Generate random 5 characters string

$rand = substr(md5(microtime()),rand(0,26),5);

Would be my best guess--Unless you're looking for special characters, too:

$seed = str_split('abcdefghijklmnopqrstuvwxyz'                 .'ABCDEFGHIJKLMNOPQRSTUVWXYZ'                 .'0123456789!@#$%^&*()'); // and any other charactersshuffle($seed); // probably optional since array_is randomized; this may be redundant$rand = '';foreach (array_rand($seed, 5) as $k) $rand .= $seed[$k];

Example

And, for one based on the clock (fewer collisions since it's incremental):

function incrementalHash($len = 5){  $charset = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";  $base = strlen($charset);  $result = '';  $now = explode(' ', microtime())[1];  while ($now >= $base){    $i = $now % $base;    $result = $charset[$i] . $result;    $now /= $base;  }  return substr($result, -5);}

Note: incremental means easier to guess; If you're using this as a salt or a verification token, don't. A salt (now) of "WCWyb" means 5 seconds from now it's "WCWyg")

If for loops are on short supply, here's what I like to use:

$s = substr(str_shuffle(str_repeat("0123456789abcdefghijklmnopqrstuvwxyz", 5)), 0, 5);

A speedy way is to use the most volatile characters of the uniqid function.

For example:

$rand = substr(uniqid('', true), -5);