Unix commands(21)

                                    1) Linux
                                    2) Gnu Hurd
                                    3) Free BSD
                                    4) Other
                                  #? 1
                                You have selected Linux
         注：var是个变量，可以换成其它的值。break用来跳出循环，如果没有break则一直循环下去。done与select对应。
                  4.loop
                      loop表达式：
                            while ...; do
                                      ....
                               done
　　           while-loop 将运行直到表达式测试为真。will run while the expression that we test for is true.
关键字"break" 用来跳出循环。而关键字”continue”用来不执行余下的部分而直接跳到下一个循环。
　　
                     for-loop表达式查看一个字符串列表 (字符串用空格分隔) 然后将其赋给一个变量：
                          1,   for var in ....; do
　                                ....