sed进阶

Posted 2021-02-05 ch122633

下面这些命令未必经常会用到，但当需要时，知道这些肯定是件好事。

一、多行命令

sed命令通常是对一行数据进行处理，然后下一行重复处理。

sed编辑器包含了三个可用来处理多行文本的特殊命令

• N：将数据流中的下一行加进来创建一个多行组来处理
• D：删除多行组中的一行
• P：打印多行组中的一行

1.1 next命令

两种删除匹配的下一行的办法：

cat data1.txt 
This is the header line.

This is a data line.

This is the last line.

sed ‘/^$/d‘ data1.txt 
This is the header line.
This is a data line.
This is the last line.

sed ‘/header/{n ; d}‘ data1.txt 
This is the header line.
This is a data line.

This is the last line.

空行处理

 

1.2 合并文本行

用大写N，可以一次性读取两行。区别与n是移动到下一行。

$ sed ‘/first/{ N ; s/
/ / }‘ data2.txt 
This is the header line.
This is the first data line. This is the second data line.
This is the last line.

$ cat data2.txt 
This is the header line.
This is the first data line.
This is the second data line.
This is the last line.

$ cat data3.txt 
On Tuesday, the Linux System
Administrator‘s group meeting will be held.
All System Administrators should attend.
Thank you for your attendance.

$ sed ‘N ; s/System.Administrator/Desktop User/‘ data3.txt
On Tuesday, the Linux Desktop User‘s group meeting will be held.
All Desktop Users should attend.
Thank you for your attendance.

N使用例子

在N后面最好匹配多行命令，而单行命令则可以放在N前面，如：

$ sed ‘N
> s/System
Administrator/Desktop
User/
> s/System Administrator/Desktop User/
> ‘ data4.txt
On Tuesday, the Linux Desktop
User‘s group meeting will be held.
All System Administrators should attend.

$ cat data4.txt 
On Tuesday, the Linux System
Administrator‘s group meeting will be held.
All System Administrators should attend.

$ sed ‘
> s/System Administrator/Desktop User/
> N
> s/System
Administrator/Desktop
User/
> ‘ data4.txt
On Tuesday, the Linux Desktop
User‘s group meeting will be held.
All Desktop Users should attend.

前后写的例子

 

二、保持空间

 

三、排除命令

 

四、改变流

 

五、模式替代

 

六、在脚本中使用sed

 

七、创建sed实用工具