Regular Expression Basics

1. Regular expressions, also known as regular expressions.

English: Regular Expression, often abbreviated as regex, regexp or RE in code), a concept in computer science.Regular expressions are usually used to retrieve and replace text that matches a certain pattern (rule).

Regular Expression_Baidu Encyclopedia (baidu.com)

As I understand it, the correct rules are arranged correctly according to the rules you set.

2. Features of regular expressions:

a. Very flexible, logical and functional;

b. Complex control of strings can be achieved quickly and in a very simple manner.

c. For newcomers, it is rather obscure and difficult to understand.

Concepts and characteristics of regular expressions

3. Purpose of regular expressions:

a. Determine whether the string complies with a certain rule (judging whether it complies with the mobile phone number and email rules).

b. Find all substrings that match the rules from a string (take the HTML tag name).

4. Commonly used escape characters:

a.Number:\d

b.Not a number:\D

c. Whitespace characters (space, tab, form feed, etc.): \s

d. Non-whitespace characters: \S

e. Word characters (26 English letters + numbers + underscore): \w

f. Non-word characters: \W

5. Custom character combination

Character set: [single character or character interval], used to match the characters in the set such as:

a.[a-z] represents the 26 lowercase letters of a-z

b.[0-9a-z] represents 10 numbers 0-9 and 26 lowercase letters a-z

c.[135a-h] means 8 letters including numbers 1, 3, 5 and letters a-h

Non-set: [^single character or character interval], used to match non-set characters.For example:

a.[^0-9] means match all non-numeric characters.

b.[^a-zA-Z] means to match all non-alphabetic characters.

()	Like math, it means it's a whole
^	matches the beginning of the input string
$	matches the end of the input string
.	Wildcard [represents any character][does not match newline]
*	Matches 0 or more times
+	Match 1 or more times
\	Escape characters
|	A choice between two items

6.Modifier

/i	Case insensitive
/A	Matching rules must match from the beginning
/s	will match all characters
/x	Whitespace characters in regular expressions are ignored