- substr: documentation ( source)
- printf: documentation ( source)
<?php
$tpl = "AR42-8LNA-%sEQ3";
$char = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
$length = strlen($char)-1;
for($i=0; i<=$length; $i++) {
printf($tpl, substr($char, $i, 1));
echo PHP_EOL;
}