PHP正则表达式 验证电子邮件地址

我们最经常遇到的验证，就是电子邮件地址验证。网站上常见。各种网页脚本也都常用“正则表达式”（regular expression）对我们输入的电子邮件地址进行验证，判断是否合法。有的还能分解出用户名和域名。现在用PHP语言实现一下电子邮件地址验证程序，用的是PHP正则表达式库。

<?php
    header ( "Content-Type: text/html; charset=UTF-8" );
    $reply = "";
    if ( isset($_POST["email_address"]) )
    {
        $email_address = $_POST["email_address"];
        $pattern = "/^([0-9A-Za-z\\-_\\.]+)@([0-9a-z]+\\.[a-z]{2,3}(\\.[a-z]{2})?)$/i";
        if ( preg_match( $pattern, $email_address ) )
        {
            $reply = "您输入的电子邮件地址合法<br /><br />\n";
            $user_name = preg_replace( $pattern ,"$1", $email_address );
            $domain_name = preg_replace( $pattern ,"$2", $email_address );
            $reply .= "用户名：".$user_name."<br />\n";
            $reply .= "域名：".$domain_name."<br />\n\n";
        }
        else
        {
            $reply = "您输入的电子邮件地址不合法";
        }
    }
?>