Can I ask what String s you are trying to concatenate and what purpose you are using it in the comparison for? I don't _think_ ANT directly supports what you are after but there might be another way around your problem.
Cindy, You don't really have Strings in Ant - you have properties. It is possible to do what you want with two properties. Ant does the implicit concat for string properties.
If you have two actual Strings, they are probably in a scripting language like BSH. If this is the case, you could just use the concat operator in that scripting language.