Grails Environment Specific Logging to a File

I need to log my Grails application across different environments. For example, a Grails embeded Jetty server in DEV environment and a Tomcat server in TEST environment. Different servers have different log directory locations. How to dynamically pick up the right location? The trick is to define the file location (a relative path in my case) as a global variable inside Config.groovy, customized it in the environment blocks, and use the variable location inside log4j closure.

The following is the Config.groovy:

def logDirectory = '.'
environments {
 development {
 }
 test {
     logDirectory = "../logs"    
 }
}

// log4j configuration
log4j = {
 appenders {
     console name:'stdout'
     rollingFile  name:'file', file: logDirectory + '/app.log', threshold: org.apache.log4j.Level.INFO, maxFileSize:"1MB", maxBackupIndex: 10, 'append':true    
 }

 error  'org.codehaus.groovy.grails.web.servlet',  //  controllers
        'org.codehaus.groovy.grails.web.pages', //  GSP
        'org.codehaus.groovy.grails.web.sitemesh', //  layouts
        'org.codehaus.groovy.grails.web.mapping.filter', // URL mapping
        'org.codehaus.groovy.grails.web.mapping', // URL mapping
        'org.codehaus.groovy.grails.commons', // core / classloading
        'org.codehaus.groovy.grails.plugins', // plugins
        'org.codehaus.groovy.grails.orm.hibernate', // hibernate integration
        'org.springframework',
        'org.hibernate',
        'org.codehaus.groovy.grails.scaffolding.view.ScaffoldingViewResolver'

 warn   'org.mortbay.log'

 root {
     info 'stdout', 'file'
     additivity = true
 }
}

It has been tested to work on Grails version is 1.1.1 with Tomcat 6.0.