URL Rewriting Module
Version 2.4

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 additional rule conditions (which can operate on a lot of variables, including HTTP headers) for granular matching and external database lookups (either via plain text tables, DBM hash files or external processes) for advanced URL substitution.

It operates on the full URLs (including the PATH_INFO part) both in per-server context (httpd.conf) and per-dir context (.htaccess) and even can generate QUERY_STRING parts on result. The rewrittten result can lead to internal sub-processing, external request redirection or to internal proxy throughput.

The latest version can be found on
http://www.engelschall.com/sw/mod_rewrite/

Copyright © 1996 The Apache Group, All rights reserved.
Copyright © 1996 Ralf S. Engelschall, All rights reserved.

Written for The Apache Group by

Ralf S. Engelschall
rse@engelschall.com
http://www.engelschall.com/

Contents

About this Module

Summary of Functionality

 The Apache webserver API (application programmers interface) has a hook (an entry point) for URL-to-filename translation which is primarily used by this module to link itself into the server. For every request, this module is called with the requested URL (or even with an URI in a proxy-context) and has the chance to re-write this request just before the Apache server continues with all following processing steps, like running the hooks of the other modules, etc.

It's rewriting engine is rule-based where a rule primarily consists of a rewriting pattern and a rewriting substitution. The patterns are full regular expressions, as commonly known in the Unix community. They are applied to the current value of the URL.

The substitutions replace the current URL value of the pattern matched and are either:

Additionally these substitutions can have in-lined mapping-function expressions to lookup external databases (either plain text, DBM hashfile or even programs which act like a map) and hence can include strings from external sources.

Finally the rule flags can control the behaviour after a rewriting rule has been matched. There is support for rewriting loops, rewriting breaks, chained rules, pseudo if-then-else constructs, forced redirects, forced MIME-types, forced proxy-module throughput etc.

When a URL expands to a non-self-referencing URI by means of a substitution, it will automatically lead to an external request redirection at the end of the rewriting process. If the generated URI is self-referencing (i.e. http://thishost[:thisport]), then this automatically gets stripped down to a URL. This provides support for so-called webclusters with homogeneous URL trees.

Optionally, any rewriting rule can be preceded by any number of additional rewriting conditions. These are pairs of condition strings (which can be constructed out of a rich set of variables) and condition patterns. The condition patterns are again regular expressions and get matched against the runtime-evaluated condition string. Preceding a rule with such conditions mean that the rule is only fully applied if the rule pattern matches and all of the preceding rule conditions do so as well. This gives you a flexible way to adjust the situation in which your rules are applied.

This functionality can be used in four contexts:

  1. Used by the administrator inside the server config file (httpd.conf) for global per-server context outside of any VirtualHost blocks.
    Here the rules are applied to all URLs, i.e. to all URLs of the main server and all URLs of the virtual servers.

  2. Used by the administrator inside the server config file (httpd.conf) for global per-server context inside of any VirtualHost blocks.
    Here the rules are applied only to URLs of a specific virtual server.

  3. Used by the administrator inside the server config file (httpd.conf) for local per-directory context inside of any Directory blocks.
    Here the rules are applied only to URLs for the specific directory.

  4. Used by the users inside their directory config files (.htaccess) for local per-directory context.
    Here the rules are applied only to URLs for the specific directory.
This consistent usage is provided for maximum flexibility. But there is a slight difference between situations 1 & 2 and 3 & 4: This difference is subtle but very important, because only this way it is possibly to do a lot of special rewriting tricks in the per-directory context!

New Features

The URL rewriting module adds a lot of new features to the Apache server which are not possible with the aliasing and rewriting mechanism provided by the standard functionality inherited from the NCSA webserver. These are listed where:

Side Effects

You can safely compile mod_rewrite into the Apache server, because this module is only triggered with its server configuration directives.

Only the RewriteRule directive is a runtime one and causes URL rewriting actions to really happen, and then only if the RewriteEngine on directive is used too. In other words: Unless you set "RewriteEngine on" there are no side effects!

Tested Apache Versions

Although this module's history starts with the Apache 1.0 API in February 1996, it was moved to the Apache 1.1 API very early. This means it will NOT run with any Apache server prior to 1.1b0!

It runs fine with any beta release of Apache 1.1 and (of course) with the current official release: Apache 1.1.1. If you want to use this module but still have an older version of the Apache server running, please upgrade first!

From version 2.1 mod_rewrite has support for Apache version 1.2-dev which already has its own POSIX library included.

Installation
You have to carry out the following steps to install this module into your Apache server.

Preconditions:

Installation for Apache 1.1.x

$ cd /tmp/mod_rewrite
$ cp mod_rewrite*[hc] /usr/local/apache/dist/src/
$ cp -r misc/for-apache-1.1.x/regexp /usr/local/apache/dist/src/
$ cp misc/for-apache-1.1.x/util_script.c.diff /usr/local/apache/dist/src/
$ cp misc/for-apache-1.1.x/mod_negotiation.c.diff /usr/local/apache/dist/src/
$ cd /usr/local/apache/dist/src/
$ patch <util_script.c.diff
$ patch <mod_negotiation.c.diff
$ vi Configuration
  |    :
  | EXTRA_LIBS= regexp/libregexp.a
  |    :
  | Module rewrite_module mod_rewrite.o
  |    :
$ ./Configure
$ (cd regexp; make)
$ make
NOTICE: 'Module rewrite_module mod_rewrite.o' must come after any other Modules that contain a URL-to-filename hook. Since it is not obvious which these are, the simple solution is to make it the last module in the Configuration list.

Installation for Apache 1.2.x

$ cd /tmp/mod_rewrite
$ cp mod_rewrite*[hc] /usr/local/apache/dist/src/
$ cd /usr/local/apache/dist/src/
$ vi Configuration
  |    :
  | Module rewrite_module mod_rewrite.o
  |    :
$ ./Configure
$ make

Configuration Directives

RewriteEngine

 Syntax: RewriteEngine {on,off}
Default: RewriteEngine off
Context: server config, virtual host, per-directory config

The RewriteEngine directive enables or disables the runtime rewriting engine. If it is set to off this module does no runtime processing at all. It does not even update the SCRIPT_URx environment variables.

Use this directive to disable the module instead of commenting out all RewriteRule directives!

RewriteOptions

Syntax: RewriteOptions Option ...
Default: -None-
Context: server config, virtual host, per-directory config

The RewriteOption directive sets some special options for the current per-server or per-directory configuration. The Option strings can be one of the following:

RewriteLog

Syntax: RewriteLog Filename
Default: -None-
Context: server config, virtual host

The RewriteLog 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 ('/') then it is assumed to be relative to the Server Root. The directive should occur only once per server config.

To disable the logging of rewriting actions it is not recommended to set Filename to /dev/null, because although the rewriting engine does not create output to a logfile it still creates the logfile output internally. This will slow down the server with no advantage to the administrator! To disable logging either remove or comment out the RewriteLog directive or use RewriteLogLevel 0!

Example: 

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

RewriteLogLevel

Syntax: RewriteLogLevel Level
Default: RewriteLogLevel 0
Context: server config, virtual host

The RewriteLogLevel directive set the verbosity level of the rewriting logfile. The default level 0 means no logging, while 9 or more means that practically all actions are logged.

To disable the logging of rewriting actions simply set Level to 0. This disables all rewrite action logs.

Notice: Using a high value for Level will slow down your Apache server dramatically! Use the rewriting logfile only for debugging or at least at Level not greater than 2!

Example: 

RewriteLogLevel 3

RewriteMap

Syntax: RewriteMap Mapname {txt,dbm,prg}:Filename
Default: not used per default
Context: server config, virtual host

The RewriteMap directive defines an external Rewriting Map which can be used inside rule substitution strings by the mapping-functions to insert/substitute fields through a key lookup.

The Mapname is the name of the map and will be used to specify a mapping-function for the substitution strings of a rewriting rule via

${ Mapname : LookupKey | DefaultValue }
When such a directive occurs the map Mapname is consulted and the key LookupKey is looked-up. If the key is found, the map-function directive is substituted by SubstValue. If the key is not found then it is substituted by DefaultValue.

The Filename must be a valid Unix filepath, containing one of the following formats:

  1. Plain Text Format

    This is a ASCII file which contains either blank lines, comment lines (starting with a '#' character) or

    MatchingKey SubstValue
    pairs - one per line. You can create such files either manually, using your favorite editor, or by using the programs mapcollect and mapmerge from the support directory of the mod_rewrite distribution.

    To declare such a map prefix, Filename with a txt: string as in the following example: 

    #
#   map.real-to-user -- maps realnames to usernames
#

Ralf.S.Engelschall    rse   # Bastard Operator From Hell 
Dr.Fred.Klabuster     fred  # Mr. DAU


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

  2. DBM Hashfile Format

    This is a binary NDBM format file containing the same contents as the Plain Text Format files. You can create such a file with any NDBM tool or with the dbmmanage program from the support directory of the Apache distribution.

    To declare such a map prefix Filename with a dbm: string.

  3. Program Format

    This is a Unix executable, not a lookup file. To create it you can use the language of your choice, but the result has to be a runable Unix binary (i.e. either object-code or a script with the magic cookie trick '#!/path/to/interpreter' as the first line).

    This program gets started once at startup of the Apache servers and then communicates with the rewriting engine over its stdin and stdout filehandles. For each map-function lookup it will receive the key to lookup as a newline-terminated string on stdin. It then has to give back the looked-up value as a newline-terminated string on stdout or the four-character string ``NULL'' if it fails (i.e. there is no corresponding value for the given key). A trivial program which will implement a 1:1 map (i.e. key == value) could be: 

    #!/usr/bin/perl
$| = 1;
while (<STDIN>) {
    # ...here any transformations 
    # or lookups should occur...
    print $_;
}

    But be very careful:

    1. ``Keep the program simple, stupid'' (KISS), because if this program hangs it will lead to a hang of the Apache server when the rule occurs.
    2. Avoid one common mistake: never do buffered I/O on stdout! This will cause a deadloop! Hence the ``$|=1'' in the above example...

    To declare such a map prefix Filename with a prg: string.

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

For plain text and DBM format files the looked-up keys are cached in-core until the mtime of the mapfile changes or the server does a restart. This way you can have map-functions in rules which are used for every request. This is no problem, because the external lookup only happens once!

RewriteBase

Syntax: RewriteBase BaseURL
Default: default is the physical directory path
Context: per-directory config

The RewriteBase directive explicitly sets the base URL for per-directory rewrites. As you will see below, RewriteRule can be used in per-directory config files (.htaccess). There it will act locally, i.e. 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.

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. But at most websites URLs are NOT directly related to physical filename paths, so this assumption will be usually be wrong! There you have to use the RewriteBase directive to specify the correct URL-prefix.

So, if your webserver's URLs are not directly related to physical file paths, you have to use RewriteBase in every .htaccess files where you want to use RewriteRule directives.

Example:

Assume the following per-directory config file: 

#
#  /abc/def/.htaccess -- per-dir config file for directory /abc/def
#  Remember: /abc/def is the physical path of /xyz, i.e. the server
#            has a 'Alias /xyz /abc/def' directive e.g.
#

RewriteEngine On

#  let the server know that we are reached via /xyz and not 
#  via the physical path prefix /abc/def
RewriteBase   /xyz

#  now the rewriting rules
RewriteRule   ^oldstuff\.html$  newstuff.html

In the above example, a request to /xyz/oldstuff.html gets correctly rewritten to the physical file /abc/def/newstuff.html.

For the Apache hackers:
The following list gives detailed information about the internal processing steps: 

Request:
  /xyz/oldstuff.html

Internal Processing:
  /xyz/oldstuff.html     -> /abc/def/oldstuff.html    (per-server Alias)
  /abc/def/oldstuff.html -> /abc/def/newstuff.html    (per-dir    RewriteRule)
  /abc/def/newstuff.html -> /xyz/newstuff.html        (per-dir    RewriteBase)
  /xyz/newstuff.html     -> /abc/def/newstuff.html    (per-server Alias)

Result:
  /abc/def/newstuff.html
This seems very complicated but is the correct Apache internal processing, because the per-directory rewriting comes too late in the process. So, when it occurs the (rewritten) request has to be re-injected into the Apache kernel! BUT: While this seems like a serious overhead, it really isn't, because this re-injection happens fully internal to the Apache server and the same procedure is used by many other operations inside Apache. So, you can be sure the design and implementation is correct.

RewriteCond

Syntax: RewriteCond TestString CondPattern
Default: -None-
Context: server config, virtual host, per-directory config

The RewriteCond directive defines a rule condition. Precede a RewriteRule directive with one ore more RewriteCond directives. The following rewriting rule is only used if its pattern matches the current state of the URI AND if these additional conditions apply, too.

TestString is a string which contains server-variables of the form

%{ NAME_OF_VARIABLE }
where NAME_OF_VARIABLE can be a string of the following list:

HTTP headers:

HTTP_USER_AGENT
HTTP_REFERER
HTTP_COOKIE
HTTP_FORWARDED
HTTP_HOST
HTTP_PROXY_CONNECTION
HTTP_ACCEPT

connection & request:

REMOTE_ADDR
REMOTE_HOST
REMOTE_USER
REMOTE_IDENT
REQUEST_METHOD
SCRIPT_FILENAME
PATH_INFO
QUERY_STRING
AUTH_TYPE

server internals:

DOCUMENT_ROOT
SERVER_ADMIN
SERVER_NAME
SERVER_PORT
SERVER_PROTOCOL
SERVER_SOFTWARE
SERVER_VERSION

system stuff:

TIME_YEAR
TIME_MON
TIME_DAY
TIME_HOUR
TIME_MIN
TIME_SEC
TIME_WDAY

specials:

API_VERSION
THE_REQUEST
REQUEST_URI
REQUEST_FILENAME
IS_SUBREQ

These variables all correspond to the similar named HTTP MIME-headers, C variables of the Apache server or struct tm fields of the Unix system.

Special Notes:

  1. The variables SCRIPT_FILENAME and REQUEST_FILENAME contain the same value, i.e. the value of the filename field of the internal request_rec 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 uri field of request_rec).

  2. There is the special format: %{ENV:variable} where variable can be any environment variable. This is looked-up via internal Apache structures and (if not found there) via getenv() from the Apache server process.

  3. There is the special format: %{HTTP:header} where header can be any HTTP MIME-header name. This is looked-up from the HTTP request. Example: %{HTTP:Proxy-Connection} is the value of the HTTP header ``Proxy-Connection:''.

  4. There is the special format: %{LA-U:url} for look-aheads like -U. This performans a internal sub-request to look-ahead for the final value of url.

  5. There is the special format: %{LA-F:file} for look-aheads like -F. This performans a internal sub-request to look-ahead for the final value of file.

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

Remember: CondPattern is a standard Extended Regular Expression with some additions:

  1. You can precede the pattern string with a '!' character (exclamation mark) to specify a non-matching pattern.

  2. There are some special variants of CondPatterns. Instead of real regular expression strings you can also use one of the following:

    • '-d' (is directory)
      Treats the TestString as a pathname and tests if it exists and is a directory.

    • '-f' (is regular file)
      Treats the TestString as a pathname and tests if it exists and is a regular file.

    • '-s' (is regular file with size)
      Treats the TestString as a pathname and tests if it exists and is a regular file with size greater then zero.

    • '-l' (is symbolic link)
      Treats the TestString as a pathname and tests if it exists and is a symbolic link.

    • '-F' (is existing file via subrequest)
      Checks if TestString 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!

    • '-U' (is existing URL via subrequest)
      Checks if TestString 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 servers performance!

    Notice: All of these tests can also be prefixed by a not ('!') character to negate their meaning.

Additionally you can set special flags for CondPattern by appending

[flags]
as the third argument to the RewriteCond directive. Flags is a comma-separated list of the following flags:

Example:

To rewrite the Homepage of a site according to the ``User-Agent:'' header of the request, you can use the following: 
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]
Interpretation: If you use Netscape Navigator as your browser (which identifies itself as 'Mozilla'), then you get the max homepage, which includes Frames, etc. If you use the Lynx browser (which is Terminal-based), then you get the min homepage, which contains no images, no tables, etc. If you use any other browser you get the standard homepage.

RewriteRule

Syntax: RewriteRule Pattern Substitution
Default: -None-
Context: server config, virtual host, per-directory config

The RewriteRule directive is the real rewriting workhorse. The directive can occur more than once. Each directive then defines one single rewriting rule. The definition order of these rules is important, because this order is used when applying the rules at run-time.

Pattern can be (for Apache 1.1.x a System V8 and for Apache 1.2.x a POSIX) regular expression which gets applied to the current URL. Here ``current'' means the value of the URL when this rule gets applied. This may not be the original requested URL, because there could be any number of rules before which already matched and made alterations to it.

Some hints about the syntax of regular expressions: 

^           Start of line
$           End of line
.           Any single character
[chars]     One of chars 
[^chars]    None of chars 

?           0 or 1 of the preceding char
*           0 or N of the preceding char
+           1 or N of the preceding char

\char       escape that specific char 
            (e.g. for specifying the chars ".[]()" etc.)

(string)    Grouping of chars (the Nth group can be used on the RHS with $N)

Additionally the NOT character ('!') is a possible pattern prefix. This gives you the ability to negate a pattern; to say, for instance: ``if the current URL does NOT match to this pattern''. This can be used for special cases where it is better to match the negative pattern or as a last default rule.

Notice! 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 $N in the substitution string!

Substitution of a rewriting rule is the string which is substituted for (or replaces) the original URL for which Pattern matched. Beside plain text you can use

  1. pattern-group back-references ($N)
  2. server-variables as in rule condition test-strings (%{VARNAME})
  3. mapping-function calls (${mapname:key|default})
Back-references are $N (N=1..9) identifiers which will be replaced by the contents of the Nth group of the matched Pattern. The server-variables are the same as for the TestString of a RewriteCond directive. The mapping-functions come from the RewriteMap directive and are explained there. These three types of variables are expanded in the order of the above list.

As already mentioned above, all the rewriting rules are applied to the Substitution (in the order of definition in the config file). The URL is completely replaced by the Substitution and the rewriting process goes on until there are no more rules (unless explicitly terminated by a L flag - see below).

There is a special substitution string named '-' which means: NO substitution! Sounds silly? No, it is useful to provide rewriting rules which only match some URLs but do no substitution, e.g. in conjunction with the C (chain) flag to be able to have more than one pattern to be applied before a substitution occurs.

Notice: There is a special feature. When you prefix a substitution field with http://thishost[:thisport] then mod_rewrite 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.

Remember: An unconditional external redirect to your own server will not work with the prefix http://thishost because of this feature. To achieve such a self-redirect, you have to use the R-flag (see below).

Additionally you can set special flags for Substitution by appending

[flags]
as the third argument to the RewriteRule directive. Flags is a comma-separated list of the following flags:

Remember: Never forget that Pattern gets applied to a complete URL in per-server configuration files. But in per-directory configuration files, the per-directory prefix (which always is the same for a specific directory!) gets automatically removed for the pattern matching and automatically added after the substitution has been done. 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.

There is one exception: If a substitution string starts with ``http://'' then the directory prefix will be not added and a external redirect or proxy throughput (if flag P is used!) is forced!

Notice! To enable the rewriting engine for per-directory configuration files you need to set ``RewriteEngine On'' in these files and ``Option FollowSymLinks'' enabled. If your administrator has disabled override of FollowSymLinks for a user's directory, then you cannot use the rewriting engine. This restriction is needed for security reasons.

Here are all possible substitution combinations and their meanings:

Inside per-server configuration (httpd.conf)
for request ``GET /somepath/pathinfo'':

Given Rule                                      Resulting Substitution
----------------------------------------------  ----------------------------------
^/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

Inside per-directory configuration for /somepath
(i.e. file .htaccess in dir /physical/path/to/somepath containing RewriteBase /somepath)
for request ``GET /somepath/localpath/pathinfo'':

Given Rule                                      Resulting Substitution
----------------------------------------------  ----------------------------------
^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

Example:

We want to rewrite URLs of the form
/ Language /~ Realname /.../ File
into
/u/ Username /.../ File . Language

We take the rewrite mapfile from above and save it under /anywhere/map.real-to-user. Then we only have to add the following lines to the Apache server configuration file: 

RewriteLog   /anywhere/rewrite.log
RewriteMap   real-to-user               txt:/anywhere/map.real-to-host
RewriteRule  ^/([^/]+)/~([^/]+)/(.*)$   /u/${real-to-user:$2|nobody}/$3.$1

Special Features

Environment Variables

 This module keeps track of two additional (non-standard) CGI/SSI environment variables named SCRIPT_URL and SCRIPT_URI. These contain the logical Web-view to the current resource, while the standard CGI/SSI variables SCRIPT_NAME and SCRIPT_FILENAME contain the physical System-view.

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

Example: 

SCRIPT_NAME=/v/sw/free/lib/apache/global/u/rse/.www/index.html
SCRIPT_FILENAME=/u/rse/.www/index.html
SCRIPT_URL=/u/rse/
SCRIPT_URI=http://en2.en.sdm.de/u/rse/
Two practical uses:
  • Creation of generic SSI-footers containing a reference about the URI of the current page: 

       :
<ht>
<center>
URI: <--#echo var="SCRIPT_URI"-->
</center>
   :

  • Creation of absolute references to a relative file, e.g. for the use with the Refresh:-header where a new file is loaded after a period of time. In this example the new file has to be referenced by an absolute URL (i.e. an URI). Here is a way to do it [by the help of embedded Perl for HTML (ePerl), which can be obtained from http://www.engelschall.com/sw/eperl/]: 

    <!DOCTYPE html PUBLIC '-//IETF//DTD HTML 2.0//EN'>
<META HTTP-EQUIV="Refresh" 
      CONTENT="4; URL=<? $URI = $ENV{'SCRIPT_URI'};
                         $URI =~ s|[^/]+$||;
                         $URI .= "other-rel-doc.html";
                         print $URI;                  !>" >
<html>
   :













Practical Examples





The author runs some websites and use this module for a lot
of tasks. Some special solutions are listed here:



There are a lot of other situations where this module can help or, indeed,
which can only be solved with the help of this module. For a complete set of
practical solutions check the mod_rewrite
Solutions Database. 








Frequently Asked Questions














Comparison to similar Modules







mod_alias

(core module)







(**) The complete simulation does only work if and only if 
the directory /XYZ has ExecCGI option set, too!




     

Result: mod_rewrite can fully replace mod_alias.





For a automatic server-internal directive conversion,

please have a look at the
mod_rewrite_compat module!














mod_userdir

(core module)



[request is /~bar/one/two.html]




Result: mod_rewrite can fully replace mod_userdir.





For a automatic server-internal directive conversion,

please have a look at the
mod_rewrite_compat module!













mod_userdir_virtual

(contributed module)






Result: mod_rewrite can fully replace mod_userdir_virtual.














mod_userpath

(contributed module)






Result: mod_rewrite can fully replace mod_userpath.











mod_uri_remap

(contributed module)






Result: mod_rewrite can fully replace mod_uri_remap.










Additional Modules







mod_rewrite_compat




Summary


This module provides backward-compatibility for the older and less powerful
core-modules mod_alias and mod_userdir. 


Installation





Usage


Use your old directives from mod_alias and
mod_userdir, which automatically get converted into the correct form
of the corresponding directive from mod_rewrite.










mod_rewrite_status




Summary


This module is similar to the core modules mod_status and
mod_info. It provides for online information about the actual
internal configuration information of mod_rewrite.


Installation


This module is contained in the standard distribution of
mod_rewrite.




Usage


Just request the URL /rewritestatus through your favorite Web browser.