1  用途：
                          1）打印信息，包括：变量的值、字符串等
                          2）shell编程中，帮助debug程序

               2  常用参数：

                          -n：打印信息之后不换行
                          -e：对字符串转义

               3  例子：

                           例子一：
                                      [root@localhost ~]# echo $LANG
                                      zh_CN.UTF-8

                           例子二：
                                      [root@localhost ~]# echo -n "please input your name: ";read name;echo "your name is:$name"
                                      please input your name: think
                                      your name is:think

                           例子三：
                                      [root@localhost ~]# echo -e "hello\fworld"
                                      hello