'01.10.2013'  или '01/10/2013' должно будет преобразовано в '01-10-2013'

<?php
$str='01.11.2013';
$pattern= '/^\d{2}.\d{2}.\d{4}$/';
$replace='/^\d{2}-\d{2}-\d{4}$/';

echo preg_replace($pattern,$replace,$str);
?>

$pattern= '/^(\d{2}).(\d{2}).(\d{4})/';
$replace='/^(\d{2})-(\d{2})-(\d{4})/';

$pattern= '/^(\d){2}.(\d){2}.(\d){4}/';
$replace='/^(\d){2}-(\d){2}-(\d){4}/';

$pattern= '/^(\d){1,2}.(\d){1,2}.(\d){2,4}/';
$replace='/^(\d){1,2}-(\d){1,2}-(\d){2,4}/';

$pattern= '/^(\d){1,2}.(\d){1,2}.(\d){4}/';
$replace='/^(\d){1,2}\-(\d){1,2}\-(\d){4}/';

$pattern = '/(\d)[^\d]{1}(\d)/';
$replace = '\1-\2';