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Apache > HTTP Server > Documentation > Version 2.4 > Modules

Apache Module mod_rewrite

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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

Summary

The mod_rewrite module uses a rule-based rewriting engine, based on a PCRE regular-expression parser, to rewrite requested URLs on the fly. By default, mod_rewrite maps a URL to a filesystem path. However, it can also be used to redirect one URL to another URL, or to invoke an internal proxy fetch.

mod_rewrite provides a flexible and powerful way to manipulate URLs using an unlimited number of rules. Each rule can have an unlimited number of attached rule conditions, to allow you to rewrite URL based on server variables, environment variables, HTTP headers, or time stamps.

mod_rewrite operates on the full URL path, including the path-info section. A rewrite rule can be invoked in apache2.conf or in .htaccess. The path generated by a rewrite rule can include a query string, or can lead to internal sub-processing, external request redirection, or internal proxy throughput.

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

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See also

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Logging

mod_rewrite offers detailed logging of its actions at the trace1 to trace8 log levels. The log level can be set specifically for mod_rewrite using the LogLevel directive: Up to level debug, no actions are logged, while trace8 means that practically all actions are logged.

Using a high trace log level for mod_rewrite will slow down your Apache HTTP Server dramatically! Use a log level higher than trace2 only for debugging!

Example

LogLevel alert rewrite:trace3

RewriteLog

Those familiar with earlier versions of mod_rewrite will no doubt be looking for the RewriteLog and RewriteLogLevel directives. This functionality has been completely replaced by the new per-module logging configuration mentioned above.

To get just the mod_rewrite-specific log messages, pipe the log file through grep:

tail -f error_log|fgrep '[rewrite:'

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RewriteBase Directive

Description:Sets the base URL for per-directory rewrites
Syntax:RewriteBase URL-path
Default:None
Context:directory, .htaccess
Override:FileInfo
Status:Extension
Module:mod_rewrite

The RewriteBase directive specifies the URL prefix to be used for per-directory (htaccess) RewriteRule directives that substitute a relative path.

This directive is required when you use a relative path in a substitution in per-directory (htaccess) context unless any of the following conditions are true:

In the example below, RewriteBase is necessary to avoid rewriting to http://example.com/opt/myapp-1.2.3/welcome.html since the resource was not relative to the document root. This misconfiguration would normally cause the server to look for an "opt" directory under the document root.

DocumentRoot "/var/www/example.com"
AliasMatch "^/myapp" "/opt/myapp-1.2.3"
<Directory "/opt/myapp-1.2.3">
    RewriteEngine On
    RewriteBase "/myapp/"
    RewriteRule "^index\.html$"  "welcome.html"
</Directory>
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RewriteCond Directive

Description:Defines a condition under which rewriting will take place
Syntax: RewriteCond TestString CondPattern [flags]
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:

If the TestString has the special value expr, the CondPattern will be treated as an ap_expr. HTTP headers referenced in the expression will be added to the Vary header if the novary flag is not given.

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 HTTP 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 httpd structures and (if not found there) via getenv() from the Apache httpd server process.
  3. %{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. These variables are available even without setting the StdEnvVars option of the SSLOptions directive.
  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 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 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 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 (apache2.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.

CondPattern is usually a perl compatible regular expression, but there is additional syntax available to perform other useful tests against the Teststring:

  1. You can prefix the pattern string with a '!' character (exclamation mark) to negate the result of the condition, no matter what kind of CondPattern is used.
  2. You can perform lexicographical string comparisons:
    <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.
    <=CondPattern
    Lexicographically less than or equal to
    Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically precedes CondPattern, or is equal to CondPattern (the two strings are equal, character for character).
    >=CondPattern
    Lexicographically greater than or equal to
    Treats the CondPattern as a plain string and compares it lexicographically to TestString. True if TestString lexicographically follows CondPattern, or is equal to CondPattern (the two strings are equal, character for character).
  3. You can perform integer comparisons:
    -eq
    Is numerically equal to
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the two are numerically equal.
    -ge
    Is numerically greater than or equal to
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the TestString is numerically greater than or equal to the CondPattern.
    -gt
    Is numerically greater than
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the TestString is numerically greater than the CondPattern.
    -le
    Is numerically less than or equal to
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the TestString is numerically less than or equal to the CondPattern. Avoid confusion with the -l by using the -L or -h variant.
    -lt
    Is numerically less than
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the TestString is numerically less than the CondPattern. Avoid confusion with the -l by using the -L or -h variant.
    -ne
    Is numerically not equal to
    The TestString is treated as an integer, and is numerically compared to the CondPattern. True if the two are numerically different. This is equivalent to !-eq.
  4. You can perform various file attribute tests:
    -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.
    -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!
    -h
    Is symbolic link, bash convention.
    See -l.
    -l
    Is symbolic link.
    Treats the TestString as a pathname and tests whether or not it exists, and is a symbolic link. May also use the bash convention of -L or -h if there's a possibility of confusion such as when using the -lt or -le tests.
    -L
    Is symbolic link, bash convention.
    See -l.
    -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.
    -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!

    This flag only returns information about things like access control, authentication, and authorization. This flag does not return information about the status code the configured handler (static file, CGI, proxy, etc.) would have returned.

    -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.
    For example:
    RewriteCond /var/www/%{REQUEST_URI} !-f
    RewriteRule ^(.+) /other/archive/$1 [R]
  5. If the TestString has the special value expr, the CondPattern will be treated as an ap_expr.

    In the below example, -strmatch is used to compare the REFERER against the site hostname, to block unwanted hotlinking.

    RewriteCond expr "! %{HTTP_REFERER} -strmatch '*://%{HTTP_HOST}/*'"
    RewriteRule "^/images" "-" [F]

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:

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}"  "(iPhone|Blackberry|Android)"
RewriteRule  "^/$"                 "/homepage.mobile.html"  [L]

RewriteRule  "^/$"                 "/homepage.std.html"     [L]

Explanation: If you use a browser which identifies itself as a mobile browser (note that the example is incomplete, as there are many other mobile platforms), the mobile version of the homepage is served. Otherwise, the standard page is served.

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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 rules in a particular context, rather than 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

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RewriteMap Directive

Description:Defines a mapping function for key-lookup
Syntax:RewriteMap MapName MapType:MapSource [MapTypeOptions]
Context:server config, virtual host
Status:Extension
Module:mod_rewrite
Compatibility:The 3rd parameter, MapTypeOptions, in only available from Apache 2.4.29 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 meaning of the MapTypeOptions argument depends on particular MapType. See the Using RewriteMap for more information.

The following combinations for MapType and MapSource can be used:

txt
A plain text file containing space-separated key-value pairs, one per line. (Details ...)
rnd
Randomly selects an entry from a plain text file (Details ...)
dbm
Looks up an entry in a dbm file containing name, value pairs. Hash is constructed from a plain text file format using the httxt2dbm utility. (Details ...)
int
One of the four available internal functions provided by RewriteMap: toupper, tolower, escape or unescape. (Details ...)
prg
Calls an external program or script to process the rewriting. (Details ...)
dbd or fastdbd
A SQL SELECT statement to be performed to look up the rewrite target. (Details ...)

Further details, and numerous examples, may be found in the RewriteMap HowTo

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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

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 or <Directory> sections are inherited. The inherited rules are virtually copied to the section where this directive is being used. If used in combination with local rules, the inherited rules are copied behind the local rules. The position of this directive - below or above of local rules - has no influence on this behavior. If local rules forced the rewriting to stop, the inherited rules won't be processed.

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

Like Inherit above, but the rules from the parent scope are applied before rules specified in the child scope.
Available in Apache HTTP Server 2.3.10 and later.

InheritDown

If this option is enabled, all child configurations will inherit the configuration of the current configuration. It is equivalent to specifying RewriteOptions Inherit in all child configurations. See the Inherit option for more details on how the parent-child relationships are handled.
Available in Apache HTTP Server 2.4.8 and later.

InheritDownBefore

Like InheritDown above, but the rules from the current scope are applied before rules specified in any child's scope.
Available in Apache HTTP Server 2.4.8 and later.

IgnoreInherit

This option forces the current and child configurations to ignore all rules that would be inherited from a parent specifying InheritDown or InheritDownBefore.
Available in Apache HTTP Server 2.4.8 and later.

AllowNoSlash

By default, mod_rewrite will ignore URLs that map to a directory on disk but lack a trailing slash, in the expectation that the mod_dir module will issue the client with a redirect to the canonical URL with a trailing slash.

When the DirectorySlash directive is set to off, the AllowNoSlash option can be enabled to ensure that rewrite rules are no longer ignored. This option makes it possible to apply rewrite rules within .htaccess files that match the directory without a trailing slash, if so desired.
Available in Apache HTTP Server 2.4.0 and later.

AllowAnyURI

When RewriteRule is used in VirtualHost or server context with version 2.2.22 or later of httpd, mod_rewrite will only process the rewrite rules if the request URI is a URL-path. This avoids some security issues where particular rules could allow "surprising" pattern expansions (see CVE-2011-3368 and CVE-2011-4317). To lift the restriction on matching a URL-path, the AllowAnyURI option can be enabled, and mod_rewrite will apply the rule set to any request URI string, regardless of whether that string matches the URL-path grammar required by the HTTP specification.
Available in Apache HTTP Server 2.4.3 and later.

Security Warning

Enabling this option will make the server vulnerable to security issues if used with rewrite rules which are not carefully authored. It is strongly recommended that this option is not used. In particular, beware of input strings containing the '@' character which could change the interpretation of the transformed URI, as per the above CVE names.

MergeBase

With this option, the value of RewriteBase is copied from where it's explicitly defined into any sub-directory or sub-location that doesn't define its own RewriteBase. This was the default behavior in 2.4.0 through 2.4.3, and the flag to restore it is available Apache HTTP Server 2.4.4 and later.

IgnoreContextInfo

When a relative substitution is made in directory (htaccess) context and RewriteBase has not been set, this module uses some extended URL and filesystem context information to change the relative substitution back into a URL. Modules such as mod_userdir and mod_alias supply this extended context info. Available in 2.4.16 and later.

LegacyPrefixDocRoot

Prior to 2.4.2