PHP Linux Script Programming Practice: Implementing Web Crawler

PHP Linux script programming practice: To implement a Web crawler, specific code examples are required

Introduction:
With the development of the Internet, there is a lot of information on the Internet. In order to easily obtain and use this information, web crawlers came into being. This article will introduce how to use PHP to write scripts in a Linux environment to implement a simple web crawler, and attach specific code examples.

1. What is a web crawler?
Web crawler is a program that automatically accesses web pages and extracts information. The crawler obtains the source code of the web page through the HTTP protocol and parses it according to predetermined rules to obtain the required information. It helps us collect and process large amounts of data quickly and efficiently.

2. Preparation
Before starting to write a web crawler, we need to install PHP and related extensions. Under Linux, you can use the following command to install:

sudo apt update
sudo apt install php php-curl

After the installation is complete, we also need a target website as an example. Let's take the "Computer Science" page in Wikipedia as an example.

3. Development process

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

<?php
// 定义目标URL
$url = "https://en.wikipedia.org/wiki/Computer_science";

// 创建cURL资源
$ch = curl_init();

// 设置cURL参数
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

// 获取网页源代码
$html = curl_exec($ch);

// 关闭cURL资源
curl_close($ch);

// 解析网页源代码
$dom = new DOMDocument();
@$dom->loadHTML($html);

// 获取所有标题
$headings = $dom->getElementsByTagName("h2");
foreach ($headings as $heading) {
    echo $heading->nodeValue . "
";
}
?>

2. After saving the file, run the following command:

php crawler.php

4. The result output is as follows:

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 titles are part of the target page. We successfully used a PHP script to obtain the title information of the Computer Science page in Wikipedia.

4. Summary
This article introduces how to use PHP to write scripts in the Linux environment to implement a simple web crawler. We use the cURL library to obtain the web page source code and use the DOMDocument class to parse the web page content. Through specific code examples, I hope readers can understand and master how to write web crawler programs.

It should be noted that crawling web pages needs to comply with relevant laws, regulations and website usage rules, and must not be used for illegal purposes. Please pay attention to privacy and copyright protection when crawling web pages, and follow ethical standards.

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