<-
Apache > HTTP Server > Documentation > Version 2.2 > Modules

Apache Module mod_rewrite

Available Languages:  en 

Description:Provides a rule-based rewriting engine to rewrite requested URLs on the fly
Status:Extension
Module Identifier:rewrite_module
Source File:mod_rewrite.c
Compatibility:Available in Apache 1.3 and later

Summary

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.

This module operates on the full URLs (including the path-info part) both in per-server context (httpd.conf) and per-directory context (.htaccess) 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.

Further details, discussion, and examples, are provided in the detailed mod_rewrite documentation.

Directives

Topics

top

Quoting Special Characters

As of Apache 1.3.20, special characters in TestString and Substitution strings can be escaped (that is, treated as normal characters without their usual special meaning) by prefixing them with a slash ('\') character. In other words, you can include an actual dollar-sign character in a Substitution string by using '\$'; this keeps mod_rewrite from trying to treat it as a backreference.

top

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., before any rewriting. This is important because the rewriting process is primarily used to rewrite logical URLs to physical pathnames.

Example

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/
top

Practical Solutions

For numerous examples of common, and not-so-common, uses for mod_rewrite, see the Rewrite Guide, and the Advanced Rewrite Guide documents.

top

RewriteBase Directive

Description:Sets the base URL for per-directory rewrites
Syntax:RewriteBase URL-path
Default:See usage for information.
Context:directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite

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 back to the path. The default setting is; RewriteBase physical-directory-path

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 usually be wrong! There you have to use the RewriteBase directive to specify the correct URL-prefix.

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.

For 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 were 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 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 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.

top

RewriteCond Directive

Description:Defines a condition under which rewriting will take place
Syntax: RewriteCond TestString CondPattern
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite

The RewriteCond directive defines a rule condition. Precede a RewriteRule directive with one or 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 can contains the following expanded constructs in addition to plain text:

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: %{SSL:variable} where variable is the name of an SSL environment variable; this can be used whether or not mod_ssl is loaded, but will always expand to the empty string if it is not. Example: %{SSL:SSL_CIPHER_USEKEYSIZE} may expand to 128.
  4. 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:''.
  5. There is the special format %{LA-U:variable} for look-aheads which perform an internal (URL-based) sub-request to determine the final value of variable. 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 REMOTE_USER variable from within the per-server context (httpd.conf file) you have to use %{LA-U:REMOTE_USER} because this variable is set by the authorization phases which come after the URL translation phase where mod_rewrite operates. On the other hand, because mod_rewrite implements its per-directory context (.htaccess file) via the Fixup phase of the API and because the authorization phases come before this phase, you just can use %{REMOTE_USER} there.
  6. There is the special format: %{LA-F:variable} which performs an internal (filename-based) sub-request to determine the final value of variable. Most of the time this is the same as LA-U above.

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

Remember: CondPattern is a perl compatible regular expression with some additions:

  1. You can prefix 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:
    • '<CondPattern' (is lexically lower)
      Treats the CondPattern as a plain string and compares it lexically to TestString. True if TestString is lexically lower than CondPattern.
    • '>CondPattern' (is lexically greater)
      Treats the CondPattern as a plain string and compares it lexically to TestString. True if TestString is lexically greater than CondPattern.
    • '=CondPattern' (is lexically equal)
      Treats the CondPattern as a plain string and compares it lexically to TestString. True if TestString is lexically equal to CondPattern, i.e the two strings are exactly equal (character by character). If CondPattern is just "" (two quotation marks) this compares TestString to the empty string.
    • '-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 than zero.
    • '-l' (is symbolic link)
      Treats the TestString as a pathname and tests if it exists and is a symbolic link.
    • '-x' (has executable permissions)
      Treats the TestString as a pathname and tests if it exists and has execution permissions. These permissions are determined depending on the underlying OS.
    • '-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 server's performance!

    Notice

    All of these tests can also be prefixed by an exclamation mark ('!') 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.

top

RewriteEngine Directive

Description:Enables or disables runtime rewriting engine
Syntax:RewriteEngine on|off
Default:RewriteEngine off
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite

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 the RewriteRule directives!

Note that, by default, rewrite configurations are not inherited. This means that you need to have a RewriteEngine on directive for each virtual host in which you wish to use it.

top

RewriteLock Directive

Description:Sets the name of the lock file used for RewriteMap synchronization
Syntax:RewriteLock file-path
Context:server config
Status:Extension
Module:mod_rewrite

This directive sets the filename for a synchronization lockfile which mod_rewrite needs to communicate with RewriteMap programs. 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.

top

RewriteLog Directive

Description:Sets the name of the file used for logging rewrite engine processing
Syntax:RewriteLog file-path
Context:server config, virtual host
Status:Extension
Module:mod_rewrite

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 then 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!

Security

See the Apache Security Tips 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.

Example

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

top

RewriteLogLevel Directive

Description:Sets the verbosity of the log file used by the rewrite engine
Syntax:RewriteLogLevel Level
Default:RewriteLogLevel 0
Context:server config, virtual host
Status:Extension
Module:mod_rewrite

The RewriteLogLevel 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.

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

Using a high value for Level will slow down your Apache server dramatically! Use the rewriting logfile at a Level greater than 2 only for debugging!

Example

RewriteLogLevel 3

top

RewriteMap Directive

Description:Defines a mapping function for key-lookup
Syntax:RewriteMap MapName MapType:MapSource
Context:server config, virtual host
Status:Extension
Module:mod_rewrite
Compatibility:The choice of different dbm types is available in Apache 2.0.41 and later

The RewriteMap directive defines a Rewriting Map 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.

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 one of the following constructs:

${ MapName : LookupKey }
${ MapName : LookupKey | DefaultValue }

When such a construct occurs the map MapName is consulted and the key LookupKey is looked-up. If the key is found, the map-function construct is substituted by SubstValue. If the key is not found then it is substituted by DefaultValue or by the empty string if no DefaultValue was specified.

For example, you might define a RewriteMap as:

RewriteMap examplemap txt:/path/to/file/map.txt

You would then be able to use this map in a RewriteRule as follows:

RewriteRule ^/ex/(.*) ${examplemap:$1}

The following combinations for MapType and MapSource can be used:

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.

Note

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!
top

RewriteOptions Directive

Description:Sets some special options for the rewrite engine
Syntax:RewriteOptions Options
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite
Compatibility:MaxRedirects is no longer available in version 2.1 and later

The RewriteOptions directive sets some special options for the current per-server or per-directory configuration. The Option string can be currently only one:

inherit
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 .htaccess configuration are inherited.
top

RewriteRule Directive

Description:Defines rules for the rewriting engine
Syntax:RewriteRule Pattern Substitution
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite
Compatibility:The cookie-flag is available in Apache 2.0.40 and later.

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 is a perl compatible 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 originally requested URL, because any number of rules may already have matched and made alterations to it.

Some hints about the syntax of regular expressions:

Text:
  .           Any single character
  [chars]     Character class: One  of chars
  [^chars]    Character class: None of chars
  text1|text2 Alternative: text1 or text2

Quantifiers:
  ?           0 or 1 of the preceding text
  *           0 or N of the preceding text (N > 0)
  +           1 or N of the preceding text (N > 1)

Grouping:
  (text)      Grouping of text
              (either to set the borders of an alternative or
              for making backreferences where the Nth group can 
              be used on the RHS of a RewriteRule with $N)

Anchors:
  ^           Start of line anchor
  $           End   of line anchor

Escaping:
  \char       escape that particular char
              (for instance to specify the chars ".[]()" etc.)

For more information about regular expressions have a look at the perl regular expression manpage ("perldoc perlre"). If you are interested in more detailed information about regular expressions and their variants (POSIX regex etc.) have a look at the following dedicated book on this topic:

Mastering Regular Expressions, 2nd Edition
Jeffrey E.F. Friedl
O'Reilly & Associates, Inc. 2002
ISBN 0-596-00289-0

Additionally in mod_rewrite 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 this pattern''. This can be used for exceptional cases, where it is easier 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. back-references $N to the RewriteRule pattern
  2. back-references %N to the last matched RewriteCond pattern
  3. server-variables as in rule condition test-strings (%{VARNAME})
  4. mapping-function calls (${mapname:key|default})

Back-references are $N (N=0..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.

Query String

The Pattern will not match against the query string. Instead, you must use a RewriteCond with the %{QUERY_STRING} variable. You can, however, 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. To combine a new query string with an old one, use the [QSA] flag (see below).

Substitution of Absolute URLs

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:

Note

Never forget that Pattern is 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!) is 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 not be added and an external redirect or proxy throughput (if flag P is used!) is forced!

Note

To enable the rewriting engine for per-directory configuration files you need to set ``RewriteEngine On'' in these files and ``Options FollowSymLinks'' must be 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 /path/to/file/map.txt. Then we only have to add the following lines to the Apache server configuration file:

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

Available Languages:  en