<?xml version="1.0"?>

<!DOCTYPE modulesynopsis SYSTEM "/style/modulesynopsis.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<modulesynopsis metafile="mod_rewrite.xml.meta">

<name>mod_rewrite</name>

<description>Provides a rule-based rewriting engine to rewrite requested

URLs on the fly</description>

<status>Extension</status>

<sourcefile>mod_rewrite.c</sourcefile>

<identifier>rewrite_module</identifier>

<compatibility>Available in Apache 1.3 and later</compatibility>

<summary>

<blockquote>

<p>``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.''</p>

<p class="cite">-- <cite>Brian Behlendorf</cite><br />

Apache Group</p>

</blockquote>

<blockquote>

<p>`` Despite the tons of examples and docs,

mod_rewrite is voodoo. Damned cool voodoo, but still

voodoo. ''</p>

<p class="cite">-- <cite>Brian Moore</cite><br />

bem@news.cmc.net</p>

</blockquote>

<p>Welcome to mod_rewrite, the Swiss Army Knife of URL

manipulation!</p>

<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>

<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 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>

<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>

<p>This module was invented and originally written in April

1996 and gifted exclusively to the The Apache Group in July 1997

by</p>

<p class="indent">

<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>

</p>

</summary>

<section id="Internal"><title>Internal Processing</title>

<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.</p>

<section id="InternalAPI"><title>API Phases</title>

<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>

<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:</p>

<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.</li>

<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 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: When you

manipulate a URL/filename in per-directory context

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.</p>

</li>

</ol>

<p>Don't forget these two points!</p>

</section>

<section id="InternalRuleset"><title>Ruleset Processing</title>

<p>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>

<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 (<directive

module="mod_rewrite">RewriteRule</directive> 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>

<p class="figure">

<img src="/images/mod_rewrite_fig1.gif" width="428"

height="385" alt="[Needs graphics capability to display]" /><br />

<dfn>Figure 1:</dfn>The control flow through the rewriting ruleset

</p>

<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>.</p>

</section>

<section id="quoting"><title>Quoting Special Characters</title>

<p>As of Apache 1.3.20, special characters in

<em>TestString</em> and <em>Substitution</em> 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 <em>Substitution</em> string by

using '<code>\$</code>'; this keeps mod_rewrite from trying

to treat it as a backreference.</p>

</section>

<section id="InternalBackRefs"><title>Regex Back-Reference Availability</title>

<p>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>

<p class="figure">

<img src="/images/mod_rewrite_fig2.gif" width="381"

height="179" alt="[Needs graphics capability to display]" /><br />

<dfn>Figure 2:</dfn> The back-reference flow through a rule.

</p>

<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>

</section>

</section>

<section id="EnvVar"><title>Environment Variables</title>

<p>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>

<p>Notice: These variables hold the URI/URL <em>as they were

initially requested</em>, <em>i.e.</em>, <em>before</em> any

rewriting. This is important because the rewriting process is

primarily used to rewrite logical URLs to physical

pathnames.</p>

<example><title>Example</title>

<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>

</example>

</section>

<section id="Solutions"><title>Practical Solutions</title>

<p>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.</p>

</section>

<directivesynopsis>

<name>RewriteEngine</name>

<description>Enables or disables runtime rewriting engine</description>

<syntax>RewriteEngine on|off</syntax>

<default>RewriteEngine off</default>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>FileInfo</override>

<usage>

<p>The <directive>RewriteEngine</directive> 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>

<p>Use this directive to disable the module instead of

commenting out all the <directive

module="mod_rewrite">RewriteRule</directive> directives!</p>

<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>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteOptions</name>

<description>Sets some special options for the rewrite engine</description>

<syntax>RewriteOptions <var>Options</var></syntax>

<default>RewriteOptions MaxRedirects=10</default>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>FileInfo</override>

<compatibility><code>MaxRedirects</code> is available in Apache 2.0.45 and

later</compatibility>

<usage>

<p>The <directive>RewriteOptions</directive> 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:</p>

<dl>

<dt><code>inherit</code></dt>

<dd>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.</dd>

<dt><code>MaxRedirects=<var>number</var></code></dt>

<dd>In order to prevent endless loops of internal redirects

issued by per-directory <directive module="mod_rewrite"

>RewriteRule</directive>s, <module>mod_rewrite</module> aborts

the request after reaching a maximum number of such redirects and

responds with an 500 Internal Server Error. If you really need

more internal redirects than 10 per request, you may increase

the default to the desired value.</dd>

</dl>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteLog</name>

<description>Sets the name of the file used for logging rewrite engine

processing</description>

<syntax>RewriteLog <em>file-path</em></syntax>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>RewriteLog</directive> 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>

<note> 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 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 <directive>RewriteLog</directive>

directive or use <code>RewriteLogLevel 0</code>!

</note>

<note type="securitywarning"><title>Security</title>

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.

</note>

<example><title>Example</title>

RewriteLog "/usr/local/var/apache/logs/rewrite.log"

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteLogLevel</name>

<description>Sets the verbosity of the log file used by the rewrite

engine</description>

<syntax>RewriteLogLevel <em>Level</em></syntax>

<default>RewriteLogLevel 0</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>RewriteLogLevel</directive> 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>

<p>To disable the logging of rewriting actions simply set

<em>Level</em> to 0. This disables all rewrite action

logs.</p>

<note> 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!

</note>

<example><title>Example</title>

RewriteLogLevel 3

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteLock</name>

<description>Sets the name of the lock file used for <directive

module="mod_rewrite">RewriteMap</directive>

synchronization</description>

<syntax>RewriteLock <em>file-path</em></syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>This directive sets the filename for a synchronization

lockfile which mod_rewrite needs to communicate with <directive

module="mod_rewrite">RewriteMap</directive>

<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>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteMap</name>

<description>Defines a mapping function for key-lookup</description>

<syntax>RewriteMap <em>MapName</em> <em>MapType</em>:<em>MapSource</em>

</syntax>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<compatibility>The choice of different dbm types is available in

Apache 2.0.41 and later</compatibility>

<usage>

<p>The <directive>RewriteMap</directive> 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>

<p>The <a id="mapfunc" 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:</p>

<p class="indent">

<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>

</p>

<p>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>

<p>The following combinations for <em>MapType</em> and

<em>MapSource</em> can be used:</p>

<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.</p>

<p class="indent">

<strong><em>MatchingKey</em>

<em>SubstValue</em></strong>

</p>

<example><title>Example</title>

<pre>

##

## map.txt -- rewriting map

##

Ralf.S.Engelschall rse # Bastard Operator From Hell

Mr.Joe.Average joe # Mr. Average

</pre>

</example>

<example>

RewriteMap real-to-user txt:/path/to/file/map.txt

</example>

</li>

<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>

<example>

<pre>

##

## map.txt -- rewriting map

##

static www1|www2|www3|www4

dynamic www5|www6

</pre>

</example>

<example>

RewriteMap servers rnd:/path/to/file/map.txt

</example>

</li>

<li>

<strong>Hash File</strong><br /> MapType:

<code>dbm[=<em>type</em>]</code>, MapSource: Unix filesystem

path to valid regular file

<p>Here the source is a binary format DBM 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. The <em>type</em> can be sdbm, gdbm, ndbm, or

db depending on <a href="/install.html#dbm">compile-time

settings</a>. If the <em>type</em> is omitted, the

compile-time default will be chosen. You can create such a

file with any DBM tool or with the following Perl

script. Be sure to adjust it to create the appropriate

type of DBM. The example creates an NDBM file.</p>

<example>

<pre>

#!/path/to/bin/perl

##

## txt2dbm -- convert txt map to dbm format

##

use NDBM_File;

use Fcntl;

($txtmap, $dbmmap) = @ARGV;

open(TXT, "&lt;$txtmap") or die "Couldn't open $txtmap!\n";

tie (%DB, 'NDBM_File', $dbmmap,O_RDWR|O_TRUNC|O_CREAT, 0644)

or die "Couldn't create $dbmmap!\n";

while (&lt;TXT&gt;) {

next if (/^\s*#/ or /^\s*$/);

$DB{$1} = $2 if (/^\s*(\S+)\s+(\S+)/);

}

untie %DB;

close(TXT);

</pre>

</example>

<example>

$ txt2dbm map.txt map.db

</example>

</li>

<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:</p>

<ul>

<li><strong>toupper</strong>:<br />

Converts the looked up key to all upper case.</li>

<li><strong>tolower</strong>:<br />

Converts the looked up key to all lower case.</li>

<li><strong>escape</strong>:<br />

Translates special characters in the looked up key to

hex-encodings.</li>

<li><strong>unescape</strong>:<br />

Translates hex-encodings in the looked up key back to

special characters.</li>

</ul>

</li>

<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 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>

<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 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>

<example>

<pre>

#!/usr/bin/perl

$| = 1;

while (&lt;STDIN&gt;) {

# ...put here any transformations or lookups...

print $_;

}

</pre>

</example>

<p>But be very careful:</p>

<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>

<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>

<li>Use the <directive

module="mod_rewrite">RewriteLock</directive> directive to

define a lockfile mod_rewrite can use to synchronize the

communication to the program. By default no such

synchronization takes place.</li>

</ol>

</li>

</ul>

<p>The <directive>RewriteMap</directive> directive can occur more than

once. For each mapping-function use one

<directive>RewriteMap</directive> 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>

<note><title>Note</title> 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!

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteBase</name>

<description>Sets the base URL for per-directory rewrites</description>

<syntax>RewriteBase <em>URL-path</em></syntax>

<default>See usage for information.</default>

<contextlist><context>directory</context><context>.htaccess</context>

</contextlist>

<override>FileInfo</override>

<usage>

<p>The <directive>RewriteBase</directive> directive explicitly

sets the base URL for per-directory rewrites. As you will see

below, <directive module="mod_rewrite">RewriteRule</directive>

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 back to the

path. The default setting is; <directive>RewriteBase</directive> <em>physical-directory-path</em></p>

<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>

<note> If your webserver's URLs are <strong>not</strong> directly

related to physical file paths, you have to use

<directive>RewriteBase</directive> in every <code>.htaccess</code>

files where you want to use <directive

module="mod_rewrite">RewriteRule</directive> directives.

</note>

<p> For example, assume the following per-directory config file:</p>

<example>

<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 were reached via /xyz and not

# via the physical path prefix /abc/def

RewriteBase /xyz

# now the rewriting rules

RewriteRule ^oldstuff\.html$ newstuff.html

</pre>

</example>

<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>

<note><title>For Apache Hackers</title>

<p>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>

<p>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.</p>

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteCond</name>

<description>Defines a condition under which rewriting will take place

</description>

<syntax> RewriteCond

<em>TestString</em> <em>CondPattern</em></syntax>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>FileInfo</override>

<usage>

<p>The <directive>RewriteCond</directive> directive defines a

rule condition. Precede a <directive

module="mod_rewrite">RewriteRule</directive> directive with one

or more <directive>RewriteCond</directive> 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>

<p><em>TestString</em> is a string which can contains the

following expanded constructs in addition to plain text:</p>

<ul>

<li>

<strong>RewriteRule backreferences</strong>: These are

backreferences of the form

<p class="indent">

<strong><code>$N</code></strong>

</p>

(0 &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).

</li>

<li>

<strong>RewriteCond backreferences</strong>: These are

backreferences of the form

<p class="indent">

<strong><code>%N</code></strong>

</p>

(1 &lt;= N &lt;= 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.

</li>

<li>

<strong>RewriteMap expansions</strong>: These are

expansions of the form

<p class="indent">

<strong><code>${mapname:key|default}</code></strong>

</p>

See <a href="#mapfunc">the documentation for

RewriteMap</a> for more details.

</li>

<li>

<strong>Server-Variables</strong>: These are variables of

the form

<p class="indent">

<strong><code>%{</code> <em>NAME_OF_VARIABLE</em>

<code>}</code></strong>

</p>

where <em>NAME_OF_VARIABLE</em> can be a string taken

from the following list:

<table>

<tr>

<th>HTTP headers:</th> <th>connection &amp; request:</th> <th></th>

</tr>

<tr>

<td>

HTTP_USER_AGENT<br />

HTTP_REFERER<br />

HTTP_COOKIE<br />

HTTP_FORWARDED<br />

HTTP_HOST<br />

HTTP_PROXY_CONNECTION<br />

HTTP_ACCEPT<br />

</td>

<td>

REMOTE_ADDR<br />

REMOTE_HOST<br />

REMOTE_PORT<br />

REMOTE_USER<br />

REMOTE_IDENT<br />

REQUEST_METHOD<br />

SCRIPT_FILENAME<br />

PATH_INFO<br />

QUERY_STRING<br />

AUTH_TYPE<br />

</td>

<td></td>

</tr>

<tr>

<th>server internals:</th> <th>system stuff:</th> <th>specials:</th>

</tr>

<tr>

<td>

DOCUMENT_ROOT<br />

SERVER_ADMIN<br />

SERVER_NAME<br />

SERVER_ADDR<br />

SERVER_PORT<br />

SERVER_PROTOCOL<br />

SERVER_SOFTWARE<br />

</td>

<td>

TIME_YEAR<br />

TIME_MON<br />

TIME_DAY<br />

TIME_HOUR<br />

TIME_MIN<br />

TIME_SEC<br />

TIME_WDAY<br />

TIME<br />

</td>

<td>

API_VERSION<br />

THE_REQUEST<br />

REQUEST_URI<br />

REQUEST_FILENAME<br />

IS_SUBREQ<br />

</td>

</tr>

</table>

<note>

<p>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 defined in

include/ap_mmn.h. The module API version

corresponds to the 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 (e.g., "<code>GET

/index.html HTTP/1.1</code>"). This does not

include 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>

</note>

</li>

</ul>

<p>Special Notes:</p>

<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>).</li>

<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.</li>

<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>''.</li>

<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 (<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.</li>

<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.</li>

</ol>

<p><em>CondPattern</em> is the condition pattern,

<em>i.e.</em>, a regular expression which is applied to the

current instance of the <em>TestString</em>, <em>i.e.</em>,

<em>TestString</em> is evaluated and then matched against

<em>CondPattern</em>.</p>

<p><strong>Remember:</strong> <em>CondPattern</em> is a

<em>perl compatible regular expression</em> with some

additions:</p>

<ol>

<li>You can prefix the pattern string with a

'<code>!</code>' character (exclamation mark) to specify a

<strong>non</strong>-matching pattern.</li>

<li>

There are some special variants of <em>CondPatterns</em>.

Instead of real regular expression strings you can also

use one of the following:

<ul>

<li>'<strong>&lt;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>.</li>

<li>'<strong>&gt;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>.</li>

<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

<em>TestString</em> is lexically equal to

<em>CondPattern</em>, i.e the two strings are exactly

equal (character by character). If <em>CondPattern</em>

is just <code>""</code> (two quotation marks) this

compares <em>TestString</em> to the empty string.</li>

<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.</li>

<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.</li>

<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.</li>

<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.</li>

<li>'<strong>-x</strong>' (has e<strong>x</strong>ecutable

permissions)<br />

Treats the <em>TestString</em> as a pathname and tests

if it exists and has execution permissions. These permissions

are determined depending on the underlying OS.</li>

<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!</li>

<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!</li>

</ul>

<note><title>Notice</title>

All of these tests can

also be prefixed by an exclamation mark ('!') to

negate their meaning.

</note>

</li>

</ol>

<p>Additionally you can set special flags for

<em>CondPattern</em> by appending</p>

<p class="indent">

<strong><code>[</code><em>flags</em><code>]</code></strong>

</p>

<p>as the third argument to the <code>RewriteCond</code>

directive. <em>Flags</em> is a comma-separated list of the

following flags:</p>

<ul>

<li>'<strong><code>nocase|NC</code></strong>'

(<strong>n</strong>o <strong>c</strong>ase)<br />

This makes the 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>.

This flag is effective only for comparisons between

<em>TestString</em> and <em>CondPattern</em>. It has no

effect on filesystem and subrequest checks.</li>

<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:

<example>

<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>

</example>

Without this flag you would have to write the cond/rule

three times.

</li>

</ul>

<p><strong>Example:</strong></p>

<p>To rewrite the Homepage of a site according to the

``<code>User-Agent:</code>'' header of the request, you can

use the following: </p>

<example>

<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>

</example>

<p>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.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>RewriteRule</name>

<description>Defines rules for the rewriting engine</description>

<syntax>RewriteRule

<em>Pattern</em> <em>Substitution</em></syntax>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>FileInfo</override>

<compatibility>The cookie-flag is available in Apache 2.0.40 and later.</compatibility>

<usage>

<p>The <directive>RewriteRule</directive> 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>

<p><a id="patterns" name="patterns"><em>Pattern</em></a> is

a perl compatible <a id="regexp" 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 any number of rules may already have matched and made

alterations to it.</p>

<p>Some hints about the syntax of regular expressions:</p>

<note><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; 0)

<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></note>

<p>For more information about regular expressions have a look at the

perl regular expression manpage ("<a

href="http://www.perldoc.com/perl5.6.1/pod/perlre.html">perldoc

perlre</a>"). If you are interested in more detailed

information about regular expressions and their variants

(POSIX regex <em>etc.</em>) have a look at the

following dedicated book on this topic:</p>

<p class="indent">

<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 />

</p>

<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>

<note><title>Notice</title>

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!

</note>

<p><a id="rhs" 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</p>

<ol>

<li>back-references <code>$N</code> to the RewriteRule

pattern</li>

<li>back-references <code>%N</code> to the last matched

RewriteCond pattern</li>

<li>server-variables as in rule condition test-strings

(<code>%{VARNAME}</code>)</li>

<li><a href="#mapfunc">mapping-function</a> calls

(<code>${mapname:key|default}</code>)</li>

</ol>

<p>Back-references are <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>

<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>

<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>

<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>

<note><title>Note</title>

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.

</note>

<note><title>Remember</title>

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).

</note>

<p>Additionally you can set special flags for

<em>Substitution</em> by appending</p>

<p class="indent">

<strong><code>[</code><em>flags</em><code>]</code></strong>

</p>

<p>

as the third argument to the <code>RewriteRule</code>

directive. <em>Flags</em> is a comma-separated list of the

following flags: </p>

<ul>

<li>

'<strong><code>redirect|R</code>

[=<em>code</em>]</strong>' (force <a id="redirect"

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 give 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>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 URL with

<code>http://thishost[:thisport]/</code>, rewriting

continues. 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>

<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.</li>

<li>'<strong><code>gone|G</code></strong>' (force URL to be

<strong>g</strong>one)<br />

This forces the current URL to be gone, <em>i.e.</em>, it

immediately sends back a HTTP response of 410 (GONE). Use

this flag to mark pages which no longer exist as gone.</li>

<li>

'<strong><code>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>

<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 one, <em>e.g.</em>,

'<code>/e/www/</code>'.</li>

<li>'<strong><code>next|N</code></strong>'

(<strong>n</strong>ext round)<br />

Re-run the rewriting process (starting again with the

first rewriting rule). 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 an infinite

loop!</strong></li>

<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 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!).</li>

<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

setup the content-type based on some conditions.

For example, the following snippet allows <code>.php</code> files to

be <em>displayed</em> by <code>mod_php</code> if they are called with

the <code>.phps</code> extension:

<example>

RewriteRule ^(.+\.php)s$ $1 [T=application/x-httpd-php-source]

</example>

</li>

<li>

'<strong><code>handler|H</code></strong>=<em>Content-handler</em>'

(force Content <strong>h</strong>andler)<br />

Force the Content-handler of the target file to be

<em>Content-handler</em>. For instance, this can be used to

simulate the <code>mod_alias</code> directive

<code>ScriptAlias</code> which internally forces all files

inside the mapped directory to have a handler of

``<code>cgi-script</code>''.</li>

<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>

<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.</li>

<li>'<strong><code>qsappend|QSA</code></strong>'

(<strong>q</strong>uery <strong>s</strong>tring

<strong>a</strong>ppend)<br />

This flag forces the 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.</li>

<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

<example>

RewriteRule /foo/(.*) /bar?arg=P1\%3d$1 [R,NE]

</example>

which would turn '<code>/foo/zed</code>' into a safe

request for '<code>/bar?arg=P1=zed</code>'.

</li>

<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>:

<example>

RewriteRule ^/abc(.*) /def$1 [PT]<br />

Alias /def /ghi

</example>

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>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>

</li>

<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!)</li>

<li>

'<strong><code>env|E=</code></strong><em>VAR</em>:<em>VAL</em>'

(set <strong>e</strong>nvironment variable)<br />

This forces an environment variable named <em>VAR</em> to

be set to the value <em>VAL</em>, where <em>VAL</em> can

contain regexp backreferences <code>$N</code> and

<code>%N</code> which will be expanded. You can use this

flag more than once to set more than one variable. The

variables can be later dereferenced in many situations, but

usually from within XSSI (via <code>&lt;!--#echo

var="VAR"--&gt;</code>) or CGI (<em>e.g.</em>

<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.</li>

<li>

'<strong><code>cookie|CO=</code></strong><em>NAME</em>:<em>VAL</em>:<em>domain</em>[:<em>lifetime</em>[:<em>path</em>]]'

(set <strong>co</strong>okie)<br />

This sets a cookie on the client's browser. The cookie's name

is specified by <em>NAME</em> and the value is

<em>VAL</em>. The <em>domain</em> field is the domain of the

cookie, such as '.apache.org',the optional <em>lifetime</em>

is the lifetime of the cookie in minutes, and the optional

<em>path</em> is the path of the cookie</li>

</ul>

<note><title>Note</title> 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!</p>

</note>

<note><title>Note</title>

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.

</note>

<p>Here are all possible substitution combinations and their

meanings:</p>

<p><strong>Inside per-server configuration

(<code>httpd.conf</code>)<br />

for request ``<code>GET

/somepath/pathinfo</code>'':</strong><br />

</p>

<note><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></note>

<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>

<note><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></note>

<p><strong>Example:</strong></p>

<p>We want to rewrite URLs of the form </p>

<p class="indent">

<code>/</code> <em>Language</em> <code>/~</code>

<em>Realname</em> <code>/.../</code> <em>File</em>

</p>

<p>into </p>

<p class="indent">

<code>/u/</code> <em>Username</em> <code>/.../</code>

<em>File</em> <code>.</code> <em>Language</em>

</p>

<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:</p>

<example>

<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>

</example>

</usage>

</directivesynopsis>

</modulesynopsis>