- print_r: documentation ( source)
<?php
$systemTZ = new DateTimeZone("UTC");
$end = new \DateTime(null, $systemTZ);
$end->sub(new \DateInterval('P30D'));
$begin= new \DateTime(null, $systemTZ);
$interval = \DateInterval::createFromDateString('1 day');
$now = new DateTime;
while ($begin >= $end) {
print_r($begin->format('Y-m-d'));
$begin = $begin->sub($interval);
}