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<BR>
<H1 ALIGN="CENTER">Module mod_rewrite<BR>URL Rewriting Engine</H1>
<p>This module provides a rule-based rewriting engine to rewrite requested
URLs on the fly.</p>
<P><A
HREF="module-dict.html#Status"
REL="Help"
><STRONG>Status:</STRONG></A> Extension
<BR>
<A
HREF="module-dict.html#SourceFile"
REL="Help"
<BR>
<A
HREF="module-dict.html#ModuleIdentifier"
REL="Help"
><STRONG>Module Identifier:</STRONG></A> rewrite_module
<BR>
<A
HREF="module-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Available in Apache 1.2 and later.
</P>
<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
(<CODE>.htaccess</CODE>) and can even generate query-string parts on result.
The rewritten result can lead to internal sub-processing, external request
redirection or even to an internal proxy throughput.
<P>
But all this functionality and flexibility has its drawback: complexity. So
don't expect to understand this entire module 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="mailto:rse@engelschall.com"><CODE>rse@engelschall.com</CODE></A><BR>
</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 has been read but before any authorization
starts and the Fixup hook which is triggered after the authorization phases
and after the per-directory config files (<CODE>.htaccess</CODE>) have been
read, but before the content handler is activated.
<P>
So, after a request comes in and Apache has determined the corresponding
server (or virtual server) the rewriting engine starts processing of all
mod_rewrite directives from the per-server configuration in the
URL-to-filename phase. A few steps later when the final data directories are
found, the per-directory configuration directives of mod_rewrite are triggered
in the Fixup phase. In both situations mod_rewrite rewrites URLs either to new
URLs or to filenames, although there is no obvious distinction between them.
This is a usage of the API which was not intended to be this way when the API
was designed, but as of Apache 1.x this is the only way mod_rewrite can
operate. To make this point more clear remember the following two points:
<OL>
<LI>Although mod_rewrite rewrites URLs to URLs, URLs to filenames and
even filenames to filenames, the API currently provides only a
URL-to-filename hook. In Apache 2.0 the two missing hooks will be
added to make the processing more clear. But this point has no
drawbacks for the user, it is just a fact which should be
remembered: Apache does more in the URL-to-filename hook than the
API intends for it.
<P>
<LI>Unbelievably mod_rewrite provides URL manipulations in per-directory
although these are reached a very long time after the URLs have
been translated to filenames. It has to be this way because
<CODE>.htaccess</CODE> files live in the filesystem, so processing
has already reached this stage. In other words: According to the
API phases at this time it is too late for any URL manipulations.
To overcome this chicken and egg problem mod_rewrite uses a trick:
mod_rewrite first rewrites the filename back to its corresponding
URL (which is usually impossible, but see the <CODE>RewriteBase</CODE>
directive below for the trick to achieve this) and then initiates
a new internal sub-request with the new URL. This restarts
processing of the API phases.
<P>
Again mod_rewrite tries hard to make this complicated step totally
transparent to the user, but you should remember here: While URL
manipulations in per-server context are really fast and efficient,
per-directory rewrites are slow and inefficient due to this chicken and
egg problem. But on the other hand this is the only way mod_rewrite can
provide (locally restricted) URL manipulations to the average user.
</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 during the directory walk of the
Apache kernel for per-directory context). Then the URL rewriting engine is
started with the contained ruleset (one or more rules together with their
conditions). The operation of the URL rewriting engine itself is exactly the
same for both configuration contexts. Only the final result processing is
different.
<P>
The order of rules in the ruleset is important because the rewriting engine
processes them in a special (and not very obvious) order. The
rule is this: The rewriting engine loops through the ruleset rule by rule
(<CODE>RewriteRule</CODE> directives) and when a particular rule matches it
optionally loops through existing corresponding conditions
(<CODE>RewriteCond</CODE> directives). For historical reasons the conditions
are given first, and so the control flow is a little bit long-winded. See
Figure 1 for more details.
<P>
<DIV ALIGN=CENTER>
<TABLE CELLSPACING=0 CELLPADDING=2 BORDER=0>
<TR>
<TD BGCOLOR="#CCCCCC"><IMG
SRC="/images/mod_rewrite_fig1.gif"
WIDTH="428" HEIGHT="385"
ALT="[Needs graphics capability to display]"></TD>
</TR>
<TR>
<TD ALIGN=CENTER>
<STRONG>Figure 1:</STRONG> The control flow through the rewriting ruleset
</TD>
</TR>
</TABLE>
</DIV>
<P>
As you can see, first the URL is matched against the <EM>Pattern</EM> of each
rule. When it fails mod_rewrite immediately stops processing this rule and
continues with the next rule. If the <EM>Pattern</EM> matches, mod_rewrite
looks for corresponding rule conditions. If none are present, it just
substitutes the URL with a new value which is constructed from the string
<EM>Substitution</EM> and goes on with its rule-looping. But if conditions
exist, it starts an inner loop for processing them in the order that
they are listed. For conditions the logic is different: we don't match a
pattern against the current URL. Instead we first create a string
<EM>TestString</EM> by expanding variables, back-references, map lookups,
<EM>etc.</EM> and then we try to match <EM>CondPattern</EM> against it. If the
pattern doesn't match, the complete set of conditions and the corresponding
rule fails. If the pattern matches, then the next condition is processed
until no more conditions are available. If all conditions match, processing
is continued with the substitution of the URL with <EM>Substitution</EM>.
<h2><a name="quoting">Quoting Special Characters</a></h2>
<p>
As of Apache 1.3.20, special characters in <i>TestString</i> and
<i>Substitution</i> strings can be escaped (that is, treated as
normal characters without their usual special meaning) by prefixing them
with a slosh ('\') character. In other words, you can include an
actual dollar-sign character in a <i>Substitution</i> string
by using '<code>\$</code>'; this keeps mod_rewrite from trying
to treat it as a backreference.
</p>
<H2><A NAME="InternalBackRefs">Regex Back-Reference Availability</A></H2>
One important thing here has to be remembered: Whenever you
use parentheses in <EM>Pattern</EM> or in one of the <EM>CondPattern</EM>,
back-references are internally created which can be used with the
strings <CODE>$N</CODE> and <CODE>%N</CODE> (see below). These
are available for creating the strings <EM>Substitution</EM> and
<EM>TestString</EM>. Figure 2 shows to which locations the back-references are
transfered for expansion.
<P>
<DIV ALIGN=CENTER>
<TABLE CELLSPACING=0 CELLPADDING=2 BORDER=0>
<TR>
<TD BGCOLOR="#CCCCCC"><IMG
SRC="/images/mod_rewrite_fig2.gif"
WIDTH="381" HEIGHT="179"
ALT="[Needs graphics capability to display]"></TD>
</TR>
<TR>
<TD ALIGN=CENTER>
<STRONG>Figure 2:</STRONG> The back-reference flow through a rule
</TD>
</TR>
</TABLE>
</DIV>
<P>
We know this was a crash course on mod_rewrite's internal processing. But
you will benefit from this knowledge when reading the following documentation
of the available directives.
<P>
<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>
RewriteEngine on|off<BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A>
<CODE>RewriteEngine off</CODE><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"
<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 the <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 in which you wish to use it.
<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> RewriteOptions <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"
<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 are inherited. In per-directory
context this means that conditions and rules of the parent directory's
<CODE>.htaccess</CODE> configuration are 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> RewriteLog <EM>file-path</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"
<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>Note</STRONG>: To disable the logging of rewriting actions it is
not recommended to set <EM>Filename</EM>
not then output to a logfile it still creates the logfile
output internally. <STRONG>This will slow down the server with no advantage
to the administrator!</STRONG>
To disable logging either remove or comment out the
<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>
</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> RewriteLogLevel <EM>Level</EM><BR>
<A
HREF="directive-dict.html#Default"
REL="Help"
><STRONG>Default:</STRONG></A> <CODE>RewriteLogLevel 0</CODE>
<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"
<A
HREF="directive-dict.html#Compatibility"
REL="Help"
><STRONG>Compatibility:</STRONG></A> Apache 1.2<BR>
<P>
The <CODE>RewriteLogLevel</CODE> directive sets the verbosity level of the
rewriting
logfile. The default level 0 means no logging, while 9 or more means
that practically all actions are logged.
<P>
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 at
a <EM>Level</EM> greater than 2 only for debugging!
</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> RewriteLock <EM>file-path</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"
<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
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> RewriteMap <EM>MapName </EM>
<EM>MapType</EM>:<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"
<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
by 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>
</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''.
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>
</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>
##
## txt2dbm -- convert txt map to dbm format
##
($txtmap, $dbmmap) = @ARGV;
open(TXT, "<$txtmap");
dbmopen(%DB, $dbmmap, 0644);
while (<TXT>) {
next if (m|^s*#.*| or m|^s*$|);
$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">
</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 program, not a map file. To create it you
can use the language of your choice, but the result has to be a
first line).
<P>
This program is started once at startup of the Apache servers and then
communicates with the rewriting engine over its <CODE>stdin</CODE> and
<CODE>stdout</CODE> file-handles. For each map-function lookup it will
receive the key to lookup as a newline-terminated string on
<CODE>stdin</CODE>. It then has to give back the looked-up value as a
newline-terminated string on <CODE>stdout</CODE> or the four-character
corresponding value
for the given key). A trivial program which will implement a 1:1 map
<P>
<TABLE BORDER=0 CELLSPACING=1 CELLPADDING=5 BGCOLOR="#F0F0F0">
<TR><TD><PRE>
$| = 1;
while (<STDIN>) {
# ...put here any transformations or lookups...
print $_;
}
</PRE></TD></TR>
</TABLE>
<P>
But be very careful:<BR>
<OL>
<LI>``<EM>Keep it simple, stupid</EM>'' (KISS), because
if this program hangs it will hang the Apache server
when the rule occurs.
<LI>Avoid one common mistake: never do buffered I/O on <CODE>stdout</CODE>!
This will cause a deadloop! Hence the ``<CODE>$|=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.
By 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>Note:</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> RewriteBase <EM>URL-path</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"
<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
processing and your rewriting rules act only on the remainder. At the end
it is automatically added back to the path.
<P>
When a substitution occurs for a new URL, this module has to re-inject the URL
into the server processing. To be able to do this it needs to know what the
corresponding URL-prefix or URL-base is. By default this prefix is the
corresponding filepath itself. <STRONG>But at most websites URLs are
NOT directly related to physical filename paths, so this
assumption will usually be wrong!</STRONG> There you have to use the
<CODE>RewriteBase</CODE> directive to specify the correct URL-prefix.
<P>
<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>
#
#
RewriteEngine On
# let the server know that we were reached via /xyz and not
RewriteBase /xyz
# now the rewriting rules
RewriteRule ^oldstuff\.html$ newstuff.html
</PRE></TD></TR>
</TABLE>
<P>
gets correctly
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<FONT SIZE=-1>
<STRONG>Note - For Apache hackers:</STRONG><BR>
The following list gives detailed information about the internal
processing steps:
<P>
<PRE>
Request:
Internal Processing:
Result:
</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 internally to the Apache server and the same
procedure is used by many other operations inside Apache. So, you can be
sure the design and implementation is correct.
</FONT>
</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> RewriteCond <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"
<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>$N</CODE>
</STRONG></BLOCKQUOTE>
(0 <= N <= 9) which provide access to the grouped parts (parenthesis!)
of the pattern from the corresponding <CODE>RewriteRule</CODE> directive (the
one following the current bunch of <CODE>RewriteCond</CODE> directives).
<P>
<LI><STRONG>RewriteCond backreferences</STRONG>: These are backreferences of
the form
<BLOCKQUOTE><STRONG>
<CODE>%N</CODE>
</STRONG></BLOCKQUOTE>
(1 <= N <= 9) which provide access to the grouped parts (parentheses!) of
the pattern from the last matched <CODE>RewriteCond</CODE> directive in the
current bunch of conditions.
<P>
<LI><STRONG>RewriteMap expansions</STRONG>: These are expansions of the form
<BLOCKQUOTE><STRONG>
<CODE>${mapname:key|default}</CODE>
</STRONG></BLOCKQUOTE>
See <A HREF="#mapfunc">the documentation for RewriteMap</A> for more details.
<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
taken from 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 & 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>
<p><STRONG>Notice:</STRONG> These variables all correspond to
the similarly named HTTP MIME-headers, C variables of the Apache
server or <CODE>struct tm</CODE> fields of the Unix system. Most
are documented elsewhere in the Manual or in the CGI specification.
Those that are special to mod_rewrite include:</p>
<dl>
<dt><code>IS_SUBREQ</code></dt>
<dd>Will contain the text "true" if the request currently
being processed is a sub-request, "false" otherwise. Sub-requests may
be generated by modules that need to resolve additional files or URIs
in order to complete their tasks.</dd>
<dt><code>API_VERSION</code></dt>
<dd>This is the version of the Apache module API (the internal
interface between server and module) in the current httpd build, as
version of Apache in use (in the release version of Apache 1.3.14, for
instance, it is 19990320:10), but is mainly of interest to module
authors.</dd>
<dt><code>THE_REQUEST</code></dt>
<dd>The full HTTP request line sent by the browser to the server
any additional headers sent by the browser.</dd>
<dt><code>REQUEST_URI</code></dt>
<dd>The resource requested in the HTTP request line. (In the
example above, this would be "/index.html".)</dd>
<dt><code>REQUEST_FILENAME</code></dt>
<dd>The full local filesystem path to the file or script
matching the request.</dd>
</dl>
</TD></TR>
</TABLE>
</UL>
<P>
Special Notes:
<OL>
<LI>The variables SCRIPT_FILENAME and REQUEST_FILENAME contain the same
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 is actually set later in an API phase and thus is not available at the
current stage. For instance when you want to rewrite according to the
<CODE>REMOTE_USER</CODE> variable from within the per-server context
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 performs an
internal (filename-based) sub-request to determine the final value of
<EM>variable</EM>. Most of the time this is the same as LA-U above.
</OL>
<P>
expression
which is applied to the current instance of the <EM>TestString</EM>,
<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 prefix 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><CondPattern</STRONG>' (is lexically lower)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexically to <EM>TestString</EM>. True if
<EM>TestString</EM> is lexically lower than <EM>CondPattern</EM>.
<P>
<LI>'<STRONG>>CondPattern</STRONG>' (is lexically greater)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexically to <EM>TestString</EM>. True if
<EM>TestString</EM> is lexically greater than <EM>CondPattern</EM>.
<P>
<LI>'<STRONG>=CondPattern</STRONG>' (is lexically equal)<BR>
Treats the <EM>CondPattern</EM> as a plain string and compares it
lexically to <EM>TestString</EM>. True if
two strings are exactly equal (character by character).
If <EM>CondPattern</EM> is just <SAMP>""</SAMP> (two quotation marks) this
compares <EM>TestString</EM> to the empty string.
<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 an exclamation mark ('!')
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>
no difference between 'A-Z' and 'a-z' both in the expanded
<EM>TestString</EM> and the <EM>CondPattern</EM>.
This flag is effective only for comparisons between
<EM>TestString</EM> and <EM>CondPattern</EM>. It has no
effect on filesystem and subrequest checks.
<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>
</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> RewriteRule <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"
<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
NAME="regexp">regular expression</A> which gets applied to the current
URL. Here ``current'' means the value of the URL when this rule gets
applied. This may not be the originally requested URL, because no
longer existingany number of rules may already have 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 > 0)
<STRONG><CODE>+</CODE></STRONG> 1 or N of the preceding text (N > 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
Apache 1.3 distribution. If you are interested in more detailed
information about regular expressions and their variants (POSIX regex, Perl
regex, <EM>etc.</EM>) have a look at the following dedicated book on this topic:
<BLOCKQUOTE>
<EM>Mastering Regular Expressions</EM><BR>
Jeffrey E.F. Friedl<BR>
Nutshell Handbook Series<BR>
O'Reilly & Associates, Inc. 1997<BR>
ISBN 1-56592-257-3<BR>
</BLOCKQUOTE>
<P>
Additionally in mod_rewrite the NOT character ('<CODE>!</CODE>') is a possible
pattern prefix. This gives you the ability to negate a pattern; to say, for
instance: ``<EM>if the current URL does <STRONG>NOT</STRONG> match this
pattern</EM>''. This can be used for exceptional cases, where it is easier to
match the negative pattern, or as a last default rule.
<P>
<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>=0..9) identifiers which
will be replaced by the contents of the <STRONG>N</STRONG>th group of the matched
<EM>Pattern</EM>. The server-variables are the same as for the
<EM>TestString</EM> of a <CODE>RewriteCond</CODE> directive. The
mapping-functions come from the <CODE>RewriteMap</CODE> directive and are
explained there. These three types of variables are expanded in the order of
the above list.
<P>
As already mentioned above, all the rewriting rules are applied to the
<EM>Substitution</EM> (in the order of definition in the config file). The
URL is <STRONG>completely replaced</STRONG> by the <EM>Substitution</EM> and the
rewriting process goes on until there are no more rules unless explicitly
terminated by a <CODE><STRONG>L</STRONG></CODE> flag - see below.
<P>
There is a special substitution string named '<CODE>-</CODE>' which means:
<STRONG>NO substitution</STRONG>! Sounds silly? No, it is useful to provide rewriting
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>Note</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
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>
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
``<CODE>/~</CODE>'' into ``<CODE>/u/</CODE>'' or always append a slash to
<CODE>/u/</CODE><EM>user</EM>, etc.<BR>
<P>
<STRONG>Note:</STRONG> When you use this flag, make sure that the
substitution field is a valid URL! If not, you are redirecting to an
invalid location! And remember that this flag itself only prefixes the
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>
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>
HTTP response of 410 (GONE). Use this flag to mark pages which no longer
exist 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
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
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. For
example, use it to rewrite the root-path URL ('<CODE>/</CODE>') to a real
<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
immediately go to the top of the loop. <BR>
<STRONG>But be careful not to create an infinite loop!</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
be chained with the following rule, <EM>etc.</EM>). This has the following
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
<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
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>
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>noescape|NE</CODE></STRONG>' (<STRONG>n</STRONG>o URI <STRONG>e</STRONG>scaping of output)<BR>
This flag keeps mod_rewrite from applying the usual URI escaping
rules to the result of a rewrite. Ordinarily, special characters
(such as '%', '$', ';', and so on) will be escaped into their
hexcode equivalents ('%25', '%24', and '%3B', respectively); this
flag prevents this from being done. This allows percent symbols
to appear in the output, as in
<pre>
RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]
</pre>
for '<code>/bar?arg=P1=zed</code>'.
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Notice:</STRONG> The <code>noescape</code> flag is only available
with Apache 1.3.20 and later versions.
</TD></TR>
</TABLE>
<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$1 [PT]
Alias /def /ghi
</PRE>
If you omit the <CODE>PT</CODE> flag then <CODE>mod_rewrite</CODE>
<CODE>filename=/def/...</CODE> as a full API-compliant URI-to-filename
translator should do. Then <CODE>mod_alias</CODE> comes and tries to do a
URI-to-filename transition which will not work.
<P>
Note: <STRONG>You have to use this flag if you want to intermix directives
of different modules which contain URL-to-filename translators</STRONG>. The
typical example is the use of <CODE>mod_alias</CODE> and
<CODE>mod_rewrite</CODE>..
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<font size=-1>
<STRONG>Note - For Apache hackers:</STRONG><BR>
If the current Apache API had a
filename-to-filename hook additionally to the URI-to-filename hook then
we wouldn't need this flag! But without such a hook this flag is the
only solution. The Apache Group has discussed this problem and will
add such a hook in Apache version 2.0.
</FONT>
</TD></TR>
</TABLE>
<P>
<LI>'<STRONG><CODE>skip|S</CODE></STRONG>=<EM>num</EM>' (<STRONG>s</STRONG>kip next rule(s))<BR>
This flag forces the rewriting engine to skip the next <EM>num</EM> rules
in sequence when the current rule matches. Use this to make pseudo
if-then-else constructs: The last rule of the then-clause becomes
<CODE>skip=N</CODE> where N is the number of rules in the else-clause.
(This is <STRONG>not</STRONG> the same as the 'chain|C' flag!)
<P>
<LI>'<STRONG><CODE>env|E=</CODE></STRONG><EM>VAR</EM>:<EM>VAL</EM>' (set <STRONG>e</STRONG>nvironment variable)<BR>
This forces an environment variable named <EM>VAR</EM> to be set to the
value <EM>VAL</EM>, where <EM>VAL</EM> can contain regexp backreferences
<CODE>$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 in many situations, but usually from
<CODE>$ENV{'VAR'}</CODE>). Additionally you can dereference it in a
following RewriteCond pattern via <CODE>%{ENV:VAR}</CODE>. Use this to strip
but remember information from URLs.
</UL>
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Note:</STRONG> Never forget that <EM>Pattern</EM> is applied to a complete URL
in per-server configuration files. <STRONG>But in per-directory configuration
files, the per-directory prefix (which always is the same for a specific
directory!) is automatically <EM>removed</EM> for the pattern matching and
automatically <EM>added</EM> after the substitution has been done.</STRONG> This feature is
essential for many sorts of rewriting, because without this prefix stripping
you have to match the parent directory which is not always possible.
<P>
There is one exception: If a substitution string starts with
``<CODE>http://</CODE>'' then the directory prefix will <STRONG>not</STRONG> be added and an
external redirect or proxy throughput (if flag <STRONG>P</STRONG> is used!) is forced!
</TD></TR>
</TABLE>
<P>
<TABLE WIDTH="70%" BORDER=0 BGCOLOR="#E0E0F0" CELLSPACING=0 CELLPADDING=10>
<TR><TD>
<STRONG>Note:</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>Options FollowSymLinks</CODE>'' must be enabled. If your administrator has
disabled override of <CODE>FollowSymLinks</CODE> for a user's directory, then
you cannot use the rewriting engine. This restriction is needed for
security reasons.
</TD></TR>
</TABLE>
<P>
Here are all possible substitution combinations and their meanings:
<P>
<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 [R] http://thishost/otherpath/pathinfo
via external redirection
^/somepath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^/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
<P>
<TABLE BGCOLOR="#F0F0F0" CELLSPACING=0 CELLPADDING=5>
<TR>
<TD>
<PRE>
<STRONG>Given Rule</STRONG> <STRONG>Resulting Substitution</STRONG>
---------------------------------------------- ----------------------------------
^localpath(.*) otherpath$1 [R] http://thishost/somepath/otherpath/pathinfo
via external redirection
^localpath(.*) otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^localpath(.*) /otherpath$1 [R] http://thishost/otherpath/pathinfo
via external redirection
^localpath(.*) /otherpath$1 [P] not supported, because silly!
---------------------------------------------- ----------------------------------
^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$1 [P] http://otherhost/otherpath/pathinfo
via internal proxy
</PRE>
</TD>
</TR>
</TABLE>
<P>
<STRONG>Example:</STRONG>
<P>
<BLOCKQUOTE>
We want to rewrite URLs of the form
<BLOCKQUOTE>
<CODE>/</CODE> <EM>Language</EM>
<CODE>/~</CODE> <EM>Realname</EM>
<CODE>/.../</CODE> <EM>File</EM>
</BLOCKQUOTE>
into
<BLOCKQUOTE>
<CODE>/u/</CODE> <EM>Username</EM>
<CODE>/.../</CODE> <EM>File</EM>
<CODE>.</CODE> <EM>Language</EM>
</BLOCKQUOTE>
<P>
We take the rewrite mapfile from above and save it under
following lines to the Apache server configuration file:
<BLOCKQUOTE>
<PRE>
RewriteRule ^/([^/]+)/~([^/]+)/(.*)$ /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>
variables named <CODE>SCRIPT_URL</CODE> and <CODE>SCRIPT_URI</CODE>. These contain
variables <CODE>SCRIPT_NAME</CODE> and <CODE>SCRIPT_FILENAME</CODE> contain the
<EM>physical</EM> System-view.
<P>
important because the rewriting process is primarily used to rewrite logical
URLs to physical pathnames.
<P>
<STRONG>Example:</STRONG>
<BLOCKQUOTE>
<PRE>
SCRIPT_URI=http://en1.engelschall.com/u/rse/
</PRE>
</BLOCKQUOTE>
<P>
<HR NOSHADE SIZE=1>
<H2><A NAME="Solutions">Practical Solutions</A></H2>
We also have an <a href="/misc/rewriteguide.html">URL Rewriting
Guide</a> available, which provides a collection of practical solutions
for URL-based problems. There you can find real-life rulesets and
additional information about mod_rewrite.
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