[Boost-build] Can I include environment variables in user-config.jam?

Subject: [Boost-build] Can I include environment variables in user-config.jam?
From: Michael Krajnak (michael.krajnak_at_[hidden])
Date: 2011-05-12 10:00:18

I'm currently building boost with stlport.

In order to do this I made various changes to user-config.jam file based 
on a variety of examples I found on the net.

Those changes include things like the following:

using stlport : 5.2.1 :
D:/dev/stlport/stlport :
D:/dev/stlport/libx86 ;

I would like to replace the string D:/dev/stlport with an environment 
variable, but I can't get this to work.  I've seen various discussions 
about this on some of the boost forums, including some that suggested 
that user-config.jam might not be the best place to do this, but never 
an example that I could follow completely.

Could someone provide a complete example of how to include an 
environment variable in user-config.jam?  Or if there is a 
recommendation for a different way to achieve the same effect I'd be 
glad to give it try.

Thanks,

Mike