Properties in NAnt are tricky since they don't have a type and simply are considered as of type string
. So this would be the solution:
<exec program="${psExec.path}" failonerror="false">
<!-- ... -->
<arg line="-c" if="${bool::parse(psExec.copyprog)}" />
</exec>
Update: Mea culpa! I was wrong. if="${psExec.copyprog}"
does also work. So there is some sort of property typing.