echo 换行不换行

echo换行输出需要转义符 -e

看以下例子：

echo -e "It is the first line." >> a; echo -e "It is the second line.c" >> a; echo -e "It is the third line." >> a; echo -e "
It is the forth line." >> a

输出：

It is the first line.                                   //默认换行
It is the second line.It is the third line.             //第二行指定不换行，因此第三行紧跟第二行
                                    
It is the forth line.                                  //第三行默认换行，而且第四行前制定换行，因此中间空了一行