What is the purpose of preg_match in PHP?

The preg_match function in PHP is used for regular expression matching. It searches for a specified pattern within a given string and returns success or failure. It is used to validate if a string matches a specific format and to extract specific content from a string.

The preg_match function takes three parameters: the regular expression pattern, the string to match against, and an optional variable to store the matching result. If the match is successful, the function returns 1, otherwise it returns 0. If a variable is provided to store the matching result, it will be populated with the content that was matched.

For example, the following code demonstrates how to use the preg_match function to validate if a string complies with an email format:

$email = "test@example.com";
$pattern = "/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/";
if (preg_match($pattern, $email)) {
    echo "邮箱格式正确";
} else {
    echo "邮箱格式不正确";
}

The regular expression pattern /^ \ w + ([-?.]?\ w +) * @ \ w + ([-?.]?\ w +) * (\ .\ w {2,3}) + $ / is used to match strings that meet the requirements of the email format. If a match is successful, it outputs “Email format is correct”, otherwise it outputs “Email format is incorrect”.