Let me include one or two exterior httpd.conf file during my primary Apache httpd.conf according to an Atmosphere Variable that's set externally.

So I must make a move like:

if $(DEV_ENV) == "main"
Include "first file"
if $(DEV_ENV) == "alt"
Include "second file"

I have been searching in the mod_setenv module but that's for setting the atmosphere variables inside the Apache configuration. How do i make use of the atmosphere variables and do evaluations on its values?

Sorry however, you can't do that kind of dynamic logic on Includes. However certainly the Debian version enables direct mention of the atmosphere variables via a substitution pattern, e.g.

Include conf/${APACHE_RUNTIME_TYPE}/*.conf

Possess a search for "Apache2 envvars" to find out more.