How to work with SetEnv in httpd.conf

How can I use variables in httpd.conf, essentially like this bash-inspired pseudo-code:

SetEnv BASE_DIR /the/basic/path/to/something
SetEnv FOO_DIR ${BASE_DIR}/foo
SetEnv BAR_DIR ${BASE_DIR}/bar

It should do the same as this:

SetEnv DIR_FOO /the/basic/path/to/something/foo
SetEnv DIR_BAR /the/basic/path/to/something/bar

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You have to include or uncomment mod_env library.

Also, for scripts you may want to set ScriptAlias for their paths.
PhazzAuthor Commented:

Thanks. The mod_env library is included.

I need to combine and concatenate the values of some environment variables and write them back in other environment variables. I'm maintaining some old CGI webapps which need to acsess those env.vars, and it is not only paths for scripts.

What is the syntax (in httpd.conf) for reading the value of an environment variable? Like my ${BASE_DIR} in my pseudo-code example.
Are all the environmental variables to be created or read as you start Apache?
If so, you would add to your envvars file.  In Ubuntu, you might find this at /etc/apache2/envvars.
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Try this:
SetEnv NEW_PATH %{ENV:BASE_DIR}/my/path

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PhazzAuthor Commented:
Unfortunately %{ENV:BASE_DIR} is not being expanded, I mean NEW_PATH gets the litteral value %{ENV:BASE_DIR}/my/path .
PhazzAuthor Commented:
In the link ,
I see a reference to a  book Pro Apache 3rd edition, by Peter Wainwright. Apparently it is possible to a have a <perl> ... </perl> section in the httpd.conf. That could probably solve my problem. But it requires the mod_perl module to be enabled in Apache, and my web admin said it is overkill and he doesn't want to do that. Well, he's probably right!

I will close the question and distribute the points 4/5 to farzanj and 1/5 to larsrohr.

PhazzAuthor Commented:
None of the experts gave me a real solution but it made me realize the implications.
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