正则表达式

1.行首与行尾字符^$

行首:

oyzhx@ubuntu:~$ grep -n '^the' regular_express.txt 
12:the symbol '*' is represented as start.   

oyzhx@ubuntu:~$ grep -n '.$' regular_express.txt 
1:"Open Source" is a good mechanism to develop programs.

*:重复前一个字符的0-无穷个的意思.//a*

oyzhx@ubuntu:~$ grep -n 'ooo*' regular_express.txt 
1:"Open Source" is a good mechanism to develop programs.
2:apple is my favorite food.
3:Football game is not use feet only.
9:Oh! The soup taste good.
18:google is the best tools for search keyword.
19:goooooogle yes!

oyzhx@ubuntu:~$ grep -n 'g..d' regular_express.txt 
1:"Open Source" is a good mechanism to develop programs.
9:Oh! The soup taste good.
16:The world <Happy> is the same with "glad".

oyzhx@ubuntu:~$ grep -n 'g.*g' regular_express.txt 
1:"Open Source" is a good mechanism to develop programs.
14:The gd software is a library for drafting programs.
18:google is the best tools for search keyword.
19:goooooogle yes!
20:go! go! Let's go.

{2}表示2个，{2,}2个以上,{2,5}2个到5个

oyzhx@ubuntu:~$ grep -n 'go{2,5}g' regular_express.txt 
18:google is the best tools for search keyword.

sed [-nefr]

-n:显示n特殊处理的那行

-e:命令行模式上进行sed的动作编辑

-f:将sed的动作写在一个文件内

-r:扩展型正则表达式的语法（默认是基础正则表达式语法）

-i:直接修改读取的文件内容，而不是由屏幕输出

[n1,[n2]] function

function 的参数

a,新增；c替换 d删除，i插入；p打印，s替换

5.扩展正则表达式

+：重复一个或一个以上的前一个RE字符. egrep -n 'go+d' aa.txt;

？：零个或一个的前一个RE字符 egrep -n 'go?d' aa.txt;

|：用或（or）的方式找出数个字符串 egrep -n 'gdlggod' aa.txt;

（）：找出“组字符串” egrep -n 'g(laloo)d' aa.txt;

（）+：多个重复组的判别 echo 'AxyzxyzxuzusC'|egrep 'A(xyz) +C';

（编辑：李大同）

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