Invoking external shell application through RubyCocoa

How would I invoke an external application through the RubyCocoa bridge? I read something about NSTask, yet I have no idea how this should be translated in RubyCocoa. My goal is to have an IB开发者_开发百科_action to trigger a method which will run a terminal application with some parameters, i.e. ls -p $mydir, where mydir comes from an IB_outlet such as an Textfield. Any directions or help would be greatly appreciated!

Usually it is invoked using ` quotes and #{} structure for variable

`ls -p #{mydir}`