def fun(self):

		cmd_tmpl = ''.join(self.out)
		params = self.params

		def f(task):
			env = task.m_env
			p = env.get_flat
			alst=[]
			for (name, meth) in params:
				if name == 'SRC':
					if meth:
						alst.append(eval('task.m_inputs%s' % meth))
					else:
						alst.append(" ".join([a.srcpath(env) for a in task.m_inputs]))
				elif name == 'TGT':
					if meth:
						alst.append(eval('task.m_outputs%s' % meth))
					else:
						alst.append(" ".join([a.bldpath(env) for a in task.m_outputs]))
				else:
					self.m_vars.append(name)
					alst.append(p(name))
			if alst:
				try:
					cmd = cmd_tmpl % tuple(alst)
				except Exception:
					task.debug()
					raise
			else:
				cmd = cmd_tmpl

			return Runner.exec_command(cmd)

		return f