<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<!--%hypertext -->
<!-- mod_rewrite.html                                 -->
<!-- Documentation for the mod_rewrite Apache module  -->
<HTML>
<HEAD>
<TITLE>Apache module mod_rewrite</TITLE>
</HEAD>

<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
<BODY
 BGCOLOR="#FFFFFF"
 TEXT="#000000"
 LINK="#0000FF"
 VLINK="#000080"
 ALINK="#FF0000"
>
<BLOCKQUOTE><!-- page indentation -->
<DIV ALIGN="CENTER">
 <IMG SRC="../images/sub.gif" ALT="[APACHE DOCUMENTATION]">
 <H3>
  Apache HTTP Server Version 1.3
 </H3>
</DIV>


<BR>
<H1 ALIGN="CENTER">Module mod_rewrite<BR>URL Rewriting Engine</H1>

This module is contained in the <CODE>mod_rewrite.c</CODE> file, with Apache
1.2 and later. It provides a rule-based rewriting engine to rewrite requested
URLs on the fly. It is not compiled into the server by default. To use
<CODE>mod_rewrite</CODE> you have to enable the following line in the server
build <CODE>Configuration</CODE> file:
<PRE>
    AddModule  modules/standard/mod_rewrite.o
</PRE>

<P>
<HR NOSHADE SIZE=1>

<BR>
<H2>Summary</H2>

<BLOCKQUOTE>
<BLOCKQUOTE>
<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>
</BLOCKQUOTE>

<BLOCKQUOTE>
<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>
</BLOCKQUOTE>
</BLOCKQUOTE>

Welcome to mod_rewrite, the Swiss Army Knife of URL manipulation!

<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>
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 even can 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>
But all this functionality and flexibility has its drawback: complexity. So
don't expect to understand this module in it's whole in just one day.

<P>
This module was invented and originally written in April 1996<BR>
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>

<P>
<HR NOSHADE SIZE=1>

<H2>Table Of Contents</H2>

<P>
<STRONG>Internal Processing</STRONG>
<UL>
    <LI><A HREF="#InternalAPI">API Phases</A>
    <LI><A HREF="#InternalRuleset">Ruleset Processing</A>
    <LI><A HREF="#InternalBackRefs">Regex Back-Reference Availability</A>
</UL>
<P>
<STRONG>Configuration Directives</STRONG>
<UL>
    <LI><A HREF="#RewriteEngine">RewriteEngine</A>
    <LI><A HREF="#RewriteOptions">RewriteOptions</A>
    <LI><A HREF="#RewriteLog">RewriteLog</A>
    <LI><A HREF="#RewriteLogLevel">RewriteLogLevel</A>
    <LI><A HREF="#RewriteLock">RewriteLock</A>
    <LI><A HREF="#RewriteMap">RewriteMap</A>
    <LI><A HREF="#RewriteBase">RewriteBase</A>
    <LI><A HREF="#RewriteCond">RewriteCond</A>
    <LI><A HREF="#RewriteRule">RewriteRule</A>
</UL>
<STRONG>Miscellaneous</STRONG>
<UL>
    <LI><A HREF="#EnvVar">Environment Variables</A>
    <LI><A HREF="#Solutions">Practical Solutions</A>
</UL>

<P>
<HR NOSHADE SIZE=1>

<CENTER>
<H1><A NAME="Internal">Internal Processing</A></H1>
</CENTER>

<P>
<HR NOSHADE SIZE=1>

<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. 

<H2><A NAME="InternalAPI">API Phases</A></H2>

<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 was read and 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>) where read,
but before the content handler is activated.

<P>
So, after a request comes in and Apache has determined the corresponding
server (or virtual server) the rewriting engine start 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 either rewrites URLs 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 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:

<OL>
<LI>The API currently provides only a URL-to-filename hook. Although
    mod_rewrite rewrites URLs to URLs, URLs to filenames and even
    filenames to filenames. 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
    then the API intends for it.
<P>
<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 were translated to filenames (this
    has to be this way, because <CODE>.htaccess</CODE> files stay in the
    filesystem, so processing has already been reached this stage of
    processing). 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 it 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 leads
    to a new processing of the API phases from the beginning. 
    <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.
</OL>

<P>
Don't forget these two points!

<H2><A NAME="InternalRuleset">Ruleset Processing</A></H2>

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 while 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. Just the final result processing is
different.

<P>
The order of rules in the ruleset is important because the rewriting engine
processes them in a special order. And this order is not very obvious. The
rule is this: The rewriting engine loops through the ruleset rule by rule
(<CODE>RewriteRule</CODE> directives!) and when a particular rule matched it
optionally loops through existing corresponding conditions
(<CODE>RewriteCond</CODE> directives). Because of historical reasons the 
conditions are given first, the control flow is a little bit 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> matched, 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 exists, it starts an inner loop for processing them in order
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 condition is available. If all conditions matched processing is
continued with the substitution of the URL with <EM>Substitution</EM>.

<H2><A NAME="InternalBackRefs">Regex Back-Reference Availability</A></H2>

One important thing here has to be remembered: Whenever you
use parenthesis in <EM>Pattern</EM> or in one of the <EM>CondPattern</EM>
back-reference are internally created which can be used with the
strings <CODE>$N</CODE> and <CODE>%N</CODE> (see below). And these
are available for creating the strings <EM>Substitution</EM> and
<EM>TestCond</EM>. Figure 2 shows at which locations the back-references are
transfered to 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 of mod_rewrite's internal processing.  But
you will benefit from this knowledge when reading the following documentation
of the available directives.

<P>
<HR NOSHADE SIZE=1>

<CENTER>
<H1><A NAME="Configuration">Configuration Directives</A></H1>
</CENTER>

<P>
<HR NOSHADE SIZE=1>

<H3><A NAME="RewriteEngine">RewriteEngine</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A>
    <CODE>RewriteEngine</CODE> {<CODE>on,off</CODE>}<BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A>
    <STRONG><CODE>RewriteEngine off</CODE></STRONG><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A>
    server config, virtual host, directory, .htaccess<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> FileInfo<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>

<P>
The <CODE>RewriteEngine</CODE> 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>
Use this directive to disable the module instead of commenting out
all <CODE>RewriteRule</CODE> directives!

<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 you wish to use it in.

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteOptions">RewriteOptions</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteOptions</CODE> <EM>Option</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>None</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host, directory,
    .htaccess<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> FileInfo<BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>

<P>
The <CODE>RewriteOptions</CODE> 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:

<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 gets inherited. In per-directory
    context this means that conditions and rules of the parent directory's
    <CODE>.htaccess</CODE> configuration gets inherited.
</UL>

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteLog">RewriteLog</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteLog</CODE> <EM>Filename</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>None</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>Not applicable</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>

<P>
The <CODE>RewriteLog</CODE> 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>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice</STRONG>: 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 create 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
<CODE>RewriteLog</CODE> directive or use <CODE>RewriteLogLevel 0</CODE>!
</TD></TR>
</TABLE>

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Security</STRONG>: 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.
</TD></TR>
</TABLE>

<P>
<STRONG>Example:</STRONG>
<BLOCKQUOTE>
<PRE>
RewriteLog "/usr/local/var/apache/logs/rewrite.log"
</PRE>
</BLOCKQUOTE>

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteLogLevel">RewriteLogLevel</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteLogLevel</CODE> <EM>Level</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <STRONG><CODE>RewriteLogLevel 0</CODE></STRONG>
<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>Not applicable</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>

<P>
The <CODE>RewriteLogLevel</CODE> directive set 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>
To disable the logging of rewriting actions simply set <EM>Level</EM> to 0.
This disables all rewrite action logs.

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> Using a high value for <EM>Level</EM> will slow down
your Apache
server dramatically! Use the rewriting logfile only for debugging or at least
at <EM>Level</EM> not greater than 2!
</TD></TR>
</TABLE>


<P>
<STRONG>Example:</STRONG>
<BLOCKQUOTE>
<PRE>
RewriteLogLevel 3
</PRE>
</BLOCKQUOTE>

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteLock">RewriteLock</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteLock</CODE> <EM>Filename</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>None</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>Not applicable</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.3<BR>

<P>
This directive sets the filename for a synchronization lockfile which
mod_rewrite needs to communicate with <SAMP>RewriteMap</SAMP>
<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
all other types of rewriting maps.

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteMap">RewriteMap</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteMap</CODE> <EM>MapName </EM>
    <EM>MapType</EM><CODE>:</CODE><EM>MapSource</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> not used per default<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>Not applicable</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2 (partially), Apache 1.3<BR>

<P>
The <CODE>RewriteMap</CODE> 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>

The <A 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:

<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>

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
the empty string if no <EM>DefaultValue</EM> was specified.

<P>
The following combinations for <EM>MapType</EM> and <EM>MapSource</EM>
can be used:

<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.

    <BLOCKQUOTE><STRONG>
    <EM>MatchingKey</EM>  <EM>SubstValue</EM>
    </STRONG></BLOCKQUOTE>

    <P>
    Example:
<P>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
##
##  map.txt -- rewriting map
##

Ralf.S.Engelschall    rse   # Bastard Operator From Hell
Mr.Joe.Average        joe   # Mr. Average
</PRE></TD></TR>
</TABLE>

<P>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
RewriteMap real-to-user txt:/path/to/file/map.txt
</PRE></TD></TR>
</TABLE>

<P>
<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''.  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>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
##
##  map.txt -- rewriting map
##

static   www1|www2|www3|www4
dynamic  www5|www6
</PRE></TD></TR>
</TABLE>

<P>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
RewriteMap servers rnd:/path/to/file/map.txt
</PRE></TD></TR>
</TABLE>

<P>
<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>
    <TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
    <TR><TD><PRE>
#!/path/to/bin/perl
##
##  txt2dbm -- convert txt map to dbm format
##

($txtmap, $dbmmap) = @ARGV;
open(TXT, "&lt;$txtmap");
dbmopen(%DB, $dbmmap, 0644);
while (&lt;TXT&gt;) {
    next if (m|^s*#.*| or m|^s*$|);
    $DB{$1} = $2 if (m|^\s*(\S+)\s+(\S+)$|);
}
dbmclose(%DB);
close(TXT)</PRE></TD></TR>
    </TABLE>
    <P>
    <TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
    <TR><TD><PRE>$ txt2dbm map.txt map.db </PRE></TD></TR>
    </TABLE>
<P>
<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:
    <UL> 
    <LI><STRONG>toupper</STRONG>:<BR>
        Converts the looked up key to all upper case.
    <LI><STRONG>tolower</STRONG>:<BR>
        Converts the looked up key to all lower case.
    <LI><STRONG>escape</STRONG>:<BR>
        Translates special characters in the looked up key to hex-encodings.
    <LI><STRONG>unescape</STRONG>:<BR>
        Translates hex-encodings in the looked up key back to special characters.
    </UL>
<P>
<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 Unix program, not a map file. To create it you can use
    the language of your choice, but the result has to be a run-able Unix
    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>
    This program gets 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>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
#!/usr/bin/perl
$| = 1;
while (&lt;STDIN&gt;) {
    # ...here any transformations
    # or lookups should occur...
    print $_;
}
</PRE></TD></TR>
</TABLE>
    <P>
    But be very careful:<BR>
    <OL>
    <LI>``<EM>Keep the program simple, stupid</EM>'' (KISS), because
        if this program hangs it will lead to a hang of the Apache server
        when the rule occurs.
    <LI>Avoid one common mistake: never do buffered I/O on <CODE>stdout</CODE>!
        This will cause a deadloop! Hence the ``<CODE>$|=1</CODE>'' in the
        above example...
    <LI>Use the <SAMP>RewriteLock</SAMP> directive to define a lockfile
        mod_rewrite can use to synchronize the communication to the program.
        Per default no such synchronization takes place.
    </OL>
</UL>

The <CODE>RewriteMap</CODE> directive can occur more than once. For each
mapping-function use one <CODE>RewriteMap</CODE> directive to declare its
rewriting mapfile. While you cannot <STRONG>declare</STRONG> a map in
per-directory context it is of course possible to <STRONG>use</STRONG>
this map in per-directory context.

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> 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!
</TD></TR>
</TABLE>

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteBase">RewriteBase</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteBase</CODE> <EM>BaseURL</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>default is the physical directory path</EM>
<BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> directory, .htaccess<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>FileInfo</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>

<P>
The <CODE>RewriteBase</CODE> directive explicitly sets the base URL for
per-directory rewrites. As you will see below, <CODE>RewriteRule</CODE> 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.

<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
<STRONG>NOT</STRONG> directly related to physical filename paths, so this
assumption will be usually be wrong!</STRONG> There you have to use the
<CODE>RewriteBase</CODE> directive to specify the correct URL-prefix.

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> If your webserver's URLs are <STRONG>not</STRONG>
directly related to physical file paths, you have to use
<CODE>RewriteBase</CODE> in every
<CODE>.htaccess</CODE> files where you want to use <CODE>RewriteRule</CODE>
directives.
</TD></TR>
</TABLE>

<P>
<STRONG>Example:</STRONG>

<BLOCKQUOTE>
   Assume the following per-directory config file:

<P>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><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 are reached via /xyz and not
#  via the physical path prefix /abc/def
RewriteBase   /xyz

#  now the rewriting rules
RewriteRule   ^oldstuff\.html$  newstuff.html
</PRE></TD></TR>
</TABLE>

<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>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<FONT SIZE=-1>
<STRONG>Notice - For the Apache hackers:</STRONG><BR>
The following list gives detailed information about the internal
processing steps:

<P>
<PRE>
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
</PRE>

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 internal 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>
</TD></TR>
</TABLE>

</BLOCKQUOTE>


<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteCond">RewriteCond</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteCond</CODE> <EM>TestString</EM>
    <EM>CondPattern</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>None</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host, directory,
     .htaccess<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>FileInfo</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2 (partially), Apache 1.3<BR>

<P>
The <CODE>RewriteCond</CODE> directive defines a rule condition. Precede a
<CODE>RewriteRule</CODE> directive with one or more <CODE>RewriteCond</CODE>
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>
<EM>TestString</EM> is a string which can contains the following
expanded constructs in addition to plain text:

<UL>
<LI><STRONG>RewriteRule 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 (parenthesis!)
of the
pattern from the corresponding <CODE>RewriteRule</CODE> directive (the one
following the current bunch of <CODE>RewriteCond</CODE> directives).

<P>
<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 (parenthesis!) of
the pattern from the last matched <CODE>RewriteCond</CODE> directive in the
current bunch of conditions.

<P>
<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
of the following list:

<P>
<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>
</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>
</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>
</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>
</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>
</TD>
</TR>
</TABLE>

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> These variables all correspond to the similar named
HTTP MIME-headers, C variables of the Apache server or <CODE>struct tm</CODE>
fields of the Unix system.
</TD></TR>
</TABLE>

</UL>

<P>
Special Notes:

<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>).

<P>
<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.

<P>
<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>''.

<P>
<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 actually is 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.

<P>
<LI>There is the special format: <CODE>%{LA-F:variable}</CODE> which perform an
internal (filename-based) sub-request to determine the final value of
<EM>variable</EM>. This is the most of the time the same as LA-U above.
</OL>

<P>
<EM>CondPattern</EM> is the condition pattern, <EM>i.e.</EM>, a regular
expression
which gets applied to the current instance of the <EM>TestString</EM>,
<EM>i.e.</EM>, <EM>TestString</EM> gets evaluated and then matched against
<EM>CondPattern</EM>.

<P>
<STRONG>Remember:</STRONG> <EM>CondPattern</EM> is a standard
<EM>Extended Regular Expression</EM> with some additions:

<OL>
<LI>You can precede the pattern string with a '<CODE>!</CODE>' character
(exclamation mark) to specify a <STRONG>non</STRONG>-matching pattern.

<P>
<LI>
There are some special variants of <EM>CondPatterns</EM>. Instead of real
regular expression strings you can also use one of the following:
<P>
<UL>
<LI>'<STRONG>&lt;CondPattern</STRONG>' (is lexicographically lower)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexicographically to <EM>TestString</EM> and results in a true expression if
<EM>TestString</EM> is lexicographically lower than <EM>CondPattern</EM>.
<P>
<LI>'<STRONG>&gt;CondPattern</STRONG>' (is lexicographically greater)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexicographically to <EM>TestString</EM> and results in a true expression if
<EM>TestString</EM> is lexicographically greater than <EM>CondPattern</EM>.
<P>
<LI>'<STRONG>=CondPattern</STRONG>' (is lexicographically equal)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexicographically to <EM>TestString</EM> and results in a true expression if
<EM>TestString</EM> is lexicographically 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> against the empty string.
<P>
<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.
<P>
<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.
<P>
<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.
<P>
<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.
<P>
<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!
<P>
<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!
</UL>
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG>
All of these tests can also be prefixed by a not ('!') character
to negate their meaning.
</TD></TR>
</TABLE>
</OL>

<P>
Additionally you can set special flags for <EM>CondPattern</EM> by appending

<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 condition 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>.
<P>
<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:
    <P>
<BLOCKQUOTE><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></BLOCKQUOTE>
    Without this flag you had to write down the cond/rule three times.
</UL>

<P>
<STRONG>Example:</STRONG>
<BLOCKQUOTE>

To rewrite the Homepage of a site according to the ``<CODE>User-Agent:</CODE>''
header of the request, you can use the following:

<BLOCKQUOTE><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></BLOCKQUOTE>

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.
</BLOCKQUOTE>

<P>
<HR NOSHADE SIZE=1>
<P>

<H3><A NAME="RewriteRule">RewriteRule</A></H3>
<A
 HREF="directive-dict.html#Syntax"
 REL="Help"
><STRONG>Syntax:</STRONG></A> <CODE>RewriteRule</CODE> <EM>Pattern</EM> <EM>Substitution</EM><BR>
<A
 HREF="directive-dict.html#Default"
 REL="Help"
><STRONG>Default:</STRONG></A> <EM>None</EM><BR>
<A
 HREF="directive-dict.html#Context"
 REL="Help"
><STRONG>Context:</STRONG></A> server config, virtual host, directory, .htaccess<BR>
<A
 HREF="directive-dict.html#Override"
 REL="Help"
><STRONG>Override:</STRONG></A> <EM>FileInfo</EM><BR>
<A
 HREF="directive-dict.html#Status"
 REL="Help"
><STRONG>Status:</STRONG></A> Extension<BR>
<A
 HREF="directive-dict.html#Module"
 REL="Help"
><STRONG>Module:</STRONG></A> mod_rewrite.c<BR>
<A
 HREF="directive-dict.html#Compatibility"
 REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2 (partially), Apache 1.3<BR>

<P>
The <CODE>RewriteRule</CODE> 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>
<A NAME="patterns"><EM>Pattern</EM></A> can be (for Apache 1.1.x a System
V8 and for Apache 1.2.x a POSIX) <A 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 original requested
URL, because there could be any number of rules before which already matched
and made alterations to it.

<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; 1)
  <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.  When you are interested in more detailed and deeper
information about regular expressions and its variants (POSIX regex, Perl
regex, <EM>etc.</EM>) have a look at the following dedicated book on this topic: 

<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 to this
pattern</EM>''. This can be used for special cases where it is better to match
the negative pattern or as a last default rule.

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> 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!
</TD></TR>
</TABLE>

<P>
<A 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

<OL>
<LI>back-references <CODE>$N</CODE> to the RewriteRule pattern
<LI>back-references <CODE>%N</CODE> to the last matched RewriteCond pattern
<LI>server-variables as in rule condition test-strings (<CODE>%{VARNAME}</CODE>)
<LI><A HREF="#mapfunc">mapping-function</A> calls (<CODE>${mapname:key|default}</CODE>)
</OL>

Back-references are <CODE>$</CODE><STRONG>N</STRONG> (<STRONG>N</STRONG>=1..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>
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>
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>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice</STRONG>: 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.
</TD></TR>
</TABLE>

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Remember:</STRONG> 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).
</TD></TR>
</TABLE>

<P>
Additionally you can set special flags for <EM>Substitution</EM> by appending

<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 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 gives 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>Notice:</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>, but rewriting goes on.
    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>'<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.
<P>
<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 no longer existing
    pages as gone.
<P>
<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>'<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 which may be wrong. For
    example, use it to rewrite the root-path URL ('<CODE>/</CODE>') to a real
    one, <EM>e.g.</EM>, '<CODE>/e/www/</CODE>'.
<P>
<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 a deadloop!</STRONG>
<P>
<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
    also be chained with its 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!).
<P>
<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>''.
<P>
<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>'<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.
<P>
<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.
<P>
<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>:
    <PRE>
    RewriteRule ^/abc(.*)  /def$1 [PT]
    Alias       /def       /ghi
    </PRE>
    If you omit the <CODE>PT</CODE> flag then <CODE>mod_rewrite</CODE>
    will do its job fine, <EM>i.e.</EM>, it rewrites <CODE>uri=/abc/...</CODE> to
    <CODE>filename=/def/...</CODE> as a full API-compliant URI-to-filename
    translator should do. Then <CODE>mod_alias</CODE> comes and tries to do a
    URI-to-filename transition which will not work.
    <P>
    Notice: <STRONG>You have to use this flag if you want to intermix directives
    of different modules which contain URL-to-filename translators</STRONG>. The
    typical example is the use of <CODE>mod_alias</CODE> and
    <CODE>mod_rewrite</CODE>..
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<font size=-1>
    <STRONG>Notice - For the Apache hackers:</STRONG><BR>
    If the current Apache API had a
    filename-to-filename hook additionally to the URI-to-filename hook then
    we wouldn't need this flag!  But without  such a hook this flag is the
    only solution. The Apache Group has discussed this problem and will
    add such hooks into Apache version 2.0.
</FONT>
</TD></TR>
</TABLE>
<P>
<LI>'<STRONG><CODE>skip|S</CODE></STRONG>=<EM>num</EM>' (<STRONG>s</STRONG>kip next rule(s))<BR>
    This flag forces the rewriting engine to skip the next <EM>num</EM> rules
    in sequence when the current rule matches. Use this to make pseudo
    if-then-else constructs: The last rule of the then-clause becomes
    a <CODE>skip=N</CODE> where N is the number of rules in the else-clause.
    (This is <STRONG>not</STRONG> the same as the 'chain|C' flag!)
<P>
<LI>'<STRONG><CODE>env|E=</CODE></STRONG><EM>VAR</EM>:<EM>VAL</EM>' (set <STRONG>e</STRONG>nvironment variable)<BR>
    This forces an environment variable named <EM>VAR</EM> to be set to the
    value <EM>VAL</EM>, where <EM>VAL</EM> can contain regexp backreferences
    <CODE>$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 at a lot of situations, but the usual location will be from
    within XSSI (via <CODE>&lt;!--#echo var="VAR"--&gt;</CODE>) or CGI (<EM>e.g.</EM>
    <CODE>$ENV{'VAR'}</CODE>).  But additionally you can also dereference it in a
    following RewriteCond pattern via <CODE>%{ENV:VAR}</CODE>. Use this to strip
    but remember information from URLs.
</UL>

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> Never forget that <EM>Pattern</EM> gets 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!) gets 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 be <STRONG>not</STRONG> added and a
external redirect or proxy throughput (if flag <STRONG>P</STRONG> is used!) is forced!
</TD></TR>
</TABLE>

<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> 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>Option FollowSymLinks</CODE>'' 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.
</TD></TR>
</TABLE>

<P>
Here are all possible substitution combinations and their meanings:

<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>
<BLOCKQUOTE>
We want to rewrite URLs of the form
<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:

<BLOCKQUOTE>
<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>
</BLOCKQUOTE>

</BLOCKQUOTE>

<P>
<HR NOSHADE SIZE=1>

<CENTER>
<H1><A NAME="Miscelleneous">Miscellaneous</A></H1>
</CENTER>

<P>
<HR NOSHADE SIZE=1>

<H2><A NAME="EnvVar">Environment Variables</A></H2>

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>
Notice: These variables hold the URI/URL <EM>as they were initially
requested</EM>, <EM>i.e.</EM>, in a state <EM>before</EM> any rewriting. This is
important because the rewriting process is primarily used to rewrite logical
URLs to physical pathnames.

<P>
<STRONG>Example:</STRONG>

<BLOCKQUOTE>
<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>
</BLOCKQUOTE>

<P>
<HR NOSHADE SIZE=1>

<H2><A NAME="Solutions">Practical Solutions</A></H2>

There is a comprehensive collection of practical solutions for URL-based
problems available by the author of mod_rewrite.  Here you will find real-life
rulesets and additional information.

<BLOCKQUOTE>
<STRONG>Apache URL Rewriting Guide</STRONG><BR>
<STRONG><A HREF="http://www.engelschall.com/pw/apache/rewriteguide/"
        >http://www.engelschall.com/pw/apache/rewriteguide/</A></STRONG>
</BLOCKQUOTE>

<HR>

<H3 ALIGN="CENTER">
 Apache HTTP Server Version 1.3
</H3>

<A HREF="./"><IMG SRC="../images/index.gif" ALT="Index"></A>
<A HREF="../"><IMG SRC="../images/home.gif" ALT="Home"></A>

</BLOCKQUOTE><!-- page indentation -->
</BODY>
</HTML>
<!--/%hypertext -->
