$idx = 45; # pretend we've already found the insertion point
@a[$idx+1 .. $#a+1] = @a[$idx .. $#a];
$a[$idx] = $newitem;

##</code><code>##

$idxmove = $#a;
while ($idxmove >= $idx) {
  $a[$idxmove+1] = $a[$idxmove];
  $idxmove--;
}
$a[$idx] = $newitem;