Scraping Links With PHP

文章目錄

• What You’ll Learn
• What You Will Need
• Common User Agents

Scraping Links With PHP

by justin on August 11, 2007

FROM:http://www.merchantos.com/makebeta/php/scraping-links-with-php/#curl_content

 

In this tutorial you will learn how to build a PHP script that scrapes links from any web page.

What You’ll Learn

1. How to use cURL to get the content from a website (URL).
2. Call PHP DOM functions to parse the HTML so you can extract links.
3. Use XPath to grab links from specific parts of a page.
4. Store the scraped links in a MySQL database.
5. Put it all together into a link scraper.
6. What else you could use a scraper for.
7. Legal issues associated with scraping content.

What You Will Need

• Basic knowledge of PHP and MySQL.
• A web server running PHP 5.
• The cURL extension for PHP.
• MySQL – if you want to store the links.

Get The Page Content

cURL is a great tool for making requests to remote servers in PHP. It can imitate a browser in pretty much every way. Here’s the code to grab our target site content:

$ch = curl_init();curl_setopt($ch, CURLOPT_USERAGENT, $userAgent);curl_setopt($ch, CURLOPT_URL,$target_url);curl_setopt($ch, CURLOPT_FAILONERROR, true);curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);curl_setopt($ch, CURLOPT_AUTOREFERER, true);curl_setopt($ch, CURLOPT_RETURNTRANSFER,true);curl_setopt($ch, CURLOPT_TIMEOUT, 10);$html = curl_exec($ch);if (!$html) {echo "<br />cURL error number:" .curl_errno($ch);echo "<br />cURL error:" . curl_error($ch);exit;}

If the request is successful $html will be filled with the content of $target_url. If the call fails then we’ll see an error message about the failure.

curl_setopt($ch, CURLOPT_URL,$target_url);

This line determines what URL will be requested. For example if you wanted to scrape this site you’d have $target_url = “/makebeta/”. I won’t go into the rest of the options that are set (except for CURLOPT_USERAGENT – see below). You can read an in depth tutorial on PHP and cURL here.

Tip: Fake Your User Agent

Many websites won’t play nice with you if you come knocking with the wrong User Agent string. What’s a User Agent string? It’s part of every request to a web server that tells it what type of agent (browser, spider, etc) is requesting the content. Some websites will give you different content depending on the user agent, so you might want to experiment. You do this in cURL with a call to curl_setopt() with CURLOPT_USERAGENT as the option:

$userAgent = 'Googlebot/2.1 (http://www.googlebot.com/bot.html)';curl_setopt($ch, CURLOPT_USERAGENT, $userAgent);

This would set cURL’s user agent to mimic Google’s. You can find a comprehensive list of user agents here: User Agents.

Common User Agents

I’ve done a bit of the leg work for you and gathered the most common user agents:

Search Engine User Agents

• Google – Googlebot/2.1 ( http://www.googlebot.com/bot.html)
• Google Image – Googlebot-Image/1.0 ( http://www.googlebot.com/bot.html)
• MSN Live – msnbot-Products/1.0 (+http://search.msn.com/msnbot.htm)
• Yahoo – Mozilla/5.0 (compatible; Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp)
• ask

Browser User Agents

• Firefox (WindowsXP) – Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6
• IE 7 – Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)
• IE 6 – Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322)
• Safari – Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en) AppleWebKit/522.11 (KHTML, like Gecko) Safari/3.0.2
• Opera – Opera/9.00 (Windows NT 5.1; U; en)

Using PHP’s DOM Functions To Parse The HTML

PHP provides with a really cool tool for working with HTML content: DOM Functions. The DOM Functions allow you to parse HTML (or XML) into an object structure (or DOM – Document Object Model). Let’s see how we do it:

$dom = new DOMDocument();@$dom->loadHTML($html);

Wow is it really that easy? Yes! Now we have a nice DOMDocument object that we can use to access everything within the HTML in a nice clean way. I discovered this over at Russll Beattie’s post on: Using PHP TO Scrape Sites As Feeds, thanks Russell!

Tip: You may have noticed I put @ in front of loadHTML(), this suppresses some annoying warnings that the HTML parser throws on many pages that have non-standard compliant code.

XPath Makes Getting The Links You Want Easy

Now for the real magic of the DOM: XPath! XPath allows you to gather collections of DOM nodes (otherwise known as tags in HTML). Say you want to only get links that are within unordered lists. All you have to do is write a query like “/html/body//ul//li//a” and pass it to XPath->evaluate(). I’m not going to go into all the ways you can use XPath because I’m just learning myself and someone else has already made a great list of examples: XPath Examples. Here’s a code snippet that will just get every link on the page using XPath:

$xpath = new DOMXPath($dom);$hrefs = $xpath->evaluate("/html/body//a");

Iterate And Store Your Links

Next we’ll iterate through all the links we’ve gathered using XPath and store them in a database. First the code to iterate through the links:

for ($i = 0; $i < $hrefs->length; $i++) 
{
$href = $hrefs->item($i);
$url = $href->getAttribute('href');
storeLink($url,$target_url);
}

FULL PROGRAM:

<?php
$target_url = "http://www.google.com";
$ch = curl_init();
$userAgent = 'Googlebot/2.1 (http://www.googlebot.com/bot.html)';
curl_setopt($ch, CURLOPT_USERAGENT, $userAgent);
curl_setopt($ch, CURLOPT_URL,$target_url);
curl_setopt($ch, CURLOPT_FAILONERROR, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_AUTOREFERER, true);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,true);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
$html = curl_exec($ch);
if (!$html) {
 echo "<br />cURL error number:" .curl_errno($ch);
 echo "<br />cURL error:" . curl_error($ch);
 exit;
}
$dom = new DOMDocument();
@$dom->loadHTML($html);
$xpath = new DOMXPath($dom);
$hrefs = $xpath->evaluate("/html/body//a");
for ($i = 0; $i < $hrefs->length; $i++) {
 
 $href = $hrefs->item($i);
 $url = $href->getAttribute('href');
 
 echo $url;
 echo "<BR>";
 
}
?>

then you can store url to your database. more details from here:http://www.merchantos.com/makebeta/php/scraping-links-with-php/#curl_content

REF:
tutorial on PHP and cURL 

You can find a comprehensive list of user agents here: User Agents.

Using PHP TO Scrape Sites As Feeds