Using Ant to merge two different properties files

I have a default properties file, and some deployment specific properties files that override certain settings from the default, based on deployment environment. I would like my Ant build script to merge the two properties files (overwriting default values with deployment specific values), and then output the resulting properties to a new file.

I tried doing it like so but I was unsuccessful:

<target depends="init" name="configure-target-environment">
    <filterset id="application-properties-filterset">
        <filtersfile file="${build.config.path}/${target.environment}/application.properties" />
    </filterset>

    <copy todir="${web-inf.path}/conf" file="${build.config.path}/application.properties" overwrite="true" failonerror="true" >
        <filterset refid="application-properties-filterset" />
    </copy>
</target>