简单的生成随机字符串：
/** 生成随机字符串** $length 字符串长度*/function random_str($length) {// 密码字符集，可任意添加你需要的字符$chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';$str = '';for($i = 0; $i < $length; $i++){// 这里提供两种字符获取方式// 第一种是使用 substr 截取$chars中的任意一位字符；// 第二种是取字符数组 $chars 的任意元素$str .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);// $str .= $chars[mt_rand(0, strlen($chars) - 1)];}return $str;}
了解原理后可以扩展一下：
/*** 生成随机字符串，数字，大小写字母随机组合** @param int $length 长度* @param int $type 类型，1 纯数字，2 纯小写字母，3 纯大写字母，4 数字和小写字母，5 数字和大写字母，6 大小写字母，7 数字和大小写字母*/function random($length = 6, $type = 1){// 取字符集数组$number = range(0, 9);$lowerLetter = range('a', 'z');$upperLetter = range('A', 'Z');// 根据type合并字符集if ($type == 1) {$charset = $number;} elseif ($type == 2) {$charset = $lowerLetter;} elseif ($type == 3) {$charset = $upperLetter;} elseif ($type == 4) {$charset = array_merge($number, $lowerLetter);} elseif ($type == 5) {$charset = array_merge($number, $upperLetter);} elseif ($type == 6) {$charset = array_merge($lowerLetter, $upperLetter);} elseif ($type == 7) {$charset = array_merge($number, $lowerLetter, $upperLetter);} else {$charset = $number;}$str = '';// 生成字符串for ($i = 0; $i < $length; $i++) {$str .= $charset[mt_rand(0, count($charset) - 1)];// 验证规则if ($type == 4 && strlen($str) >= 2) {if (!preg_match('/\d+/', $str) || !preg_match('/[a-z]+/', $str)) {$str = substr($str, 0, -1);$i = $i - 1;}}if ($type == 5 && strlen($str) >= 2) {if (!preg_match('/\d+/', $str) || !preg_match('/[A-Z]+/', $str)) {$str = substr($str, 0, -1);$i = $i - 1;}}if ($type == 6 && strlen($str) >= 2) {if (!preg_match('/[a-z]+/', $str) || !preg_match('/[A-Z]+/', $str)) {$str = substr($str, 0, -1);$i = $i - 1;}}if ($type == 7 && strlen($str) >= 3) {if (!preg_match('/\d+/', $str) || !preg_match('/[a-z]+/', $str) || !preg_match('/[A-Z]+/', $str)) {$str = substr($str, 0, -2);$i = $i - 2;}}}return $str;}
