Gradle: Change setting using P option

build.gradle

defaultTasks 'dbsetting'

def envList = ['dev', 'qa', 'prod']

if (!hasProperty('env')) {
    ext.env = System.env['GRADLE_ENV'] ?: envList[0]
}

if(!envList.find{it == ext.env}){
    throw new Exception("There is no environment named '$ext.env'")
}


ext.setting = {
    def slurper = new ConfigSlurper()
    def files = files("env/default.gradle",
            "env/${env}.gradle",
            "${System.properties['user.home']}/.gradle/${env}.gradle")

    files.inject(new ConfigObject()) { config, file ->
        file.exists() ? config.merge(slurper.parse(file.toURL())) : config
    }
}()

task dbsetting << {  
    println "dbname: $setting.database.dbname"
    println "user: $setting.database.username"
    println "password: $setting.database.password"
}