mod_rewrite.html.en

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      information about regular expressions and their variants
      (POSIX regex etc.) the following book is dedicated to this topic:</p>

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

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

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

      <p>The <a id="rhs" name="rhs"><em>substitution</em></a> of a
      rewrite rule is the string which is substituted for (or
      replaces) the original URL which <em>Pattern</em>
      matched. In addition to plain text, it can include</p>

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

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

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

        <li><a href="#mapfunc">mapping-function</a> calls
        (<code>${mapname:key|default}</code>)</li>
      </ol>
      <p>Back-references are identifiers of the form 
	      <code>$</code><strong>N</strong>
      (<strong>N</strong>=0..9), which will be replaced
      by the contents of the <strong>N</strong>th group of the
      matched <em>Pattern</em>. The server-variables are the same
      as for the <em>TestString</em> of a <code>RewriteCond</code>
      directive. The mapping-functions come from the
      <code>RewriteMap</code> directive and are explained there.
      These three types of variables are expanded in the order above.</p>

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

      <p>There is a special substitution string named
      '<code>-</code>' which means: <strong>NO
      substitution</strong>! This is useful in providing
      rewriting rules which <strong>only</strong> match
      URLs but do not substitute anything for them. It is commonly used 
      in conjunction with the <strong>C</strong> (chain) flag, in order 
      to apply more than one pattern before substitution occurs.</p>


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

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

        <li>
		'<strong><code>cookie|CO=</code></strong><em>NAME</em>:<em>VAL</em>:<em>domain</em>[:<em>lifetime</em>[:<em>path</em>]]'
        (set <strong>co</strong>okie)<br />
        This sets a cookie in the client's browser.  The cookie's name
        is specified by <em>NAME</em> and the value is
        <em>VAL</em>. The <em>domain</em> field is the domain of the
        cookie, such as '.apache.org', the optional <em>lifetime</em>
	is the lifetime of the cookie in minutes, and the optional 
	<em>path</em> is the path of the cookie</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>$N</code> and
        <code>%N</code>) which will be expanded. You can use this
        flag more than once, to set more than one variable. The
        variables can later be dereferenced in many situations, most commonly
	from within XSSI (via <code>&lt;!--#echo
        var="VAR"--&gt;</code>) or CGI (<code>$ENV{'VAR'}</code>). 
	You can also dereference the variable in a later RewriteCond pattern, using
        <code>%{ENV:VAR}</code>. Use this to strip 
        information from URLs, while maintaining a record of that information.</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 - 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 - 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>handler|H</code></strong>=<em>Content-handler</em>'
        (force Content <strong>h</strong>andler)<br />
         Force the Content-handler of the target file to be
        <em>Content-handler</em>. For instance, this can be used to
        simulate the <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> directive
	<code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code>, 
	which internally forces all files
        inside the mapped directory to have a handler of
        ``<code>cgi-script</code>''.</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
        rewrite rules. This corresponds to the Perl
        <code>last</code> command or the <code>break</code> command
        in C. Use this flag to prevent the currently
        rewritten URL from being rewritten further by following
        rules. 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). This time, the URL to match is no longer
        the original URL, but rather the URL returned by the last rewriting rule.
        This corresponds to the Perl <code>next</code> command or
        the <code>continue</code> command in C. Use
        this flag to restart the rewriting process -
        to immediately go to the top of the loop.<br />
         <strong>Be careful not to create an infinite
        loop!</strong></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,
        ignoring difference between 'A-Z' and
        'a-z' when <em>Pattern</em> is matched against the current
        URL.</li>

        <li>
          '<strong><code>noescape|NE</code></strong>'
          (<strong>n</strong>o URI <strong>e</strong>scaping of
          output)<br />
          This flag prevents mod_rewrite from applying the usual URI
          escaping rules to the result of a rewrite. Ordinarily,
          special characters (such as '%', '$', ';', and so on)
          will be escaped into their hexcode equivalents ('%25',
          '%24', and '%3B', respectively); this flag prevents this
          from happening. This allows percent symbols to appear in
          the output, as in 
<div class="example"><p><code>
    RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]
</code></p></div>
          which would turn '<code>/foo/zed</code>' into a safe
          request for '<code>/bar?arg=P1=zed</code>'. 
        </li>

        <li>
          '<strong><code>nosubreq|NS</code></strong>'
          (<strong>n</strong>ot for internal
          <strong>s</strong>ub-requests)<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 class="module"><a href="../mod/mod_include.html">mod_include</a></code> tries to find out
          information about possible directory default files
          (<code>index.xxx</code> files). On sub-requests it is not
          always useful, and can even cause errors, if
          the complete set of rules are applied. Use this flag to
          exclude some rules.<br />
          To decide whether or not to use this rule: if you
          prefix URLs with CGI-scripts, to force them to be
	  processed by the CGI-script, it's likely that you 
          will run into problems (or significant overhead) on
          sub-requests. In these cases, use this flag.
        </li>

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

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

        <li>
          '<strong><code>passthrough|PT</code></strong>'
          (<strong>p</strong>ass <strong>t</strong>hrough to next
          handler)<br />
           This flag forces the rewrite engine to set the
          <code>uri</code> field of the internal
          <code>request_rec</code> structure to the value of the
          <code>filename</code> field. This flag is just a hack to
          enable post-processing of the output of
          <code>RewriteRule</code> directives, using
          <code>Alias</code>, <code>ScriptAlias</code>,
          <code>Redirect</code>, and other directives from
          various URI-to-filename translators. For example, to rewrite
          <code>/abc</code> to <code>/def</code> using
          <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>, and then
          <code>/def</code> to <code>/ghi</code> using
          <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code>: 
<div class="example"><p><code>
    RewriteRule ^/abc(.*)  /def$1 [PT]<br />
    Alias       /def       /ghi
</code></p></div>
          If you omit the <code>PT</code> flag,
          <code>mod_rewrite</code> will rewrite 
	  <code>uri=/abc/...</code> to
          <code>filename=/def/...</code> as a full API-compliant
          URI-to-filename translator should do. Then
          <code>mod_alias</code> will try to do a
          URI-to-filename transition, which will fail. 

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