title: How to set an Ant property only if it is unset
body: <p>I can't figure out how to set an Ant property on the condition that it has not been set (i.e it is not defined in the properties file and should automatically default).</p>
  
  <p>So far, I only have the following code:</p>
  
  <pre><code>&lt;condition property="core.bin" value="../bin"&gt;
      &lt;isset property="core.bin"/&gt;
  &lt;/condition&gt;
  </code></pre>
  
  <p>But this only seems to work if the value is defined in a <code>&lt;property&gt;</code> tag.</p>
  
  <p>Does anyone know how to conditionally set a property for the first time if it currently unset?</p>