regular expression

元字符

. ^ $ * + ? { [ ] } \ | ( )

.  (除换行外的)任意字符
^  行开头
$  行结束
[] 用来包括一类(class)字符，如[abc]；也可用[a-c]代替；元字符在括号内不代表任何特殊意义; '^'如果在类开头则是非的意思，如[^5]表示匹配除'5'外任何字符
() 用来包括一组(group)字符，可以使用`\index`在同一个正则表达式中代替同一匹配
|  或者
\  转义字符

字符匹配

\d [0-9]
\D [^0-9]
\s [ \t\n\r\f\v] 任何空白字符
\S [^ \t\n\r\f\v]
\w regex pattern is expressed in bytes: [a-zA-Z0-9_]
   regex pattern is a string: all the characters marked as letters in the Unicode database
\W [^a-zA-Z0-9_]

\A matches only at the start of the string
\Z matches only at the end of the string
\b word boundary
\B not word boundary

重复

{m,n} - 重复m到n次
{m, } - 至少重复m次

*     - {0,}
+     - {1,}
?     - {0,1}

贪婪匹配

var re = /^(\d+)(0*)$/;
re.exec('102300'); //('102300', '102300', '')

非贪婪匹配

var re = /^(\d+?)(0*)$/;
re.exec('102300'); //('102300', '1023', '00')

非贪婪匹配在重复后加?即可:

{m,n}?
{m, }?

*?
+?
??

组

(?:p) - 无法使用`\index`找到子模式

lookahead and lookbehind

正向先行断言(zero-width positive lookahead assertion)：

(?=p) - 要求字符串与 p 匹配，但结果集并不包含匹配 p 的字符

负向先行断言(zero-width negative lookahead assertion)：

(?!p) - 要求字符串不与 p 匹配


bar(?=bar)     finds the 1st bar ("bar" which has "bar" after it)
bar(?!bar)     finds the 2nd bar ("bar" which does not have "bar" after it)
(?<=foo)bar    finds the 1st bar ("bar" which has "foo" before it)
(?<!foo)bar    finds the 2nd bar ("bar" which does not have "foo" before it)

https://stackoverflow.com/questions/2973436/regex-lookahead-lookbehind-and-atomic-groups
https://stackoverflow.com/questions/19605150/regex-for-password-must-contain-at-least-eight-characters-at-least-one-number-a

示例

匹配url

^(ht|f)tp(s?)\:\/\/[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&amp;%\$#_]*)?$

8～32位字符，英文字母、数字和符号必须同时存在，符号仅限!@#$%^*()

^(?=.*[A-Za-z])(?=.*\d)(?=.*[!@#$%^*()])[A-Za-z\d!@#$%^*()]{8,32}$

英文字母开头，4～16位字符，只能包含英文字母，数字，下划线(_)

^[a-zA-Z][a-zA-Z0-9_]{3,15}$

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