php正则的使用[替换，匹配]

 // 隐藏电话的中间四位
 echo parseMobile('15836365252');
 function parseMobile($mobile, $start = 4, $len = 4){
     $firstLen = $start - 1;
     $lastLen = 11 - $len - $firstLen;
     $preg = '/(\d{'.$firstLen.'})(\d{'.$lastLen.'})/';
     return preg_replace($preg, '$1****$3', $mobile);
 }

 // 验证邮箱格式是否正确
 echo checkEmail('aaa.bbb@163.com');
 function checkEmail($mail){
     $bool = false;
     if(strlen($mail) >= 8 && strlen($mail) <= 40 && (strpos($mail,'@') !== false) && (strpos($mail,'.') !== false)){
         $preg = '/^([a-z0-9]+)([a-z0-9_\\.\\-]*)([a-z0-9]+)@([a-z0-9]+)([a-z0-9_\\.\\-]*)([a-z0-9]+)(\\.)([a-z]{2,5})$/i';
         preg_match($preg, $mail) AND $bool = true;
     }
     return $bool;
 }

 // 隐藏IP地址的后面两段
 echo parseIp('192.168.115.210');
 function parseIp($ip){
     $preg = '/(\d+).(\d+).(\d+).(\d+)/';
     return preg_replace($preg, '$1.$2.***.***', $ip);
 }