Build a Simple PHP Web Crawler on Linux: Step-by-Step Guide

With the growth of the Internet, information online is abundant. To facilitate access, web crawlers have emerged. This article introduces how to write a simple web crawler using PHP on a Linux environment, providing concrete code examples.

What is a Web crawler?

A web crawler is an automated program that visits web pages and extracts information. It retrieves page source code via HTTP and parses it according to predefined rules, enabling rapid collection and processing of large amounts of data.

Preparation

Before writing the crawler, install PHP and related extensions. On Linux you can run:

sudo apt update
sudo apt install php php-curl

After installation, choose a target website as an example; here we use the Wikipedia page “Computer science”.

Development Process

Create a PHP file named crawler.php with the following code:

<?php
// Define target URL
$url = "https://en.wikipedia.org/wiki/Computer_science";

// Initialize cURL
$ch = curl_init();

// Set cURL options
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

// Get page source
$html = curl_exec($ch);

// Close cURL
curl_close($ch);

// Parse page source
$dom = new DOMDocument();
@$dom->loadHTML($html);

// Get all headings
$headings = $dom->getElementsByTagName("h2");
foreach ($headings as $heading) {
    echo $heading->nodeValue . "
";
}
?>

Save the file and run it with: php crawler.php The output will list headings from the target page, for example:

Contents
History[edit]
Terminology[edit]
Areas of computer science[edit]
Subfields[edit]
Relation to other fields[edit]
See also[edit]
Notes[edit]
References[edit]
External links[edit]

These headings are part of the target page. We have successfully retrieved the title information from Wikipedia’s computer science page using a PHP script.

The article demonstrates using PHP on Linux to build a simple web crawler, employing cURL to fetch page source and the DOMDocument class to parse content. The code examples aim to help readers understand and master web crawler development.

Note that web crawling must comply with relevant laws, website terms of service, and respect privacy and copyright; it should not be used for illegal purposes.