Apache HTTP Server Version 2.4
Apache HTTP Server Version 2.4
There are two kinds of environment variables that affect the Apache HTTP Server.
First, there are the environment variables controlled by the underlying operating system. These are set before the server starts. They can be used in expansions in configuration files, and can optionally be passed to CGI scripts and SSI using the PassEnv directive.
Second, the Apache HTTP Server provides a mechanism for storing information in named variables that are also called environment variables. This information can be used to control various operations such as logging or access control. The variables are also used as a mechanism to communicate with external programs such as CGI scripts. This document discusses different ways to manipulate and use these variables.
Although these variables are referred to as environment variables, they are not the same as the environment variables controlled by the underlying operating system. Instead, these variables are stored and manipulated in an internal Apache structure. They only become actual operating system environment variables when they are provided to CGI scripts and Server Side Include scripts. If you wish to manipulate the operating system environment under which the server itself runs, you must use the standard environment manipulation mechanisms provided by your operating system shell.
Setting Environment Variables Using Environment Variables Special Purpose Environment Variables Examples
| Related Modules | Related Directives |
|---|---|
The most basic way to set an environment variable in Apache
is using the unconditional SetEnv directive. Variables may also be passed from
the environment of the shell which started the server using the
PassEnv directive.
For additional flexibility, the directives provided by
mod_setenvif allow environment variables to be set
on a per-request basis, conditional on characteristics of particular
requests. For example, a variable could be set only when a
specific browser (User-Agent) is making a request, or only when
a specific Referer [sic] header is found. Even more flexibility
is available through the mod_rewrite's RewriteRule which uses the
[E=...] option to set environment variables.
Finally, mod_unique_id sets the environment
variable UNIQUE_ID for each request to a value which is
guaranteed to be unique across "all" requests under very
specific conditions.