regular expression

1. qualifiers ：（“ ？”,“ + ”,“ * ”）

？： The characters decorated in the front need to appear 0 Time or 1 Time , Modifier characters are optional

*： Characters decorated in front , appear 0 Times or times

+ ： Decorated characters , appear 1 More than once

If you specify the number of modifier characters ： ab{ Number of times }c
If you specify the number of occurrences of modifier characters, the range is [3,5]：ab{3,5} c
If you specify the number of occurrences of modifier characters, the range is 3 To infinity ：ab{3,} c

–> If you decorate multiple characters Enclosed in brackets
namely ： (ab){2,}c

2. or |

a(b|c): matching a Behind is b perhaps c String

3. Character class [ ]

[abc]： Match by abc Words that make up
Can be in [] Specified range inside ：
[a-z]: All lowercase letters
[A-Z]: All capital letters
[0-9]: All figures
[a-zA-Z0-9]: All upper and lower case letters and numbers
if [^]: Match except the ones listed after the cusp 【 outside 】 The characters of

4. Metacharacters

A series of common character types defined in regular expressions
Most of them are \ start ：
\d Represents a numeric character be equal to [0-9]
\w Characters representing words （ english 、 Numbers and underscores ）
\s For the blank （ contain Tab And line breaks ）
\b Represents the word character boundary
\B Represents non word character boundaries
\D Represents non numeric characters
\W Represents non word characters
\S Represents a non blank character
. Arbitrary character （ Does not include line breaks ）
^ Match the beginning of the line
$ Match the end of the line

5. Greed matches laziness

Greedy matching ： When matching, it will match as many characters as possible by default * + {}
Laziness matches ： Add another one to the right of the matching symbol ？, Switch the default greedy matching to lazy matching