获取当月所有周五的日期

<?php
$today=getdate();
$i=mktime(0,0,0,$today['mon'],1,$today['year']);
$arr = [];
while(1){
$day=getdate($i);
if ($day['mon']!=$today['mon']) break;
if ($day['wday']==5){
    $arr[]= "{$day['year']}-{$day['mon']}-{$day['mday']}";
    }
    $i+=24*3600;
}
var_dump($arr);die;
?>