Read environment variables from logback configuration file

Question

I have this logback.xml file:

<configuration debug="true" scan="true" scanPeriod="60 seconds">

  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</Pattern>
    </layout>
  </appender>

  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <File>${MY_HOME}/logs/mylog.log</File>

    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
      <FileNamePattern>logs/my.%d{yyyy-MM-dd}.log</FileNamePattern>
      <MaxHistory>30</MaxHistory>
    </rollingPolicy>

    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level - %msg%n</Pattern>
    </layout>

  </appender> 

  <root level="TRACE">
    <appender-ref ref="FILE"/>
  </root>

</configuration>

And ${MY_HOME} is a defined system variable (echo $MY_HOME on linux shows the correct path).

The thing is that logback doesnt seem to read it properly, it stores the logs under MY_HOME_IS_UNDEFINED/logs/my.log

What am I doing wrong? Thanks a lot!

EDIT: I made a mistake and put OSC_HOME where I really meant MY_HOME. Sorry about that

Answer 1

Contrary to what the others have said, the logback documentation explicitly states that "During substitution, properties are looked up in the local scope first, in the context scope second, in the system properties scope third, and in the OS environment fourth and last". So if the property is defined in the environment, logback will find it.

I was having the same issue when running my project in Eclipse. If that's the issue you're having, it can be fixed by going to Run Configurations -> Environment and adding MY_HOME to the environment variables.

Not really sure why it isn't loading the native environment by default. There's even an option called "Append environment to native environment" which doesn't seem to have any effect for me.