Learn regular expressions (regexp)

Regular expressions （RegExp）

summary ： Regular expression is a String matching weapon , Can help us search 、 obtain 、 Substitute string

Regular expressions are mainly composed of two parts ： Pattern （patterns） And modifiers （flags）

Method	The descriptor
exec	One that performs a search match in a string RegExp Method , It returns an array （ If no match is found, return null）.
test	A test in a string to see if it matches RegExp Method , It returns true or false.
match	One that performs a search match in a string String Method , It returns an array , When there is no match, it will return null.
matchAll	A string that performs a search for all matches String Method , It returns an iterator （iterator）.
search	A match is tested in a string String Method , It returns the matching location index , Or return on failure -1.
replace	One that performs a search match in a string String Method , And replace the matching substring with the replacement string .
split	A regular expression or a fixed string to separate a string , And store the separated substrings in the array Of String Method

Modifier flag

flag	meaning
g	All of the , All must match
i	Ignore case
m	Multi-line matching

The rules - Character class

character	meaning
\d (digit)	Numbers ： from 0 To 9 The characters of
\s (space)	The space symbol
\w (word)	“ a word ” character , Underline Latin letters or numbers
. ( spot )	It is associated with " Any character other than a newline character " matching

Reverse class ：

• \D The digital ： except \d Any character other than , For example, letters .
• \S Non space symbol ： except \s Any character other than , For example, letters .
• \W Not a single character ： except \w Any character other than , For example, non Latin letters or spaces .

The rules - Anchor point

Symbol ^ And symbols $ It has special meaning in regular expressions , They are called “ Anchor point ”

• Symbol ^ Match the beginning of the text ;
• Symbol $ Match the end of the text ;

Word boundaries : \b ( The next position corresponds to \b)

The rules - Escape string

Use special characters as regular characters , Just put a backslash in front of it ;

for example ：[] \ ^ $ . | ? * + ( ）

aggregate （Sets） And scope （Ranges）

Sometimes we just need to select one of multiple matching characters ：

• Square brackets […] A few characters or character classes in mean “ Search for any one of the given characters ”;

aggregate （Sets）

for instance ,[eao] It means finding in 3 Characters ‘a’、‘e’ perhaps `‘o’ Any one of ;

Range （Ranges）

• Square brackets can also contain character ranges ;
• for instance ,[a-z] Will match from a To z Letters in the range ,[0-5] From 0 To 5 The number of ;
• [0-9A-F] Represents two ranges ： It searches for a character , Number satisfied 0 To 9 Or letters A To F;
• \d —— and [0-9] identical ;  \w —— and [a-zA-Z0-9_] identical ;

quantifiers （Quantifiers）

The words used to describe the quantity we need are called quantifiers （ Quantifiers ）.

Number {n}

• The exact number of digits ：{5}
• The number of digits in a certain range ：{3,5}

abbreviation ：

• +： representative “ One or more ”, amount to {1,}
• ?： representative “ Zero or one ”, amount to {0,1}. let me put it another way , It makes symbols optional ;
• *： Represents the “ Zero or more ”, amount to {0,}. in other words , This character can appear or not appear many times ;

greedy （Greedy） And inertia （lazy） Pattern

Greedy mode ： By default, the matching rule is to find the matching content , Will continue to look back , Always find the last matching content

Lazy mode ： The quantifier in lazy mode is the opposite of that in greedy mode .  As long as the corresponding content is obtained , No more backward matching .

More regular queries ： https://c.runoob.com/front-end/854/

2022.0713