善用 PHP 正则表达式，提升字符串处理效率

function isValidEmail($email) {    $pattern = '/^[_a-z0-9-]+(.[_a-z0-9-]+)*@[a-z0-9-]+(.[a-z0-9-]+)*(.[a-z]{2,})$/';    return preg_match($pattern, $email);}

$string = 'Hello World!';$string = preg_replace('/s+/', '', $string); // 替换所有空格echo $string; // 输出：HelloWorld!

$html = '<a href="https://www.example.com">Example</a>';preg_match_all('/<a href="(.+?)">/', $html, $matches);print_r($matches[1]); // 输出：['https://www.example.com']</a>

$date = '2023-04-18';$pattern = '/^(19|20)d{2}-(0[1-9]|1[012])-(0[1-9]|[12]d|3[01])$/';if (preg_match($pattern, $date)) {    echo '有效的日期格式';}