PHP simple web crawler development example

With the rapid development of the Internet, data has become one of the most important resources in today's information age. As a technology that automatically obtains and processes network data, web crawlers are attracting more and more attention and application. This article will introduce how to use PHP to develop a simple web crawler and realize the function of automatically obtaining network data.

1. Overview of web crawlers

A web crawler is a technology that automatically obtains and processes network resources. Its main working process is to simulate browser behavior, automatically access specified URL addresses and extract all Data required. Generally speaking, a web crawler can be divided into the following steps:

1. Define the target URL to crawl;
2. Send an HTTP request to obtain the web page source code;
3. Parse the web page source code, extract the required data;
4. store the data, and continue to crawl the next URL.

2. PHP development environment preparation

Before we start developing web crawlers, we need to prepare the PHP development environment. The specific operations are as follows:

1. Download and install PHP, which can be downloaded from the official website (https://www.php.net/) or other mirror websites;
2. Install a Web server , such as Apache, Nginx, etc.;
3. Configure PHP environment variables to ensure that PHP can run in the command line.

3. Writing a web crawler

Next, we will start writing a web crawler. Suppose we want to crawl the titles and URLs in Baidu search results pages and write them into a CSV file. The specific code is as follows:

<?php
// 定义爬取的目标 URL
$url = 'https://www.baidu.com/s?wd=php';

// 发送 HTTP 请求获取网页源代码
$html = file_get_contents($url);

// 解析网页源代码，提取所需数据
$doc = new DOMDocument();
@$doc->loadHTML($html);
$xpath = new DOMXPath($doc);
$nodes = $xpath->query('//h3[@class="t"]/a');

// 存储数据，并继续爬取下一个 URL
$fp = fopen('result.csv', 'w');
foreach ($nodes as $node) {
  $title = $node->nodeValue;
  $link = $node->getAttribute('href');
  fputcsv($fp, [$title, $link]);
}
fclose($fp);
?>

The above code first defines the target URL to be crawled, and then Use the file_get_contents() function in PHP to send an HTTP request and obtain the source code of the web page. Next, use the DOMDocument class and the DOMXPath class to parse the web page source code and extract the data we need. Finally, use the fputcsv() function to write the data to a CSV file.

4. Run the web crawler

After completing the code writing, we can run the script in the command line to automatically obtain the title and URL in the Baidu search results page and write it into a CSV file. The specific operations are as follows:

1. Open the command line window;
2. Enter the directory where the script is located;
3. Run the script, the command is php spider.php；
4. Wait for the script to complete.

5. Summary

This article introduces how to use PHP to develop a simple web crawler and realize the function of automatically obtaining network data. Of course, this is just a simple sample code, and actual web crawlers may be more complex. But no matter what kind of web crawler we are, we should abide by laws, regulations and ethics, and do not engage in illegal or harmful behaviors.

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