How to use variable within a variable in ant?

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Hi,
I want to use a variable within variable scenario. For eg.

<property name="var1" value="somevar" />
<property name="somevar" value="anothervalue" />

Now I want to use something like ${${var1}}  to retrieve ${somevar}. How do
I do it? On unix shell, eval works fine but when I try ant exec task to run
eval, it doesnt recognize the command.

Thanks