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.
The SetEnvIf directive defines
environment variables based on attributes of the request. The
attribute specified in the first argument can be one of three
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.
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
Request_Method - the name of the method
being used (GET, POST, et
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
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
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 will
recognize occurrences of $1..$9 within
value and replace them by parenthesized subexpressions
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