sed全名叫stream editor，流編輯器，用程序的方式來編輯文本，相當的hacker啊。sed基本上就是玩正則模式匹配，所以，玩sed的人，正則表達式一般都比較強。
用s命令替換
使用下面的這段文本做演示：
$ cat pets.txt
This is my cat
my cat's name is betty
This is my dog
my dog's name is frank
This is my fish
my fish's name is george
This is my goat
my goat's name is adam
把其中的my字符串替換成Hao Chen’s，下面的語句應該很好理解（s表示替換命令，/my/表示匹配my，/Hao Chen’s/表示把匹配替換成Hao Chen’s，/g 表示一行上的替換所有的匹配）：
把其中的my字符串替換成Hao Chen’s，下面的語句應該很好理解（s表示替換命令，/my/表示匹配my，/Hao Chen’s/表示把匹配替換成Hao Chen’s，/g 表示一行上的替換所有的匹配）：
注意：如果你要使用單引號，那麼你沒辦法通過\’這樣來轉義，就有雙引號就可以了，在雙引號內可以用\”來轉義。
再注意：上面的sed並沒有對文件的內容改變，只是把處理過後的內容輸出，如果你要寫回文件，你可以使用重定向，如：
$ sed"s/my/Hao Chen's/g"pets.txt > hao_pets.txt
或使用 -i 參數直接修改文件內容：
$ sed -i "s/my/Hao Chen's/g" pets.txt
正則表達式的一些最基本的東西
^ 表示一行的開頭。如：/^#/ 以#開頭的匹配。
$ 表示一行的結尾。如：/}$/ 以}結尾的匹配。
\< 表示詞首。 如 \<abc 表示以 abc 為首的詞。
\> 表示詞尾。 如 abc\> 表示以 abc 結尾的詞。
. 表示任何單個字符。
* 表示某個字符出現了0次或多次。
[ ] 字符集合。 如：[abc]表示匹配a或b或c，還有[a-zA-Z]表示匹配所有的26個字符。如果其中有^表示反，如[^a]表示非a的字符
去掉某html中的tags：
html.txt
< code>b<This</>b< is what < code>spanstyle="text-decoration: underline;"<I</>span< meant. Understand?
看看我們的sed命令
# 如果你這樣搞的話，就會有問題
$ sed 's/< >//g' html.txt
Understand?
# 要解決上面的那個問題，就得像下面這樣。
# 其中的'[^<]' 指定了除了<的字符重復0次或多次。
$ sed 's/<[^>]*>//g' html.txt
This is what I meant. Understand?
我們再來看看指定需要替換的內容：
$ sed"3s/my/your/g"pets.txt
This is my cat
my cat's name is betty
This is your dog
my dog's name is frank
This is my fish
my fish's name is george
This is my goat
my goat's name is adam
下面的命令只替換第3到第6行的文本。
$ sed "3,6s/my/your/g"pets.txt
This is my cat
my cat's name is betty
This is your dog
your dog's name is frank
This is your fish
your fish's name is george
This is my goat
my goat's name is adam
只替換每一行的第一個s：
$ sed 's/s/S/1' my.txt
ThiS is my cat, my cat's name is betty
ThiS is my dog, my dog's name is frank
ThiS is my fish, my fish's name is george
ThiS is my goat, my goat's name is adam
只替換每一行的第二個s：
$ sed's/s/S/2'my.txt
This iS my cat, my cat's name is betty
This iS my dog, my dog's name is frank
This iS my fish, my fish's name is george
This iS my goat, my goat's name is adam
只替換第一行的第3個以後的s：
$ sed's/s/S/3g'my.txt
This is my cat, my cat'S name iS betty
This is my dog, my dog'S name iS frank
This is my fiSh, my fiSh'S name iS george
This is my goat, my goat'S name iS adam
多個匹配
如果我們需要一次替換多個模式，可參看下面的示例：（第一個模式把第一行到第三行的my替換成your，第二個則把第3行以後的This替換成了That）
$ sed '1,3s/my/your/g; 3,$s/This/That/g'my.txt
This is your cat, your cat's name is betty
This is your dog, your dog's name is frank
That is your fish, your fish's name is george
That is my goat, my goat's name is adam
上面的命令等價於：（注：下面使用的是sed的-e命令行參數）
Sed -e '1,3s/my/your/g' -e '3,$s/This/That/g' my.txt
我們可以使用&來當做被匹配的變量，然後可以在基本左右加點東西。如下所示：
$ sed 's/my/[&]/g' my.txt
This is [my] cat, [my] cat's name is betty
This is [my] dog, [my] dog's name is frank
This is [my] fish, [my] fish's name is george
This is [my] goat, [my] goat's name is adam
圓括號匹配
使用圓括號匹配的示例：（圓括號括起來的正則表達式所匹配的字符串會可以當成變量來使用，sed中使用的是\1,\2…）
$ sed 's/This is my \([^,]*\),.*is \(.*\)/\1:\2/g' my.txt
cat:betty
dog:frank
fish:george
goat:adam
上面這個例子中的正則表達式有點復雜，解開如下（去掉轉義字符）：
正則為：This is my ([^,]*),.*is (.*)
匹配為：This is my (cat),……….is (betty)
然後：\1就是cat，\2就是betty
sed的命令
回到最一開始的例子pets.txt，讓我們來看幾個命令：
$ cat pets.txt
This is my cat
my cat's name is betty
This is my dog
my dog's name is frank
This is my fish
my fish's name is george
This is my goat
my goat's name is adam
N命令
先來看N命令 —— 把下一行的內容納入當成緩沖區做匹配。
下面的的示例會把原文本中的偶數行納入奇數行匹配，而s只匹配並替換一次，所以，就成了下面的結果：
$ sed'N;s/my/your/'pets.txt
This is your cat
my cat's name is betty
This is your dog
my dog's name is frank
This is your fish
my fish's name is george
This is your goat
my goat's name is adam
也就是說，原來的文件成了：
This is my cat\n my cat's name is betty
This is my dog\n my dog's name is frank
This is my fish\n my fish's name is george
This is my goat\n my goat's name is adam
這樣一來，下面的例子你就明白了，
$ sed'N;s/\n/,/'pets.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
a命令和i命令
a命令就是append， i命令就是insert，它們是用來添加行的。如：
# 其中的1i表明，其要在第1行前插入一行（insert）
$ sed "1 i This is my monkey, my monkey's name is wukong"my.txt
This is my monkey, my monkey's name is wukong
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
# 其中的1a表明，其要在最後一行後追加一行（append）
$ sed"$ a This is my monkey, my monkey's name is wukong"my.txt
This is my cat, my cat's name is betty
This is my monkey, my monkey's name is wukong
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
我們可以運用匹配來添加文本：
# 注意其中的/fish/a，這意思是匹配到/fish/後就追加一行
$ sed"/fish/a This is my monkey, my monkey's name is wukong"my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my monkey, my monkey's name is wukong
This is my goat, my goat's name is adam
c命令
c 命令是替換匹配行
$ sed "2 c This is my monkey, my monkey's name is wukong" my.txt
This is my cat, my cat's name is betty
This is my monkey, my monkey's name is wukong
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
$ sed"/fish/c This is my monkey, my monkey's name is wukong"my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my monkey, my monkey's name is wukong
This is my goat, my goat's name is adam
d命令
刪除匹配行
$ sed'/fish/d'my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my goat, my goat's name is adam
$ sed'2d'my.txt
This is my cat, my cat's name is betty
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
$ sed'2,$d'my.txt
This is my cat, my cat's name is betty
p命令
打印命令
你可以把這個命令當成grep式的命令
# 匹配fish並輸出，可以看到fish的那一行被打了兩遍，
# 這是因為sed處理時會把處理的信息輸出
$ sed'/fish/p'my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my fish, my fish's name is george
This is my goat, my goat's name is adam
# 使用n參數就好了
$ sed -n '/fish/p'my.txt
This is my fish, my fish's name is george
# 從一個模式到另一個模式
$ sed -n '/dog/,/fish/p'my.txt
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
#從第一行打印到匹配fish成功的那一行
$ sed-n '1,/fish/p'my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
