Screen scraping your way into RSS by Dennis Pallett
<span style="font-weight:bold; font-size: 1.2em">Introduction</span>
RSS is one the hottest technologies at the moment, and even big web publishers
(such as the New York Times) are getting into RSS as well. However, there are
still a lot of websites that do not have RSS feeds.
If you still want to be able to check those websites in your favourite
aggregator, you need to create your own RSS feed for those websites. This can
be done automatically with PHP, using a method called screen scrapping. Screen
scrapping is usually frowned upon, as it's mostly used to steal content from
other websites.
I personally believe that in this case, to automatically generate a RSS feed,
screen scrapping is not a bad thing. Now, on to the code!
<span style="font-weight:bold; font-size: 1.2em">Getting the
content</span> For this article, we'll use PHPit as an example, despite
the fact that PHPit already has RSS
feeds.
We'll want to generate a RSS feed from the content listed on the
frontpage. The first step in screen scraping is getting the complete
page. In PHP this can be done very easily, by using implode(file("", "[the url
here]")); IF your web host allows it. If you can't use file() you'll have to
use a different method of getting the page, e.g. using the
CURL library.
Now that we have the content available, we can parse it for the content using
some regular expressions. The key to screen scraping is looking for patterns
that match the content, e.g. are all the content items wrapped in <div>'s
or something else? If you can successfully discover a pattern, then you can use
preg_match_all() to get all the content items.
For PHPit, the pattern that match the content is <div
class="contentitem">[Content Here]<div>. You can verify this yourself
by going to the main page of PHPit, and viewing the source.
Now that we have a match we can get all the content items. The next step is to
retrieve the individual information, i.e. url, title, author, text. This can be
done by using some more regular expression and str_replace() on the each
content items.
By now we have the following code;
<?php
// Get page
$url = "http://www.phpit.net/";;$data =
implode("", file($url));
// Get content itemspreg_match_all (
"/<div class="contentitem">([^`]*?)</div>/", $data, $matches);Like I
said, the next step is to retrieve the individual information, but first let's
make a beginning on our feed, by setting the appropriate header (text/xml) and
printing the channel information, etc.
// Begin feed
header ("Content-Type: text/xml; charset=ISO-8859-1");
echo "<?xml version="1.0" encoding="ISO-8859-1" ?>
";
?>
<rss version="2.0"
xmlns:dc="http://purl.org/dc/elements/1.1/";
xmlns:content="http://purl.org/rss/1.0/modules/content/";
xmlns:admin="http://webns.net/mvcb/";
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";>
<channel>
<title>PHPit Latest Content</title>
<description>The latest content from PHPit (
http://www.phpit.net),screen scraped!</description>
<link>http://www.phpit.net<;/link>
<language>en-us</language>
<?
Now it's time to loop through the items, and print their RSS XML. We first loop
through each item, and get all the information we get, by using more regular
expressions and preg_match(). After that the RSS for the item is printed.
<?php
// Loop through each content item
foreach ($matches[0] as $match) {
// First, get title
preg_match ("/">([^`]*?)</a></h3>/", $match, $temp);
$title = $temp['1'];
$title = strip_tags($title);
$title = trim($title);
// Second, get url
preg_match ("/<a href="([^`]*?)">/", $match, $temp);
$url = $temp['1'];
$url = trim($url);
// Third, get text
preg_match ("/<p>([^`]*?)<span class="byline">/", $match, $temp);
$text = $temp['1'];
$text = trim($text);
// Fourth, and finally, get author
preg_match(
"/<span class="byline">By ([^`]*?)</span>/",$match,$temp);
$author = $temp['1'];
$author = trim($author);
// Echo RSS XML
echo "<item>
";
echo " <title>" . strip_tags($title) . "</title>
";
echo " <link>http://www.phpit.net"; . strip_tags($url) . "</link>
";
echo " <description>" . strip_tags($text) . "</description>
";
echo " <content:encoded><![CDATA[
";
echo $text . "
";
echo " ]]></content:encoded>
";
echo " <dc:creator>" . strip_tags($author) . "</dc:creator>
";
echo " </item>
";
}
?>
And finally, the RSS file is closed off.
</channel>
</rss>
That's all. If you put all the code together, like in the demo script, then
you'll have a perfect RSS feed.
<span style="font-weight:bold; font-size: 1.2em">Conclusion</span>
In this tutorial I have shown you how to create a RSS feed from a website that
does not have a RSS feed themselves yet. Though the regular expression is
different for each website, the principle is exactly the same.
One thing I should mention is that you shouldn't immediately screen scrape a
website's content. E-mail them first about a RSS feed. Who knows, they might
set one up themselves, and that would be even better.
Download sample script
About the Author
Dennis Pallett is a young tech writer, with much experience in ASP, PHP and
other web technologies. He enjoys writing, and has written several articles and
tutorials. To find more of his work, look at his websites at
http://www.phpit.net,
http://www.aspit.net and
http://www.ezfaqs.com
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