sed中 n命令的疑惑

lifayi2008

关于n命令 sed awk 101 hacks中是这样说的：

The sed n command lets you change that flow. The sed n command
will print the current pattern space, clear the current pattern space,
read the next line from the input-file, and continue the command
flow.

Let us assume that you have 2 sed commands before and 2 after the
n command as shown below.
sed-command-1
sed-command-2
n
sed-command-3
sed-command-4

In this case, sed-command-1 and sed-command-2 will be applied to
the current line in the pattern space; when sed encounters the n
command, it will clear the current line from the pattern space, read
the next line from the input-file, and apply sed-command-3 and sedcommand-
4 to this newly read line in the sed pattern space.

在实际试验中
sed -n n employee.txt     假如n有打印功能的话，为什么这里什么也不打印？
sed n employee.txt         假如n没有打印功能的话，这里为什么会打印所有行而不是偶数行？

lifayi2008

n命令是否会打印也受-n选项的控制？

yestreenstars

谁跟你说n有打印功能~

lifayi2008

sed n employee.txt         假如n没有打印功能的话，这里为什么会打印所有行而不是偶数行？回复 3# yestreenstars


   

yestreenstars

回复 4# lifayi2008

执行下面这个试试，就算没有n也照样打印，sed默认就会打印的。

1. sed '' employee.txt

复制代码

lifayi2008

你的sed还要恶补 回复 5# yestreenstars


   

expert1

-n 和n搞混了

-n是抑制自动打印
n把下一行放到pattern space，是覆盖。

q1208c

回复 5# yestreenstars


你的sed还要恶补

ly5066113

回复 3# yestreenstars


n 确实有打印功能。
info sed


`n'
     If auto-print is not disabled, print the pattern space, then,
     regardless, replace the pattern space with the next line of input.
     If there is no more input then `sed' exits without processing any
     more commands.

expert1

回复 9# ly5066113


    这样的写法是不是有点奇怪呢，默认是无需加的，只有不打印的时候才会加-n,谁穷极无聊加个‘n'