PHP Regular Expression: How to extract substrings before and after multiple specific characters from a string

Regular expression is a powerful text matching tool that can find and extract specific substrings in strings. In PHP programming, we usually need to extract data before and after multiple specific characters from a string. In this case, we can use regular expressions to achieve this.

This article will introduce how to use PHP regular expressions to extract substrings before and after multiple specific characters from a string. We will use the preg_match_all function and regular expressions to achieve this functionality.

1. Use the preg_match_all function

In PHP, we can use the preg_match_all function for regular expression matching. The prototype of this function is as follows:

preg_match_all ( string $pattern , string $subject [, array &$matches [, int $flags = PREG_PATTERN_ORDER [, int $offset = 0 ]]] ) : int

Among them, $pattern is the regular expression pattern, $subject is the string to be matched, $matches is the matching result, $flags is an optional parameter, indicating the matching pattern, The default is PREG_PATTERN_ORDER, $offset represents the position in the string to start searching.

2. Building regular expressions

Before using the preg_match_all function, we need to first build the regular expression we need. In this example, we need to extract the substrings before and after multiple specific characters from a string. We can do this in the following two steps:

(1) Match the substrings before and after specific characters. String

We can use the regular expression pattern (.*)Specific characters to match the substring before a specific character, where .* means matching zero or Multiple arbitrary characters, the specific character is the character we need to extract.

For example, if we need to extract all the characters before world and PHP from the string Hello world! My name is PHP., We can use the regular expression /^(.*)world.*s(.*)PHP.*/.

The /^ here represents the starting position of the matching string, and s represents matching a space character.

(2) Match the substring after specific characters

We can use the regular expression pattern Specific characters (.*) Match the substring after specific characters , where .* means matching zero or more arbitrary characters, and the specific characters are the characters we need to extract.

For example, if we need to extract all the characters after world and PHP from the string Hello world! My name is PHP., We can use the regular expression /world(.*)PHP(.*)/.

3. Full Code Example

The following is a complete PHP code example that demonstrates how to extract substrings before and after multiple specific characters from a string.

<?php
// 待匹配的字符串
$str = 'Hello world! My name is PHP.';

// 正则表达式模式
$pattern = '/^(.*)world.*s(.*)PHP.*/';

// 使用 preg_match_all 函数匹配字符串
preg_match_all($pattern, $str, $matches, PREG_PATTERN_ORDER);

// 输出匹配结果
print_r($matches[1]); // 输出：Array ( [0] => Hello ) 
print_r($matches[2]); // 输出：Array ( [0] => My name is )
?>

The above code first defines a string to be matched $str, and then constructs the regular expression pattern $pattern. Then use the preg_match_all function to match the string and store the matching results in the $matches array. Finally, the matching results are output.

In the above code example, we can see the results of using the /^(.*)world.*s(.*)PHP.*/ regular expression pattern matching : Hello and My name is are stored in the $matches[1] and $matches[2] arrays respectively.

4. Summary

This article explains how to use PHP regular expressions to extract substrings before and after multiple specific characters from a string. We first build the regular expression pattern, then use the preg_match_all function to perform the matching and store the matching results in an array. Through the examples in this article, we can see that regular expressions can be used to easily implement string matching and substring extraction functions.

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