How does PHP perform web scraping and data scraping?

PHP is a server-side scripting language that is widely used in fields such as website development and data processing. Among them, web crawling and data crawling are one of the important application scenarios of PHP. This article will introduce the basic principles and common methods of how to crawl web pages and data with PHP.

1. The principles of web crawling and data crawling
Web page crawling and data crawling refer to automatically accessing web pages through programs and obtaining the required information. The basic principle is to obtain the HTML source code of the target web page through the HTTP protocol, and then extract the required data by parsing the HTML source code.

2. PHP web page crawling and data crawling methods

1. Use the file_get_contents() function
   The file_get_contents() function is a core function of PHP that can obtain and return Specify the HTML source code of the URL. The method of using this function to crawl web pages is as follows:

$url = "URL of the target web page";
$html = file_get_contents($url);
echo $html;
?>
In the above code, the $url variable stores the URL of the target web page. The HTML source code of the web page is assigned to the $html variable through the file_get_contents() function, and then the echo statement is used. output.

2. Using cURL library
   cURL is a powerful PHP library for data transmission, which can be used to implement more complex web page crawling and data crawling functions. The cURL library supports multiple protocols such as HTTP, HTTPS, FTP and SMTP, and has rich functions and configuration options. The method of using cURL to crawl web pages is as follows:

$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, "URL of the target web page") ;
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$html = curl_exec($curl);
curl_close($curl);
echo $html;
?>
In the above code, a cURL handle is first initialized through the curl_init() function, and then the cURL URL and other options are set through the curl_setopt() function, including the CURLOPT_RETURNTRANSFER option, which is used to return the obtained web page content instead of outputting it directly. Finally, use the curl_exec() function to execute the cURL request and assign the obtained HTML source code of the web page to the $html variable.

3. Use third-party libraries and tools
   In addition to the above two methods, you can also use third-party libraries and tools to crawl web pages and data. For example, Goutte is a PHP library based on the Guzzle HTTP client, specifically used for web scraping and data scraping. Goutte provides a simple API and rich functions, which can easily perform operations such as web form submission and link jump. In addition, there are some mature web crawler frameworks, such as Scrapy, etc., which can be written in Python.

3. Precautions and practical experience

1. Abide by the rules and laws of the website
   When crawling web pages and data, you should abide by the rules of the website and laws, unauthorized scraping is prohibited to avoid legal disputes. You can check the website's robots.txt file to understand the website's crawling rules and avoid visiting pages that are prohibited from crawling.
2. Set appropriate delay and concurrency control
   In order to avoid excessive load pressure on the target website and prevent the IP from being blocked, appropriate delay and concurrency control should be set. You can use the sleep() function to set the delay time and control the time interval between two crawl requests; use multi-threading or queue technology to control the number of concurrent requests to prevent too many requests from being initiated at the same time.
3. Data processing and storage
   The obtained web page data usually needs to be processed and stored. Tools such as regular expressions, DOM parsers, or XPath parsers can be used for data extraction and extraction. The processed data can be stored in the database or exported to other formats (such as CSV, JSON, etc.) for subsequent analysis and processing.

Summary:
PHP provides a variety of ways to implement web page crawling and data crawling functions. Commonly used ones include the file_get_contents() function and the cURL library. Additionally, third-party libraries and tools can be used for more complex web scraping and data scraping. When crawling web pages and data, you need to abide by the rules and laws of the website, set appropriate delay and concurrency controls, and process and store the acquired data reasonably. These methods and practical experience can help developers perform web page crawling and data crawling tasks more efficiently and stably.

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