Generating (pseudo)random alpha-numeric strings

Question

How can I generate a (pseudo)random alpha-numeric string, something like: 'd79jd8c' in PHP?

Answer 1

First make a string with all your possible characters:

 $characters = 'abcdefghijklmnopqrstuvwxyz0123456789';

You could also use range() to do this more quickly.

Then, in a loop, choose a random number and use it as the index to the $characters string to get a random character, and append it to your string:

 $string = '';
 $max = strlen($characters) - 1;
 for ($i = 0; $i < $random_string_length; $i++) {
      $string .= $characters[mt_rand(0, $max)];
 }

$random_string_length is the length of the random string.

Answer 2

I like this function for the job

function randomKey($length) {
    $pool = array_merge(range(0,9), range('a', 'z'),range('A', 'Z'));

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

echo randomKey(20);

Answer 3

Generate cryptographically strong, random (potentially) 8-character string using the openssl_random_pseudo_bytes function:

echo bin2hex(openssl_random_pseudo_bytes(4));

Procedural way:

function randomString(int $length): string
{
    return bin2hex(openssl_random_pseudo_bytes($length));
}

Update:

PHP7 introduced the random_x() functions which should be even better. If you come from PHP 5.X, use excellent paragonie/random_compat library which is a polyfill for random_bytes() and random_int() from PHP 7.

function randomString($length)
{
    return bin2hex(random_bytes($length));
}

Answer 4

One line solution:

echo substr( str_shuffle( str_repeat( 'abcdefghijklmnopqrstuvwxyz0123456789', 10 ) ), 0, 7 );

You can change the substr parameter in order to set a different length for your string.

Answer 5

I know it's an old post but I'd like to contribute with a class I've created based on Jeremy Ruten's answer and improved with suggestions in comments:

    class RandomString
    {
      private static $characters = 'abcdefghijklmnopqrstuvwxyz0123456789';
      private static $string;
      private static $length = 8; //default random string length

      public static function generate($length = null)
      {

        if($length){
          self::$length = $length;
        }

        $characters_length = strlen(self::$characters) - 1;

        for ($i = 0; $i < self::$length; $i++) {
          self::$string .= self::$characters[mt_rand(0, $characters_length)];
        }

        return self::$string;

      }

    }

Answer 6

Use the ASCII table to pick a range of letters, where the: $range_start , $range_end is a value from the decimal column in the ASCII table.

I find that this method is nicer compared to the method described where the range of characters is specifically defined within another string.

// range is numbers (48) through capital and lower case letters (122)
$range_start = 48;
$range_end   = 122;
$random_string = "";
$random_string_length = 10;

for ($i = 0; $i < $random_string_length; $i++) {
  $ascii_no = round( mt_rand( $range_start , $range_end ) ); // generates a number within the range
  // finds the character represented by $ascii_no and adds it to the random string
  // study **chr** function for a better understanding
  $random_string .= chr( $ascii_no );
}

echo $random_string;

See More:

• chr function
• mt_rand function

Answer 7

Simple guys .... but remember each byte is random between 0 and 255 which for a random string will be fine. Also remember you'll have two characters to represent each byte.

$str = bin2hex(random_bytes(32));  // 64 character string returned

Answer 8

You can use the following code. It is similar to existing functions except that you can force special character count:

function random_string() {
    // 8 characters: 7 lower-case alphabets and 1 digit
    $character_sets = [
        ["count" => 7, "characters" => "abcdefghijklmnopqrstuvwxyz"],
        ["count" => 1, "characters" => "0123456789"]
    ];
    $temp_array = array();
    foreach ($character_sets as $character_set) {
        for ($i = 0; $i < $character_set["count"]; $i++) {
            $random = random_int(0, strlen($character_set["characters"]) - 1);
            $temp_array[] = $character_set["characters"][$random];
        }
    }
    shuffle($temp_array);
    return implode("", $temp_array);
}

Answer 9

Maybe I missed something here, but here's a way using the uniqid() function.

Answer 10

I have made the following quick function just to play around with the range() function. It just might help someone sometime.

Function pseudostring($length = 50) {

    // Generate arrays with characters and numbers
    $lowerAlpha = range('a', 'z');
    $upperAlpha = range('A', 'Z');
    $numeric = range('0', '9');

    // Merge the arrays
    $workArray = array_merge($numeric, array_merge($lowerAlpha, $upperAlpha));
    $returnString = "";

    // Add random characters from the created array to a string
    for ($i = 0; $i < $length; $i++) {
        $character = $workArray[rand(0, 61)];
        $returnString .= $character;
    }

    return $returnString;
}

Answer 11

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

Answer 12

If you want a very easy way to do this, you can lean on existing PHP functions. This is the code I use:

substr( sha1( time() ), 0, 15 )

time() gives you the current time in seconds since epoch, sha1() encrypts it to a string of 0-9a-f, and substr() lets you choose a length. You don't have to start at character 0, and whatever the difference is between the two numbers will be the length of the string.

Answer 13

First list the desired characters

$chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

Use the str_shuffle($string) function. This function will provide you a randomly shuffled string.

$alpha=substr(str_shuffle($chars), 0, 50);

50 is the Length of string.

Answer 14

Jeremy's answer is great. If, like me, you're unsure of how to implement range(), you can see my version using range().

<?php
$character_array = array_merge(range('a', 'z'), range(0, 9));
$string = "";
    for($i = 0; $i < 6; $i++) {
        $string .= $character_array[rand(0, (count($character_array) - 1))];
    }
echo $string;
?>

This does the exact same thing as Jeremy's but uses merged arrays where he uses a string, and uses count() where he uses strlen().

Answer 15

This is something I use:

$cryptoStrong = true; // can be false
$length = 16; // Any length you want
$bytes = openssl_random_pseudo_bytes($length, $cryptoStrong);
$randomString = bin2hex($bytes);

You can see the Docs for openssl_random_pseudo_bytes here, and the Docs for bin2hex here

Answer 16

1 line:

$FROM = 0; $TO = 'zzzz';
$code = base_convert(rand( $FROM ,base_convert( $TO , 36,10)),10,36);
echo $code;

Answer 17

The modern way to do that with type hint / rand_int for real randomeness

function random_string(int $size): string
{
    $characters = array_merge(
        range(0, 9),
        range('A', 'Z')
    );

    $string = '';
    $max = count($characters) - 1;
    for ($i = 0; $i < $size; $i++) {
        $string .= $characters[random_int(0, $max)];
    }

    return $string;
}

Answer 18

public function randomString($length = 8)
{
    $characters = implode([
        'ABCDEFGHIJKLMNOPORRQSTUWVXYZ',
        'abcdefghijklmnoprqstuwvxyz',
        '0123456789',
        //'!@#$%^&*?'
    ]);

    $charactersLength = strlen($characters) - 1;
    $string           = '';

    while ($length) {
        $string .= $characters[mt_rand(0, $charactersLength)];
        --$length;
    }

    return $string;
}