The preg_match() function in PHP is used for regular expression matching

PHP is a commonly used server-side programming language. Its built-in functions contain many powerful functions. One of the very important functions is the preg_match() function. This function is used for regular expression matching and can help developers process string data quickly and efficiently. This article will introduce the specific usage of the preg_match() function and give some code examples to help readers better understand and apply this function.

1. Introduction to preg_match() function

The preg_match() function is a built-in regular expression function in PHP. Its main function is to match the specified regular expression pattern. The syntax format of this function is as follows:

int preg_match(string $pattern, string $subject, array &$matches = null, int $flags = 0, int $offset = 0)

Parameters Description:

$pattern: required, indicating the regular expression pattern to be matched, passed in as a string.

$subject: required, indicating the string that needs to be matched, passed in as a string.

$matches: Optional, indicating that the matched results will be stored in the array and passed in as an array. The default value is null.

$flags: Optional, indicating the option flags for regular expression matching, passed in as an integer. The default value is 0.

$offset: Optional, indicating the position from which to start searching for matching text, passed in as an integer. The default value is 0.

The function return value is an integer, indicating the number of successful matches.

2. Preg_match() function example

Mastering the specific usage of the preg_match() function will help developers perform more efficient programming work. Below we will use several examples to demonstrate some commonalities and characteristics of the preg_match() function.

Example 1: Simple matching operation

$pattern = '/^d{4}-d{2}-d{2}$/'; //Match date format
$subject = '2022-07-12';

if(preg_match($pattern, $subject)){

echo '日期合法';

}else{

echo '日期不合法';

}
?>

Code analysis:

The main function of this code segment is to match the specified date format. The $pattern variable stores the regular expression pattern of the date format, and the $subject variable stores the date string that needs to be matched. In the if statement, we use the preg_match() function to perform a simple regular expression matching operation on the string. If the match is successful, "date is legal" is output, otherwise "date is illegal" is output.

Example 2: Array storage matching results

$pattern = '/^[a-zA-Z] w $/';// Match English names
$subject = "Lily Luo";
$matches = array();

if(preg_match($pattern, $subject, $matches)){

var_dump($matches); //打印匹配结果

}else {

echo '匹配失败';

}
?>

Code analysis:

This code matches English names through regular expressions and stores the matched results in the array $ matches. In the preg_match() function, we specify the location where the $matches array is stored, so when printing the output results, we can directly use the var_dump() function to output the matching results.

Example 3: Multiple matching results

$pattern = '/php w /i';//Matching PHP language related resource websites
$subject = 'The best PHP resources are php.net and phpclasses.org';
$matches = array();

if(preg_match_all($pattern, $subject, $matches)){

var_dump($matches); //打印结果

}else{

echo '匹配失败';

}
?>

Code analysis:

This code is mainly used to match multiple matching requirements in a piece of text words and store all matching results in the array $matches. In the preg_match_all() function, we use an additional matching flag i, which indicates that case is ignored when matching. When printing the output results, each element in the $matches array is an array, recording the number of matched results and the specific results.

The above is the detailed content of The preg_match() function in PHP is used for regular expression matching. For more information, please follow other related articles on the PHP Chinese website!