[APACHE DOCUMENTATION]

Apache HTTP Server Version 1.3

Module mod_setenvif

This module is contained in the mod_setenvif.c file, and is compiled in by default. It provides for the ability to set environment variables based upon attributes of the request.

Summary

The mod_setenvif module allows you to set environment variables according to whether different aspects of the request match regular expressions you specify. These envariables can be used by other parts of the server to make decisions about actions to be taken.

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

Directives

The BrowserMatch Directive

Syntax: BrowserMatch regex envar[=value] [...]
Default: none
Context: server config
Override: none
Status: Base
Module: mod_setenvif
Compatibility: Apache 1.2 and above (in Apache 1.2 this directive was found in the now-obsolete mod_browser module)

The BrowserMatch directive defines environment variables based on the User-Agent HTTP request header field. The first argument should be a POSIX.2 extended regular expression (similar to an egrep-style regex). 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 value given by value. If a User-Agent string matches more than one entry, they will be merged. Entries are processed in the order in which they appear, and later entries can override earlier ones.

For example: 

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

Note that the regular expression string is case-sensitive. For cane-INsensitive matching, see the BrowserMatchNoCase directive.

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

The BrowserMatchNoCase Directive

Syntax: BrowserMatchNoCase regex envar[=value] [...]
Default: none
Context: server config
Override: none
Status: Base
Module: mod_setenvif
Compatibility: Apache 1.2 and above (in Apache 1.2 this directive was found in the now-obsolete mod_browser module)

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

The SetEnvIf Directive

Syntax: SetEnvIf attribute regex envar[=value] [...]
Default: none
Context: server config
Override: none
Status: Base
Module: mod_setenvif
Compatibility: Apache 1.3 and above

The SetEnvIf directive defines environment variables based on attributes of the request. These attributes can be the values of various HTTP request header fields (see RFC2068 for more information about these), or of other aspects of the request, including the following:

Some of the more commonly used request header field names include Host, User-Agent, and Referer.

Example: 

   SetEnvIf Request_URI "\.(gif)|(jpg)|(xbm)$" object_is_image
   SetEnvIf Referer www\.mydomain\.com intra_site_referral

The first will set the envariable object_is_image if the request was for an image file, and the second sets intra_site_referral if the referring page was somewhere on the www.mydomain.com Web site.

The SetEnvIfNoCase Directive

Syntax: SetEnvIfNoCase attribute regex envar[=value] [...]
Default: none
Context: server config
Override: none
Status: Base
Module: mod_setenvif
Compatibility: Apache 1.3 and above

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 Apache\.Org site=apache

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

Apache HTTP Server Version 1.3

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