How to write a crawler program using PHP

In the Internet age, information is like an endless river, pouring out continuously. Sometimes we need to grab some data from the Web for analysis or other purposes. At this time, the crawler program is particularly important. Crawler programs, as the name suggests, are programs used to automatically obtain the content of Web pages.

As a widely used programming language, PHP has advanced Web programming technology and can well solve the problem of crawler programming. This article will introduce how to use PHP to write crawler programs, as well as precautions and some advanced techniques.

1. Building a basic crawler framework

The basic process of a crawler is:

• Send an HTTP request;
• Get the response and Analyze;
• Extract key information and process it.

To build a basic crawler framework, we need to use cURL and DOM related functions in PHP. The specific process is as follows:

1.1 Send HTTP request

Use cURL to send HTTP requests in PHP. You can call the curl_init() function to create a new cURL session and set the corresponding parameters through curl_setopt(). (Such as URL address, request method, etc.):

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
// 其他参数设置
$response = curl_exec($ch);
curl_close($ch);

1.2 Get the response and parse it

After getting the response, we need to parse the HTML data. This process requires the use of DOM related functions, because HTML documents are tree structures composed of tags, attributes, text, etc., and these data can be accessed and processed through DOM functions. The following is a sample code for parsing HTML with DOM:

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

1.3 Extract key information and process it

The last step is to extract the target data and process it. DOM provides some methods to locate and extract elements such as tags, attributes, and text. We can use these methods to extract the information we need, such as:

$xpath = new DOMXPath($dom);
$elements = $xpath->query('//div[@class="content"]');
foreach ($elements as $element) {
    // 其他处理代码
}

2. Case Analysis

Below we use an example to learn how to use PHP to write a crawler program.

2.1 Analyze the target website

Suppose we want to crawl the articles in the "Connotation Jokes" section from the Encyclopedia of Embarrassing Things. First we need to open the target website and analyze its structure:

• Target URL: https://www.qiushibaike.com/text;
• Target content: paragraph text and its evaluation , number of likes.

2.2 Writing a crawler program

With the above analysis, we can start writing a crawler program. The complete code is as follows:

<?php
// 目标URL
$url = "https://www.qiushibaike.com/text";

// 发送HTTP请求
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$ch_data = curl_exec($ch);
curl_close($ch);

// 解析HTML
$dom = new DOMDocument();
@$dom->loadHTML($ch_data);

// 提取目标数据
$xpath = new DOMXPath($dom);
$elements = $xpath->query('//div[@class="content"]');
foreach ($elements as $element) {
    $content = trim(str_replace(" ", "", $element->nodeValue));
    echo $content . "
";
}
?>

Through the above code, we can get a simple version of the crawler program, which can grab connotative paragraphs from the target website and extract them for printing.

3. Notes and advanced techniques

When using PHP to write crawler programs, you need to pay attention to the following:

• Follow the robots of the target website .txt protocol, do not abuse crawlers and cause the website to crash;
• When using tools such as cURL, you need to set header information such as User-Agent and Referer to simulate browser behavior;
• The obtained The HTML data is properly encoded to prevent garbled code problems;
• Avoid frequent visits to the target website. If you operate too frequently, the IP address may be blocked by the website;
• Manual intervention is required to obtain verification codes, etc. The content requires the use of advanced skills such as image recognition technology.

Through the above precautions and advanced techniques, we can better cope with different crawler needs and achieve more efficient and stable data collection.

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