# Module mod_setenvif

This module provides the ability to set environment variables based upon attributes of the request.

Status: Base
Source File: mod_setenvif.c
Module Identifier: setenvif_module
Compatibility: Available in Apache 1.3 and later.

## 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 environment variables 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

For additional information, we proved a document on Environment Variables in Apache.

## Directives

- BrowserMatch
- BrowserMatchNoCase
- SetEnvIf
- SetEnvIfNoCase

## BrowserMatch directive

Syntax: BrowserMatch regex envar[=value] [envar[=value]] ...
Default: none
Context: server config, virtual host, directory, .htaccess
Override: FileInfo
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

## BrowserMatchNoCase directive

Syntax: BrowserMatchNoCase regex envar[=value] [envar[=value]] ...
Default: none
Context: server config, virtual host, directory, .htaccess
Override: FileInfo
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

## SetEnvIf directive

Syntax: SetEnvIf attribute regex envar[=value] [envar[=value]] ...
Default: none
Context: server config, virtual host, directory, .htaccess
Override: FileInfo
Status: Base
Module: mod_setenvif
Compatibility: Apache 1.3 and above; the Request_Protocol keyword and environment-variable matching are only available with 1.3.7 and later

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 RFC2616 for more information about these), or of other aspects of the request, including the following:

- `Remote_Host` - the hostname (if available) of the client making the request
- `Remote_Addr` - the IP address of the client making the request
- `Remote_User` - the authenticated username (if available)
- `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 portion of the URL following the scheme and host portion

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

If the attribute name doesn't match any of the special keywords, nor any of the request's header field names, it is tested as 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.

Example:

       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\.com intra_site_referral
            :
       SetEnvIf object_is_image xbm XBIT_PROCESSING=1

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.com` Web site.

## SetEnvIfNoCase directive

Syntax: SetEnvIfNoCase attribute regex envar[=value] [envar[=value]] ...
Default: none
Context: server config, virtual host, directory, .htaccess
Override: FileInfo
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` environment variable to be set to "`apache`" if the HTTP request header field `Host:` was included and contained `Apache.Org`, `apache.org`, or any other combination.