ext.projectNames = ["project1", "project2", "project3"]

projectNames.each { name ->
    if (isIncluded(name)) {
        println "project $name is INTERNAL to this build"
        include name
    } else {
        println "project $name is external to this build"
    }
}

def isIncluded(String projectName) {
    if (System.getProperty("useLocal") != null) {
        def localProjects = System.getProperty("useLocal").split(",")
        return (projectName in localProjects)
    }
    return false
}