The simplest and best way to invoke ant from within an ant build script is to use the core '''ant''' task provided for that purpose.

Typical examples of usage:
 <ant antfile="subproject/subbuild.xml" target="compile"/>

 <ant dir="subproject"/>

However, if you want to run ant in a way not supported by the core ant task, such as to pass non-standard command line parameters, one can use the core '''java''' task instead:
 <java classname="org.apache.tools.ant.launch.Launcher">
   <classpath path="${java.class.path}"/>
   <arg value="-projecthelp"/>
 </java>
or
 <java dir=".." classname="org.apache.tools.ant.launch.Launcher" fork="true" failonerror="true">
   <classpath path="${java.class.path}"/>
   <arg value="-projecthelp"/>
 </java>

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I found this useful for doing TestDrivenDevelopmentInAnt -- writing ant scripts that test other ant scripts.

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CategoryAnt