https://medium.com/@ldjb/how-to-tweet-your-toots-with-php-and-ifttt-2ee891b9cf3e

mastofeed.php

<?php

define("ATOM_FEED", "https://mastodon.social/@Gargron.atom");
define("NEW_STATUS_BY", "New status by");

header("Content-type: application/atom+xml; charset=utf-8");

$data = new SimpleXMLElement(file_get_contents(ATOM_FEED));

$toRemove = [];

for ($i=0; $i<count($data->entry); ++$i) {
	if (strpos($data->entry[$i]->title, NEW_STATUS_BY) !== 0) {
		array_unshift($toRemove, $i);
	}
	else {
		$data->entry[$i]->content = strip_tags($data->entry[$i]->content, "<p><br>");
		if (strpos($data->entry[$i]->content, "<p>@") === 0) {
			array_unshift($toRemove, $i);
		}
		else {
			$data->entry[$i]->content = str_replace("@", "[AT]", $data->entry[$i]->content);
		}
	}
}

foreach($toRemove as $i) {
	unset($data->entry[$i]);
}

echo $data->asXML();