|The Apache HTTP Server Reference Manual
by Apache Software Foundation
Paperback (6"x9"), 862 pages
RRP £19.95 ($29.95)
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.
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 specification1 .
- It is not possible to override or change the standard CGI variables using the environment manipulation directives.
- When suexec is used to launch CGI scripts, the environment will be cleaned down to a set of safe variables before CGI scripts are launched. The list of safe variables is defined at compile-time in suexec.c.
- For portability reasons, the names of environment variables may contain only letters, numbers, and the underscore character. In addition, the first character may not be a number. Characters which do not match this restriction will be replaced by an underscore when passed to CGI scripts and SSI pages.
- The SetEnv directive runs late during request processing meaning that directives such as SetEnvIf and RewriteCond will not see the variables set with it.
|ISBN 9781906966034||The Apache HTTP Server Reference Manual||See the print edition|