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。

这里有简单的代码:

echo implode("",array_map(create_function('$s','return substr($s,mt_rand(0,strlen($s)),1);'),array_fill(0,16,"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")));

这里有一个简单的指南:

要更改字符串的长度，请将16更改为另一个值。 若要从不同字符中选择，请更改字符串。

从php7开始，就有了random_bytes函数。 https://www.php.net/manual/ru/function.random-bytes.php 你可以生成一个这样的随机字符串

<?php
$bytes = random_bytes(5);
var_dump(bin2hex($bytes));
?>

如果您使用的是PHP 7 +

public function generateRandom(){

$string = bin2hex(openssl_random_pseudo_bytes(10)); // 20 chars

// OR

$string = base64_encode(random_bytes(10)); // ~14 characters, includes /=+

// or

$string = substr(str_replace(['+', '/', '='], '', base64_encode(random_bytes(32))), 0, 32); // 32 characters, without /=+

// or

$string = bin2hex(random_bytes(10)); // 20 characters, only 0-9a-f

}

递归解决方案:

public static function _random(string $set , int $length): string
{
    $setLength = strlen($set);
    $randomKey = random_int(0, $setLength - 1);

    $firstPiece = substr($set, 0, $randomKey);
    $secondPiece = substr($set, $randomKey, $setLength - $randomKey);

    $removedCharacter = $firstPiece[strlen($firstPiece) - 1] ?? null;
    if(null === $removedCharacter || $length === 0) {
        return '';
    }
    $firstPieceWithoutTheLastChar = substr($firstPiece, 0, -1);

    return $removedCharacter . self::_random($firstPieceWithoutTheLastChar . $secondPiece, $length - 1);
}

不错的表现，https://3v4l.org/aXaJ6/perf

一个完整的解决方案(课程加测试)，部分基于上面的一些建议…

class TokenFactory
{
    private const LENGTH = 12;
    private const ALLOWED = '123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ~!@#$%^&*{}';
    private const MIN_NUMBER_OF_DIGITS = 1;
    private const MIN_NUMBER_OF_CAPS = 1;
    private const MIN_NUMBER_OF_SPECIALS = 1;
    private const MIN_NUMBER_OF_LETTERS = 1;

    /**
     * @return string
     * @throws \Exception
     */
    public function make(): string
    {
        $pass = $this->generateToken();

        if ($this->isTokenValid($pass)) {
            return $pass;
        } else {
            return $this->make();
        }
    }

    /**
     * @return string
     * @throws \Exception
     */
    private function generateToken(): string
    {
        $allowedCharacters = self::ALLOWED;
        $token              = '';
        $max               = mb_strlen($allowedCharacters, '8bit') - 1;
        for ($i = 0; $i < self::LENGTH; ++$i) {
            $token .= $allowedCharacters[random_int(0, $max)];
        }
        return $token;
    }

    /**
     * @param $token
     * @return bool
     */
    private function isTokenValid($token): bool
    {
        $numberOfDigits   = preg_match_all("/[0-9]/", $token);
        $numberOfCaps     = preg_match_all("/[A-Z]/", $token);
        $numberOfSpecials = preg_match_all("/[~!@#\$%^&*{}]/", $token);
        $numberOfLetters  = preg_match_all("/[a-z]/", $token);

        return
            $numberOfDigits > self::MIN_NUMBER_OF_DIGITS
            && $numberOfCaps > self::MIN_NUMBER_OF_CAPS
            && $numberOfSpecials > self::MIN_NUMBER_OF_SPECIALS
            && $numberOfLetters > self::MIN_NUMBER_OF_LETTERS
            ;
    }
}

class TokenFactoryTest
{
    public function test_correct_syntax()
    {
        /**
         * Arrange
         */
        $length = 12;
        $numberOfChecks = 1000;

        /**
         * Act & Assert
         */
        $class = new TokenFactory();

        $i = 0;
        while ($i < $numberOfChecks) {
            $generatedToken = $class->make();

            $numberOfDigits = preg_match_all( "/[0-9]/", $generatedToken );
            $numberOfCaps = preg_match_all( "/[A-Z]/", $generatedToken );
            $numberOfSpecials   = preg_match_all("/[~!@#\$%^&*{}]/", $generatedToken);
            $numberOfLetters   = preg_match_all("/[a-z]/", $generatedToken);

            Assert::assertEquals($length, strlen($generatedToken));
            Assert::assertTrue($numberOfDigits >= 1, 'Digit error: ' . $generatedToken);
            Assert::assertTrue($numberOfCaps >= 1, 'Caps error: ' . $generatedToken);
            Assert::assertTrue($numberOfSpecials >= 1, 'Specials error: ' . $generatedToken);
            Assert::assertTrue($numberOfLetters >= 1, 'Letters error: ' . $generatedToken);

            $i++;
        }
    }
}

顺便说一句，请确保在适合您需要的地方捕获该异常!