shell及脚本3——正则表达式

it2022-05-05 166

一.正则表达式

1.1. 什么是正则表达式

　　正则表达式是处理字符串的方法，以行为单位，通过一些特殊符号的辅助，让用户可以轻易进行查找、删除、替换某特定字符串的操作。

1.2. 正则表达式与通配符的区别

　　网友看法，有些道理，直接摘抄了：

　　通配符是系统level的，通配符多用在文件名上，比如查找find，ls，cp，等等；

　　而正则表达式需要相关工具的支持: egrep, awk, vi, perl。在文本过滤工具里，都是用正则表达式，比如像awk，sed等，是针对文件的内容的。不是所有工具（命令）都支持正则表达式。

　　说白了就是有些命令支持正则表达式，一些不支持。

1.3. 语系对正则表达式的影响

　　不通语系，对字符的翻译规则不通，例如

　　LANG=C, 顺序为：0,1,2,3,4....A,B,C,D......Za,b,c,d....z

　　LANG=zh_CN,顺序为：0,1,2,3,4....a,A,b,B,c,C,d,D......z,Z

1.4. 一些特殊符号

　　特殊符号可以规避语系的影响，一些常用的特殊符号：

　　 [:alnum:] 所有的字母和数字，0-9，A-Z,a-z 　　[:alpha:] 所有的字母，A-Z,a-z 　　[:blank:] 所有呈水平排列的空白字符，空格和TAB 　　[:cntrl:] 所有的控制字符，CR,LF,TAL,DEL等　　[:digit:] 所有的数字，0-9 　　 [:graph:] 所有的可打印字符，不包括空格（空格和TAB）外的所有按键　　[:lower:] 所有的小写字母，,a-z 　　[:print:] 所有的可打印字符，包括空格　　[:punct:] 所有的标点字符　　[:space:] 所有呈水平或垂直排列的空白字符　　[:upper:] 所有的大写字母，A-Z 　　[:xdigit:] 所有的十六进制数，0-9，A-Z,a-z的数字与字符

二.基础正则表达式

2.1.练习，使用grep

2.1.1. grep的高级功能

grep [-A] [-B] ‘搜索字符串’ filename

-A: after + 数字n，除了该行，列出后面的n行，-An，无空格

-B：before + 数字n，除了该行，列出前面的n行，-Bn，无空格

:/$ dmesg | grep -n 'eth' 1564:[ 2.427478] e1000 0000:02:01.0 eth0: (PCI:66MHz:32-bit) 00:0c:29:93:15:12 1565:[ 2.427489] e1000 0000:02:01.0 eth0: Intel(R) PRO/1000 Network Connection 1569:[ 2.433153] e1000 0000:02:01.0 ens33: renamed from eth0 :/$ dmesg | grep -n -A3 -B2 'eth'　　#-A和-B紧接数字，没有空格 1562-[ 2.364718] Console: switching to colour frame buffer device 100x37 1563-[ 2.395386] [drm] Initialized vmwgfx 2.9.0 20150810 for 0000:00:0f.0 on minor 0 1564:[ 2.427478] e1000 0000:02:01.0 eth0: (PCI:66MHz:32-bit) 00:0c:29:93:15:12 1565:[ 2.427489] e1000 0000:02:01.0 eth0: Intel(R) PRO/1000 Network Connection 1566-[ 2.427823] ahci 0000:02:05.0: version 3.0 1567-[ 2.428781] ahci 0000:02:05.0: AHCI 0001.0300 32 slots 30 ports 6 Gbps 0x3fffffff impl SATA mode 1568-[ 2.428784] ahci 0000:02:05.0: flags: 64bit ncq clo only 1569:[ 2.433153] e1000 0000:02:01.0 ens33: renamed from eth0 1570-[ 2.445075] scsi host3: ahci 1571-[ 2.445243] scsi host4: ahci 1572-[ 2.445375] scsi host5: ahci

2.1.2. 基础正则表达式练习

使用鸟哥的例子，regular_express.txt

2.1.2.1 查找特定字符串和反向选取

:~/test$ grep -n 'the' regular_express.txt 8:I can't finish the test.^M 12:the symbol '*' is represented as start. 15:You are the best is mean you are the no. 1. 16:The world <Happy> is the same with "glad". 18:google is the best tools for search keyword.:~/test$ grep -vn 'the' regular_express.txt 　　#反向选取 1:"Open Source" is a good mechanism to develop programs. 2:apple is my favorite food. 3:Football game is not use feet only. 4:this dress doesn't fit me. 5:However, this dress is about $ 3183 dollars.^M 6:GNU is free air not free beer.^M 7:Her hair is very beauty.^M 9:Oh! The soup taste good.^M 10:motorcycle is cheap than car. 11:This window is clear. 13:Oh! My god! 14:The gd software is a library for drafting programs.^M 17:I like dog. 19:goooooogle yes! 20:go! go! Let's go.

2.1.2.2 利用[]查找字符集合

:~/test$ grep -n 't[ae]st' regular_express.txt 　　#[ae]表示1个字符，a或者e 8:I can't finish the test.^M 9:Oh! The soup taste good.^M :~/test$ grep -n 'oo' 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.^M 18:google is the best tools for search keyword. 19:goooooogle yes!:~/test$ grep -n '[^g]oo' regular_express.txt 　　 #[^g]不是g，查找oo且前面不是g的，第1行和第9行没有了 2:apple is my favorite food. 3:Football game is not use feet only. 18:google is the best tools for search keyword. 19:goooooogle yes! :~/test$ grep -n '[^a-z]oo' regular_express.txt 　　　　#找oo且前面不是小写字符的 3:Football game is not use feet only.:~/test$ grep -n '[^[:lower:]]oo' regular_express.txt #[:lower:]小写字符的另一种写法 3:Football game is not use feet only. :~/test$ grep -n '[0-9]' regular_express.txt 　　　　　　　　#找数字5:However, this dress is about $ 3183 dollars.^M 15:You are the best is mean you are the no. 1. :~/test$ grep -n '[[:digit:]]' regular_express.txt 　　　　 #数字的另一种写法[:digit:]5:However, this dress is about $ 3183 dollars.^M 15:You are the best is mean you are the no. 1.

2.1.2.3 行首^与行尾$字符

注意：[^]代表反向选取，在括号外面^[]表示行首

:~/test$ grep -n '^the' regular_express.txt 　　#找行首是the的 12:the symbol '*' is represented as start. :~/test$ grep -n '^[a-z]' regular_express.txt #行首是小写字符的 2:apple is my favorite food. 4:this dress doesn't fit me. 10:motorcycle is cheap than car. 12:the symbol '*' is represented as start. 18:google is the best tools for search keyword. 19:goooooogle yes! 20:go! go! Let's go. :~/test$ grep -n '^[^a-zA-Z]' regular_express.txt 　　#行首不是字符的 1:"Open Source" is a good mechanism to develop programs. :~/test$ grep -n '\.$' regular_express.txt 　　　　#行尾是点.的，点前加了转义字符，以为.本身是特殊字符20:go! go! Let's go.

2.1.2.3 任意一个字符.与重复字符*

*：重复前一个字符0到无穷多次的意思，例如a*,代表 “空~无穷多个a”。与通配符不同，通配符中*表示0到多个字符，a*表示a或者“a若干字符”

. : 一定有一个任意字符

:~/test$ grep -n 'g..d' regular_express.txt 　　　　　　　　# g..d表示g和d之间一定有2个任意字符 1:"Open Source" is a good mechanism to develop programs. 9:Oh! The soup taste good.^M 16:The world <Happy> is the same with "glad". :~/test$ grep -n 'ooo*' regular_express.txt 　　　　　　　　#ooo*，表示有2~无穷多个o 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.^M 18:google is the best tools for search keyword. 19:goooooogle yes!:~/test$ grep -n 'g.*g' regular_express.txt 　　　　　　　　# g.*g，找g开头，g结尾的字符，“.*”可以理解成0个或人一多个字符，与通配符中的*相当了1:"Open Source" is a good mechanism to develop programs.14:The gd software is a library for drafting programs.^M18:google is the best tools for search keyword.19:goooooogle yes!20:go! go! Let's go.:~/test$ grep -n 'g*g' regular_express.txt 　　　　　　　　# g*g，不一定是g开头，g结尾，因为g*表示0~无穷多个g，1:"Open Source" is a good mechanism to develop programs.3:Football game is not use feet only.9:Oh! The soup taste good.^M13:Oh! My god!14:The gd software is a library for drafting programs.^M16:The world <Happy> is the same with "glad".17:I like dog.18:google is the best tools for search keyword.19:goooooogle yes!20:go! go! Let's go.

2.1.2.4 限定连续重复的字符范围{}

:~/test$ grep -n 'go\{2,5\}g' regular_express.txt 　　# \{2,5\},2到5个o 18:google is the best tools for search keyword. :~/test$ grep -n 'go\{2\}g' regular_express.txt 　　　# \{2\},2个o 18:google is the best tools for search keyword. :~/test$ grep -n 'go\{2,\}g' regular_express.txt 　　# \{2,\},2个及以上个o 18:google is the best tools for search keyword. 19:goooooogle yes!:~/test$ grep -n 'go\{,5\}g' regular_express.txt 　　# \{,5\},5个及以下个o 18:google is the best tools for search keyword. :~/test$ grep -n 'go\{,10\}g' regular_express.txt 　　# \{,10\},10个及以下个o 18:google is the best tools for search keyword. 19:goooooogle yes!

2.基础正则表达式字符总结

^word: word在行首

word$: word在行尾

. ：一定有一个任意字符

\ ：转义

* ： 0~无穷多个前一字符

[list] ：在list中的1个字符

[n1-n2] ：在字符范围内的1个字符

[^lish] ：反向选取

\{n1,n2\} ：连续n1到n2个前一字符

3.sed命令

管道命令，可以进行数据替换、删除、新增、选取特定行等。

4.awk命令

按字段处理

5.扩展的正则表达式

+ 　　重复1个或1个以上前一个字符

？　　 0个或1个前一个字符

| 　　或 'glad|good'

（）　分组 g(la|oo)d

（）+ 1个或多个重复组

转载于:https://www.cnblogs.com/liuwanpeng/p/6226656.html

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