"20191225_092558" を "2019-12-25-00-00-00" へ変更

コード

$str = "20191225_092558";
echo substr($str,0,4).'-'.substr($str,4,2).'-'.substr($str,6,2).'-00-00-00';
echo substr($str,0,4).'-'.substr($str,4,2).'-'.substr($str,6,2).'-'.substr($str,9,2).'-'.substr($str,11,2).'-00';