<?php
$target_day = date('Y/m/d', strtotime('-1 day'));
$xml = "https://jvndb.jvn.jp/ja/rss/jvndb_new.rdf";
$xmlData = simplexml_load_file($xml);
foreach ($xmlData->item as $entry){
$dc = $entry->children('http://purl.org/dc/elements/1.1/');
$day = date('Y/m/d', strtotime($dc->date));
if($day == $target_day){
$string.= date('Y/m/d h:i', strtotime($dc->date))."<br>";
$string.= $entry->title."<br>";
$string.= $entry->link."<br>";
}
}
?>
<html>
<body>
<?php echo $string; ?>
</body>
</html>

OK、次はslack webhook