thufir@arrakis:~/java$ 
thufir@arrakis:~/java$ ruby java.rb 
clean...

./tasks.rb:6:in `clean': undefined method `System' for Tasks:Module (NoMethodError)
        from java.rb:5
thufir@arrakis:~/java$ 
thufir@arrakis:~/java$ cat tasks.rb 
module Tasks

        def Tasks.clean
                puts "clean...\n\n"
                Dir.chdir("/home/thufir/java/src/")
                System("echo foo")
        end

        def Tasks.compile
                puts "compile...\n\n"
        end


        def Tasks.package
                puts "package...\n\n"
        end

end

thufir@arrakis:~/java$ 
thufir@arrakis:~/java$