Apache Module mod_rewrite

duraboys 2011. 4. 29. 18:11

2011. 4. 29. 18:11

http://httpd.apache.org/docs/current/mod/mod_rewrite.html

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, of server variables, environment variables, HTTP headers, or time stamps. Even external database lookups in various formats can be used to achieve highly 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 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

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 backslash ('\') 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.

Environment Variables

This module keeps track of two additional (non-standard) CGI/SSI environment variables named SCRIPT_URL and SCRIPT_URI. These contain the logicalWeb-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, that is, before any rewriting. This is important to note 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/

Rewriting in Virtual Hosts

By default, mod_rewrite configuration settings from the main server context are not inherited by virtual hosts. To make the main server settings apply to virtual hosts, you must place the following directives in each <VirtualHost> section:

RewriteEngine On RewriteOptions Inherit

Practical Solutions

For numerous examples of common, and not-so-common, uses for mod_rewrite, see the extended rewrite documentation.

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). In such a case, it will act locally, stripping the local directory prefix before processing, and applying rewrite rules only to the remainder. When processing is complete, the prefix 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. However, for most websites, URLs are NOT directly related to physical filename paths, so this assumption will often be wrong! Therefore, you can use the RewriteBase directive to specify the correct URL-prefix.

If your webserver's URLs are not directly related to physical file paths, you will need to use RewriteBase in every .htaccess file 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 in fact correct Apache internal processing. Because the per-directory rewriting comes late in the process, the rewritten request has to be re-injected into the Apache kernel, as if it were a new request. (See mod_rewrite technical details.) This is not the serious overhead it may seem to be - this re-injection is completely internal to the Apache server (and the same procedure is used by many other operations within Apache).

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. One or more RewriteCond can precede a RewriteRule directive. The following rule is then only used if both the current state of the URI matches its pattern, and if these conditions are met.

TestString is a string which can contain the following expanded constructs in addition to plain text:

RewriteRule backreferences: These are backreferences of the form $N (0 <= N <= 9), which provide access to the grouped parts (in parentheses) of the pattern, from the RewriteRule which is subject to the current set of RewriteCond conditions..
RewriteCond backreferences: These are backreferences of the form %N (1 <= N <= 9), which provide access to the grouped parts (again, in parentheses) of the pattern, from the last matched RewriteCond in the current set of conditions.
RewriteMap expansions: These are expansions of the form ${mapname:key|default}. See the documentation for RewriteMap for more details.

Server-Variables: These are variables of the form %{ NAME_OF_VARIABLE } where NAME_OF_VARIABLE can be a string taken from the following list:

HTTP headers:	connection & request:
HTTP_USER_AGENT HTTP_REFERER HTTP_COOKIE HTTP_FORWARDED HTTP_HOST HTTP_PROXY_CONNECTION HTTP_ACCEPT	REMOTE_ADDR REMOTE_HOST REMOTE_PORT REMOTE_USER REMOTE_IDENT REQUEST_METHOD SCRIPT_FILENAME PATH_INFO QUERY_STRING AUTH_TYPE
server internals:	date and time:	specials:
DOCUMENT_ROOT SERVER_ADMIN SERVER_NAME SERVER_ADDR SERVER_PORT SERVER_PROTOCOL SERVER_SOFTWARE	TIME_YEAR TIME_MON TIME_DAY TIME_HOUR TIME_MIN TIME_SEC TIME_WDAY TIME	API_VERSION THE_REQUEST REQUEST_URI REQUEST_FILENAME IS_SUBREQ HTTPS

These variables all correspond to the similarly named HTTP MIME-headers, C variables of the Apache server or struct tm fields of the Unix system. Most are documented elsewhere in the Manual or in the CGI specification.

SERVER_NAME and SERVER_PORT depend on the values of UseCanonicalName and UseCanonicalPhysicalPort respectively.

Those that are special to mod_rewrite include those below.

IS_SUBREQ: 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.
API_VERSION: 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.
THE_REQUEST: The full HTTP request line sent by the browser to the server (e.g., "GET /index.html HTTP/1.1"). This does not include any additional headers sent by the browser. This value has not been unescaped (decoded), unlike most other variables below.
REQUEST_URI: The resource requested in the HTTP request line. (In the example above, this would be "/index.html".)
REQUEST_FILENAME: The full local filesystem path to the file or script matching the request, if this has already been determined by the server at the timeREQUEST_FILENAME is referenced. Otherwise, such as when used in virtual host context, the same value as REQUEST_URI.
HTTPS: Will contain the text "on" if the connection is using SSL/TLS, or "off" otherwise. (This variable can be safely used regardless of whether or not mod_ssl is loaded).

Other things you should be aware of:

The variables SCRIPT_FILENAME and REQUEST_FILENAME contain the same value - the value of the filename field of the internal request_recstructure of the Apache server. The first name is the commonly known CGI variable name while the second is the appropriate counterpart of REQUEST_URI (which contains the value of the uri field of request_rec).

If a substitution occurred and the rewriting continues, the value of both variables will be updated accordingly.

If used in per-server context (i.e., before the request is mapped to the filesystem) SCRIPT_FILENAME and REQUEST_FILENAME cannot contain the full local filesystem path since the path is unknown at this stage of processing. Both variables will initially contain the value of REQUEST_URI in that case. In order to obtain the full local filesystem path of the request in per-server context, use an URL-based look-ahead %{LA-U:REQUEST_FILENAME} to determine the final value of REQUEST_FILENAME.
%{ENV:variable}, where variable can be any environment variable, is also available. This is looked-up via internal Apache structures and (if not found there) via getenv() from the Apache server process.
%{SSL:variable}, where variable is the name of an SSL environment variable, 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.
%{HTTP:header}, where header can be any HTTP MIME-header name, can always be used to obtain the value of a header sent in the HTTP request. Example: %{HTTP:Proxy-Connection} is the value of the HTTP header ``Proxy-Connection:''.
If a HTTP header is used in a condition this header is added to the Vary header of the response in case the condition evaluates to to true for the request. It is not added if the condition evaluates to false for the request. Adding the HTTP header to the Vary header of the response is needed for proper caching.

It has to be kept in mind that conditions follow a short circuit logic in the case of the 'ornext|OR' flag so that certain conditions might not be evaluated at all.
%{LA-U:variable} can be used for look-aheads which perform an internal (URL-based) sub-request to determine the final value of variable. This can be used to access variable for rewriting which is not available at the current stage, but will be set in a later phase.
For instance, to rewrite according to the REMOTE_USER variable from within the per-server context (httpd.conf file) you must use %{LA-U:REMOTE_USER} - this variable is set by the authorization phases, which come after the URL translation phase (during which 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} in that context.
%{LA-F:variable} can be used to perform 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, a regular expression which is applied to the current instance of the TestString. TestString is first evaluated, before being matched against CondPattern.

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

You can prefix the pattern string with a '!' character (exclamation mark) to specify a non-matching pattern.
There are some special variants of CondPatterns. Instead of real regular expression strings you can also use one of the following:
- '<CondPattern' (lexicographically precedes)
  Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically precedesCondPattern.
- '>CondPattern' (lexicographically follows)
  Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically followsCondPattern.
- '=CondPattern' (lexicographically equal)
  Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString is lexicographically equal toCondPattern (the two strings are exactly equal, character for character). If CondPattern is "" (two quotation marks) this compares TestStringto the empty string.
- '-d' (is directory)
  Treats the TestString as a pathname and tests whether or not it exists, and is a directory.
- '-f' (is regular file)
  Treats the TestString as a pathname and tests whether or not it exists, and is a regular file.
- '-s' (is regular file, with size)
  Treats the TestString as a pathname and tests whether or not it exists, and is a regular file with size greater than zero.
- '-l' (is symbolic link)
  Treats the TestString as a pathname and tests whether or not it exists, and is a symbolic link.
- '-x' (has executable permissions)
  Treats the TestString as a pathname and tests whether or not it exists, and has executable permissions. These permissions are determined according to the underlying OS.
- '-F' (is existing file, via subrequest)
  Checks whether or not TestString is a valid file, accessible via all the server's currently-configured access controls for that path. This uses an internal subrequest to do the check, so use it with care - it can impact your server's performance!
- '-U' (is existing URL, via subrequest)
  Checks whether or not TestString is a valid URL, accessible via all the server's currently-configured access controls for that path. This uses an internal subrequest to do the check, so use it with care - it can impact your server's performance!
Note:
All of these tests can also be prefixed by an exclamation mark ('!') to negate their meaning.
You can also set special flags for CondPattern by appending [flags] as the third argument to the RewriteCond directive, where flags is a comma-separated list of any of the following flags:
- 'nocase|NC' (no case)
  This makes the test case-insensitive - differences between 'A-Z' and 'a-z' are ignored, both in the expanded TestString and the CondPattern. This flag is effective only for comparisons between TestString and CondPattern. It has no effect on filesystem and subrequest checks.
- 'ornext|OR' (or next condition)
  Use this to combine rule conditions with a local OR instead of the implicit AND. Typical example:
```
RewriteCond %{REMOTE_HOST}  =host1  [OR]
RewriteCond %{REMOTE_HOST}  =host2  [OR]
RewriteCond %{REMOTE_HOST}  =host3
RewriteRule ...some special stuff for any of these hosts...
```
  Without this flag you would have to write the condition/rule pair three times.
- 'novary|NV' (no vary)
  If a HTTP header is used in the condition, this flag prevents this header from being added to the Vary header of the response.
  Using this flag might break proper caching of the response if the representation of this response varies on the value of this header. So this flag should be only used if the meaning of the Vary header is well understood.

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]

Explanation: If you use a browser which identifies itself as 'Mozilla' (including Netscape Navigator, Mozilla etc), then you get the max homepage (which could include frames, or other special features). If you use the Lynx browser (which is terminal-based), then you get the min homepage (which could be a version designed for easy, text-only browsing). If neither of these conditions apply (you use any other browser, or your browser identifies itself as something non-standard), you get the std (standard) homepage.

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

RewriteMap directives of the type prg are not started during server initialization if they're defined in a context that does not have RewriteEngine set toon

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.

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!

The RewriteLog log file format is as follows:

Description	Example
Remote host IP address	192.168.200.166
Remote login name	Will usually be "-"
HTTP user auth name	Username, or "-" if no auth
Date and time of request	[28/Aug/2009:13:09:09 --0400]
Virtualhost and virtualhost ID	[www.example.com/sid#84a650]
Request ID, and whether it's a subrequest	[rid#9f0e58/subreq]
Log entry severity level	(2)
Text error message	forcing proxy-throughput with http://127.0.0.1:8080/index.html

Security

See the Apache Security Tips document for details on how 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"

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

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. Empty values behave as if the key was absent, therefore it is not possible to distinguish between empty-valued keys and absent keys.

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:

Standard Plain Text
MapType: txt, MapSource: Unix filesystem path to valid regular file
This is the standard rewriting map feature where the MapSource is a plain ASCII file containing either blank lines, comment lines (starting with a '#' character) or pairs like the following - one per line.

MatchingKey SubstValue
Example
```
##
##  map.txt -- rewriting map
##

Ralf.S.Engelschall    rse   # Bastard Operator From Hell
Mr.Joe.Average        joe   # Mr. Average
```
RewriteMap real-to-user txt:/path/to/file/map.txt
Randomized Plain Text
MapType: rnd, MapSource: Unix filesystem path to valid regular file
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 ``|'' 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. For example, you might use the following map file and directives to provide a random load balancing between several back-end server, via a reverse-proxy. Images are sent to one of the servers in the 'static' pool, while everything else is sent to one of the 'dynamic' pool.

Example:
Rewrite map file
```
##
##  map.txt -- rewriting map
##

static   www1|www2|www3|www4
dynamic  www5|www6
```
Configuration directives
RewriteMap servers rnd:/path/to/file/map.txt RewriteRule ^/(.*\.(png|gif|jpg)) http://${servers:static}/$1 [NC,P,L] RewriteRule ^/(.*) http://${servers:dynamic}/$1 [P,L]
Hash File
MapType: dbm[=type], MapSource: Unix filesystem path to valid regular file
Here the source is a binary format DBM file containing the same contents as a Plain Text format file, but in a special representation which is optimized for really fast lookups. The type can be sdbm, gdbm, ndbm, or db depending on compile-time settings. If the type is omitted, the compile-time default will be chosen.

To create a dbm file from a source text file, use the httxt2dbm utility.

$ httxt2dbm -i mapfile.txt -o mapfile.map
Internal Function
MapType: int, MapSource: Internal Apache function
Here, the source is an internal Apache function. Module authors can provide additional internal functions by registering them with theap_register_rewrite_mapfunc API. The functions that are provided by default are:
- toupper:
  Converts the key to all upper case.
- tolower:
  Converts the key to all lower case.
- escape:
  Translates special characters in the key to hex-encodings.
- unescape:
  Translates hex-encodings in the key back to special characters.
External Rewriting Program
MapType: prg, MapSource: Unix filesystem path to valid regular file
Here the source is a program, not a map file. To create it you can use a language of your choice, but the result has to be an executable program (either object-code or a script with the magic cookie trick '#!/path/to/interpreter' as the first line).

This program is started once, when the Apache server is started, and then communicates with the rewriting engine via its stdin and stdout file-handles. 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:

External rewriting programs are not started if they're defined in a context that does not have RewriteEngine set to on
.
```
#!/usr/bin/perl
$| = 1;
while (<STDIN>) {
    # ...put here any transformations or lookups...
    print $_;
}
```
But be very careful:
1. ``Keep it simple, stupid'' (KISS). If this program hangs, it will cause Apache to hang when trying to use the relevant rewrite rule.
2. A common mistake is to use buffered I/O on stdout. Avoid this, as it will cause a deadloop! ``$|=1'' is used above, to prevent this.
3. The RewriteLock directive can be used to define a lockfile which mod_rewrite can use to synchronize communication with the mapping program. By default no such synchronization takes place.

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!

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 currently only be one of the following:

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.

Rules inherited from the parent scope are applied after rules specified in the child scope.

RewriteRule Directive

Description:	Defines rules for the rewriting engine
Syntax:	`RewriteRule Pattern Substitution [flags]`
Context:	server config, virtual host, directory, .htaccess
Override:	FileInfo
Status:	Extension
Module:	mod_rewrite

The RewriteRule directive is the real rewriting workhorse. The directive can occur more than once, with each instance defining a single rewrite rule. The order in which these rules are defined is important - this is the order in which they will be applied at run-time.

Pattern is a perl compatible regular expression. On the first RewriteRule it is applied to the (%-decoded) URL-path of the request; subsequent patterns are applied to the output of the last matched RewriteRule.

What is matched?

In VirtualHost context, The Pattern will initially be matched against the part of the URL after the hostname and port, and before the query string (e.g. "/app1/index.html").

In Directory and htaccess context, the Pattern will initially be matched against the filesystem path, after removing the prefix that lead the server to the current RewriteRule (e.g. "app1/index.html" or "index.html" depending on where the directives are defined).

If you wish to match against the hostname, port, or query string, use a RewriteCond with the %{HTTP_HOST}, %{SERVER_PORT}, or %{QUERY_STRING} variables respectively.

Per-directory Rewrites

The rewrite engine may be used in .htaccess files and in <Directory> sections, with some additional complexity.
To enable the rewrite engine in this context, you need to set "RewriteEngine On" and "Options FollowSymLinks" must be enabled. If your administrator has disabled override of FollowSymLinks for a user's directory, then you cannot use the rewrite engine. This restriction is required for security reasons.
When using the rewrite engine in .htaccess files the per-directory prefix (which always is the same for a specific directory) is automaticallyremoved for the RewriteRule pattern matching and automatically added after any relative (not starting with a slash or protocol name) substitution encounters the end of a rule set. See the RewriteBase directive for more information regarding what prefix will be added back to relative substutions.
If you wish to match against the full URL-path in a per-directory (htaccess) RewriteRule, use the %{REQUEST_URI} variable in aRewriteCond.
The removed prefix always ends with a slash, meaning the matching occurs against a string which never has a leading slash. Therefore, aPattern with ^/ never matches in per-directory context.
Although rewrite rules are syntactically permitted in <Location> and <Files> sections, this should never be necessary and is unsupported.

For some hints on regular expressions, see the mod_rewrite Introduction.

In mod_rewrite, the NOT character ('!') is also available as a possible pattern prefix. This enables you 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.

Note

When using the NOT character to negate a pattern, you cannot include grouped wildcard parts in that pattern. This is because, when the pattern does NOT match (ie, the negation matches), there are no contents for the groups. Thus, if negated patterns are used, you cannot use $N in the substitution string!

The Substitution of a rewrite rule is the string that replaces the original URL-path that was matched by Pattern. The Substitution may be a:

file-system path: Designates the location on the file-system of the resource to be delivered to the client.
URL-path: A DocumentRoot-relative path to the resource to be served. Note that mod_rewrite tries to guess whether you have specified a file-system path or a URL-path by checking to see if the first segment of the path exists at the root of the file-system. For example, if you specify a Substitution string of/www/file.html, then this will be treated as a URL-path unless a directory named www exists at the root or your file-system, in which case it will be treated as a file-system path. If you wish other URL-mapping directives (such as Alias) to be applied to the resulting URL-path, use the [PT] flag as described below.
Absolute URL: If an absolute URL is specified, mod_rewrite checks to see whether the hostname matches the current host. If it does, the scheme and hostname are stripped out and the resulting path is treated as a URL-path. Otherwise, an external redirect is performed for the given URL. To force an external redirect back to the current host, see the [R] flag below.
- (dash): A dash indicates that no substitution should be performed (the existing path is passed through untouched). This is used when a flag (see below) needs to be applied without changing the path.

In addition to plain text, the Substition string can include

back-references ($N) to the RewriteRule pattern
back-references (%N) to the last matched RewriteCond pattern
server-variables as in rule condition test-strings (%{VARNAME})
mapping-function calls (${mapname:key|default})

Back-references are identifiers of the form $N (N=0..9), 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 above.

As already mentioned, all rewrite rules are applied to the Substitution (in the order in which they are defined in the config file). The URL is completely replaced by the Substitution and the rewriting process continues until all rules have been applied, or it is explicitly terminated by a L flag.

Modifying the Query String

By default, the query string is passed through unchanged. You can, however, create URLs in the substitution string containing a query string part. Simply use a question mark inside the substitution string to indicate that the following text should be re-injected into the query string. When you want to erase an existing query string, end the substitution string with just a question mark. To combine new and old query strings, use the [QSA]flag.

Additionally you can set special actions to be performed by appending [flags] as the third argument to the RewriteRule directive. Flags is a comma-separated list, surround by square brackets, of any of the flags in the following table. More details, and examples, for each flag, are available in the Rewrite Flags document.

Flag and syntax	Function
B	Escape non-alphanumeric characters before applying the transformation. details ...
chain\|C	Rule is chained to the following rule. If the rule fails, the rule(s) chained to it will be skipped. details ...
cookie\|CO=NAME:VAL	Sets a cookie in the client browser. Full syntax is: CO=NAME:VAL:domain[:lifetime[:path[:secure[:httponly]]]] details ...
discardpath\|DPI	Causes the PATH_INFO portion of the rewritten URI to be discarded. details ...
env\|E=[!]VAR[:VAL]	Causes an environment variable VAR to be set (to the value VAL if provided). The form !VAR causes the environment variableVAR to be unset.details ...
forbidden\|F	Returns a 403 FORBIDDEN response to the client browser. details ...
gone\|G	Returns a 410 GONE response to the client browser. details ...
Handler\|H=Content-handler	Causes the resulting URI to be sent to the specified Content-handler for processing. details ...
last\|L	Stop the rewriting process immediately and don't apply any more rules. Especially note caveats for per-directory and .htaccess context (see also the END flag). details ...
next\|N	Re-run the rewriting process, starting again with the first rule, using the result of the ruleset so far as a starting point. details ...
nocase\|NC	Makes the pattern pattern comparison case-insensitive. details ...
noescape\|NE	Prevent mod_rewrite from applying hexcode escaping of special characters in the result of the rewrite. details ...
nosubreq\|NS	Causes a rule to be skipped if the current request is an internal sub-request. details ...
proxy\|P	Force the substitution URL to be internally sent as a proxy request. details ...
passthrough\|PT	Forces the resulting URI to be passed back to the URL mapping engine for processing of other URI-to-filename translators, such as `Alias` or `Redirect`. details ...
qsappend\|QSA	Appends any query string created in the rewrite target to any query string that was in the original request URL. details ...
redirect\|R[=code]	Forces an external redirect, optionally with the specified HTTP status code. details ...
skip\|S=num	Tells the rewriting engine to skip the next num rules if the current rule matches. details ...
type\|T=MIME-type	Force the MIME-type of the target file to be the specified type. details ...

Home directory expansion

When the substitution string begins with a string resembling "/~user" (via explicit text or backreferences), mod_rewrite performs home directory expansion independent of the presence or configuration of mod_userdir.

This expansion does not occur when the PT flag is used on the RewriteRule directive.

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                      invalid, not supported

^/somepath(.*) otherpath$1  [R]                 invalid, not supported

^/somepath(.*) otherpath$1  [P]                 invalid, not supported
----------------------------------------------  ----------------------------------
^/somepath(.*) /otherpath$1                     /otherpath/pathinfo

^/somepath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                via external redirection

^/somepath(.*) /otherpath$1 [P]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^/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]  doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^/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
(/physical/path/to/somepath/.htacccess, with 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]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^localpath(.*) /otherpath$1                     /otherpath/pathinfo

^localpath(.*) /otherpath$1 [R]                 http://thishost/otherpath/pathinfo
                                                via external redirection

^localpath(.*) /otherpath$1 [P]                 doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^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]  doesn't make sense, not supported
----------------------------------------------  ----------------------------------
^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

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