Random A1phaNumEr1c infinite length string function

gistfile1.php

<?php 
echo passgen(20); //K4YFnMW5muf0kZTMl6h3

function passgen($length = 20)
{
    // define base string - add multiplex to pad to an infinate length
    $alpha = str_repeat(
        "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ",
        intval($length + 1)
    );
    $numeric = str_repeat(
        "0123456789",
        intval($length + 1)
    );

    //shuffle the base string and set first character as an alpha
    return substr(str_shuffle($alpha), 0, 1)
         . substr(str_shuffle($alpha.$numeric), 0, intval($length - 1));
}
?>

Added multiplex onto numbers to increase the number entropy in resulting hash