The other day I wanted to do something like this, and have the property passed to a junit task:
% ant -Dcom.blogspot.jfkbits.tmpfile=/tmp/grzlgmpfer-78
My task never saw the property; Ant doesn't automatically pass-through properties. That's fine, it just surprised me, coming from the shell environment variable mindset.
It turns out that sysproperty, syspropertyset, and jvmarg are the only ways to do it.
The jvmarg nested element is the simplest form, as in the example from the Ant documentation:
If you have a lot of properties this gets tedious.
If the properties you want to pass have a common prefix, as in the example com.blogspot.jfkbits, you can use syspropertyset with the prefix attribute, like this:
<propertyref prefix="com.blogspot.jfkbits" />
<!-- tests go here -->
Update 17 July 2006:Added text for jvmarg, since that is a way to pass system properties that I previously omitted, and tweaked the description of how to use syspropertyset.