![[APACHE DOCUMENTATION]](images/sub.gif)
The Apache HTTP Server provides a mechanism for storing information in named variables that are 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.
| Related Modules mod_env mod_rewrite mod_setenvif mod_unique_id |
Related Directives BrowserMatch BrowserMatchNoCase PassEnv RewriteRule SetEnv SetEnvIf SetEnvIfNoCase UnsetEnv |
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.
In addition to all environment variables set within the Apache configuration and passed from the shell, CGI scripts and SSI pages are provided with a set of environment variables containing meta-information about the request as required by the CGI specification.
suexec.c.| Related Modules mod_access mod_cgi mod_include mod_log_config mod_rewrite |
Related Directives Allow CustomLog Deny LogFormat RewriteCond RewriteRule |
One of the primary uses of environment variables is to communicate information to CGI scripts. As discussed above, the environment passed to CGI scripts includes standard meta-information about the request in addition to any variables set within the Apache configuration. For more details, see the CGI tutorial.
Server-parsed (SSI) documents processed by mod_include's
server-parsed handler can print environment
variables using the echo element, and can use
environment variables in flow control elements to makes parts
of a page conditional on characteristics of a request. Apache
also provides SSI pages with the standard CGI environment
variables as discussed above. For more details, see the SSI tutorial.
Access to the server can be controlled based on the value of
environment variables using the allow from env=
and deny from env= directives. In combination with
SetEnvIf, this allows for flexible control of
access to the server based on characteristics of the client.
For example, you can use these directives to deny access to a
particular browser (User-Agent).
Environment variables can be logged in the accrsion
configured in the script's context).
When exchanging binary files between the mainframe host and a Unix machine or Windows PC, be sure to use the ftp "binary" (TYPE I) command, or use the rcp -b command from the mainframe host (the -b switch is not supported in unix rcp's).