正则表达式基础->

描述：（grep）

正则表达式是一种字符模式，用于在查找过程中匹配指定的字符。在大多数程序里，正则表达式都被置于两个正斜杠之间，它匹配被查找的行中任何位置出现的相同模式

基础正则表达式

正则表达式	描述
\	转义字符，将特殊字符进行转义，忽略其特殊意义
^	匹配行首，awk中，^是匹配字符串的开始
$	匹配行尾，awk中，$是匹配字符串的结尾
^$	表示空行
.	匹配除换行符\n之外的任意一个字符
[ ]	匹配包含在[字符]之中的任意单个字符
[^ ]	匹配[^字符]之外的任意一个字符
[ - ]	匹配 [ ] 指定范围内的任意一个字符
?	匹配之前的项目1次或者0次
+	匹配之前的项1次或多次
*	匹配之前的项0次或多次，.*
( )	匹配表达式，创建一个用于匹配的子串
{ n }	匹配之前的项至少需要匹配n次
{n,}	之前的项至少需要匹配n次
{n,m}	指定之前的项至少匹配n次，最多匹配m次，n<=m
|	交替匹配 | 两边的任意一项ab（c|d）匹配abc 或 abd

特定字符：

>[[:space:]]   空格

[[:digit:]]　　[0-9]

[[:lower:]]　　[a-z]

[[:upper:]]　　[A-Z]

[[:alpha:]]　　[a-Z]

正则表达式练习

[root@web02 ]# cat test.txt （练习文本）
I am timfly student!
I learn linux is very happy.
test

I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not .

命令：

#过滤率以m开头，以m结尾的行
[root@web02 ]# grep "^m" test.txt
my blog is http://timfly.blog.51cto.com
my qq num is .
[root@web02 ]# grep "m$" test.txt
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com

 #排除空行，并打印行号
[root@web02 ]# grep -vn "^$" test.txt
:I am timfly student!
:I learn linux is very happy.
:test
:I like badminton ball ,billiard ball and chinese chess!
:my blog is http://timfly.blog.51cto.com
:our site is http://www.timfly123.com
:my qq num is .
:not .

#匹配任意一个字符，但不包括空行
[root@web02 ]# grep "." test.txt
I am timfly student!
I learn linux is very happy.
test
I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not 

#匹配所有
[root@web02 ]# grep "." test.txt
I am timfly student!
I learn linux is very happy.
test
I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not 

#匹配单个任意字符
[root@web02 ]# grep "tim.ly" test.txt
I am timfly student!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com

#匹配以.结尾的
[root@web02 ]# grep "\.$" test.txt
I learn linux is very happy.
my qq num is .
not .

#精确匹配到
[root@web02 ]# grep -o "8*" test.txt 

[root@web02 ]# grep -o "tim*" test.txt
tim
tim
tim

#匹配有abc的行，数字所在的行，所有小写字母
[root@web02 ]# grep "[abc]" test.txt
I am timfly student!
I learn linux is very happy.
I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com

[root@web02 ]# grep "[0-9]" test.txt
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not .

[root@web02 ]# grep "[a-z]" test.txt
I am timfly student!
I learn linux is very happy.
test
I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not .

[root@web02 ]# grep "[a-z]" test.txt
I am timfly student!
I learn linux is very happy.
test
I like badminton ball ,billiard ball and chinese chess!
my blog is http://timfly.blog.51cto.com
our site is http://www.timfly123.com
my qq num is .
not .

#重复8三次
[root@web02 ]# grep "8\{3\}" test.txt    ##带转义字符
not .
[root@web02 ]# grep "8{3}" test.txt 　　　　##不带转义字符也没有正则
[root@web02 ]# egrep "8{3}" test.txt 　　　　##正则匹配
not .
[root@web02 ]# grep -E "8{3}" test.txt 　　　　##加-E 参数
not .

#重复数字8，-5次
[root@web02 ]# egrep  "8{3,5}" test.txt
not .

#重复8一次或以上
[root@web02 ]# grep -E "8{1,}" test.txt
not .