Introduction 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!
Getting the
content 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 items preg_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.
Conclusion 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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