nant: expanding properties in a string - nant

Question

Summary:
How do I expand a property with value "download\${bulidmode}\project\setup.msi" to "download\Debug\project\setup.msi" if the property buildmode contained debug so I can use it as the file="" part of < copy >
Detail:
I have a bit of a requirement to be able to expand properties within a string in nant.
For example I have a target that is copying file A to B. A and B both come from a simple two field CSV file which I'm iterating through using
<foreach item="Line" in="filelist.csv" delim="," property="source.file,target.file">
<property name="sourcefile" value="${path::combine(source.dir,source)}" />
<property name="targetfile" value="${path::combine(download.dir,destination)}" />
<echo message="Copy ${sourcefile} to ${targetfile}" />
<copy file="${sourcefile" tofile="${destination}" />
</foreach>
and the filelist.csv will be
build\manifest.xml
solutiondirectory\setup-proj-directory\Release\setupproj.msi,ProductA\ProductA.msi
solutiondirectory\another-proj-dir\Release\setupproj.msi,ProductB\ProductB.msi
(The reason we split these out is that we write multi-tiered applications and deploy by MSI to each tier - so one product has multiple msi's all built with the same version numbers)
Anyway - I want to change this to that I no longer have "Release" in the filelist.csv file but something like ${build.mode}. I would wrap the above code with a
<foreach item="String" in="Release,Debug" delim="," property="build.mode">
....as above
</foreach>
and the property embedded within the string in the file gets expanded.
I've been beating my head against a brick wall for a few hours, but just can't figure it out.
Thanks

Answer 1

It is possible with a custom function :
<?xml version="1.0"?>
<project>
<script language="C#" prefix="vbfox" >
<code>
<![CDATA[
[Function("expand")]
public string ExpandString(string str)
{
return Project.Properties.ExpandProperties(str, Location.UnknownLocation);
}
]]>
</code>
</script>
<property name="hello" value="{path::combine('_hello_', '_world_')}" />
<property name="hello" value="${'$' + hello}" />
<echo message="${hello}" />
<echo message="${vbfox::expand(hello)}" />
</project>