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149dc5253eef0f0289fad126961eec1c9e1407a2rbowen<title>Advanced Techniques with mod_rewrite - Apache HTTP Server</title>
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af33a4994ae2ff15bc67d19ff1a7feb906745bf8rbowen<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
b630661b71a5495a95831a05a6a2299fb1c7c771rbowen<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div>
3f08db06526d6901aa08c110b5bc7dde6bc39905nd<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>Advanced Techniques with mod_rewrite</h1>
b6e6d2139d50d64fc4bbd01c4f07d7a4accfec8cnd<p><span>Available Languages: </span><a href="/en/rewrite/advanced.html" title="English"> en </a></p>
9a58dc6a2b26ec128b1270cf48810e705f1a90dbsf<p>This document supplements the <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code>
9a58dc6a2b26ec128b1270cf48810e705f1a90dbsf<a href="/mod/mod_rewrite.html">reference documentation</a>. It provides
53abc235688d883cfa15cdfec354ba03128f357arbowena few advanced techniques using mod_rewrite.</p>
b630661b71a5495a95831a05a6a2299fb1c7c771rbowen<div class="warning">Note that many of these examples won't work unchanged in your
b630661b71a5495a95831a05a6a2299fb1c7c771rbowenparticular server configuration, so it's important that you understand
b630661b71a5495a95831a05a6a2299fb1c7c771rbowenthem, rather than merely cutting and pasting the examples into your
b630661b71a5495a95831a05a6a2299fb1c7c771rbowenconfiguration.</div>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#sharding">URL-based sharding accross multiple backends</a></li>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen<li><img alt="" src="/images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<li><img alt="" src="/images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen<li><img alt="" src="/images/down.gif" /> <a href="#autorefresh">Document With Autorefresh</a></li>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<li><img alt="" src="/images/down.gif" /> <a href="#structuredhomedirs">Structured Userdirs</a></li>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<li><img alt="" src="/images/down.gif" /> <a href="#redirectanchors">Redirecting Anchors</a></li>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<li><img alt="" src="/images/down.gif" /> <a href="#time-dependent">Time-Dependent Rewriting</a></li>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<li><img alt="" src="/images/down.gif" /> <a href="#setenvvars">Set Environment Variables Based On URL Parts</a></li>
3cfb051391f3d6aa28a25ca3feb81e841242f9d5humbedooh</ul><h3>See also</h3><ul class="seealso"><li><a href="/mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="access.html">Controlling access</a></li><li><a href="vhosts.html">Virtual hosts</a></li><li><a href="proxy.html">Proxying</a></li><li><a href="rewritemap.html">Using RewriteMap</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li></ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen<h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2>
9a58dc6a2b26ec128b1270cf48810e705f1a90dbsf <p>A common technique for distributing the burden of
9a58dc6a2b26ec128b1270cf48810e705f1a90dbsf server load or storage space is called "sharding".
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen When using this method, a front-end server will use the
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen url to consistently "shard" users or objects to separate
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen backend servers.</p>
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen <p>A mapping is maintained, from users to target servers, in
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen external map files. They look like:</p>
353e838f5716b394f2f9bf38549e1550a5e73570rbowenuser1 physical_host_of_user1<br />
353e838f5716b394f2f9bf38549e1550a5e73570rbowenuser2 physical_host_of_user2<br />
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen <p>We put this into a <code>map.users-to-hosts</code> file. The
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen aim is to map;</p>
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen <p>thus every URL path need not be valid on every backend physical
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen host. The following ruleset does this for us with the help of the map
1525d3506d73644ae695624f16b15cc73cc1c7acrbowen files assuming that server0 is a default server which will be used if
c2a88a7ef740c408aba42af38ddfb9ab8a7398d9nd a user has no entry in the map:</p>
488228a03efe42d9f0b03334a4753ce79a6dc5cchumbedoohRewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
4aa603e6448b99f9371397d439795c91a93637eandRewriteRule ^/u/([^/]+)/?(.*) http://${users-to-hosts:$1|server0}/u/$1/$2</pre>
53abc235688d883cfa15cdfec354ba03128f357arbowen <p>See the <code class="directive"><a href="/mod/mod_rewrite.html#rewritemap">RewriteMap</a></code>
53abc235688d883cfa15cdfec354ba03128f357arbowen documentation for more discussion of the syntax of this directive.</p>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen <p>We wish to dynamically generate content, but store it
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen statically once it is generated. This rule will check for the
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen existence of the static file, and if it's not there, generate
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen it. The static files can be removed periodically, if desired (say,
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen via cron) and will be regenerated on demand.</p>
b0306ceedec510a7b4ebe3a1b70c366bf5f2727crbowen This is done via the following ruleset:
4aa603e6448b99f9371397d439795c91a93637eand<pre class="prettyprint lang-config"># This example is valid in per-directory context only
04a56f9892b2481f1d10336848cc3a140780cf20humbedoohRewriteCond %{REQUEST_URI} !-U
4aa603e6448b99f9371397d439795c91a93637eandRewriteRule ^(.+)\.html$ /regenerate_page.cgi [PT,L]</pre>
53abc235688d883cfa15cdfec354ba03128f357arbowen <p>The <code>-U</code> operator determines whether the test string
53abc235688d883cfa15cdfec354ba03128f357arbowen (in this case, <code>REQUEST_URI</code>) is a valid URL. It does
53abc235688d883cfa15cdfec354ba03128f357arbowen this via a subrequest. In the event that this subrequest fails -
53abc235688d883cfa15cdfec354ba03128f357arbowen that is, the requested resource doesn't exist - this rule invokes
53abc235688d883cfa15cdfec354ba03128f357arbowen the CGI program <code>/regenerate_page.cgi</code>, which generates
53abc235688d883cfa15cdfec354ba03128f357arbowen the requested resource and saves it into the document directory, so
53abc235688d883cfa15cdfec354ba03128f357arbowen that the next time it is requested, a static copy can be served.</p>
53abc235688d883cfa15cdfec354ba03128f357arbowen <p>In this way, documents that are infrequently updated can be served in
53abc235688d883cfa15cdfec354ba03128f357arbowen static form. if documents need to be refreshed, they can be deleted
53abc235688d883cfa15cdfec354ba03128f357arbowen from the document directory, and they will then be regenerated the
53abc235688d883cfa15cdfec354ba03128f357arbowen next time they are requested.</p>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen <p>We wish to randomly distribute load across several servers
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen using mod_rewrite.</p>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen <p>We'll use <code class="directive"><a href="/mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen to accomplish this.</p>
4aa603e6448b99f9371397d439795c91a93637eandRewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]</pre>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<p><code>serverlist.txt</code> will contain a list of the servers:</p>
353e838f5716b394f2f9bf38549e1550a5e73570rbowenservers one.example.com|two.example.com|three.example.com<br />
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<p>If you want one particular server to get more of the load than the
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowenothers, add it more times to the list.</p>
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<p>Apache comes with a load-balancing module -
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowen<code class="module"><a href="/mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
ed84b2ae96180924248fbbc86b68d86ae8d88cb3rbowenfeatureful than anything you can cobble together using mod_rewrite.</p>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen<h2><a name="autorefresh" id="autorefresh">Document With Autorefresh</a></h2>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen <p>Wouldn't it be nice, while creating a complex web page, if
0f6366523dec7face01fcad3eadcc1378e34e663rbowen the web browser would automatically refresh the page every
0f6366523dec7face01fcad3eadcc1378e34e663rbowen time we save a new version from within our editor?
0f6366523dec7face01fcad3eadcc1378e34e663rbowen Impossible?</p>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen <p>No! We just combine the MIME multipart feature, the
0f6366523dec7face01fcad3eadcc1378e34e663rbowen web server NPH feature, and the URL manipulation power of
0f6366523dec7face01fcad3eadcc1378e34e663rbowen <code class="module"><a href="/mod/mod_rewrite.html">mod_rewrite</a></code>. First, we establish a new
0f6366523dec7face01fcad3eadcc1378e34e663rbowen URL feature: Adding just <code>:refresh</code> to any
0f6366523dec7face01fcad3eadcc1378e34e663rbowen URL causes the 'page' to be refreshed every time it is
0f6366523dec7face01fcad3eadcc1378e34e663rbowen updated on the filesystem.</p>
4aa603e6448b99f9371397d439795c91a93637eand<pre class="prettyprint lang-config">RewriteRule ^(/[uge]/[^/]+/?.*):refresh /internal/cgi/apache/nph-refresh?f=$1</pre>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen <p>this leads to the internal invocation of the URL</p>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen/internal/cgi/apache/nph-refresh?f=/u/foo/bar/page.html
0f6366523dec7face01fcad3eadcc1378e34e663rbowen <p>The only missing part is the NPH-CGI script. Although
0f6366523dec7face01fcad3eadcc1378e34e663rbowen one would usually say "left as an exercise to the reader"
0f6366523dec7face01fcad3eadcc1378e34e663rbowen ;-) I will provide this, too.</p>
0f6366523dec7face01fcad3eadcc1378e34e663rbowen## nph-refresh -- NPH/CGI script for auto refreshing pages
0f6366523dec7face01fcad3eadcc1378e34e663rbowen## Copyright (c) 1997 Ralf S. Engelschall, All Rights Reserved.
0f6366523dec7face01fcad3eadcc1378e34e663rbowen# split the QUERY_STRING variable
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh@pairs = split( /&/, $ENV{'QUERY_STRING'} );
0f6366523dec7face01fcad3eadcc1378e34e663rbowenforeach $pair (@pairs) {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh ( $name, $value ) = split( /=/, $pair );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $name = 'QS_' . $name;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh eval "\$$name = \"$value\"";
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh$QS_s = 1 if ( $QS_s eq '' );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh$QS_n = 3600 if ( $QS_n eq '' );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedoohif ( $QS_f eq '' ) {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "<b>ERROR</b>: No file given\n";
ac811ad71a8af43080082a96c032280a05e1a4c3humbedoohif ( !-f $QS_f ) {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "<b>ERROR</b>: File $QS_f not found\n";
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub print_http_headers_multipart_begin {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $bound = "ThisRandomString12345";
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "Content-type: multipart/x-mixed-replace;boundary=$bound\n";
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh &print_http_headers_multipart_next;
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub print_http_headers_multipart_next {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "\n--$bound\n";
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub print_http_headers_multipart_end {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "\n--$bound--\n";
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub displayhtml {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh local ($buffer) = @_;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $len = length($buffer);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print "Content-length: $len\n\n";
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh print $buffer;
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub readfile {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh local ($file) = @_;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh local ( *FP, $size, $buffer, $bytes );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh ( $x, $x, $x, $x, $x, $x, $x, $size ) = stat($file);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $size = sprintf( "%d", $size );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh open( FP, "<$file" );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $bytes = sysread( FP, $buffer, $size );
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh return $buffer;
0f6366523dec7face01fcad3eadcc1378e34e663rbowen$buffer = &readfile($QS_f);
0f6366523dec7face01fcad3eadcc1378e34e663rbowen&print_http_headers_multipart_begin;
0f6366523dec7face01fcad3eadcc1378e34e663rbowen&displayhtml($buffer);
0f6366523dec7face01fcad3eadcc1378e34e663rbowensub mystat {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh local ($file) = $_[0];
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh local ($time);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh ( $x, $x, $x, $x, $x, $x, $x, $x, $x, $mtime ) = stat($file);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh return $mtime;
0f6366523dec7face01fcad3eadcc1378e34e663rbowen$mtimeL = &mystat($QS_f);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh$mtime = $mtime;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedoohfor ( $n = 0 ; $n & lt ; $QS_n ; $n++ ) {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $mtime = &mystat($QS_f);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh if ( $mtime ne $mtimeL ) {
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $mtimeL = $mtime;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $buffer = &readfile($QS_f);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh &print_http_headers_multipart_next;
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh &displayhtml($buffer);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh $mtimeL = &mystat($QS_f);
ac811ad71a8af43080082a96c032280a05e1a4c3humbedooh sleep($QS_s);
0f6366523dec7face01fcad3eadcc1378e34e663rbowen&print_http_headers_multipart_end;
4aa603e6448b99f9371397d439795c91a93637eand##EOF##</pre>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<h2><a name="structuredhomedirs" id="structuredhomedirs">Structured Userdirs</a></h2>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>Some sites with thousands of users use a
43289eb78809cbdec92c7d90433a8852233f0b2brbowen structured homedir layout, <em>i.e.</em> each homedir is in a
43289eb78809cbdec92c7d90433a8852233f0b2brbowen subdirectory which begins (for instance) with the first
43289eb78809cbdec92c7d90433a8852233f0b2brbowen character of the username. So, <code>/~larry/anypath</code>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen is <code>/home/<strong>l</strong>/larry/public_html/anypath</code>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <code>/home/<strong>w</strong>/waldo/public_html/anypath</code>.</p>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>We use the following ruleset to expand the tilde URLs
43289eb78809cbdec92c7d90433a8852233f0b2brbowen into the above layout.</p>
4aa603e6448b99f9371397d439795c91a93637eandRewriteRule ^/~(<strong>([a-z])</strong>[a-z0-9]+)(.*) /home/<strong>$2</strong>/$1/public_html$3</pre>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<h2><a name="redirectanchors" id="redirectanchors">Redirecting Anchors</a></h2>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>By default, redirecting to an HTML anchor doesn't work,
43289eb78809cbdec92c7d90433a8852233f0b2brbowen because mod_rewrite escapes the <code>#</code> character,
43289eb78809cbdec92c7d90433a8852233f0b2brbowen turning it into <code>%23</code>. This, in turn, breaks the
43289eb78809cbdec92c7d90433a8852233f0b2brbowen redirection.</p>
9a58dc6a2b26ec128b1270cf48810e705f1a90dbsf <dd>This technique will of course also work with other
43289eb78809cbdec92c7d90433a8852233f0b2brbowen special characters that mod_rewrite, by default, URL-encodes.</dd>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<h2><a name="time-dependent" id="time-dependent">Time-Dependent Rewriting</a></h2>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>We wish to use mod_rewrite to serve different content based on
43289eb78809cbdec92c7d90433a8852233f0b2brbowen the time of day.</p>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>There are a lot of variables named <code>TIME_xxx</code>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen for rewrite conditions. In conjunction with the special
43289eb78809cbdec92c7d90433a8852233f0b2brbowen lexicographic comparison patterns <code><STRING</code>,
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <code>>STRING</code> and <code>=STRING</code> we can
43289eb78809cbdec92c7d90433a8852233f0b2brbowen do time-dependent redirects:</p>
488228a03efe42d9f0b03334a4753ce79a6dc5cchumbedoohRewriteCond %{TIME_HOUR}%{TIME_MIN} >0700
488228a03efe42d9f0b03334a4753ce79a6dc5cchumbedoohRewriteCond %{TIME_HOUR}%{TIME_MIN} <1900
488228a03efe42d9f0b03334a4753ce79a6dc5cchumbedoohRewriteRule ^foo\.html$ foo.day.html [L]
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>This provides the content of <code>foo.day.html</code>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <code>07:01-18:59</code> and at the remaining time the
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <div class="warning"><code class="module"><a href="/mod/mod_cache.html">mod_cache</a></code>, intermediate proxies
43289eb78809cbdec92c7d90433a8852233f0b2brbowen and browsers may each cache responses and cause the either page to be
43289eb78809cbdec92c7d90433a8852233f0b2brbowen shown outside of the time-window configured.
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <code class="module"><a href="/mod/mod_expires.html">mod_expires</a></code> may be used to control this
43289eb78809cbdec92c7d90433a8852233f0b2brbowen effect. You are, of course, much better off simply serving the
43289eb78809cbdec92c7d90433a8852233f0b2brbowen content dynamically, and customizing it based on the time of day.</div>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen<h2><a name="setenvvars" id="setenvvars">Set Environment Variables Based On URL Parts</a></h2>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>At time, we want to maintain some kind of status when we
43289eb78809cbdec92c7d90433a8852233f0b2brbowen perform a rewrite. For example, you want to make a note that
43289eb78809cbdec92c7d90433a8852233f0b2brbowen you've done that rewrite, so that you can check later to see if a
43289eb78809cbdec92c7d90433a8852233f0b2brbowen request can via that rewrite. One way to do this is by setting an
43289eb78809cbdec92c7d90433a8852233f0b2brbowen environment variable.</p>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>Use the [E] flag to set an environment variable.</p>
4aa603e6448b99f9371397d439795c91a93637eandRewriteRule ^/horse/(.*) /pony/$1 [E=<strong>rewritten:1</strong>]</pre>
43289eb78809cbdec92c7d90433a8852233f0b2brbowen <p>Later in your ruleset you might check for this environment
43289eb78809cbdec92c7d90433a8852233f0b2brbowen variable using a RewriteCond:</p>
4aa603e6448b99f9371397d439795c91a93637eand<pre class="prettyprint lang-config">RewriteCond %{ENV:rewritten} =1</pre>
53abc235688d883cfa15cdfec354ba03128f357arbowen <p>Note that environment variables do not survive an external
53abc235688d883cfa15cdfec354ba03128f357arbowen redirect. You might consider using the [CO] flag to set a
53abc235688d883cfa15cdfec354ba03128f357arbowen cookie.</p>
b6e6d2139d50d64fc4bbd01c4f07d7a4accfec8cnd<p><span>Available Languages: </span><a href="/en/rewrite/advanced.html" title="English"> en </a></p>
ed62c84ee0911cfebbd8da319ac00757b555707chumbedooh</div><div class="top"><a href="#page-header"><img src="/images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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07dc96d063d49299da433f84b5c5681da9bbdf68rbowen<p class="apache">Copyright 2014 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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