I have this logback.xml file:
You perhaps mean MY_HOME. In your config file there is reference for OSC_HOME. See Variable substitution rules of Logback for details.
You can pass environment variable as a Java System property and then Logback will perform the variable substitution. You can pass this as JVM option in your command line. For example:
java -DMY_HOME=${MY_HOME} -cp ... MainClass
Or You can define MY_HOME in your config file itself.
${MY_HOME}/logs/mylog.log