title: Play 2 Configuration Substitution not working
body: <p>I'm not very familiar with play but working on an application whereby the properties are loaded via a <strong>.properties</strong> file and a variable is passed through the command line.</p>
  
  <p>E.g. </p>
  
  <p>Note this is a play 2.2.3 app</p>
  
  <pre><code>play -Dhost=app123 -Dconfig.file=app.properties run
  </code></pre>
  
  <p>In the properties file:</p>
  
  <pre><code>app.host=${host}
  </code></pre>
  
  <p>When I check the configuration loaded at runtime using</p>
  
  <pre><code>Play.configuration
  </code></pre>
  
  <p>or</p>
  
  <pre><code>ConfigFactory.load
  </code></pre>
  
  <p>The substitution for <strong>app.host</strong> does not seem to work - the property is evaluated to <strong>${host}</strong> as the literal String (instead of <strong>app123</strong>).</p>
  
  <p>Is there something that needs to be set for substitution to work?</p>
  
  <p>Thanks!</p>