Converting a reference to a property (in build.xml for ant)

[ion]

So, OK. I have this tool which generates some code, and I call it like
this:

<exec dir="${lib}" executable="cmd">
<arg line="/c codeGenerator.bat" />
<env key="CLASSPATH" path="${jars}/library.jar;"/>
</exec>

Now, I'm converting my build.xml file to use inherited references. So,
I want to define a folder somewhere else, and have it resolve to jars
here. Something like

<property name="jars">
<path refid="lib"/>
</property>

or somehow to get this CLASSPATH environment variable to point to the
folder referenced by 'lib'.
How do I do this?