PHP to add to an RSS file, without generating RSS via PHP - php

Question

I need to add a new item element to my RSS file, via PHP, without just generating the RSS from PHP. I know this will require removing older items, to match the number that I want displayed, but I don't know how to add them to the file in the first place.
My code looks somewhat like this:
<rss version="2.0">
<channel>
<title>My Site Feed</title>
<link>http://www.mysitethathasfeed.com/feed/</link>
<description>
A nice site that features a feed.
</description>
<item>
<title>Launched!</title>
<link>http://www.mysitethathasfeed.com/feed/view.php?ID=launched</link>
<description>
We just launched the site! Come join the celebration!
</description>
</item>
</channel>
</rss>

Answer 1

// Load the XML/RSS from a file.
$rss = file_get_cotents('path_to_file');
$dom = new DOMDocument();
$dom->loadXML($rss);
Use http://php.net/manual/en/book.dom.php to learn how to modify the dom you loaded.

Answer 2

Extending the answer from Kyle (oh OOP inheritence), and references from the PHP Manual
<?php
$rss = file_get_contents('feed.rss');
$dom = new DOMDocument();
$dom->loadXML($rss);
// should have only 1 node in the list
$nodeList = $dom->getElementsByTagName('channel');
// assuming there's only 1 channel tag in the RSS file:
$nChannel = $nodeList->item(0);
// now create the new item
$newNode = $dom->createElement('item');
$newNode->appendChild($dom->createElement('title', 'a new title post'));
$newNode->appendChild($dom->createElement('link', 'http://www.mysitethathasfeed.com/feed/view.php?ID=launched'));
$newNode->appendChild($dom->createElement('description', 'This is the 2nd post of our feed.'));
// add item to channel
$nChannel->appendChild($newNode);
$rss = $dom->saveXML();
file_put_contents('feed.rss', $rss);