在第二行后面一行加上两行字,例如 "this is first line!" "this is second line!"
woody@xiaoc:~/tmp$ cat -n /etc/passwd |sed '2a This is first line! \ //使用续航符\后按回车输入后续行
> This is second line!' // 以' 再回车结束
1 root:x:0:0:root:/root:/bin/bash
2 daemon:x:1:1:daemon:/usr/sbin:/bin/sh
This is first line!
This is second line!
3 bin:x:2:2:bin:/bin:/bin/sh