sed中 n命令的疑惑

lifayi2008

關(guān)于n命令 sed awk 101 hacks中是這樣說的：

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.

在實際試驗中
sed -n n employee.txt     假如n有打印功能的話，為什么這里什么也不打��？
sed n employee.txt         假如n沒有打印功能的話，這里為什么會打印所有行而不是偶數(shù)行？

lifayi2008

n命令是否會打印也受-n選項的控制？

yestreenstars

誰跟你說n有打印功能~

lifayi2008

sed n employee.txt         假如n沒有打印功能的話，這里為什么會打印所有行而不是偶數(shù)行？回復(fù) 3# yestreenstars


   

yestreenstars

回復(fù) 4# lifayi2008

執(zhí)行下面這個試試，就算沒有n也照樣打印，sed默認(rèn)就會打印的。

1. sed '' employee.txt

復(fù)制代碼

lifayi2008

你的sed還要惡補(bǔ) 回復(fù) 5# yestreenstars


   

expert1

-n 和n搞混了

-n是抑制自動打印
n把下一行放到pattern space，是覆蓋。

q1208c

回復(fù) 5# yestreenstars


你的sed還要惡補(bǔ)

ly5066113

回復(fù) 3# yestreenstars


n 確實有打印功能。
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

回復(fù) 9# ly5066113


    這樣的寫法是不是有點奇怪呢，默認(rèn)是無需加的，只有不打印的時候才會加-n,誰窮極無聊加個‘n'