mod_setenvif Allows the setting of environment variables based on characteristics of the request Base mod_setenvif.c setenvif_module

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
 Environment Variables in Apache BrowserMatch Sets environment variables conditional on HTTP User-Agent BrowserMatch regex [!]env-variable[=value] [[!]env-variable[=value]] ... server config virtual hostdirectory .htaccess FileInfo

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:

BrowserMatchNoCase Robot is_a_robot
SetEnvIfNoCase 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
 BrowserMatchNoCase Sets environment variables conditional on User-Agent without respect to case BrowserMatchNoCase regex [!]env-variable[=value] [[!]env-variable[=value]] ... server config virtual hostdirectory .htaccess FileInfo 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 Sets environment variables based on attributes of the request SetEnvIf attribute regex [!]env-variable[=value] [[!]env-variable[=value]] ... server config virtual hostdirectory .htaccess FileInfo

The SetEnvIf directive defines environment variables based on attributes of the request. The attribute specified in the first argument can be one of three 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
    • 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 resource requested on the HTTP request line -- generally the portion of the URL following the scheme and host portion without the 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 Perl compatible regular expression. This is similar to a POSIX.2 egrep-style 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.

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
:
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.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].

 SetEnvIfNoCase Sets environment variables based on attributes of the request without respect to case SetEnvIfNoCase attribute regex [!]env-variable[=value] [[!]env-variable[=value]] ... server config virtual hostdirectory .htaccess FileInfo 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.