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Apache HTTP Server Version 2.4

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Apache Module mod_setenvif

Description:Allows the setting of environment variables based on characteristics of the request
Status:Base
Module Identifier:setenvif_module
Source File:mod_setenvif.c

Summary

The mod_setenvif module allows you to set internal environment variables according to whether different aspects of the request match regular expressions you specify. These environment variables can be used by other parts of the server to make decisions about actions to be taken, as well as becoming available to CGI scripts and SSI pages.

The directives are considered in the order they appear in the configuration files. So more complex sequences can be used, such as this example, which sets netscape if the browser is mozilla but not MSIE.

BrowserMatch ^Mozilla netscape
BrowserMatch MSIE !netscape

When the server looks up a path via an internal subrequest such as looking for a DirectoryIndex or generating a directory listing with mod_autoindex, per-request environment variables are not inherited in the subrequest. Additionally, SetEnvIf directives are not separately evaluated in the subrequest due to the API phases mod_setenvif takes action in.

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BrowserMatch Directive

Description:Sets environment variables conditional on HTTP User-Agent
Syntax:BrowserMatch regex [!]env-variable[=value] [[!]env-variable[=value]] ...
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Base
Module:mod_setenvif

The BrowserMatch is a special cases of the SetEnvIf directive that sets environment variables conditional on the User-Agent HTTP request header. The following two lines have the same effect:

BrowserMatch Robot is_a_robot
SetEnvIf User-Agent Robot is_a_robot

Some additional examples:

BrowserMatch ^Mozilla forms jpeg=yes browser=netscape
BrowserMatch "^Mozilla/[2-3]" tables agif frames javascript
BrowserMatch MSIE !javascript
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BrowserMatchNoCase Directive

Description:Sets environment variables conditional on User-Agent without respect to case
Syntax:BrowserMatchNoCase regex [!]env-variable[=value] [[!]env-variable[=value]] ...
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Base
Module:mod_setenvif

The BrowserMatchNoCase directive is semantically identical to the BrowserMatch directive. However, it provides for case-insensitive matching. For example:

BrowserMatchNoCase mac platform=macintosh
BrowserMatchNoCase win platform=windows

The BrowserMatch and BrowserMatchNoCase directives are special cases of the SetEnvIf and SetEnvIfNoCase directives. The following two lines have the same effect:

BrowserMatchNoCase Robot is_a_robot
SetEnvIfNoCase User-Agent Robot is_a_robot
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SetEnvIf Directive

Description:Sets environment variables based on attributes of the request
Syntax:SetEnvIf attribute regex [!]env-variable[=value] [[!]env-variable[=value]] ...
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Base
Module:mod_setenvif

The SetEnvIf directive defines environment variables based on attributes of the request. The attribute specified in the first argument can be one of four things:

  1. An HTTP request header field (see RFC2616 for more information about these); for example: Host, User-Agent, Referer, and Accept-Language. A regular expression may be used to specify a set of request headers.
  2. One of the following aspects of the request:
    • Remote_Host - the hostname (if available) of the client making the request
    • Remote_Addr - the IP address of the client making the request
    • Server_Addr - the IP address of the server on which the request was received (only with versions later than 2.0.43)
    • Request_Method - the name of the method being used (GET, POST, et cetera)
    • Request_Protocol - the name and version of the protocol with which the request was made (e.g., "HTTP/0.9", "HTTP/1.1", etc.)
    • Request_URI - the resource requested on the HTTP request line -- generally the portion of the URL following the scheme and host portion without the query string. See the RewriteCond directive of mod_rewrite for extra information on how to match your query string.
  3. The name of an environment variable in the list of those associated with the request. This allows SetEnvIf directives to test against the result of prior matches. Only those environment variables defined by earlier SetEnvIf[NoCase] directives are available for testing in this manner. 'Earlier' means that they were defined at a broader scope (such as server-wide) or previously in the current directive's scope. Environment variables will be considered only if there was no match among request characteristics and a regular expression was not used for the attribute.

The second argument (regex) is a regular expression. If the regex matches against the attribute, then the remainder of the arguments are evaluated.

The rest of the arguments give the names of variables to set, and optionally values to which they should be set. These take the form of

  1. varname, or
  2. !varname, or
  3. varname=value

In the first form, the value will be set to "1". The second will remove the given variable if already defined, and the third will set the variable to the literal value given by value. Since version 2.0.51, Apache httpd will recognize occurrences of $1..$9 within value and replace them by parenthesized subexpressions of regex. $0 provides access to the whole string matched by that pattern.

SetEnvIf Request_URI "\.gif$" object_is_image=gif
SetEnvIf Request_URI "\.jpg$" object_is_image=jpg
SetEnvIf Request_URI "\.xbm$" object_is_image=xbm
    
SetEnvIf Referer www\.mydomain\.example\.com intra_site_referral
    
SetEnvIf object_is_image xbm XBIT_PROCESSING=1
    
SetEnvIf Request_URI "\.(.*)$" EXTENSION=$1

SetEnvIf ^TS  ^[a-z]  HAVE_TS

The first three will set the environment variable object_is_image if the request was for an image file, and the fourth sets intra_site_referral if the referring page was somewhere on the www.mydomain.example.com Web site.

The last example will set environment variable HAVE_TS if the request contains any headers that begin with "TS" whose values begins with any character in the set [a-z].

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SetEnvIfExpr Directive

Description:Sets environment variables based on an ap_expr expression
Syntax:SetEnvIfExpr expr [!]env-variable[=value] [[!]env-variable[=value]] ...
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Base
Module:mod_setenvif

The SetEnvIfExpr directive defines environment variables based on an <If> ap_expr. These expressions will be evaluated at runtime, and applied env-variable in the same fashion as SetEnvIf.

SetEnvIfExpr "tolower(req('X-Sendfile')) == 'd:\images\very_big.iso')" iso_delivered

This would set the environment variable iso_delivered every time our application attempts to send it via X-Sendfile

A more useful example would be to set the variable rfc1918 if the remote IP address is a private address according to RFC 1918:

SetEnvIfExpr "-R '10.0.0.0/8' || -R '172.16.0.0/12' || -R '192.168.0.0/16'" rfc1918

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SetEnvIfNoCase Directive

Description:Sets environment variables based on attributes of the request without respect to case
Syntax:SetEnvIfNoCase attribute regex [!]env-variable[=value] [[!]env-variable[=value]] ...
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Base
Module:mod_setenvif

The SetEnvIfNoCase is semantically identical to the SetEnvIf directive, and differs only in that the regular expression matching is performed in a case-insensitive manner. For example:

SetEnvIfNoCase Host Example\.Org site=example

This will cause the site environment variable to be set to "example" if the HTTP request header field Host: was included and contained Example.Org, example.org, or any other combination.