dang x=${y:-xinzhi} , echo x=xinzhi ,na "y" shi shuyu meiyou she zhi ne haishi "y" wei kong ?
dang x=${y:-xinzhi} , echo x=xinzhi ,na "y" shi shuyu meiyou she zhi ne haishi "y" wei kong ? bu hao yisi ,centos xia bu neng mei you an zhuang zhong wen chajian .