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I would like to create a crawler using php that would give me a list of all the pages on a specific domain (starting from the homepage: www.example.com).

How can I do this in php?

I don't know how to recursively find all the pages on a website starting from a specific page and excluding external links.

chris
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2 Answers2

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For the general approach, check out the answers to these questions:

In PHP, you should be able to simply fetch a remote URL with file_get_contents(). You could perform a naive parse of the HTML by using a regular expression with preg_match() to find <a href=""> tags and parse the URL out of them (See this question for some typical approaches).

Once you've extract the raw href attribute, you could use parse_url() to break into it components and figure out if its a URL you want to fetch - remember also the URLs may be relative to the page you've fetched.

Though fast, a regex isn't the best way of parsing HTML though - you could also try the DOM classes to parse the HTML you fetch, for example:

$dom = new DOMDocument();
$dom->loadHTML($content);

$anchors = $dom->getElementsByTagName('a');

if ( count($anchors->length) > 0 ) {
    foreach ( $anchors as $anchor ) {
        if ( $anchor->hasAttribute('href') ) {
            $url = $anchor->getAttribute('href');

            //now figure out whether to processs this
            //URL and add it to a list of URLs to be fetched
        }
    }
}

Finally, rather than write it yourself, see also this question for other resources you could use.

Community
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Paul Dixon
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Overview

Here are some notes on the basics of the crawler.

It is a console app - It doesn't need a rich interface, so I figured a console application would do. The output is done as an html file and the input (what site to view) is done through the app.config. Making a windows app out of this seemed like overkill.
The crawler is designed to only crawl the site it originally targets. It would be easy to change that if you want to crawl more than just a single site, but that is the goal of this little application.
Originally the crawler was just written to find bad links. Just for fun I also had it collect information on page and viewstate sizes. It will also list all non-html files and external urls, just in case you care to see them.
The results are shown in a rather minimalistic html report. This report is automatically opened in Internet Explorer when the crawl is finished.

Getting the Text from an Html Page

The first crucial piece of building a crawler is the mechanism for going out and fetching the html off of the web (or your local machine, if you have the site running locally.). Like so much else, .NET has classes for doing this very thing built into the framework.

    private static string GetWebText(string url)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
        request.UserAgent = "A .NET Web Crawler";
        WebResponse response = request.GetResponse();
        Stream stream = response.GetResponseStream();
        StreamReader reader = new StreamReader(stream);
        string htmlText = reader.ReadToEnd();
        return htmlText;
    }

The HttpWebRequest class can be used to request any page from the internet. The response (retrieved through a call to GetResponse()) holds the data you want. Get the response stream, throw it in a StreamReader, and read the text to get your html. for Reference: http://www.juicer.headrun.com

animuson
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notemonk
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