求教sed

chong232

1. chong232@chong232-ubuntu:~$ seq  4 | sed  -e '1!N;G'
   
2. 1
   
3. 
   
4. 2
   
5. 3
   
6. 
   
7. 4

复制代码

我感觉4后面应该还有一空行， 为什么没有？

hbmhalley

N
Add a newline to the pattern space, then append the next line of input to the pattern space. If there is no more input then sed exits without processing any more commands.

N command on the last line
Most versions of sed exit without printing anything when the N command is issued on the last line of a file. GNU sed prints pattern space before exiting unless of course the -n command switch has been specified. This choice is by design.
For example, the behavior of

          sed N foo bar
would depend on whether foo has an even or an odd number of lines. Or, when writing a script to read the next few lines following a pattern match, traditional implementations of sed would force you to write something like

          /foo/{ $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N }
instead of just

          /foo/{ N;N;N;N;N;N;N;N;N; }
In any case, the simplest workaround is to use $d;N in scripts that rely on the traditional behavior, or to set the POSIXLY_CORRECT variable to a non-empty value.

           

L_kernel

info sed文档对N命令的行为写得很清楚了。

`N'
     Add a newline to the pattern space, then append the next line of
     input to the pattern space.  If there is no more input then `sed'
     exits without processing any more commands.

chong232

L_kernel 发表于 2012-05-24 13:42
info sed文档对N命令的行为写得很清楚了。

额，我只是man了一下，上面没有介绍，多谢楼上两位帮忙！看来man不靠谱啊！

L_kernel

chong232 发表于 2012-05-24 13:49
额，我只是man了一下，上面没有介绍，多谢楼上两位帮忙！看来man不靠谱啊！

靠谱，只是没有那么详细。熟悉了的情况下，可以作为快速查找。

cjaizss

完蛋,没有-n的我就看不懂了

wsxedcer

回复 1# chong232

楼主 试试这个看看效果 ，比较下

1. seq  5 | sed   'N;$!G'

复制代码

chong232

wsxedcer 发表于 2012-05-24 16:45
回复 1# chong232

楼主 试试这个看看效果 ，比较下

能看懂了，多谢