sed入门(转载)

sed入门(转载) 原出处:http://phi.sinica.edu.tw/aspac/reports/96/96005/index.html
1.Introduction
Sed(Stream EDitor)為 UNIX 系統上提供將編輯工作自動化的編輯器 , 使用者無需直接編輯資料。使用者可利用 sed 所提供 20 多種不同的函數參數 , 組合(註解 [1])它們完成不同的編輯動作。此外 , 由於 sed 都以行為單位編輯文件 , 故其亦是行編輯器(line editor)。
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Shell expression operators. Need to review frequently.

String Comparison Result
string1 = string2 True if the strings are equal
string1 != string2 True if the strings are not equal
-n string True if the string is not null
-z string True if the string is null (an empty string)
Arithmetic Comparison Result
expression1 -eq expression2 True if the expressions are equal
expression1 -ne expression2 True if the expressions are not equal
expression1 -gt expression2 True if expression1 is greater than expression2
expression1 -ge expression2 True if expression1 is greater than or equal to
expression2
expression1 -lt expression2 True if expression1 is less than expression2
expression1 -le expression2 True if expression1 is less than or equal to
expression2
! expression True if the expression is false, and vice versa
File Conditional Result
-d file True if the file is a directory
-e file True if the file exists. Note that historically the -e option
has not been portable, so -f is usually used.
-f file True if the file is a regular file
-g file True if set-group-id is set on file
-r file True if the file is readable
-s file True if the file has nonzero size
-u file True if set-user-id is set on file
-w file True if the file is writable
-x file True if the file is executable