这是另一个解决方案。

function genRandomString($length = 10)
{
    if($length < 1)
        $length = 1;
    return substr(preg_replace("/[^A-Za-z0-9]/", '', base64_encode(openssl_random_pseudo_bytes($length * 2))), 0, $length);
}

PS.我在Ubuntu上使用PHP 7.2。

Laravel解决方案: 如果你正在使用Laravel框架，你可以像这样使用它的StringHelper。

使用“照亮\支持\斯特”;

Str：：random（$strlentgh = 16）

具体回答这个问题，有两个问题:

当你回显$randstring时，它不在作用域内。 字符在循环中没有连接在一起。

以下是更正后的代码片段:

function generateRandomString($length = 10) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[random_int(0, $charactersLength - 1)];
    }
    return $randomString;
}

用下面的调用输出随机字符串:

// Echo the random string.
// Optionally, you can give it a desired string length.
echo generateRandomString();

请注意，这个答案的以前版本使用rand()而不是random_int()，因此生成可预测的随机字符串。因此，根据这个答案的建议，它被更改为更安全。

具有上面讨论的一些函数的类。

$options['numeric'] = true;
$options['uppercase'] = true;
$options['lowercase'] = true;
$new = new RandomString($options);

class RandomString
{
    /**
     * @var array
     */
    private $default = ['numeric' => true, 'uppercase' => true, 'lowercase' => true];

    /**
     * @var array
     */
    private $options;

    /**
     * array
     */
    private $whitelist = ['numeric', 'uppercase', 'lowercase'];

    /**
     * RandomString constructor.
     *
     * @param array $options
     */
    public function __construct(array $options = [])
    {
        $this->options = $this->default;
        if(!empty($options))
        {
            $options = array_intersect_key($options, array_flip($this->whitelist));
            if(empty($options))
            {
                $this->options = $this->default;
            }else
            {
                $this->options = $options;
            }
        }
    }

    /**
     * @return string
     */
    private function returnCharacters(){

        $options = $this->options;

        $numbers = '0123456789';
        $uppercase = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
        $lowercase = "abcdefghijklmnopqrstuvwxyz";

        $characters = '';
        if(isset($options['numeric']) && $options['numeric'] === true){
            $characters .= $numbers;
        }

        if(isset($options['uppercase']) && $options['uppercase'] === true){
            $characters .= $uppercase;
        }

        if(isset($options['lowercase']) && $options['lowercase'] === true){
            $characters .= $lowercase;
        }
        return $characters;
    }

    /**
     * @param $length
     * @param $quantity
     * @return string
     */
    public function randomString($length, $quantity) {

        $string = '';
        $characters = $this->returnCharacters();

        for ($j = 0; $j < $quantity; $j++) {
            for($i = 0; $i < $length; $i++){
                $string .= $characters[mt_rand(0, strlen($characters) - 1)];
            }
            $string .= "\n";
        }
        return $string;
    }

    /**
     * @return array
     */
    public function getOptions()
    {
        return $this->options;
    }

    /**
     * @return mixed
     */
    public function getWhitelist()
    {
        return $this->whitelist;
    }

如果你需要大量无重复的随机字符串，这里有一个经过小修改的递归代码:

function generateRandomString($length = 10)
{
    global $generatedStrings;
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, strlen($characters) - 1)];
    }
    if (isset($generatedStrings[$randomString])) {
        $randomString = generateRandomString($length);
    }
    $generatedStrings[$randomString] = $randomString;
    return $randomString;
}

$generatedStrings = array();

foreach(range(1, 100000) as $num) {
    echo "\n".$num."\t : ".generateRandomString();
}

function gen_uid($l=5){
   return substr(str_shuffle("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"), 10, $l);
}
echo gen_uid();

默认值[5]:WvPJz

echo gen_uid(30);

价值[30]:cAiGgtf1lDpFWoVwjykNKXxv6SC4Q2