正则表达式基础->
2024-09-24 14:26:55
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 .
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