[Neah Bay]

<?php


 function rand_string($len = 16, $keyword = '') {
     if (strlen($keyword) > $len) {//关键字不能比总长度长
        return false;
     }
     $str = '';
     $chars = 'abcdefghijkmnpqrstuvwxyz23456789ABCDEFGHIJKMNPQRSTUVWXYZ'; //去掉1跟字母l防混淆            
     if ($len > strlen($chars)) {//位数过长重复字符串一定次数
        $chars = str_repeat($chars, ceil($len / strlen($chars)));
     }
     $chars = str_shuffle($chars); //打乱字符串
    $str = substr($chars, 0, $len);
     if (!empty($keyword)) {
         $start = $len - strlen($keyword);
         $str = substr_replace($str, $keyword, mt_rand(0, $start), strlen($keyword)); //从随机位置插入关键字
    }
     return $str;
 }


 echo rand_string(16,"ab"); //output example:V8bNY6SmkeywordB
 ?>