code: def get_command(self, command):
  		
  		shutit_global.shutit_global_object.yield_to_draw()
  		if command in ('md5sum','sed','head'):
  			if self.get_current_shutit_pexpect_session_environment().distro == 'osx':
  				return 'g' + command
  		return command
docs: Helper function for osx - return gnu utils rather than default for
  		   eg head and md5sum where possible and needed.