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3.66  Apache Module mod_rewrite



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 (p. 1111).

Directives:

RewriteBase

RewriteCond

RewriteEngine

RewriteLock

RewriteLog

RewriteLogLevel

RewriteMap

RewriteOptions

RewriteRule

See also:

3.66.1  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.

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

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/

3.66.3  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

3.66.4  Practical Solutions

For numerous examples of common, and not-so-common, uses for mod_rewrite, see the Rewrite Guide (p. 1146), and the Advanced Rewrite Guide (p. 1175) documents.

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 (p. 1139).) 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:

Other things you should be aware of:

  1. The variables SCRIPT_FILENAME and REQUEST_FILENAME contain the same value - the value of the filename field of the internal request_rec structure 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.

  2. %{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.
  3. %{SSL:variable}, where variable is the name of an SSL environment variable (p. 882), 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. %{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 an HTTP header is used in a condition, this header is added to the Vary header of the response in case the condition evaluates 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.

  5. %{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 a 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.

  6. %{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:

  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’ (lexicographically precedes)
      Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically precedes CondPattern.
    • >CondPattern’ (lexicographically follows)
      Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically follows CondPattern.
    • =CondPattern’ (lexicographically equal)
      Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString is lexicographically equal to CondPattern (the two strings are exactly equal, character for character). If CondPattern is "" (two quotation marks) this compares TestString to 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.

  3. 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 to on.

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!

Security

See the Apache Security Tips (p. 1393) 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.

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!

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.

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 URL-path (p. 178) of the request; subsequent patterns are applied to the output of the last matched RewriteRule.

What is matched? The Pattern will initially be matched against the part of the URL after the hostname and port, and before the query string. 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.

For some hints on regular expressions, see the mod_rewrite Introduction (p. 1115).

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

  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 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, surrounded by square brackets, of any of the following flags:

B’ (escape backreferences)
Apache has to unescape URLs before mapping them, so backreferences will be unescaped at the time they are applied. Using the B flag, non-alphanumeric characters in backreferences will be escaped. For example, consider the rule:
RewriteRule ^(.*)$ index.php?show=$1

This will map /C++ to index.php?show=/C++. But it will also map /C%2b%2b to index.php?show=/C++, because the %2b has been unescaped. With the B flag, it will instead map to index.php?show=/C%2b%2b.

This escaping is particularly necessary in a proxy situation, when the backend may break if presented with an unescaped URL.

chain|C’ (chained with next rule)
This flag chains the current rule with the next rule (which itself can be chained with the following rule, and so on). This has the following effect: if a rule matches, then processing continues as usual - the flag has no effect. If the rule does not match, then all following chained rules are skipped. For instance, it can be used to remove the “.www” part, inside a per-directory rule set, when you let an external redirect happen (where the “.www” part should not occur!).
cookie|CO=NAME:VAL:domain[:lifetime[:path[:secure[:httponly]]]]’ (set cookie)
This sets a cookie in the client’s browser. The cookie’s name is specified by NAME and the value is VAL. The domain field is the domain of the cookie, such as ‘.apache.org’, the optional lifetime is the lifetime of the cookie in minutes, and the optional path is the path of the cookie. If secure is set to ‘secure’, ‘true’ or ‘1’, the cookie is only transmitted via secured connections. If httponly is set to ‘HttpOnly’, ‘true’ or ‘1’, the HttpOnly flag is used, making the cookie not accessible to JavaScript code on browsers that support this feature.
discardpathinfo|DPI’ (discard PATH_INFO)
In per-directory context, the URI each RewriteRule compares against is the concatenation of the current values of the URI and PATH_INFO.

The current URI can be the initial URI as requested by the client, the result of a previous round of mod_rewrite processing, or the result of a prior rule in the current round of mod_rewrite processing.

In contrast, the PATH_INFO that is appended to the URI before each rule reflects only the value of PATH_INFO before this round of mod_rewrite processing. As a consequence, if large portions of the URI are matched and copied into a substitution in multiple RewriteRule directives, without regard for which parts of the URI came from the current PATH_INFO, the final URI may have multiple copies of PATH_INFO appended to it.

Use this flag on any substitution where the PATH_INFO that resulted from the previous mapping of this request to the filesystem is not of interest. This flag permanently forgets the PATH_INFO established before this round of mod_rewrite processing began. PATH_INFO will not be recalculated until the current round of mod_rewrite processing completes. Subsequent rules during this round of processing will see only the direct result of substitutions, without any PATH_INFO appended.

env|E=VAR[:VAL]’ (set environment variable)
This forces an environment variable named VAR to be set. The value will be VAL if provided, where VAL can contain regexp backreferences ($N and %N) which will be expanded. You can use this flag more than once, to set more than one variable. The variables can later be dereferenced in many situations, most commonly from within XSSI (via <!--#echo var="VAR"-->) or CGI ($ENV{’VAR’}). You can also dereference the variable in a later RewriteCond pattern, using %{ENV:VAR}. Use this to strip information from URLs, while maintaining a record of that information.
forbidden|F’ (force URL to be forbidden)
This forces the current URL to be forbidden - it immediately sends back a HTTP response of 403 (FORBIDDEN). Use this flag in conjunction with appropriate RewriteConds to conditionally block some URLs.
gone|G’ (force URL to be gone)
This forces the current URL to be gone - it immediately sends back a HTTP response of 410 (GONE). Use this flag to mark pages which no longer exist as gone.
handler|H=Content-handler’ (force Content handler)
Force the Content-handler of the target file to be Content-handler. For instance, this can be used to simulate the mod_alias directive ScriptAlias, which internally forces all files inside the mapped directory to have a handler of “cgi-script”.
last|L’ (last rule)
Stop the rewriting process here and don’t apply any more rewrite rules. This corresponds to the Perl last command or the break command in C. Use this flag to prevent the currently rewritten URL from being rewritten further by following rules. Remember, however, that if the RewriteRule generates an internal redirect (which frequently occurs when rewriting in a per-directory context), this will reinject the request and will cause processing to be repeated starting from the first RewriteRule.
next|N’ (next round)
Re-run the rewriting process (starting again with the first rewriting rule). This time, the URL to match is no longer the original URL, but rather the URL returned by the last rewriting rule. This corresponds to the Perl next command or the continue command in C. Use this flag to restart the rewriting process - to immediately go to the top of the loop. Be careful not to create an infinite loop!
nocase|NC’ (no case)
This makes the Pattern case-insensitive, ignoring difference between ‘A-Z’ and ‘a-z’ when Pattern is matched against the current URL.
noescape|NE’ (no URI escaping of output)
This flag prevents mod_rewrite from applying the usual URI escaping rules to the result of a rewrite. Ordinarily, special characters (such as ‘%’, ‘$’, ‘;’, and so on) will be escaped into their hexcode equivalents (‘%25’, ‘%24’, and ‘%3B’, respectively); this flag prevents this from happening. This allows percent symbols to appear in the output, as in

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

which would turn ‘/foo/zed’ into a safe request for ‘/bar?arg=P1=zed’.

nosubreq|NS’ (not for internal sub-requests)
This flag forces the rewriting engine to skip a rewriting rule if the current request is an internal sub-request. For instance, sub-requests occur internally in Apache when mod_include tries to find out information about possible directory default files (index.xxx files). On sub-requests it is not always useful, and can even cause errors, if the complete set of rules are applied. Use this flag to exclude some rules.

To decide whether or not to use this rule: if you prefix URLs with CGI-scripts, to force them to be processed by the CGI-script, it’s likely that you will run into problems (or significant overhead) on sub-requests. In these cases, use this flag.

proxy|P’ (force proxy)
This flag forces the substitution part to be internally sent as a proxy request and immediately (rewrite processing stops here) put through the proxy module (p. 729). You must make sure that the substitution string is a valid URI (typically starting with http://hostname) which can be handled by the Apache proxy module. If not, you will get an error from the proxy module. Use this flag to achieve a more powerful implementation of the ProxyPass (p. 729) directive, to map remote content into the namespace of the local server.

Note: mod_proxy must be enabled in order to use this flag.

passthrough|PT’ (pass through to next handler)
This flag forces the rewrite engine to set the uri field of the internal request_rec structure to the value of the filename field. This flag is just a hack to enable post-processing of the output of RewriteRule directives, using Alias, ScriptAlias, Redirect, and other directives from various URI-to-filename translators. For example, to rewrite /abc to /def using mod_rewrite, and then /def to /ghi using mod_alias:

RewriteRule ^/abc(.*) /def$1 [PT]
Alias /def /ghi

If you omit the PT flag, mod_rewrite will rewrite uri=/abc/to filename=/def/as a full API-compliant URI-to-filename translator should do. Then mod_alias will try to do a URI-to-filename transition, which will fail.

Note: You must use this flag if you want to mix directives from different modules which allow URL-to-filename translators. The typical example is the use of mod_alias and mod_rewrite.

The PT flag implies the L flag: rewriting will be stopped in order to pass the request to the next phase of processing.

qsappend|QSA’ (query string append)
This flag forces the rewrite engine to append a query string part of the substitution string to the existing string, instead of replacing it. Use this when you want to add more data to the query string via a rewrite rule.
redirect|R [=code]’ (force redirect)
Prefix Substitution with http://thishost[:thisport]/ (which makes the new URL a URI) to force a external redirection. If no code is given, a HTTP response of 302 (MOVED TEMPORARILY) will be returned. If you want to use other response codes, simply specify the appropriate number or use one of the following symbolic names: temp (default), permanent, seeother. Use this for rules to canonicalize the URL and return it to the client - to translate “/~” into “/u/”, or to always append a slash to /u/user, etc.
Note: When you use this flag, make sure that the substitution field is a valid URL! Otherwise, you will be redirecting to an invalid location. Remember that this flag on its own will only prepend http://thishost[:thisport]/ to the URL, and rewriting will continue. Usually, you will want to stop rewriting at this point, and redirect immediately. To stop rewriting, you should add the ‘L’ flag.

While this is typically used for redirects, any valid status code can be given here. If the status code is outside the redirect range (300-399), then the Substitution string is dropped and rewriting is stopped as if the L flag was used.

skip|S=num’ (skip next rule(s))
This flag forces the rewriting engine to skip the next num rules in sequence, if the current rule matches. Use this to make pseudo if-then-else constructs: The last rule of the then-clause becomes skip=N, where N is the number of rules in the else-clause. (This is not the same as the ‘chain—C’ flag!)
type|T=MIME-type’ (force MIME type)
Force the MIME-type of the target file to be MIME-type. This can be used to set up the content-type based on some conditions. For example, the following snippet allows .php files to be displayed by mod_php if they are called with the .phps extension:

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

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.

Per-directory Rewrites

The rewrite engine may be used in .htaccess (p. 1365) files. To enable the rewrite engine for these files 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 automatically removed for the pattern matching and automatically added after the substitution has been done. This feature is essential for many sorts of rewriting; without this, you would always 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 using flag P) is forced. See the RewriteBase directive for more information.

The rewrite engine may also be used in <Directory> sections with the same prefix-matching rules as would be applied to .htaccess files. It is usually simpler, however, to avoid the prefix substitution complication by putting the rewrite rules in the main server or virtual host context, rather than in a <Directory> section.

Although rewrite rules are syntactically permitted in <Location> sections, this should never be necessary and is unsupported.

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

ISBN 9781906966034The Apache HTTP Server Reference ManualSee the print edition