def push_to_background(self):
        """
        Push the current job into the background and return to the shell.
        """
        if self.child_thread:
            self.stash.write_message('pushing current job to background ...\n')
            self.child_thread.set_background()
            self.script_will_end()
        else:
            self.stash.write_message('no running foreground job\n')
            self.stash.io.write(self.stash.runtime.get_prompt())

        Push the current job into the background and return to the shell.
        
system/shruntime.py