title: Read environment variables from logback configuration file
body: <p>I have this logback.xml file:</p>
  
  <pre><code>&lt;configuration debug="true" scan="true" scanPeriod="60 seconds"&gt;
  
    &lt;appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"&gt;
      &lt;layout class="ch.qos.logback.classic.PatternLayout"&gt;
        &lt;Pattern&gt;%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n&lt;/Pattern&gt;
      &lt;/layout&gt;
    &lt;/appender&gt;
  
    &lt;appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
      &lt;File&gt;${MY_HOME}/logs/mylog.log&lt;/File&gt;
  
      &lt;rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"&gt;
        &lt;FileNamePattern&gt;logs/my.%d{yyyy-MM-dd}.log&lt;/FileNamePattern&gt;
        &lt;MaxHistory&gt;30&lt;/MaxHistory&gt;
      &lt;/rollingPolicy&gt;
  
      &lt;layout class="ch.qos.logback.classic.PatternLayout"&gt;
        &lt;Pattern&gt;%d{HH:mm:ss.SSS} [%thread] %-5level - %msg%n&lt;/Pattern&gt;
      &lt;/layout&gt;
  
    &lt;/appender&gt; 
  
    &lt;root level="TRACE"&gt;
      &lt;appender-ref ref="FILE"/&gt;
    &lt;/root&gt;
  
  &lt;/configuration&gt;
  </code></pre>
  
  <p>And <code>${MY_HOME}</code> is a defined system variable (<code>echo $MY_HOME</code> on linux shows the correct path).</p>
  
  <p>The thing is that logback doesnt seem to read it properly, it stores the logs under <code>MY_HOME_IS_UNDEFINED/logs/my.log</code></p>
  
  <p>What am I doing wrong? Thanks a lot!</p>
  
  <p>EDIT: I made a mistake and put OSC_HOME where I really meant MY_HOME. Sorry about that</p>