str_shuffle

Aoccdrnig to rseearch at an Elingsh uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is that the frist and lsat ltteer is at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae we do not raed ervey lteter by it slef but the wrod as a wlohe.
Hree's a cdoe taht slerbmcas txet in tihs way:
<?php
 function scramble_word($word) {
 if (strlen($word) < 2)
 return $word;
 else
 return $word{0} . str_shuffle(substr($word, 1, -1)) . $word{strlen($word) - 1};
 }
 echo preg_replace('/(\w+)/e', 'scramble_word("1円")', 'A quick brown fox jumped over the lazy dog.');
?>

It may be ufseul if you wnat to cetare an aessblicce CTCPAHA.

This page is missing a very important notice:
Caution
This function does not generate cryptographically secure values, and should not be used for cryptographic purposes. If you need a cryptographically secure value, consider using random_int(), random_bytes(), or openssl_random_pseudo_bytes() instead.

<?php
 function str_rand(int $length = 20) : string {
 $ascii_codes = range(48, 57) + range(97, 122);
 $codes_lenght = (count($ascii_codes)-1);
 shuffle($ascii_codes);
 $string = '';
 for($i = 1; $i <= $length; $i++){
 $previous_char = $char ?? '';
 $char = chr($ascii_codes[random_int(0, $codes_lenght)]);
 while($char == $previous_char){
 $char = chr($ascii_codes[random_int(0, $codes_lenght)]);
 }
 $string .= $char;
 }
 return str_shuffle($string);
 }
?>

This function is affected by srand():
<?php
srand(12345);
echo str_shuffle('Randomize me') . '<br/>'; // "demmiezr aon"
echo str_shuffle('Randomize me') . '<br/>'; // "izadmeo rmen"
srand(12345);
echo str_shuffle('Randomize me') . '<br/>'; // "demmiezr aon" again
?>

A proper unicode string shuffle;
<?php
function str_shuffle_unicode($str) {
 $tmp = preg_split("//u", $str, -1, PREG_SPLIT_NO_EMPTY);
 shuffle($tmp);
 return join("", $tmp);
}
?>

$str = "Şeker yârim"; // My sweet love
echo str_shuffle($str); // i�eymrŢekr �
echo str_shuffle_unicode($str); // Şr mreyeikâ

As noted in this documentation str_shuffle is NOT cryptographically secure, however I have seen many code examples online of people using nothing more than this to generate say random passwords. So I though I'd share my function which while it makes use of str_shuffle also rely's on random_int() for added security. I use this function to generate salts to use when working with hashes but it can also be used to generate default passwords for new users for example.
It starts with a universe of possible characters, in this case all letters (upper and lower case), 0-9, and several special characters.
It then will run str_shuffle on the universe of characters a random number of times, using random_int() (currently set to 1-10)
Then once the universe of possible characters has been shuffled it using random_int() once more to select the character as a random position within the shuffled string, as does that once for each character you want in the output.
 function secret_gen( $len=64 ) {
 $secret = "";
 $charset = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()_-+=`~,<>.[]: |';
 for ( $x = 1l $x <= random_int( 1, 10 ), $x++ ){
 $charset = str_shuffle( $charset );
 }
 for ( $s = 1; $s <= $len; $s++ ) {
 $secret .= substr( $charset, random_int( 0, 86 ), 1 );
 }
 return $secret;
}

Unshuffle, using:
<?php
$string = "Hello World!";
$seed = 1234567890;
mt_srand($seed);
echo $sh = str_shuffle($string); //print 'eloWHl rodl!'
echo str_unshuffle($sh, $seed); //print 'Hello World!'
?>

<?php
function str_unshuffle($str, $seed){
 $unique = implode(array_map('chr',range(0,254)));
 $none = chr(255);
 $slen = strlen($str);
 $c = intval(ceil($slen/255));
 $r = '';
 for($i=0; $i<$c; $i++){
 $aaa = str_repeat($none, $i*255);
 $bbb = (($i+1)<$c) ? $unique : substr($unique, 0, $slen%255);
 $ccc = (($i+1)<$c) ? str_repeat($none, strlen($str)-($i+1)*255) : "";
 $tmp = $aaa.$bbb.$ccc;
 mt_srand($seed);
 $sh = str_shuffle($tmp);
 for($j=0; $j<strlen($bbb); $j++){
 $r .= $str{strpos($sh, $unique{$j})};
 }
 }
 return $r;
}

str_shuffle isn't recommendable for passwords. Each character exists only one time).
A function like the following one is better for this.
<?php
 function generatePassword($length = 8) {
 $possibleChars = "abcdefghijklmnopqrstuvwxyz";
 $password = '';
 for($i = 0; $i < $length; $i++) {
 $rand = rand(0, strlen($possibleChars) - 1);
 $password .= substr($possibleChars, $rand, 1);
 }
 return $password;
 }
?>

To cobine functionality and simplicity of the two functions below we can have:
<?php
function generatePasswd($numAlpha=6,$numNonAlpha=2)
{
 $listAlpha = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
 $listNonAlpha = ',;:!?.$/*-+&@_+;./*&?$-!,';
 return str_shuffle(
 substr(str_shuffle($listAlpha),0,$numAlpha) .
 substr(str_shuffle($listNonAlpha),0,$numNonAlpha)
 );
}
?>

Shuffle for all encoding formats
<?php
function unicode_shuffle($string, $chars, $format = 'UTF-8')
{
 for($i=0; $i<$chars; $i++)
 $rands[$i] = rand(0, mb_strlen($string, $format));
 
 $s = NULL;
 
 foreach($rands as $r)
 $s.= mb_substr($string, $r, 1, $format);
 
 return $s;
}
?>

<?php
//get random string with your desire length
 function getRandom($length){
 
 $str = 'abcdefghijklmnopqrstuvwzyz';
 $str1= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
 $str2= '0123456789';
 $shuffled = str_shuffle($str);
 $shuffled1 = str_shuffle($str1);
 $shuffled2 = str_shuffle($str2);
 $total = $shuffled.$shuffled1.$shuffled2;
 $shuffled3 = str_shuffle($total);
 $result= substr($shuffled3, 0, $length);
 return $result;
 }
 echo getRandom(8);
//output -->
//GATv3JPX
//g7AzhDtR
//DTboKtiL
//CuWZR4cs
//tmTXbzBC
?>

/**
 * Test shuffleString
 */
function testShuffleString() {
 $shuffled = shuffleString("ĄęźćÓ");
 if (\mb_strlen($shuffled) != 5) {
 throw new \UnexpectedValueException("Invalid count of characters");
 }
 if ($shuffled == "ĄęźćÓ") {
 throw new \UnexpectedValueException("The same string");
 }
 foreach (["Ą", "ę", "ź", "ć", "Ó"] as $char) {
 if (\mb_strpos($shuffled, $char) === false) {
 throw new \UnexpectedValueException("Character not found");
 }
 }
}
/**
 * Shuffle string
 *
 * @param $stringValue String to shuffle
 * @param string $startWith Shuffle $stringValue and append to $startWith
 * @return string Shuffled string
 * @author Krzysztof Piasecki<krzysiekpiasecki@gmail.com>
 */
function shuffleString($stringValue, $startWith = "") {
 $range = \range(0, \mb_strlen($stringValue));
 shuffle($range);
 foreach($range as $index) {
 $startWith .= \mb_substr($stringValue, $index, 1);
 }
 return $startWith;
};
testShuffleString();
echo shuffleString("Hello"); // > 'elHol' (something like this)
echo shuffleString("World!", "Hello "); // > 'Hello do!lrW' (something like this)

Very, very simple random password generator, without using rand() function:
<?php
function random_password($chars = 8) {
 $letters = 'abcefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
 return substr(str_shuffle($letters), 0, $chars);
}
?>