Introduction and application of regular metacharacters

1. Metacharacters:

Each regular expression is composed of metacharacters and modifiers

[Metacharacters] ->Some characters with special meaning between two /

reg = /^\d$/  //只能是一个0-9之间的数字

　1. Characters with special meaning Metacharacter

##　\: Escape character, translate the meaning of the following characters

　^: Start with a certain metacharacter

　$: ends with a metacharacter　

\n: matches a newline character

　.: Any character except \n　

　(): Grouping-> Divide a large regular pattern into several small regular patterns 　

　x|y: One of x or y

　[xyz]: One of x, y or z A

##　[^xyz]: Any character except three

　[a-z]: Any character between a-z

　[^a-z]: Except any character between a-z

　\d: A character between 0-9 \D Any characters except numbers between 0-9

##　\b: A boundary character "w1 w2 w3"

##\w: Any character among numbers, letters, and underscores [0-9a-zA-Z_]

##\s: Matches a whitespace character, a space, a tab character, a form feed character.. .

##　2. Quantifier metacharacter representing the number of occurrences

　*: Appear zero to multiple times

　 + ： Appears 1 or more times

　? ：Occurs zero or 1 times

　{n} ：Occurs n times

　{n,} :Occurs n to multiple times

　{n,m}: appears n to m times

　

 reg = /^\d+wo\d+$/;  reg = /^(\d+)wo(\d+)$/;

var reg = /^0.2$/   // 以0开头 2结尾，中间可以是除了\n的任意字符

var reg = /^\d+$/;//只能是多个数字console.log(reg.test('2017'))//true//一个简单的验证手机号的正则:11位数字，第一位为1var reg = /^1\d{10}$/;

2. Application of metacharacters

　[]

　 1. All characters appearing in square brackets The characters are all characters that represent their own meaning (no special meaning).

　2. Square brackets do not recognize two digits

　

var reg = /^[12-68]$/ -> ;Represents one of 1, 2-6, and one of 8. This method is wrong

　()

1. Function 1 of grouping: Change the default priority of x|y

　　　　　　　var reg = /^18|19$/;//符合条件的有18、19、181、189、119、819、1819

　　　　　　　var reg = /^(18|19)$/  //18、19

　1. Regular rules for valid numbers: positive numbers, negative numbers, zero, decimals

##　1), "." may or may not appear, but once it appears, it must be followed by Followed by one or more digits

　　2), there may be +/- at the beginning or not

　　3), the integer part, A single digit can be one between 0-9, and multiple digits cannot start with 0

　The regular rules are as follows

　

var reg = /^[+-]?(\d|([1-9]\d+))(\.\d+)?$/

The above is the detailed content of Introduction and application of regular metacharacters. For more information, please follow other related articles on the PHP Chinese website!