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.

A regular expression only needs quoting when it contains space, in which case single and double quotes are equivalent. Unlike `mod_rewrite`, `mod_setenvif` strips every other backslash when parsing the expression; thus `\\` requires `\\\`, and `\\\` requires `\\\\\`.

### Directives

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

### See also

- Environment Variables in Apache HTTP Server

## 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

## 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

## 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 RFC 2616 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].

### See also

- Environment Variables in Apache HTTP Server, for additional examples.

## 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 expression. These expressions will be evaluated at runtime, and applied env-variable in the same fashion as `SetEnvIf`, including backreferences.

        SetEnvIfExpr "tolower(req('X-Sendfile')) == 'd:\images\very_big.iso')" iso_delivered
        SetEnvIfExpr "tolower(req('X-Sendfile')) =~ /(.*\.iso$)/" iso-path=$1

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

### See also

- Expressions in Apache HTTP Server, for a complete reference and more examples.
- `<If>` can be used to achieve similar results.
- `mod_filter`

## 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.