Apache HTTP Server Version 2.4
Apache HTTP Server Version 2.4
This document discusses the flags which are available to the
RewriteRule directive,
providing detailed explanations and examples.
Introduction B (escape backreferences) C|chain CO|cookie DPI|discardpath E|env END F|forbidden G|gone H|handler L|last N|next NC|nocase NE|noescape NS|nosubreq P|proxy PT|passthrough QSA|qsappend QSD|qsdiscard R|redirect S|skip T|type
A RewriteRule can have
its behavior modified by one or more flags. Flags are included in
square brackets at the end of the rule, and multiple flags are separated
by commas.
RewriteRule pattern target [Flag1,Flag2,Flag3]
Each flag (with a few exceptions) has a short form, such as
CO, as well as a longer form, such as cookie.
While it is most common to use
the short form, it is recommended that you familiarize yourself with the
long form, so that you remember what each flag is supposed to do.
Some flags take one or more arguments. Flags are not case sensitive.
Flags that alter metadata associated with the request (T=, H=, E=) have no affect in per-directory and htaccess context, when a substitution (other than '-') is performed during the same round of rewrite processing.
Presented here are each of the available flags, along with an example of how you might use them.
The [B] flag instructs RewriteRule to escape non-alphanumeric
characters before applying the transformation.
mod_rewrite has to unescape URLs before mapping them,
so backreferences are 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 "^search/(.*)$" "/search.php?term=$1"
Given a search term of 'x & y/z', a browser will encode it as
'x%20%26%20y%2Fz', making the request 'search/x%20%26%20y%2Fz'. Without the B
flag, this rewrite rule will map to 'search.php?term=x & y/z', which
isn't a valid URL, and so would be encoded as
search.php?term=x%20&y%2Fz=, which is not what was intended.
With the B flag set on this same rule, the parameters are re-encoded
before being passed on to the output URL, resulting in a correct mapping to
/search.php?term=x%20%26%20y%2Fz.
Note that you may also need to set AllowEncodedSlashes to On to get this
particular example to work, as httpd does not allow encoded slashes in URLs, and
returns a 404 if it sees one.
This escaping is particularly necessary in a proxy situation, when the backend may break if presented with an unescaped URL.
The [C] or [chain] flag indicates that the RewriteRule is chained to the next
rule. That is, if the rule matches, then it is processed as usual and
control moves on to the next rule. However, if it does not match, then
the next rule, and any other rules that are chained together, are
skipped.
The [CO], or [cookie] flag, allows you to set a cookie when a
particular RewriteRule
matches. The argument consists of three required fields and four optional
fields.
The full syntax for the flag, including all attributes, is as follows:
[CO=NAME:VALUE:DOMAIN:lifetime:path:secure:httponly]
You must declare a name, a value, and a domain for the cookie to be set.
www.example.com, or it may be a domain,
such as .example.com. It must be at least two parts
separated by a dot. That is, it may not be merely .com or
.net. Cookies of that kind are forbidden by the cookie
security model.You may optionally also set the following values:
/customers/ or /files/download/./ - that is, the entire
website.secure, true, or 1,
the cookie will only be permitted to be translated via secure (https)
connections.HttpOnly, true, or
1, the cookie will have the HttpOnly flag set,
which means that the cookie is inaccessible to JavaScript code on
browsers that support this feature.Consider this example:
RewriteEngine On RewriteRule "^/index\.html" "-" [CO=frontdoor:yes:.example.com:1440:/]
In the example give, the rule doesn't rewrite the request.
The "-" rewrite target tells mod_rewrite to pass the request
through unchanged. Instead, it sets a cookie
called 'frontdoor' to a value of 'yes'. The cookie is valid for any host
in the .example.com domain. It is set to expire in 1440
minutes (24 hours) and is returned for all URIs.
The DPI flag causes the PATH_INFO portion of the rewritten URI to be discarded.
This flag is available in version 2.2.12 and later.
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.
With the [E], or [env] flag, you can set the value of an environment variable. Note that some environment variables may be set after the rule is run, thus unsetting what you have set. See the Environment Variables document for more details on how Environment variables work.
The full syntax for this flag is:
[E=VAR:VAL]
[E=!VAR]
VAL may contain backreferences ($N or
%N) which are expanded.
Using the short form
[E=VAR]
you can set the environment variable named VAR to an
empty value.
The form
[E=!VAR]
allows to unset a previously set environment variable named
VAR.
Environment variables can then be used in a variety of contexts, including CGI programs, other RewriteRule directives, or CustomLog directives.
The following example sets an environment variable called 'image' to a value of '1' if the requested URI is an image file. Then, that environment variable is used to exclude those requests from the access log.
RewriteRule "\.(png|gif|jpg)$" "-" [E=image:1] CustomLog "logs/access_log" combined env=!image
Note that this same effect can be obtained using SetEnvIf. This technique is offered as
an example, not as a recommendation.
Using the [END] flag terminates not only the current round of rewrite processing (like [L]) but also prevents any subsequent rewrite processing from occurring in per-directory (htaccess) context.
This does not apply to new requests resulting from external redirects.
Using the [F] flag causes the server to return a 403 Forbidden status
code to the client. While the same behavior can be accomplished using
the Deny directive, this
allows more flexibility in assigning a Forbidden status.
The following rule will forbid .exe files from being
downloaded from your server.
RewriteRule "\.exe" "-" [F]
This example uses the "-" syntax for the rewrite target, which means that the requested URI is not modified. There's no reason to rewrite to another URI, if you're going to forbid the request.
When using [F], an [L] is implied - that is, the response is returned immediately, and no further rules are evaluated.
The [G] flag forces the server to return a 410 Gone status with the response. This indicates that a resource used to be available, but is no longer available.
As with the [F] flag, you will typically use the "-" syntax for the rewrite target when using the [G] flag:
RewriteRule "oldproduct" "-" [G,NC]
When using [G], an [L] is implied - that is, the response is returned immediately, and no further rules are evaluated.
Forces the resulting request to be handled with the specified handler. For example, one might use this to force all files without a file extension to be parsed by the php handler:
RewriteRule "!\." "-" [H=application/x-httpd-php]
The regular expression above - !\. - will match any request
that does not contain the literal . character.
This can be also used to force the handler based on some conditions.
For example, the following snippet used in per-server context allows
.php files to be displayed by mod_php
if they are requested with the .phps extension:
RewriteRule "^(/source/.+\.php)s$" "$1" [H=application/x-httpd-php-source]
The regular expression above - ^(/source/.+\.php)s$ - will
match any request that starts with /source/ followed by 1 or
n characters followed by .phps literally. The backreference
$1 referrers to the captured match within parenthesis of the regular
expression.
The [L] flag causes mod_rewrite to stop processing
the rule set. In most contexts, this means that if the rule matches, no
further rules will be processed. This corresponds to the
last command in Perl, or the break command in
C. Use this flag to indicate that the current rule should be applied
immediately without considering further rules.
If you are using RewriteRule in either
.htaccess files or in
<Directory> sections,
it is important to have some understanding of how the rules are
processed. The simplified form of this is that once the rules have been
processed, the rewritten request is handed back to the URL parsing
engine to do what it may with it. It is possible that as the rewritten
request is handled, the .htaccess file or
<Directory> section
may be encountered again, and thus the ruleset may be run again from the
start. Most commonly this will happen if one of the rules causes a
redirect - either internal or external - causing the request process to
start over.
It is therefore important, if you are using RewriteRule directives in one of these
contexts, that you take explicit steps to avoid rules looping, and not
count solely on the [L] flag to terminate execution of a series of
rules, as shown below.
An alternative flag, [END], can be used to terminate not only the current round of rewrite processing but prevent any subsequent rewrite processing from occurring in per-directory (htaccess) context. This does not apply to new requests resulting from external redirects.
The example given here will rewrite any request to
index.php, giving the original request as a query string
argument to index.php, however, the RewriteCond ensures that if the request
is already for index.php, the RewriteRule will be skipped.
RewriteBase "/"
RewriteCond "%{REQUEST_URI}" "!=/index.php"
RewriteRule "^(.*)" "/index.php?req=$1" [L,PT]
The [N] flag causes the ruleset to start over again from the top, using the result of the ruleset so far as a starting point. Use with extreme caution, as it may result in loop.
The [Next] flag could be used, for example, if you wished to replace a certain string or letter repeatedly in a request. The example shown here will replace A with B everywhere in a request, and will continue doing so until there are no more As to be replaced.
RewriteRule "(.*)A(.*)" "$1B$2" [N]
You can think of this as a while loop: While this
pattern still matches (i.e., while the URI still contains an
A), perform this substitution (i.e., replace the
A with a B).
In 2.4.8 and later, this module returns an error after 32,000 iterations to protect against unintended looping. An alternative maximum number of iterations can be specified by adding to the N flag.
# Be willing to replace 1 character in each pass of the loop RewriteRule "(.+)[><;]$" "$1" [N=64000] # ... or, give up if after 10 loops RewriteRule "(.+)[><;]$" "$1" [N=10]
Use of the [NC] flag causes the RewriteRule to be matched in a
case-insensitive manner. That is, it doesn't care whether letters appear
as upper-case or lower-case in the matched URI.
In the example below, any request for an image file will be proxied
to your dedicated image server. The match is case-insensitive, so that
.jpg and .JPG files are both acceptable, for
example.
RewriteRule "(.*\.(jpg|gif|png))$" "http://images.example.com$1" [P,NC]
By default, special characters, such as & and
?, for example, will be converted to their hexcode
equivalent. Using the [NE] flag prevents that from happening.
RewriteRule "^/anchor/(.+)" "/bigpage.html#$1" [NE,R]
The above example will redirect /anchor/xyz to
/bigpage.html#xyz. Omitting the [NE] will result in the #
being converted to its hexcode equivalent, %23, which will
then result in a 404 Not Found error condition.
Use of the [NS] flag prevents the rule from being used on
subrequests. For example, a page which is included using an SSI (Server
Side Include) is a subrequest, and you may want to avoid rewrites
happening on those subrequests. Also, when mod_dir
tries to find out information about possible directory default files
(such as index.html files), this is an internal
subrequest, and you often want to avoid rewrites on such subrequests.
On subrequests, it is not always useful, and can even cause errors, if
the complete set of rules are applied. Use this flag to exclude
problematic rules.
To decide whether or not to use this rule: if you prefix URLs with CGI-scripts, to force them to be processed by the CGI-script, it's likely that you will run into problems (or significant overhead) on sub-requests. In these cases, use this flag.
Images, javascript files, or css files, loaded as part of an HTML page, are not subrequests - the browser requests them as separate HTTP requests.
Use of the [P] flag causes the request to be handled by
mod_proxy, and handled via a proxy request. For
example, if you wanted all image requests to be handled by a back-end
image server, you might do something like the following:
RewriteRule "/(.*)\.(jpg|gif|png)$" "http://images.example.com/$1.$2" [P]
Use of the [P] flag implies [L] - that is, the request is immediately pushed through the proxy, and any following rules will not be considered.
You must make sure that the substitution string is a valid URI
(typically starting with http://hostname) which can be
handled by the mod_proxy. If not, you will get an
error from the proxy module. Use this flag to achieve a
more powerful implementation of the ProxyPass directive,
to map remote content into the namespace of the local server.
Take care when constructing the target URL of the rule, considering the security impact from allowing the client influence over the set of URLs to which your server will act as a proxy. Ensure that the scheme and hostname part of the URL is either fixed, or does not allow the client undue influence.
Using this flag triggers the use of mod_proxy, without handling of persistent connections. This
means the performance of your proxy will be better if you set it up with ProxyPass or
ProxyPassMatch
This is because this flag triggers the use of the default worker, which does not handle connection pooling.
Avoid using this flag and prefer those directives, whenever you can.
Note: mod_proxy must be enabled in order
to use this flag.
The target (or substitution string) in a RewriteRule is assumed to be a
file path, by default. The use of the [PT] flag causes it to be treated
as a URI instead. That is to say, the
use of the [PT] flag causes the result of the RewriteRule to be passed back through
URL mapping, so that location-based mappings, such as Alias, Redirect, or ScriptAlias, for example, might have a
chance to take effect.
If, for example, you have an
Alias
for /icons, and have a RewriteRule pointing there, you should
use the [PT] flag to ensure that the
Alias is evaluated.
Alias "/icons" "/usr/local/apache/icons" RewriteRule "/pics/(.+)\.jpg$" "/icons/$1.gif" [PT]
Omission of the [PT] flag in this case will cause the Alias to be ignored, resulting in a 'File not found' error being returned.
The PT flag implies the L flag:
rewriting will be stopped in order to pass the request to
the next phase of processing.
Note that the PT flag is implied in per-directory
contexts such as
<Directory> sections
or in .htaccess files. The only way to circumvent that
is to rewrite to -.
When the replacement URI contains a query string, the default behavior
of RewriteRule is to discard
the existing query string, and replace it with the newly generated one.
Using the [QSA] flag causes the query strings to be combined.
Consider the following rule:
RewriteRule "/pages/(.+)" "/page.php?page=$1" [QSA]
With the [QSA] flag, a request for /pages/123?one=two will be
mapped to /page.php?page=123&one=two. Without the [QSA]
flag, that same request will be mapped to
/page.php?page=123 - that is, the existing query string
will be discarded.
When the requested URI contains a query string, and the target URI does
not, the default behavior of RewriteRule is to copy that query
string to the target URI. Using the [QSD] flag causes the query string
to be discarded.
This flag is available in version 2.4.0 and later.
Using [QSD] and [QSA] together will result in [QSD] taking precedence.
If the target URI has a query string, the default behavior will be
observed - that is, the original query string will be discarded and
replaced with the query string in the RewriteRule target
URI.
Use of the [R] flag causes a HTTP redirect to be issued to the browser.
If a fully-qualified URL is specified (that is, including
http://servername/) then a redirect will be issued to that
location. Otherwise, the current protocol, servername, and port number
will be used to generate the URL sent with the redirect.
Any valid HTTP response status code may be specified,
using the syntax [R=305], with a 302 status code being used by
default if none is specified. The status code specified need not
necessarily be a redirect (3xx) status code. However,
if a status code is outside the redirect range (300-399) then the
substitution string is dropped entirely, and rewriting is stopped as if
the L were used.
In addition to response status codes, you may also specify redirect
status using their symbolic names: temp (default),
permanent, or seeother.
You will almost always want to use [R] in conjunction with [L] (that is,
use [R,L]) because on its own, the [R] flag prepends
http://thishost[:thisport] to the URI, but then passes this
on to the next rule in the ruleset, which can often result in 'Invalid
URI in request' warnings.
The [S] flag is used to skip rules that you don't want to run. The
syntax of the skip flag is [S=N], where N signifies
the number of rules to skip (provided the
RewriteRule matches). This can be thought of as a goto
statement in your rewrite ruleset. In the following example, we only want
to run the RewriteRule if the
requested URI doesn't correspond with an actual file.
# Is the request for a non-existent file?
RewriteCond "%{REQUEST_FILENAME}" "!-f"
RewriteCond "%{REQUEST_FILENAME}" "!-d"
# If so, skip these two RewriteRules
RewriteRule ".?" "-" [S=2]
RewriteRule "(.*\.gif)" "images.php?$1"
RewriteRule "(.*\.html)" "docs.php?$1"
This technique is useful because a RewriteCond only applies to the
RewriteRule immediately
following it. Thus, if you want to make a RewriteCond apply
to several RewriteRules, one possible technique is to
negate those conditions and add a RewriteRule with a [Skip] flag. You can
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:
# Does the file exist?
RewriteCond "%{REQUEST_FILENAME}" "!-f"
RewriteCond "%{REQUEST_FILENAME}" "!-d"
# Create an if-then-else construct by skipping 3 lines if we meant to go to the "else" stanza.
RewriteRule ".?" "-" [S=3]
# IF the file exists, then:
RewriteRule "(.*\.gif)" "images.php?$1"
RewriteRule "(.*\.html)" "docs.php?$1"
# Skip past the "else" stanza.
RewriteRule ".?" "-" [S=1]
# ELSE...
RewriteRule "(.*)" "404.php?file=$1"
# END
It is probably easier to accomplish this kind of configuration using
the <If>, <ElseIf>, and <Else> directives instead.
Sets the MIME type with which the resulting response will be
sent. This has the same effect as the AddType directive.
For example, you might use the following technique to serve Perl source code as plain text, if requested in a particular way:
# Serve .pl files as plain text RewriteRule "\.pl$" "-" [T=text/plain]
Or, perhaps, if you have a camera that produces jpeg images without file extensions, you could force those images to be served with the correct MIME type by virtue of their file names:
# Files with 'IMG' in the name are jpg images. RewriteRule "IMG" "-" [T=image/jpg]
Please note that this is a trivial example, and could be better done
using <FilesMatch>
instead. Always consider the alternate
solutions to a problem before resorting to rewrite, which will
invariably be a less efficient solution than the alternatives.
If used in per-directory context, use only - (dash)
as the substitution for the entire round of mod_rewrite processing,
otherwise the MIME-type set with this flag is lost due to an internal
re-processing (including subsequent rounds of mod_rewrite processing).
The L flag can be useful in this context to end the
current round of mod_rewrite processing.