ant target to run only based on condition [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

Ant task to check if a file exists?

<target name="buildjunit">      
    <mkdir dir="${BUILD_TEST_DIR}" />
    <ant antfile="build.xml" dir="${app}\dcs" target="compile-junit" inheritAll="false">
        <property name="BUILD" value="${COMP_BUILD}" />
        <property name="VER" value="${PREVIOUS_VERSION}" />
        <property name="build.local" value="true" />
        <property name="CONFIG" value="${CONFIG_HOME}/ESW/ESWCONFIG/ITT" />
    </ant>
</target>

I want to build ant target compile-junit only if some of the jar doesnt exist in perticulary directory, how can i do it? ie compile-junit target inside buidljunit should ru开发者_开发技巧n only when there is no jar file exist in the directory project/jarlocation/dcs.

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Slight variation to the question I commented as similar. To run when it doesn't exist replace 'if' with 'unless':

<target name="check-abc">
    <available file="abc.txt" property="abc.present"/>
</target>

<target name="do-unless-abc" depends="check-abc" unless="abc.present">
    ...
</target>