正则表达式速通

Github上的正规学习地址：https://github.com/ziishaned/learn-regex

Meta Characters

Meta character Description Note
. Period matches any single character except a line break. 任意字符
[ ] Character class. Matches any character contained between the square brackets. [a-z0-9]
[^ ] Negated character class. Matches any character that is not contained between the square brackets 反 [ ]
* Matches 0 or more repetitions of the preceding symbol. [0,
+ Matches 1 or more repetitions of the preceding symbol. [1,
? Makes the preceding symbol optional. [0,1]
{n,m} Braces. Matches at least “n” but not more than “m” repetitions of the preceding symbol. (ab){3}
(xyz) Character group. Matches the characters xyz in that exact order.
| Alternation. Matches either the characters before or the characters after the symbol.
\ Escapes the next character. This allows you to match reserved characters `[ ] ( ) { } . * + ? ^ $ \ `
^ Matches the beginning of the input.
$ Matches the end of the input.

Shorthand Character Sets

Shorthand Description
. Any character except new line
\w Matches alphanumeric characters: [a-zA-Z0-9_]
\W Matches non-alphanumeric characters: [^\w]
\d Matches digits: [0-9]
\D Matches non-digits: [^\d]
\s Matches whitespace characters: [\t\n\f\r\p{Z}] （空格）
\S Matches non-whitespace characters: [^\s]

Lookarounds

Symbol Description Chinese
?= Positive Lookahead 正先行断言-存在
?! Negative Lookahead 负先行断言-排除
?<= Positive Lookbehind 正后发断言-存在
?<! Negative Lookbehind 负后发断言-排除 
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"(T|t)he(?=\sfat)" => The fat cat sat on the mat. （The会标亮）
"(T|t)he\sfat" => The fat cat sat on the mat. （The fat会标亮）

Flags

用斜杠/

Flag Description
i Case insensitive: Match will be case-insensitive. 忽略大小写
g Global Search: Match all instances, not just the first.
m Multiline: Anchor meta characters work on each line. 多行修饰符（不懂）

Greedy vs Lazy Matching

By default, a regex will perform a greedy match, which means the match will be as long as possible. We can use ? to match in a lazy way, which means the match should be as short as possible.

More

\b：单词边界

(?i)：后面全部忽略大小写

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