Ant properties are immutable; they cannot be changed once initialized. However, it can be done in the following way although it causes the immutable property violation:

<?xml version="1.0"?>

<project name="example" default="run">

<taskdef name="groovy"

classname="org.codehaus.groovy.ant.Groovy"

classpath="lib/groovy-all-1.1-rc-1.jar"/>

<target name="run">

<echo>java.library.path = ${java.library.path}</echo>

<groovy>

properties["java.library.path"] = "changed"

</groovy>

<echo>java.library.path = ${java.library.path}</echo>

</target>

</project>