> of these rules is
        <strong>important</strong>, because this order is used when
        applying the rules at run-time.</p>
  
        <p><a id="patterns" name="patterns"><em>Pattern</em></a> can
        be (for Apache 1.1.x a System V8 and for Apache 1.2.x and
        later a POSIX) <a id="regexp" name="regexp">regular
        expression</a> which gets applied to the current URL. Here
        ``current'' means the value of the URL when this rule gets
        applied. This may not be the originally requested URL,
        because any number of rules may already have matched and made
        alterations to it.</p>
  
        <p>Some hints about the syntax of regular expressions:</p>
  
        <table bgcolor="#F0F0F0" cellspacing="0" cellpadding="5">
          <tr>
            <td valign="TOP">
  <pre>
  <strong>Text:</strong>
    <strong><code>.</code></strong>           Any single character
    <strong><code>[</code></strong>chars<strong><code>]</code></strong>     Character class: One  of chars
    <strong><code>[^</code></strong>chars<strong><code>]</code></strong>    Character class: None of chars
    text1<strong><code>|</code></strong>text2 Alternative: text1 or text2
  
  <strong>Quantifiers:</strong>
    <strong><code>?</code></strong>           0 or 1 of the preceding text
    <strong><code>*</code></strong>           0 or N of the preceding text (N &gt; 0)
    <strong><code>+</code></strong>           1 or N of the preceding text (N &gt; 1)
  
  <strong>Grouping:</strong>
    <strong><code>(</code></strong>text<strong><code>)</code></strong>      Grouping of text
                (either to set the borders of an alternative or
                for making backreferences where the <strong>N</strong>th group can 
                be used on the RHS of a RewriteRule with <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 that particular char
                (for instance to specify the chars "<code>.[]()</code>" <em>etc.</em>)
  </pre>
            </td>
          </tr>
        </table>
  
        <p>For more information about regular expressions either have
        a look at your local regex(3) manpage or its
        <code>src/regex/regex.3</code> copy in the Apache 1.3
        distribution. If you are interested in more detailed
        information about regular expressions and their variants
        (POSIX regex, Perl regex, <em>etc.</em>) have a look at the
        following dedicated book on this topic:</p>
  
        <blockquote>
          <em>Mastering Regular Expressions</em><br />
           Jeffrey E.F. Friedl<br />
           Nutshell Handbook Series<br />
           O'Reilly &amp; Associates, Inc. 1997<br />
           ISBN 1-56592-257-3<br />
        </blockquote>
  
        <p>Additionally in mod_rewrite the NOT character
        ('<code>!</code>') is a possible pattern prefix. This gives
        you the ability 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>
  
  <note><title>Notice</title>
  When using the NOT character
            to negate a pattern you cannot have grouped wildcard
            parts in the pattern. This is impossible because when the
            pattern does NOT match, there are no contents for the
            groups. In consequence, if negated patterns are used, you
            cannot use <code>$N</code> in the substitution
            string!
  </note>
  
        <p><a id="rhs" name="rhs"><em>Substitution</em></a> of a
        rewriting rule is the string which is substituted for (or
        replaces) the original URL for which <em>Pattern</em>
        matched. Beside plain text you can use</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>${mapname:key|default}</code>)</li>
        </ol>
        Back-references are <code>$</code><strong>N</strong>
        (<strong>N</strong>=0..9) identifiers 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 of
        the above list. 
  
        <p>As already mentioned above, all the rewriting rules are
        applied to the <em>Substitution</em> (in the order of
        definition in the config file). The URL is <strong>completely
        replaced</strong> by the <em>Substitution</em> and the
        rewriting process goes on until there are no more rules
        unless explicitly terminated by a
        <code><strong>L</strong></code> flag - see below.</p>
  
        <p>There is a special substitution string named
        '<code>-</code>' which means: <strong>NO
        substitution</strong>! Sounds silly? No, it is useful to
        provide rewriting rules which <strong>only</strong> match
        some URLs but do no substitution, <em>e.g.</em>, in
        conjunction with the <strong>C</strong> (chain) flag to be
        able to have more than one pattern to be applied before a
        substitution occurs.</p>
  
        <p>One more note: You can even create URLs in the
        substitution string containing a query string part. Just use
        a question mark inside the substitution string to indicate
        that the following stuff should be re-injected into the
        QUERY_STRING. When you want to erase an existing query
        string, end the substitution string with just the question
        mark.</p>
  
  <note><title>Note</title>
  There is a special feature:
            When you prefix a substitution field with
            <code>http://</code><em>thishost</em>[<em>:thisport</em>]
            then <strong>mod_rewrite</strong> automatically strips it
            out. This auto-reduction on implicit external redirect
            URLs is a useful and important feature when used in
            combination with a mapping-function which generates the
            hostname part. Have a look at the first example in the
            example section below to understand this.
  </note>
  
  <note><title>Remember</title>
   An unconditional external
            redirect to your own server will not work with the prefix
            <code>http://thishost</code> because of this feature. To
            achieve such a self-redirect, you have to use the
            <strong>R</strong>-flag (see below).
  </note>
  
        <p>Additionally you can set special flags for
        <em>Substitution</em> by appending</p>
  
        <blockquote>
          <strong><code>[</code><em>flags</em><code>]</code></strong>
        </blockquote>
        as the third argument to the <code>RewriteRule</code>
        directive. <em>Flags</em> is a comma-separated list of the
        following flags: 
  
        <ul>
          <li>
            '<strong><code>redirect|R</code>
            [=<em>code</em>]</strong>' (force <a id="redirect"
            name="redirect"><strong>r</strong>edirect</a>)<br />
             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) is used. If you want to use other response
            codes in the range 300-400 just specify them as a number
            or use one of the following symbolic names:
            <code>temp</code> (default), <code>permanent</code>,
            <code>seeother</code>. Use it for rules which should
            canonicalize the URL and give it back to the client,
            <em>e.g.</em>, translate ``<code>/~</code>'' into
            ``<code>/u/</code>'' or always append a slash to
            <code>/u/</code><em>user</em>, etc.<br />
             
  
            <p><strong>Note:</strong> When you use this flag, make
            sure that the substitution field is a valid URL! If not,
            you are redirecting to an invalid location! And remember
            that this flag itself only prefixes the URL with
            <code>http://thishost[:thisport]/</code>, rewriting
            continues. Usually you also want to stop and do the
            redirection immediately. To stop the rewriting you also
            have to provide the 'L' flag.</p>
          </li>
  
          <li>'<strong><code>forbidden|F</code></strong>' (force URL
          to be <strong>f</strong>orbidden)<br />
           This forces the current URL to be forbidden,
          <em>i.e.</em>, it immediately sends back a HTTP response of
          403 (FORBIDDEN). Use this flag in conjunction with
          appropriate RewriteConds to conditionally block some
          URLs.</li>
  
          <li>'<strong><code>gone|G</code></strong>' (force URL to be
          <strong>g</strong>one)<br />
           This forces the current URL to be gone, <em>i.e.</em>, it
          immediately sends back a HTTP response of 410 (GONE). Use
          this flag to mark pages which no longer exist as gone.</li>
  
          <li>
            '<strong><code>proxy|P</code></strong>' (force
            <strong>p</strong>roxy)<br />
             This flag forces the substitution part to be internally
            forced as a proxy request and immediately (<em>i.e.</em>,
            rewriting rule processing stops here) put through the <a
            href="mod_proxy.html">proxy module</a>. You have to make
            sure that the substitution string is a valid URI
            (<em>e.g.</em>, typically starting with
            <code>http://</code><em>hostname</em>) which can be
            handled by the Apache proxy module. If not you 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 some remote stuff into the namespace of the local
            server. 
  
            <p>Notice: To use this functionality make sure you have
            the proxy module compiled into your Apache server
            program. If you don't know please check whether
            <code>mod_proxy.c</code> is part of the ``<code>httpd
            -l</code>'' output. If yes, this functionality is
            available to mod_rewrite. If not, then you first have to
            rebuild the ``<code>httpd</code>'' program with mod_proxy
            enabled.</p>
          </li>
  
          <li>'<strong><code>last|L</code></strong>'
          (<strong>l</strong>ast rule)<br />
           Stop the rewriting process here and don't apply any more
          rewriting rules. This corresponds to the Perl
          <code>last</code> command or the <code>break</code> command
          from the C language. Use this flag to prevent the currently
          rewritten URL from being rewritten further by following
          rules. For example, use it to rewrite the root-path URL
          ('<code>/</code>') to a real one, <em>e.g.</em>,
          '<code>/e/www/</code>'.</li>
  
          <li>'<strong><code>next|N</code></strong>'
          (<strong>n</strong>ext round)<br />
           Re-run the rewriting process (starting again with the
          first rewriting rule). Here the URL to match is again not
          the original URL but the URL from the last rewriting rule.
          This corresponds to the Perl <code>next</code> command or
          the <code>continue</code> command from the C language. Use
          this flag to restart the rewriting process, <em>i.e.</em>,
          to immediately go to the top of the loop.<br />
           <strong>But be careful not to create an infinite
          loop!</strong></li>
  
          <li>'<strong><code>chain|C</code></strong>'
          (<strong>c</strong>hained with next rule)<br />
           This flag chains the current rule with the next rule
          (which itself can be chained with the following rule,
          <em>etc.</em>). This has the following effect: if a rule
          matches, then processing continues as usual, <em>i.e.</em>,
          the flag has no effect. If the rule does
          <strong>not</strong> match, then all following chained
          rules are skipped. For instance, use it 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 to occur!).</li>
  
          <li>
          '<strong><code>type|T</code></strong>=<em>MIME-type</em>'
          (force MIME <strong>t</strong>ype)<br />
           Force the MIME-type of the target file to be
          <em>MIME-type</em>. For instance, this can be used to
          simulate the <code>mod_alias</code> directive
          <code>ScriptAlias</code> which internally forces all files
          inside the mapped directory to have a MIME type of
          ``<code>application/x-httpd-cgi</code>''.</li>
  
          <li>
            '<strong><code>nosubreq|NS</code></strong>' (used only if
            <strong>n</strong>o internal
            <strong>s</strong>ub-request)<br />
             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>mod_include</code> tries to find out
            information about possible directory default files
            (<code>index.xxx</code>). On sub-requests it is not
            always useful and even sometimes causes a failure to if
            the complete set of rules are applied. Use this flag to
            exclude some rules.<br />
             
  
            <p>Use the following rule for your decision: whenever you
            prefix some URLs with CGI-scripts to force them to be
            processed by the CGI-script, the chance is high that you
            will run into problems (or even overhead) on
            sub-requests. In these cases, use this flag.</p>
          </li>
  
          <li>'<strong><code>nocase|NC</code></strong>'
          (<strong>n</strong>o <strong>c</strong>ase)<br />
           This makes the <em>Pattern</em> case-insensitive,
          <em>i.e.</em>, there is no difference between 'A-Z' and
          'a-z' when <em>Pattern</em> is matched against the current
          URL.</li>
  
          <li>'<strong><code>qsappend|QSA</code></strong>'
          (<strong>q</strong>uery <strong>s</strong>tring
          <strong>a</strong>ppend)<br />
           This flag forces the rewriting engine to append a query
          string part in the substitution string to the existing one
          instead of replacing it. Use this when you want to add more
          data to the query string via a rewrite rule.</li>
  
          <li>
            '<strong><code>noescape|NE</code></strong>'
            (<strong>n</strong>o URI <strong>e</strong>scaping of
            output)<br />
             This flag keeps 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 being done. This allows percent symbols to appear in
            the output, as in 
  <example>
      RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]
  </example>
  
            which would turn '<code>/foo/zed</code>' into a safe
            request for '<code>/bar?arg=P1=zed</code>'. 
          </li>
  
          <li>
            '<strong><code>passthrough|PT</code></strong>'
            (<strong>p</strong>ass <strong>t</strong>hrough to next
            handler)<br />
             This flag forces the rewriting 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
            be able to post-process the output of
            <code>RewriteRule</code> directives by
            <code>Alias</code>, <code>ScriptAlias</code>,
            <code>Redirect</code>, <em>etc.</em> directives from
            other URI-to-filename translators. A trivial example to
            show the semantics: If you want to rewrite
            <code>/abc</code> to <code>/def</code> via the rewriting
            engine of <code>mod_rewrite</code> and then
            <code>/def</code> to <code>/ghi</code> with
            <code>mod_alias</code>: 
  <example>
      RewriteRule ^/abc(.*)  /def$1 [PT]<br />
      Alias       /def       /ghi
  </example>
            If you omit the <code>PT</code> flag then
            <code>mod_rewrite</code> will do its job fine,
            <em>i.e.</em>, it rewrites <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> comes and tries to do a
            URI-to-filename transition which will not work. 
  
            <p>Note: <strong>You have to use this flag if you want to
            intermix directives of different modules which contain
            URL-to-filename translators</strong>. The typical example
            is the use of <code>mod_alias</code> and
            <code>mod_rewrite</code>..</p>
  
  <note><title>For Apache hackers</title>
                 If the current Apache API had a filename-to-filename
                hook additionally to the URI-to-filename hook then we
                wouldn't need this flag! But without such a hook this
                flag is the only solution. The Apache Group has
                discussed this problem and will add such a hook in
                Apache version 2.0.
  </note>
          </li>
  
          <li>'<strong><code>skip|S</code></strong>=<em>num</em>'
          (<strong>s</strong>kip next rule(s))<br />
           This flag forces the rewriting engine to skip the next
          <em>num</em> rules in sequence when 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!)</li>
  
          <li>
          '<strong><code>env|E=</code></strong><em>VAR</em>:<em>VAL</em>'
          (set <strong>e</strong>nvironment variable)<br />
           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>$N</code> and
          <code>%N</code> which will be expanded. You can use this
          flag more than once to set more than one variable. The
          variables can be later dereferenced in many situations, but
          usually from within XSSI (via <code>&lt;!--#echo
          var="VAR"--&gt;</code>) or CGI (<em>e.g.</em>
          <code>$ENV{'VAR'}</code>). Additionally you can dereference
          it in a following RewriteCond pattern via
          <code>%{ENV:VAR}</code>. Use this to strip but remember
          information from URLs.</li>
        </ul>
  
  <note><title>Note</title> Never forget that <em>Pattern</em> is
  applied to a complete URL in per-server configuration
  files. <strong>But in per-directory configuration 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.</strong> This feature is essential for many sorts of rewriting,
  because without this prefix stripping you have to match the parent
  directory which is not always possible.
  
              <p>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 flag
              <strong>P</strong> is used!) is forced!</p>
  </note>
  
  <note><title>Note</title>
   To enable the rewriting engine
            for per-directory configuration files you need to set
            ``<code>RewriteEngine On</code>'' in these files
            <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 rewriting engine. This restriction is
            needed for security reasons.
  </note>
  
        <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>
  
        <table bgcolor="#F0F0F0" cellspacing="0" cellpadding="5">
          <tr>
            <td>
  <pre>
  <strong>Given Rule</strong>                                      <strong>Resulting Substitution</strong>
  ----------------------------------------------  ----------------------------------
  ^/somepath(.*) otherpath$1                      not supported, because invalid!
  
  ^/somepath(.*) otherpath$1  [R]                 not supported, because invalid!
  
  ^/somepath(.*) otherpath$1  [P]                 not supported, because invalid!
  ----------------------------------------------  ----------------------------------
  ^/somepath(.*) /otherpath$1                     /otherpath/pathinfo
  
  ^/somepath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                  via external redirection
  
  ^/somepath(.*) /otherpath$1 [P]                 not supported, because silly!
  ----------------------------------------------  ----------------------------------
  ^/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]  not supported, because silly!
  ----------------------------------------------  ----------------------------------
  ^/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>
            </td>
          </tr>
        </table>
  
        <p><strong>Inside per-directory configuration for
        <code>/somepath</code><br />
         (<em>i.e.</em>, file <code>.htaccess</code> in dir
        <code>/physical/path/to/somepath</code> containing
        <code>RewriteBase /somepath</code>)<br />
         for request ``<code>GET
        /somepath/localpath/pathinfo</code>'':</strong><br /> 
       </p>
  
        <table bgcolor="#F0F0F0" cellspacing="0" cellpadding="5">
          <tr>
            <td>
  <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]                 not supported, because silly!
  ----------------------------------------------  ----------------------------------
  ^localpath(.*) /otherpath$1                     /otherpath/pathinfo
  
  ^localpath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                  via external redirection
  
  ^localpath(.*) /otherpath$1 [P]                 not supported, because silly!
  ----------------------------------------------  ----------------------------------
  ^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]  not supported, because silly!
  ----------------------------------------------  ----------------------------------
  ^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>
            </td>
          </tr>
        </table>
  
        <p><strong>Example:</strong></p>
  
        <p>We want to rewrite URLs of the form </p>
  
          <blockquote>
            <code>/</code> <em>Language</em> <code>/~</code>
            <em>Realname</em> <code>/.../</code> <em>File</em>
          </blockquote>
          into 
  
          <blockquote>
            <code>/u/</code> <em>Username</em> <code>/.../</code>
            <em>File</em> <code>.</code> <em>Language</em>
          </blockquote>
  
          <p>We take the rewrite mapfile from above and save it under
          <code>/path/to/file/map.txt</code>. Then we only have to
          add the following lines to the Apache server configuration
          file:</p>
  
  <example>
  <pre>
  RewriteLog   /path/to/file/rewrite.log
  RewriteMap   real-to-user               txt:/path/to/file/map.txt
  RewriteRule  ^/([^/]+)/~([^/]+)/(.*)$   /u/${real-to-user:$2|nobody}/$3.$1
  </pre>
  </example>
  
  </usage>
  </directivesynopsis>
  
  </modulesynopsis>
  
  
  
  

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