URL Rewriting Guide

Available Languages: en

- - -

This document supplements the mod_rewrite - reference documentation. - It describes how one can use Apache's mod_rewrite - to solve typical URL-based problems with which webmasters are - commonony confronted. We give detailed descriptions on how to - solve each problem by configuring URL rewriting rulesets.

- -

ATTENTION: Depending on your server configuration - it may be necessary to slightly change the examples for your - situation, e.g. adding the [PT] flag when - additionally using mod_alias and - mod_userdir, etc. Or rewriting a ruleset - to fit in .htaccess context instead - of per-server context. Always try to understand what a - particular ruleset really does before you use it. This - avoids many problems.

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Canonical URLs
Canonical Hostnames
Moved DocumentRoot
Trailing Slash Problem
Move Homedirs to Different Webserver
Search pages in more than one directory
Set Environment Variables According To URL Parts
Virtual User Hosts
Redirect Homedirs For Foreigners
Redirecting Anchors
Time-Dependent Rewriting
Backward Compatibility for YYYY to XXXX migration
Content Handling
Access Restriction
Other

Canonical URLs

- - - -

Description:

On some webservers there are more than one URL for a - resource. Usually there are canonical URLs (which should be - actually used and distributed) and those which are just - shortcuts, internal ones, etc. Independent of which URL the - user supplied with the request he should finally see the - canonical one only.

Solution:

We do an external HTTP redirect for all non-canonical - URLs to fix them in the location view of the Browser and - for all subsequent requests. In the example ruleset below - we replace /~user by the canonical - /u/user and fix a missing trailing slash for - /u/user.

- -

-RewriteRule   ^/~([^/]+)/?(.*)    /u/$1/$2  [R]
-RewriteRule   ^/([uge])/([^/]+)$  /$1/$2/   [R]
-

- -

Canonical Hostnames

- -

Description:

The goal of this rule is to force the use of a particular - hostname, in preference to other hostnames which may be used to - reach the same site. For example, if you wish to force the use - of www.example.com instead of - example.com, you might use a variant of the - following recipe.

Solution:

For sites running on a port other than 80:

-RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST}   !^$
-RewriteCond %{SERVER_PORT} !^80$
-RewriteRule ^/(.*)         http://fully.qualified.domain.name:%{SERVER_PORT}/$1 [L,R]
-

- -

And for a site running on port 80

-RewriteCond %{HTTP_HOST}   !^fully\.qualified\.domain\.name [NC]
-RewriteCond %{HTTP_HOST}   !^$
-RewriteRule ^/(.*)         http://fully.qualified.domain.name/$1 [L,R]
-

- -

Moved `DocumentRoot`

- - - -

Description:

Usually the DocumentRoot -of the webserver directly relates to the URL "/". -But often this data is not really of top-level priority. For example, -you may wish for visitors, on first entering a site, to go to a -particular subdirectory /about/. This may be accomplished -using the following ruleset:

Solution:

We redirect the URL / to - /about/: -

- -

-RewriteEngine on
-RewriteRule   ^/$  /about/  [R]
-

- -

Note that this can also be handled using the RedirectMatch directive:

- -

-RedirectMatch ^/$ http://example.com/e/www/ -

- -

Trailing Slash Problem

- - - -

Description:

The vast majority of "trailing slash" problems can be dealt - with using the techniques discussed in the FAQ - entry. However, occasionally, there is a need to use mod_rewrite - to handle a case where a missing trailing slash causes a URL to - fail. This can happen, for example, after a series of complex - rewrite rules.

Solution:

The solution to this subtle problem is to let the server - add the trailing slash automatically. To do this - correctly we have to use an external redirect, so the - browser correctly requests subsequent images etc. If we - only did a internal rewrite, this would only work for the - directory page, but would go wrong when any images are - included into this page with relative URLs, because the - browser would request an in-lined object. For instance, a - request for image.gif in - /~quux/foo/index.html would become - /~quux/image.gif without the external - redirect!

- -

So, to do this trick we write:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo$  foo/  [R]
-

- -

Alternately, you can put the following in a - top-level .htaccess file in the content directory. - But note that this creates some processing overhead.

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteCond    %{REQUEST_FILENAME}  -d
-RewriteRule    ^(.+[^/])$           $1/  [R]
-

- -

Move Homedirs to Different Webserver

- - - -

Description:

Many webmasters have asked for a solution to the - following situation: They wanted to redirect just all - homedirs on a webserver to another webserver. They usually - need such things when establishing a newer webserver which - will replace the old one over time.

Solution:

The solution is trivial with mod_rewrite. - On the old webserver we just redirect all - /~user/anypath URLs to - http://newserver/~user/anypath.

- -

-RewriteEngine on
-RewriteRule   ^/~(.+)  http://newserver/~$1  [R,L]
-

- -

Search pages in more than one directory

- - - -

Description:

Sometimes it is necessary to let the webserver search - for pages in more than one directory. Here MultiViews or - other techniques cannot help.

Solution:

We program a explicit ruleset which searches for the - files in the directories.

- -

-RewriteEngine on
-
-#   first try to find it in custom/...
-#   ...and if found stop and be happy:
-RewriteCond         /your/docroot/dir1/%{REQUEST_FILENAME}  -f
-RewriteRule  ^(.+)  /your/docroot/dir1/$1  [L]
-
-#   second try to find it in pub/...
-#   ...and if found stop and be happy:
-RewriteCond         /your/docroot/dir2/%{REQUEST_FILENAME}  -f
-RewriteRule  ^(.+)  /your/docroot/dir2/$1  [L]
-
-#   else go on for other Alias or ScriptAlias directives,
-#   etc.
-RewriteRule   ^(.+)  -  [PT]
-

- -

Set Environment Variables According To URL Parts

- - - -

Description:

Perhaps you want to keep status information between - requests and use the URL to encode it. But you don't want - to use a CGI wrapper for all pages just to strip out this - information.

Solution:

We use a rewrite rule to strip out the status information - and remember it via an environment variable which can be - later dereferenced from within XSSI or CGI. This way a - URL /foo/S=java/bar/ gets translated to - /foo/bar/ and the environment variable named - STATUS is set to the value "java".

- -

-RewriteEngine on
-RewriteRule   ^(.*)/S=([^/]+)/(.*)    $1/$3 [E=STATUS:$2]
-

- -

Virtual User Hosts

- - - -

Description:

Assume that you want to provide - www.username.host.domain.com - for the homepage of username via just DNS A records to the - same machine and without any virtualhosts on this - machine.

Solution:

For HTTP/1.0 requests there is no solution, but for - HTTP/1.1 requests which contain a Host: HTTP header we - can use the following ruleset to rewrite - http://www.username.host.com/anypath - internally to /home/username/anypath:

- -

-RewriteEngine on
-RewriteCond   %{HTTP_HOST}                 ^www\.[^.]+\.host\.com$
-RewriteRule   ^(.+)                        %{HTTP_HOST}$1          [C]
-RewriteRule   ^www\.([^.]+)\.host\.com(.*) /home/$1$2
-

- -

Redirect Homedirs For Foreigners

- - - -

Description:

We want to redirect homedir URLs to another webserver - www.somewhere.com when the requesting user - does not stay in the local domain - ourdomain.com. This is sometimes used in - virtual host contexts.

Solution:

Just a rewrite condition:

- -

-RewriteEngine on
-RewriteCond   %{REMOTE_HOST}  !^.+\.ourdomain\.com$
-RewriteRule   ^(/~.+)         http://www.somewhere.com/$1 [R,L]
-

- -

Redirecting Anchors

- - - -

Description:: -
By default, redirecting to an HTML anchor doesn't work, - because mod_rewrite escapes the # character, - turning it into %23. This, in turn, breaks the - redirection.
-
Solution:: -
Use the [NE] flag on the - RewriteRule. NE stands for No Escape. -
-

- -

Time-Dependent Rewriting

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Description:

When tricks like time-dependent content should happen a - lot of webmasters still use CGI scripts which do for - instance redirects to specialized pages. How can it be done - via mod_rewrite?

Solution:

There are a lot of variables named TIME_xxx - for rewrite conditions. In conjunction with the special - lexicographic comparison patterns <STRING, - >STRING and =STRING we can - do time-dependent redirects:

- -

-RewriteEngine on
-RewriteCond   %{TIME_HOUR}%{TIME_MIN} >0700
-RewriteCond   %{TIME_HOUR}%{TIME_MIN} <1900
-RewriteRule   ^foo\.html$             foo.day.html
-RewriteRule   ^foo\.html$             foo.night.html
-

- -

This provides the content of foo.day.html - under the URL foo.html from - 07:00-19:00 and at the remaining time the - contents of foo.night.html. Just a nice - feature for a homepage...

- -

Backward Compatibility for YYYY to XXXX migration

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Description:

How can we make URLs backward compatible (still - existing virtually) after migrating document.YYYY - to document.XXXX, e.g. after translating a - bunch of .html files to .phtml?

Solution:

We just rewrite the name to its basename and test for - existence of the new extension. If it exists, we take - that name, else we rewrite the URL to its original state.

- - -

-#   backward compatibility ruleset for
-#   rewriting document.html to document.phtml
-#   when and only when document.phtml exists
-#   but no longer document.html
-RewriteEngine on
-RewriteBase   /~quux/
-#   parse out basename, but remember the fact
-RewriteRule   ^(.*)\.html$              $1      [C,E=WasHTML:yes]
-#   rewrite to document.phtml if exists
-RewriteCond   %{REQUEST_FILENAME}.phtml -f
-RewriteRule   ^(.*)$ $1.phtml                   [S=1]
-#   else reverse the previous basename cutout
-RewriteCond   %{ENV:WasHTML}            ^yes$
-RewriteRule   ^(.*)$ $1.html
-

- -

Content Handling

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From Old to New (intern)

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Description:

Assume we have recently renamed the page - foo.html to bar.html and now want - to provide the old URL for backward compatibility. Actually - we want that users of the old URL even not recognize that - the pages was renamed.

Solution:

We rewrite the old URL to the new one internally via the - following rule:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  bar.html
-

- - - -

From Old to New (extern)

- - - -

Description:

Assume again that we have recently renamed the page - foo.html to bar.html and now want - to provide the old URL for backward compatibility. But this - time we want that the users of the old URL get hinted to - the new one, i.e. their browsers Location field should - change, too.

Solution:

We force a HTTP redirect to the new URL which leads to a - change of the browsers and thus the users view:

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  bar.html  [R]
-

- - - -

From Static to Dynamic

- - - -

Description:

How can we transform a static page - foo.html into a dynamic variant - foo.cgi in a seamless way, i.e. without notice - by the browser/user.

Solution:

We just rewrite the URL to the CGI-script and force the - correct MIME-type so it gets really run as a CGI-script. - This way a request to /~quux/foo.html - internally leads to the invocation of - /~quux/foo.cgi.

- -

-RewriteEngine  on
-RewriteBase    /~quux/
-RewriteRule    ^foo\.html$  foo.cgi  [T=application/x-httpd-cgi]
-

- - -

Access Restriction

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Blocking of Robots

- - - -

Description:

How can we block a really annoying robot from - retrieving pages of a specific webarea? A - /robots.txt file containing entries of the - "Robot Exclusion Protocol" is typically not enough to get - rid of such a robot.

Solution:

We use a ruleset which forbids the URLs of the webarea - /~quux/foo/arc/ (perhaps a very deep - directory indexed area where the robot traversal would - create big server load). We have to make sure that we - forbid access only to the particular robot, i.e. just - forbidding the host where the robot runs is not enough. - This would block users from this host, too. We accomplish - this by also matching the User-Agent HTTP header - information.

- -

-RewriteCond %{HTTP_USER_AGENT}   ^NameOfBadRobot.*
-RewriteCond %{REMOTE_ADDR}       ^123\.45\.67\.[8-9]$
-RewriteRule ^/~quux/foo/arc/.+   -   [F]
-

- - - -

Blocked Inline-Images

- - - -

Description:

Assume we have under http://www.quux-corp.de/~quux/ - some pages with inlined GIF graphics. These graphics are - nice, so others directly incorporate them via hyperlinks to - their pages. We don't like this practice because it adds - useless traffic to our server.

Solution:

While we cannot 100% protect the images from inclusion, - we can at least restrict the cases where the browser - sends a HTTP Referer header.

- -

-RewriteCond %{HTTP_REFERER} !^$
-RewriteCond %{HTTP_REFERER} !^http://www.quux-corp.de/~quux/.*$ [NC]
-RewriteRule .*\.gif$        -                                    [F]
-

- -

-RewriteCond %{HTTP_REFERER}         !^$
-RewriteCond %{HTTP_REFERER}         !.*/foo-with-gif\.html$
-RewriteRule ^inlined-in-foo\.gif$   -                        [F]
-

- - - -

Proxy Deny

- - - -

Description:

How can we forbid a certain host or even a user of a - special host from using the Apache proxy?

Solution:

We first have to make sure mod_rewrite - is below(!) mod_proxy in the Configuration - file when compiling the Apache webserver. This way it gets - called before mod_proxy. Then we - configure the following for a host-dependent deny...

- -

-RewriteCond %{REMOTE_HOST} ^badhost\.mydomain\.com$
-RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
-

- -

...and this one for a user@host-dependent deny:

- -

-RewriteCond %{REMOTE_IDENT}@%{REMOTE_HOST}  ^badguy@badhost\.mydomain\.com$
-RewriteRule !^http://[^/.]\.mydomain.com.*  - [F]
-

- - - -

Other

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External Rewriting Engine

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Description:

A FAQ: How can we solve the FOO/BAR/QUUX/etc. - problem? There seems no solution by the use of - mod_rewrite...

Solution:

Use an external RewriteMap, i.e. a program which acts - like a RewriteMap. It is run once on startup of Apache - receives the requested URLs on STDIN and has - to put the resulting (usually rewritten) URL on - STDOUT (same order!).

- -

-RewriteEngine on
-RewriteMap    quux-map       prg:/path/to/map.quux.pl
-RewriteRule   ^/~quux/(.*)$  /~quux/${quux-map:$1}
-

- -

-#!/path/to/perl
-
-#   disable buffered I/O which would lead
-#   to deadloops for the Apache server
-$| = 1;
-
-#   read URLs one per line from stdin and
-#   generate substitution URL on stdout
-while (<>) {
-    s|^foo/|bar/|;
-    print $_;
-}
-

- -

This is a demonstration-only example and just rewrites - all URLs /~quux/foo/... to - /~quux/bar/.... Actually you can program - whatever you like. But notice that while such maps can be - used also by an average user, only the - system administrator can define it.

- - - -

URL Rewriting Guide

See also

Time-Dependent Rewriting

Backward Compatibility for YYYY to XXXX migration

From Old to New (intern)

From Old to New (extern)

From Static to Dynamic

Blocking of Robots

Blocked Inline-Images

Proxy Deny

External Rewriting Engine