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。 源代码如下：
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
\n"; $user_name = preg_replace( $pattern,"$1",$email_address ); $domain_name = preg_replace( $pattern,"$2",$email_address ); $reply .= "用户名：".$user_name."
\n"; $reply .= "域名：".$domain_name."
\n\n"; } else { $reply = "您输入的电子邮件地址不合法"; } } ?>电子<a href="/tag/youjian/" target="_blank" class="keywords">邮件</a>地址验证程序
电子邮件地址验证程序
\n"; $user_name = preg_replace( $pattern,"$1",$email_address ); $domain_name = preg_replace( $pattern,"$2",$email_address ); $reply .= "用户名：".$user_name."
\n"; $reply .= "域名：".$domain_name."
\n\n"; } else { $reply = "您输入的电子邮件地址不合法"; } } ?>