我想要特定字符和预设长度的伪随机字符串。我希望当前版本的PHP具有最高质量的伪随机性，此时它可以是v5、v6、v7或v8，并且可以使用默认配置或特殊配置。为了解决这种混乱，我在这里选取了其他几个答案，并包含了函数可用性条件。

使用。要全局使用它，给$VALID_ID_CHARS赋值你想要的字符，然后调用它:

$VALID_ID_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
$myNewRandomId = makeId(6);

function makeId($desiredLen)
{
    global $VALID_ID_CHARS;
    if ($desiredLen < 1) {
        throw new \RangeException("Length must be a positive integer");
    }
    $vLen = 0;
    if (function_exists('mb_strlen')) {
        $vLen = mb_strlen($VALID_ID_CHARS, '8bit') - 1;
    } else {
        $vLen = strlen($VALID_ID_CHARS) - 1;
    }
    if (function_exists('random_int')) {
        $pieces = [];
        for ($i = 0; $i < $desiredLen; ++$i) {
            $pieces[] = $VALID_ID_CHARS[random_int(0, $vLen)];
        }
        return implode('', $pieces);
    }
    if (function_exists('openssl_random_pseudo_bytes')) {
        $random = openssl_random_pseudo_bytes($desiredLen);
        $id = '';
        for ($i = 0; $i < $desiredLen; ++$i) {
            $id .= $VALID_ID_CHARS[ord($random[$i]) % $vLen];
        }
        return $id;
    }
    http_response_code(500);
    die('random id generation failed. either random_int or openssl_random_pseudo_bytes is needed');
}

实现这个函数的更好方法是:

function RandomString($length) {
    $keys = array_merge(range(0,9), range('a', 'z'));

    $key = "";
    for($i=0; $i < $length; $i++) {
        $key .= $keys[mt_rand(0, count($keys) - 1)];
    }
    return $key;
}

echo RandomString(20);

mt_rand在PHP 7中更加随机。rand函数是mt_rand的别名。

//generateRandomString http://stackoverflow.com/questions/4356289/php-random-string-generator
function randomString($length = 32, $string= "0123456789abcdefghijklmnopqrstuvwxyz" ) {
    //$string can be:
    //0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
    //0123456789abcdefghijklmnopqrstuvwxyz
    return substr(str_shuffle( $string), 0, $length);
}

以前的答案会生成不安全或难以输入的密码。

这是安全的，并且提供了用户更有可能实际使用的密码，而不是因为一些薄弱的东西而被丢弃。

// NOTE: On PHP 5.x you will need to install https://github.com/paragonie/random_compat

/**
 * Generate a password that can easily be typed by users.
 *
 * By default, this will sacrifice strength by skipping characters that can cause
 * confusion. Set $allowAmbiguous to allow these characters.
 */
static public function generatePassword($length=12, $mixedCase=true, $numericCount=2, $symbolCount=1, $allowAmbiguous=false, $allowRepeatingCharacters=false)
{
  // sanity check to prevent endless loop
  if ($numericCount + $symbolCount > $length) {
    throw new \Exception('generatePassword(): $numericCount + $symbolCount are too high');
  }

  // generate a basic password with just alphabetic characters
  $chars  = 'qwertyupasdfghjkzxcvbnm';
  if ($mixedCase) {
    $chars .= 'QWERTYUPASDFGHJKZXCVBNML';
  }
  if ($allowAmbiguous) {
    $chars .= 'iol';
    if ($mixedCase) {
      $chars .= 'IO';
    }
  }

  $password = '';
  foreach (range(1, $length) as $index) {
    $char = $chars[random_int(0, strlen($chars) - 1)];

    if (!$allowRepeatingCharacters) {
      while ($char == substr($password, -1)) {
        $char = $chars[random_int(0, strlen($chars) - 1)];
      }
    }

    $password .= $char;
  }


  // add numeric characters
  $takenSubstitutionIndexes = [];

  if ($numericCount > 0) {
    $chars = '23456789';
    if ($allowAmbiguous) {
      $chars .= '10';
    }

    foreach (range(1, $numericCount) as $_) {
      $index = random_int(0, strlen($password) - 1);
      while (in_array($index, $takenSubstitutionIndexes)) {
        $index = random_int(0, strlen($password) - 1);
      }

      $char = $chars[random_int(0, strlen($chars) - 1)];
      if (!$allowRepeatingCharacters) {
        while (substr($password, $index - 1, 1) == $char || substr($password, $index + 1, 1) == $char) {
          $char = $chars[random_int(0, strlen($chars) - 1)];
        }
      }

      $password[$index] = $char;
      $takenSubstitutionIndexes[] = $index;
    }
  }

  // add symbols
  $chars = '!@#$%&*=+?';
  if ($allowAmbiguous) {
    $chars .= '^~-_()[{]};:|\\/,.\'"`<>';
  }

  if ($symbolCount > 0) {
    foreach (range(1, $symbolCount) as $_) {
      $index = random_int(0, strlen($password) - 1);
      while (in_array($index, $takenSubstitutionIndexes)) {
        $index = random_int(0, strlen($password) - 1);
      }

      $char = $chars[random_int(0, strlen($chars) - 1)];
      if (!$allowRepeatingCharacters) {
        while (substr($password, $index - 1, 1) == $char || substr($password, $index + 1, 1) == $char) {
          $char = $chars[random_int(0, strlen($chars) - 1)];
        }
      }

      $password[$index] = $char;
      $takenSubstitutionIndexes[] = $index;
    }
  }

  return $password;
}

该函数的编辑版本工作正常，但我发现只有一个问题:您使用了错误的字符来包含$字符，因此'字符有时是生成的随机字符串的一部分。

要解决这个问题，请更改:

$characters = ’0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ’;

to:

$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

这种方法只使用包含的字符，'字符永远不会是生成的随机字符串的一部分。

试试这个:

function generate_name ($length = LENGTH_IMG_PATH) {
    $image_name = "";
    $possible = "0123456789abcdefghijklmnopqrstuvwxyz";

    $i = 0;

    while ($i < $length) {

        $char = substr($possible, mt_rand(0, strlen($possible)-1), 1);

        if (!strstr($image_name, $char)) {
            $image_name .= $char;
            $i++;
        }
    }
    return $image_name;
}