Detailed explanation of preg_match_all function in php regular expressions

Functions in php regular expression We have created a preg_match function for you before. I believe you all know something about it. So what is the specific use of the preg_match_all function in php regular expressions? Today we will take you to understand the detailed explanation of preg_match_all function in PHP regular expressions!

Before understanding regular expressions, you need to master some basic knowledge of commonly used regular expressions. If you can remember these, it is best to remember them. If you can’t remember, you can look them up when you need to use them. Just multiple The special character , so regular expressions are special. You can view more detailed instructions for details.

You can check the PHP manual for specific instructions on the preg_match_all function. This article uses preg_match_all to test the effect of regular expressions.

Example code:

$html = &#39;<p id="biuuu">jb51.net</p><p id="biuuu_2">jb51.net2</p><p id="biuuu_3">jb51.net3</p>&#39;;

Example requirements: Take out the ID and content of each p element, such as biuuu, biuuu_2, biuuu_3, jb51.net, jb51. net2 and jb51.net3 (some commonly used website grabbing methods are matched in this way)

Analysis:

String is a basic HTML Element, each p element corresponds to an ID and content, and is independent. First consider how to extract the ID value and content within a p, such as: jb51.net, and then match other similar elements. Two values ​​need to be taken out from a p, that is, two matching expressions. The first expression is used to match the ID value (biuuu), and the second expression is used to match the content of the ID (jb51.net). Regular Expressions commonly used in expressions use parentheses, then the previous elements will become the following form:

<p id="(biuuu)">(jb51.net)</p> 
<p id="(表达式1)">(表达式2)</p>

Okay, use the above parentheses to divide the area that needs to be matched, and the next step is how To match the content in each expression, we guess that an ID may be letters, numbers or underscores. Then this becomes basic. It can be achieved by using square brackets, as follows:

Expression 1:

[a-zA-Z0-9_]+ （表示匹配大小写字母，数字和下划线）

How to match expression 2, because the content of the ID can be any character, but be careful that it cannot match the < or > characters, because if you match these two characters, it will be All p used later are matched, so elements starting with these two characters need to be excluded, that is, the < or > characters are not matched, as follows:

Expression 2:

[^<>]+ （表示不匹配<和>字符）

In this way, the subexpression that needs to be matched is realized, but an expression that needs to be matched is also needed. The method is as follows:
Expression: / '\"(Expression 1)\ "'>(Expression 2)<\/p>/
Pay attention to the double quotes" and / need to be escaped using the \escape character, and then put the first two expressions in,
As follows:

 &#39;\"([a-z0-9_]+)\"&#39;>/<p id=\"([a-z0-9_]+)\">([^<>]+)<\/p>/

In this way, a regular expression matching the ID value and content of each p element is implemented, and then the preg_match_all function is used to test as follows:

$html = &#39;<p id="biuuu">jb51.net</p><p id="biuuu_2">jb51.net2</p><p id="biuuu_3">jb51.net3</p>&#39;; 
preg_match_all('/([^<>]+)<\/p>/',$html,$result); 
var_dump($result);

Result :

array(3) { 
[0]=> array(3) 
{ [0]=> string(30) "<p id="biuuu">jb51.net</p>" 
  [1]=> string(33) "<p id="biuuu_2">jb51.net2</p>" 
  [2]=> string(33) "<p id="biuuu_3">jb51.net3</p>" 
  } 
[1]=> array(3) { 
  [0]=> string(5) "biuuu" 
  [1]=> string(7) "biuuu_2" 
  [2]=> string(7) "biuuu_3" 
  } 
[2]=> array(3) { 
  [0]=> string(8) "jb51.net" 
  [1]=> string(9) "jb51.net2" 
  [2]=> string(9) "jb51.net3" 
  } 
  }

There are three expressions, which display the matching value of each expression and store them in the form of an array. This way, the ID and content of each p element are taken out. The most important thing is to use regular expressions. You still need to know what is needed, and then you need to perform matching with clear ideas, and appropriately use the preg_match_all function to perform output debugging, which is very convenient.

Summary:

After reading this article and the previous article, I believe that everyone has their own understanding and understanding of these two functions in PHP regular expressions. I hope this will be helpful to your work!

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