| 正规表示法(Regular Expression,RE，或称为常规表示法)通过一些特殊字符的排列，用以搜寻/取代/删除一列或多列文字字符串，可以让使用者轻易的达到搜寻/取代某特定字符串的处理程序。简单来说就是处理字符串的方法，只要工具程序支持这种表示法，支持正规表示法的工具程序很多，包括vi, sed, awk等等。 正规表示法与通配符不同，通配符代表的是bash操作接口的一个功能。 使用正规表示法时，需要留意当时环境的语系，由于一般联系正规表示法时，使用的是兼容于POSIX的标准，因此就使用C这个语系，因此，底下的很多联系都是使用LANG=C这个语系数据进行的。另外，要了解一些特殊符号：   grep的一些进阶选项-A : 后面加数字，为after, 除了列出该行外，后续的n 行也列出来 -B : 后面加数字，为before, 除了列出该行外，前面的n 行也列出来  基础正规表示法练习首先将语系设置为C [super@localhost /]# echo $LANGzh_CN.UTF-8[super@localhost /]# export LANG=C; export LC_ALL=C[super@localhost /]# echo $LANGC练习文件： [super@localhost /]# cat regular_express.txt"Open Source" is a good mechanism to develop programs.apple is my favorite food.Football game is not use feet only.this dress doesn't fit me.However, this dress is about $ 3183 dollars.GNU is free air not free beer.Her hair is very beauty.I can't finish the test.Oh! The soup taste good.motorcycle is cheap than car.This window is clear.the symbol '*' is represented as start.Oh! My god!The gd software is a library for drafting programs.You are the best is mean you are the no. 1.The world <Happy> is the same with "glad".I like dog.google is the best tools for search keyword.goooooogle yes!go! go! Let's go.# I am VBird搜寻特定字符串，寻找'the' -n : 显示行号 [super@localhost /]# grep -n 'the' regular_express.txt8:I can't finish the test.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.取得不管大小写的'the',-i : 忽略大小写的区别 [super@localhost /]# grep -in 'the' regular_express.txt8:I can't finish the test.9:Oh! The soup taste good.12:the symbol '*' is represented as start.14:The gd software is a library for drafting programs.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.利用中括号[]来搜寻集合字符搜寻'test'和'taste', 不管[]中有几个字符，他都仅代表某一个字符 [super@localhost /]# grep -n 't[ae]st' regular_express.txt8:I can't finish the test.9:Oh! The soup taste good.查找'oo'，[super@localhost /]# grep -n 'oo' regular_express.txt1:"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!查找'oo'，但前面不是'g'[super@localhost /]# grep -n '[^g]oo' regular_express.txt2: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! #前面也可能是o，所以满足条件要求'oo'前面不是小写字母[super@localhost /]# grep -n '[^a-z]oo' regular_express.txt3:Football game is not use feet only.取得有数字的那一行[super@localhost leiothrix_lutea]# grep -n '[0-9]' regular_express.txt5:However, this dress is about $ 3183 dollars.15:You are the best is mean you are the no. 1.使用的特殊字符实现'oo'前面不是小写字母[super@localhost leiothrix_lutea]# grep -n '[^[:lower:]]oo' regular_express.txt 3:Football game is not use feet only.行首和行尾字符'^'; '$'行首'the'的列出 [super@localhost test]# grep -n '^the' regular_express.txt12:the symbol '*' is represented as start.开头时小写的那一行列出[super@localhost test]# grep -n '^[a-z]' regular_express.txt2: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.取代[super@localhost test]# grep -n '^[[:lower:]]' regular_express.txt开头不是英文字母[super@localhost test]# grep -n '^[^a-zA-Z]' regular_express.txt1:"Open Source" is a good mechanism to develop programs.21:# I am VBird行尾为小数点'.' 结束的，因为小数点具有其他意义，所以必须使用跳脱字符（\)来解除其特殊意义。[super@localhost test]# grep -n '\.$' regular_express.txt1:"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.6:GNU is free air not free beer.......找出空白行[super@localhost test]# grep -n '^$' regular_express.txt21:不显示空白行和批注行'#'[super@localhost test]# grep -v '^$' /etc/rsyslog.conf | grep -v '^#'任意字符'.'，与任意字符'*' 在正规表示法中，'.'代表：一定有一个任意字符的意思 '*'：代表前一个字符，0到无穷多次的意思 找出g??d的字符串， [super@localhost test]# grep -n 'g..d' regular_express.txt1:"Open Source" is a good mechanism to develop programs.9:Oh! The soup taste good.16:The world <Happy> is the same with "glad".'o*'代表有0-无穷多个o的意思，因此，如果用'o*'的话，就会把文本中的所有内容都显示出来找到至少含有两个'o'的字符串，就需要'ooo*' [super@localhost test]# grep -n 'ooo*' regular_express.txt1:"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!找出两个'g'之间至少有一个'o'的字符串[super@localhost test]# grep -n 'goo*g' regular_express.txt18:google is the best tools for search keyword.19:goooooogle yes!找出一行中还有两个'g'的，即开头是g，结尾是g，中间任意字符'.*'代表零个或多个任意字符[super@localhost test]# grep -n 'g.*g' regular_express.txt1:"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.限定连续RE字符范围{} {}在shell中有特殊意义，因此，也必须使用跳脱字符'\'让他失去特殊意义才行 \{n,m\}代表连续n到m个的前一个RE字符要找到两个oo的字符串， [super@localhost test]# grep -n 'o\{2\}' regular_express.txt1:"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!'g'和'g'之间有2-3个'o'[super@localhost test]# grep -n 'go\{2,3\}g' regular_express.txt18:google is the best tools for search keyword.正规表示法的特殊字符与一般指令列输入指令的通配符并不相同，找到以a为开头的任何档名的文件， [super@localhost test]# ls -l a* /etc #但好像不是这么简单。。[super@localhost test]# ls /etc | grep '^a.*'参考 鸟哥的Linux私房菜 ---------------------------------------------------------------------------------------------------------------------- 我们尊重原创，也注重分享，文章来源于微信公众号：Jar的荒野秘境，建议关注公众号查看原文。如若侵权请联系qter@qter.org。 ---------------------------------------------------------------------------------------------------------------------- |
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