title: Conditional property in Ant properties' file
body: <p>Is it possible to set a property value in Ant <strong>property files</strong> (as opposed to <code>build.xml</code>) in a conditional way? For example, if <code>apache.root</code> property is set - the <code>my_property</code> will be <code>${apache.root}/myapp</code>, <code>/var/www/myapp</code> otherwise. If not, what would be the common practice - reusable <code>build.xml</code> files?</p>