正则表达式的使用

在Shell命令行中，用户可以使用grep命令来测试

Grep命令参数解析

测试用例：

[root@haha day6]# grep -n '"' test_file  1:fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. 3:"Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 5:"I know every day that buying books, buying books, what else will I do besides buying books!" The wife was angry and yelling, pulled out the chair, gave a hard meal, and sat down on it. 7:"I'm blind. When I was young, I thought you could read a word, but I thought you could do something big!" [root@haha day6]#  

[root@haha day6]# grep -no '"' test_file  1:" 1:" 1:" 1:" 1:" 1:" 3:" 

[root@haha day6]# grep -noq '"' test_file  [root@haha day6]# echo $? 0 

[root@haha day6]# grep -nol '"' test_file  test_file 

[root@haha day6]# grep -A 3 fter test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 

[root@haha day6]# grep -B 2 Buy test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 

[root@haha day6]# grep -C 2 Buy test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. "I know every day that buying books, buying books, what else will I do besides buying books!" The wife was angry and yelling, pulled out the chair, gave a hard meal, and sat down on it. 

[root@haha day6]# grep -c I test_file  9 

[root@haha day6]# grep -v I test_file  "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. "Not bought, borrowed? Who still buys books to read now? Also lend it to you! Hey! " My wife shrugged me off and stood up and went out. 

[root@haha day6]# grep -w Buy test_file  "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 

[root@haha day6]# grep -i buy test_file  "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. "I know every day that buying books, buying books, what else will I do besides buying books!" The wife was angry and yelling, pulled out the chair, gave a hard meal, and sat down on it. "No, I didn't buy it …". "Not bought, borrowed? Who still buys books to read now? Also lend it to you! Hey! " My wife shrugged me off and stood up and went out. 

基本正则表达式

基本正则表达式（Basic Regular Expression，BRE），又称为标准正则表达式，是最早制订的正则表达
式规范，仅支持最基本的字符集。基本正则表达式是POSIX规范制订的两种正则表达式语法标准之
一。

测试用例：

[root@haha day6]# grep -i '^"buy' test_file  "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 

[root@haha day6]# grep -i 'table.$' test_file  "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. 

[root@haha day6]# grep -i ^.*$ test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. "Buy books again!" With a loud drink, my wife snatched the book from my hand and slammed it on the table. "I know every day that buying books, buying books, what else will I do besides buying books!" The wife was angry and yelling, pulled out the chair, gave a hard meal, and sat down on it. 

[root@haha day6]# egrep -w [.] test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. "No, I didn't buy it …". 

[root@haha day6]# egrep [a-c] test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. 

正则表达式字符集

测试用例：

[root@haha day6]# egrep [[:upper:]] test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. 

[root@haha day6]# egrep [[:xdigit:]] test_file  fter receiving the book Nostalgia and Rhyme, I rubbed it slowly, "My article has finally been printed", and I couldn't help crying, "I have been writing for more than ten years, …". Open the table of contents and find my article, "Oh, on page 58". My hand trembled slightly. 

扩展正则表达式

扩展正则表达式（Extended Regular Expression，ERE）支持比基本正则表达式更多的字符，但是扩
展正则表达式对有些基本正则表达式所支持的字符并不支持。前面介绍的字符“^”、“$”、“.”、“*”、
“[]”以及“[^]”这6个字符在扩展正则表达式都得到了支持，并且其意义和用法都完全相同。

测试用例：

[root@haha day6]# egrep -q ^.+$ test_file  [root@haha day6]# echo $? 0 

案例

• 匹配学号

[root@haha day6]# echo 0 | egrep ^"0([0][1-9]|[1-3][0-9]|[4][0-3])"$ 0 

• ipv4地址

[root@haha day6]# echo 12.122.12.12 | grep -oP '(((\d{1,2})|(1\d{2})|(2[0-4]\d)|(25[0-5]))\.){3}((\d{1,2})|(1\d{2})|(2[0-4]\d)|(25[0-5]))' 12.122.12.12 

• 邮箱地址

[root@haha day6]# echo | grep -oP ^[a-zA-Z0-9_-]+@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)+$  

• 8位强密码

[root@haha day6]# echo Lc12254@ |grep -oP '(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[^a-zA-Z0-9]).{8,}' Lc12254@ 

• url正则表达式

[root@haha day6]# echo https://www.cnblogs.com/eliwen/p/12742421.html | grep -oP "(http|ftp|https):\/\/[\w\-_]+(\.[\w\-_]+)+([\w\-\.,@?^=%&:/~\+#]*[\w\-\@?^=%&/~\+#])?"
https://www.cnblogs.com/eliwen/p/12742421.html