Need to set Apache ServerName directive based on environment vars

Question

Hi

I have an Apache config which gets deployed to several different webserver platforms (uat, staging, development etc). The platforms are identical Redhat environments.

Each platform has an environment var "HOST_PLATFORM" of "uat", "staging", "development" etc.

I'd really like to be able to do something like this in my vhost:

<VirtualHost>
  ServerName www.%{HOST_PLATFORM}.foo

Is this possible? I can't get it to work but it seems like a fairly basic feature.

Any help at this point would be much appreciated!

TIA

sim