Summary of regular expressions (practical summary)

This time I will bring you a summary of regular expressions (practical summary), what are the precautions for using regular expressions in practice, the following is a practical case, let’s take a look .

Regular expression is a text pattern composed of ordinary characters (such as characters a to z) and special characters (called metacharacters). The pattern describes one or more strings to be matched when searching for text bodies. Regular expressions serve as a template that matches a character pattern with a searched string.

The editor below summarizes some knowledge points about regular expressions. The specific content is as follows:

1. Metacharacters

[Metacharacters with special meanings]
\d -> matches a number from 0 to 9, equivalent to [0-9], and its opposite is \D -> matches a number except Any character from 0-9
\w -> Matches a number or character from 0-9, a-z, A-Z, _, equivalent to [0-9a-zA-Z_]
\s -> Matches A whitespace character (space, tab...)
\b -> Matches a word boundary
\t -> Matches a tab character
\n -> Matches a newline
. -> Matches any character except \n
^ -> Begins with a certain metacharacter
$ -> Ends with a certain metacharacter
\ -> Transfer Character
x|y -> One of x or y
[xyz] -> Any one of x, y, z
[^xyz] -> Except any one of xyz
[a-z] -> Matches any character in a-z
[^a-z] -> Matches any character except a-z
() -> Grouping in regular expressions

Note:

1) Regarding []

a, [+] ->All characters appearing in square brackets represent their own meaning
b. [12-65] ->This is not 12-65 but one of the three 1/2-6/5

2) About ()

a. The function of grouping is to change the default priority, for example: /^18|19$/, 181, 189, 119, 819, 1819... all match, not 18 or 19 as we think, But changing it to /^(18|19)$/ is simply 18 or 19
b. While capturing the content of the regular match, you can also capture the content of the group match ->Group capture
c. Group reference, for example: /^(\d)(\w)\2\1$/, where \2 is exactly the same as the second group, and \1 is exactly the same as the first group. The content, for example: "0aa0" is consistent with

[quantifier metacharacter representing quantity]

* -> 0 to multiple
+ -> 1 to multiple
? -> 0 to 1
{n} -> appears n times
{n,} -> appears n to multiple times
{n,m} -> appears n to m times

Note:

1) Several situations about ?

a. Place it after the non-quantifier metacharacter to represent the occurrence 0-1 times
b. Place it after the quantifier metacharacter to represent the greediness when canceling the capture, for example: reg=/\d+/; reg.exec("2015") -> "2015" But if the regular Write like this reg=/\d+?/; reg.exec("2015") -> "2"
c. Add ?: at the beginning of the group, which means that the current group only matches and does not capture, for example:/^ (?:\d+)$/
d. Add ?= at the beginning of the group to perform forward search, for example: /^abcdef(?=1|2)$/ Only "abcdef1" and "abcdef2" are consistent
e. Add ?! at the beginning of the group, negative pre-check, for example: /^abcdef(?!1|2)$/ Except "abcdef1" and "abcdef2" do not match, the others as long as it is "abcdef (any things)" are consistent with

[Metacharacters representing their own meaning]

In addition to the above, in the literal mode, any other characters we appear represent their own meaning

var num=12;
var reg=/^\w"+num+"$/; ->Here "+num+" does not splice the value of the variable, and whether it is " or + They are all metacharacters

->For the method that requires splicing strings and variables, we can only use the instance method to create regular expressions

2 and modifiers

i -> ignoreCase ignores the case of letters
g -> global global matching (adding g can solve the laziness during regular capture)
m -> multiline multiline matching

3. Regular rules commonly used in projects

1)

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

of valid digits 2)

 var reg = /^\w+((-\w+)|(\.\w+))*@[A-Za-z0-9]+((\.|-)[A-Za-z0-9]+)*\.[A-Za-z0-9]+$/;

 var reg = /^1\d{10}$/;

 var reg = /^((18|19)|([2-5]\d)|(6[0-5]))$/;

 var reg = /^[\u4e00-\u9fa5]{2,4}$/;

 var reg = /^(\d{6})(\d{4})(\d{2})(\d{2})(?:\d{2})(\d)(?:\d|X)$/;
 //-> 12828(省市县) 1990(年) 12(月) 04(日) 06 1(奇数是男偶数是女) 7(数字或者X)

4. Regular matching

5. Regular capture

-> Regular capture is lazy and greedy
-> To solve laziness, add the global modifier g## at the end of the regular expression # -> To solve greediness, add ?

after reading the case in this article. I believe you have mastered the method. For more exciting information, please pay attention to other related articles on the PHP Chinese website!

Recommended reading:

##What are the new features in regular expressions

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