Generating (pseudo)random alpha-numeric strings

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);

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));
}

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.

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

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;

      }

    }

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

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

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;
}

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);
}

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();

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.

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.

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

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().

1 line:

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

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;
}

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;
}