Backport some changes from 2.4 to 2.2, as they are also valid here.

    </dd>

  </dl>

  <p>See the <directive module="mod_rewrite">RewriteMap</directive>

  documentation for more discussion of the syntax of this directive.</p>

</section>

<section id="on-the-fly-content">

    <dd>

      This is done via the following ruleset:

<example>

# This example is valid in per-directory context only<br />

RewriteCond %{REQUEST_FILENAME}   <strong>!-s</strong><br />

RewriteRule ^page\.<strong>html</strong>$          page.<strong>cgi</strong>   [T=application/x-httpd-cgi,L]

</example>

      <p>Here a request for <code>page.html</code> leads to an

      internal run of a corresponding <code>page.cgi</code> if

      <code>page.html</code> is missing or has filesize

      null. The trick here is that <code>page.cgi</code> is a

      CGI script which (additionally to its <code>STDOUT</code>)

      writes its output to the file <code>page.html</code>.

      Once it has completed, the server sends out

      <code>page.html</code>. When the webmaster wants to force

      a refresh of the contents, he just removes

      <code>page.html</code> (typically from <code>cron</code>).</p>

<highlight language="config">

# This example is valid in per-directory context only

RewriteCond %{REQUEST_URI}   !-U

RewriteRule ^(.+)\.html$          /regenerate_page.cgi   [PT,L]

</highlight>

    <p>The <code>-U</code> operator determines whether the test string

    (in this case, <code>REQUEST_URI</code>) is a valid URL. It does

    this via a subrequest. In the event that this subrequest fails -

    that is, the requested resource doesn't exist - this rule invokes

    the CGI program <code>/regenerate_page.cgi</code>, which generates

    the requested resource and saves it into the document directory, so

    that the next time it is requested, a static copy can be served.</p>

    <p>In this way, documents that are infrequently updated can be served in

    static form. if documents need to be refreshed, they can be deleted

    from the document directory, and they will then be regenerated the

    next time they are requested.</p>

    </dd>

  </dl>

<seealso><a href="vhosts.html">Virtual hosts</a></seealso>

<seealso><a href="proxy.html">Proxying</a></seealso>

<seealso><a href="rewritemap.html">Using RewriteMap</a></seealso>

<seealso><a href="advanced.html">Advanced techniques and tricks</a></seealso>

<seealso><a href="advanced.html">Advanced techniques</a></seealso>

<seealso><a href="avoid.html">When not to use mod_rewrite</a></seealso>

<section id="introduction"><title>Introduction</title>

Using the B flag, non-alphanumeric characters in backreferences

will be escaped. For example, consider the rule:</p>

<example>

RewriteRule ^(/.*)$ /index.php?show=$1

</example>

<highlight language="config">RewriteRule ^search/(.*)$ /search.php?term=$1</highlight>

<p>Given a search term of 'x &amp; y/z', a browser will encode it as

'x%20%26%20y%2Fz', making the request 'search/x%20%26%20y%2Fz'. Without the B

flag, this rewrite rule will map to 'search.php?term=x & y/z', which

isn't a valid URL, and so would be encoded as

<code>search.php?term=x%20&amp;y%2Fz=</code>, which is not what was intended.</p>

<p>This will map <code>/C++</code> to

<code>/index.php?show=/C++</code>. But it will also map

<code>/C%2b%2b</code> to <code>/index.php?show=/C++</code>, because

the <code>%2b</code> has been unescaped.  With the B flag, it will

instead map to <code>/index.php?show=/C%2b%2b</code>.</p>

<p>With the B flag set on this same rule, the parameters are re-encoded

before being passed on to the output URL, resulting in a correct mapping to

<code>/search.php?term=x%20%26%20y%2Fz</code>.</p>

<p>Note that you may also need to set <directive

module="core">AllowEncodedSlashes</directive> to <code>On</code> to get this

particular example to work, as httpd does not allow encoded slashes in URLs, and

returns a 404 if it sees one.</p>

<p>This escaping is particularly necessary in a proxy situation,

when the backend may break if presented with an unescaped URL.</p>

<p>You may optionally also set the following values:</p>

<dl>

<dt>Lifetime</dt>

<dd>The time for which the cookie will persist, in minutes.</dd>

<dd>A value of 0 indicates that the cookie will persist only for the

</section>

<section id="flag_s"><title>S|skip</title>

<p>The [S] flag is used to skip rules that you don't want to run. This

can be thought of as a <code>goto</code> statement in your rewrite

ruleset. In the following example, we only want to run the <directive

module="mod_rewrite">RewriteRule</directive> if the requested URI

doesn't correspond with an actual file.</p>

<example>

# Is the request for a non-existent file?<br />

RewriteCond %{REQUEST_FILENAME} !-f<br />

RewriteCond %{REQUEST_FILENAME} !-d<br />

# If so, skip these two RewriteRules<br />

RewriteRule .? - [S=2]<br />

<br />

RewriteRule (.*\.gif) images.php?$1<br />

<p>The [S] flag is used to skip rules that you don't want to run. The 

syntax of the skip flag is [S=<em>N</em>], where <em>N</em> signifies 

the number of rules to skip. This can be thought of as a <code>goto</code> 

statement in your rewrite ruleset. In the following example, we only want 

to run the <directive module="mod_rewrite">RewriteRule</directive> if the 

requested URI doesn't correspond with an actual file.</p>

<highlight language="config">

# Is the request for a non-existent file?

RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond %{REQUEST_FILENAME} !-d

# If so, skip these two RewriteRules

RewriteRule .? - [S=2]

RewriteRule (.*\.gif) images.php?$1

RewriteRule (.*\.html) docs.php?$1

</example>

</highlight>

<p>This technique is useful because a <directive

module="mod_rewrite">RewriteCond</directive> only applies to the

<seealso><a href="vhosts.html">Virtual hosts</a></seealso>

<seealso><a href="proxy.html">Proxying</a></seealso>

<seealso><a href="rewritemap.html">Using RewriteMap</a></seealso>

<seealso><a href="advanced.html">Advanced techniques and tricks</a></seealso>

<seealso><a href="advanced.html">Advanced techniques</a></seealso>

<seealso><a href="avoid.html">When not to use mod_rewrite</a></seealso>

<section id="introduction"><title>Introduction</title>

      <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 1 shows to which locations the back-references are

      transferred for expansion as well as illustrating the flow of the

      RewriteRule, RewriteCond matching.</p>

      the strings <em>Substitution</em> and <em>TestString</em> as 

      outlined in the following chapters. Figure 1 shows to which 

      locations the back-references are transferred for expansion as 

      well as illustrating the flow of the RewriteRule, RewriteCond 

      matching. In the next chapters, we will be exploring how to use 

      these back-references, so do not fret if it seems a bit alien 

      to you at first.

      </p>

<p class="figure">

      <img src="../images/rewrite_rule_flow.png" 

      <img src="../images/rewrite_backreferences.png"

      alt="Flow of RewriteRule and RewriteCond matching" /><br />

      <dfn>Figure 1:</dfn> The back-reference flow through a rule.

      <dfn>Figure 1:</dfn> The back-reference flow through a rule.<br />

      In this example, a request for <code>/test/1234</code> would be transformed into <code>/admin.foo?page=test&amp;id=1234&amp;host=admin.example.com</code>.

</p>

</section>

<li><var>[flags]</var>: options affecting the rewritten request.</li>

</ol>

<p>The <var>Pattern</var> is always a <a href="#regex">regular

expression</a> matched against the URL-Path of the incoming request

(the part after the hostname but before any question mark indicating

the beginning of a query string).</p>

<p>The <var>Pattern</var> is a <a href="#regex">regular expression</a>. 

It is initially (for the first rewrite rule or until a substitution occurs) 

matched against the URL-path of the incoming request (the part after the 

hostname but before any question mark indicating the beginning of a query 

string) or, in per-directory context, against the request's path relative 

to the directory for which the rule is defined. Once a substitution has 

occured, the rules that follow are matched against the substituted

value.

</p>

<p class="figure">

      <img src="../images/syntax_rewriterule.png"