function randomString($length = 5) {
    return substr(str_shuffle(implode(array_merge(range('A','Z'), range('a','z'), range(0,9)))), 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;
}

这将创建一个20个字符的十六进制字符串:

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

在PHP 7 (random_bytes())中:

$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

函数作用域中的$randstring与调用它的作用域不相同。你必须把返回值赋给一个变量。

$randstring = RandomString();
echo $randstring;

或者直接回显返回值:

echo RandomString();

另外，在函数中有一个小错误。在for循环中，您需要使用.=，以便每个字符都被追加到字符串中。通过使用=，您将用每个新字符覆盖它，而不是追加。

$randstring .= $characters[rand(0, strlen($characters))];

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;
}

这一个是从管理员来源:

/** Get a random string
* @return string 32 hexadecimal characters
*/
function rand_string() {
    return md5(uniqid(mt_rand(), true));
}

管理员，用PHP编写的数据库管理工具。