Extract and process text data in PHP with regular expressions

In PHP programming, regular expressions are a powerful tool for processing text data. It helps us find, replace and extract content of specific patterns in strings. In this article, we will introduce how to use regular expressions in PHP and some commonly used regular functions.

1. preg_match() function
   The preg_match() function is used to find content matching a specified pattern in a string. Its basic syntax is as follows:

preg_match(pattern, subject, matches);

Among them, pattern is the regular expression pattern, subject is the string to be matched, and matches is an array used to store the matching results.

Here is a simple example that demonstrates how to use the preg_match() function to find whether a string contains "apple":

$subject = "I have an apple";
$pattern