As stated in http://logback.qos.ch/setup.html conditional processing in configuration files requires the Janino library. When running in an OSGi environment (e.g. an Eclipse RCP application) simply placing commons-compiler.jar and janino.jar on your application's class path is not sufficient enough. You will get the following exception:

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12:50:47,754 |-INFO in ch.qos.logback.classic.joran.action.RootLoggerAction - Setting level of ROOT logger to DEBUG
12:50:47,755 |-INFO in ch.qos.logback.core.joran.action.AppenderRefAction - Attaching appender named [stdout] to Logger[ROOT]
12:50:47,755 |-INFO in ch.qos.logback.core.joran.action.AppenderRefAction - Attaching appender named [file] to Logger[ROOT]
12:50:47,810 |-ERROR in ch.qos.logback.core.joran.conditional.IfAction - Failed to parse condition [property("xxx.instance").equals("SIM_LOCAL")] org.codehaus.janino.JaninoRuntimeException: Cannot load class 'ch.qos.logback.core.joran.conditional.PropertyWrapperForScripts' through the parent loader
    at org.codehaus.janino.JaninoRuntimeException: Cannot load class 'ch.qos.logback.core.joran.conditional.PropertyWrapperForScripts' through the parent loader
    at     at org.codehaus.janino.SimpleCompiler$1.getDelegate(SimpleCompiler.java:306)
    at     at org.codehaus.janino.SimpleCompiler$1.accept(SimpleCompiler.java:291)
    at     at org.codehaus.janino.UnitCompiler.getType(UnitCompiler.java:5159)
    at     at org.codehaus.janino.UnitCompiler.access$16700(UnitCompiler.java:185)
    at     at org.codehaus.janino.UnitCompiler$29.getSuperclass2(UnitCompiler.java:8154)
    at     at org.codehaus.janino.IClass.getSuperclass(IClass.java:406)
    at     at org.codehaus.janino.IClass.getIMethods(IClass.java:223)
    at     at org.codehaus.janino.IClass.getIMethods(IClass.java:199)
    at     at org.codehaus.janino.UnitCompiler.compile2(UnitCompiler.java:409)
    at     at org.codehaus.janino.UnitCompiler.compile2(UnitCompiler.java:393)
    at     at org.codehaus.janino.UnitCompiler.access$400(UnitCompiler.java:185)
    at     at org.codehaus.janino.UnitCompiler$2.visitPackageMemberClassDeclaration(UnitCompiler.java:347)
    at     at org.codehaus.janino.Java$PackageMemberClassDeclaration.accept(Java.java:1139)
    at     at org.codehaus.janino.UnitCompiler.compile(UnitCompiler.java:354)
    at     at org.codehaus.janino.UnitCompiler.compileUnit(UnitCompiler.java:322)
    at     at org.codehaus.janino.SimpleCompiler.compileToClassLoader(SimpleCompiler.java:383)
    at     at org.codehaus.janino.ClassBodyEvaluator.compileToClass(ClassBodyEvaluator.java:315)
    at     at org.codehaus.janino.ClassBodyEvaluator.cook(ClassBodyEvaluator.java:233)
    at     at org.codehaus.janino.SimpleCompiler.cook(SimpleCompiler.java:192)
    at     at org.codehaus.commons.compiler.Cookable.cook(Cookable.java:84)
    at     at org.codehaus.commons.compiler.Cookable.cook(Cookable.java:77)
    at     at ch.qos.logback.core.joran.conditional.PropertyEvalScriptBuilder.build(PropertyEvalScriptBuilder.java:51)
    at     at ch.qos.logback.core.joran.conditional.IfAction.begin(IfAction.java:67)
    at     at ch.qos.logback.core.joran.spi.Interpreter.callBeginAction(Interpreter.java:275)
    at     at ch.qos.logback.core.joran.spi.Interpreter.startElement(Interpreter.java:147)
    at     at ch.qos.logback.core.joran.spi.Interpreter.startElement(Interpreter.java:129)
    at     at ch.qos.logback.core.joran.spi.EventPlayer.play(EventPlayer.java:50)
    at     at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:149)
    at     at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:135)
    at     at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:99)
    at     at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:49)
    at     at ch.qos.logback.classic.util.ContextInitializer.configureByResource(ContextInitializer.java:77)
    at     at ch.qos.logback.classic.util.ContextInitializer.autoConfig(ContextInitializer.java:152)
    at     at org.slf4j.impl.StaticLoggerBinder.init(StaticLoggerBinder.java:85)
    at     at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:55)
    at     at org.slf4j.LoggerFactory.bind(LoggerFactory.java:141)
    at     at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:120)
    at     at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:331)
    at     at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:283)
    at     at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:304)
    at     at com.xxx.yyy.client.ui.lifecycle.StartHandler.<init>(StartHandler.java:22)
    at     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at     at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at     at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at     at org.eclipse.e4.core.internal.di.ConstructorRequestor.execute(ConstructorRequestor.java:42)
    at     at org.eclipse.e4.core.internal.di.InjectorImpl.internalMake(InjectorImpl.java:343)
    at     at org.eclipse.e4.core.internal.di.InjectorImpl.make(InjectorImpl.java:264)
    at     at org.eclipse.e4.core.contexts.ContextInjectionFactory.make(ContextInjectionFactory.java:162)
    at     at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.createFromBundle(ReflectionContributionFactory.java:104)
    at     at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.doCreate(ReflectionContributionFactory.java:73)
    at     at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.create(ReflectionContributionFactory.java:55)
    at     at org.eclipse.e4.ui.internal.workbench.swt.E4Application.createE4Workbench(E4Application.java:235)
    at     at org.eclipse.e4.ui.internal.workbench.swt.E4Application.start(E4Application.java:145)
    at     at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at     at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
    at     at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
    at     at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
    at     at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
    at     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at     at java.lang.reflect.Method.invoke(Method.java:497)
    at     at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
    at     at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
    at     at org.eclipse.equinox.launcher.Main.run(Main.java:1515)
    at     at org.eclipse.equinox.launcher.Main.main(Main.java:1488)
12:50:47,811 |-ERROR in ch.qos.logback.core.joran.conditional.IfAction - Failed to determine "if then else" result
12:50:47,811 |-INFO in ch.qos.logback.classic.joran.action.ConfigurationAction - End of configuration.
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