How to use PHP to implement a crawler and capture data

With the continuous development of the Internet, a large amount of data is stored on various websites, which is of great value to business and scientific research. However, these data are not necessarily easy to obtain. At this point, the crawler becomes a very important and effective tool, which can automatically access the website and capture data.

PHP is a popular interpreted programming language. It is easy to learn and has efficient code. It is suitable for implementing crawlers.

This article will introduce how to use PHP to implement crawlers and capture data from the following aspects.

1. How the crawler works

The main workflow of the crawler is divided into three parts: sending requests, parsing pages and saving data.

First, the crawler will send a request to the specified page, and the request contains some parameters (such as query string, request header, etc.). After the request is successful, the server will return an HTML file or data in JSON format, which is the target data we need.

Then, the crawler will parse the data and use regular expressions or parsing libraries (such as simple_html_dom) to extract the target data. Usually, we need to save the extracted data in a file or database.

2. Use PHP to implement a crawler

Below, we will use an example to explain in detail how to use PHP to implement a crawler.

For example, if we need to crawl the video information of a certain UP host from station B, we first need to determine the web page address (URL) to be crawled, and then use the CURL library in PHP to send a request and obtain the HTML file. .

<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://space.bilibili.com/5479652");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
curl_close($ch);
echo $output;
?>

In the above code, the curl_init() function is used to initialize the CURL library, and the curl_setopt() function is used to set some request parameters, such as the requested URL address, whether to obtain the returned HTML file, etc. The curl_exec() function is used to send requests and get results, and the curl_close() function is used to close the CURL handle.

Note: The anti-crawling mechanism of station B is relatively strict, and some request header parameters need to be set, such as User-Agent, etc. Otherwise, a 403 error will be returned. You can add User-Agent, Referer and other parameters in the request header, as shown below:

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36',
    'Referer: https://space.bilibili.com/5479652'
));

After the request parameters are set, you can use regular expressions or DOM (Document Object Model) parsing to extract the target data. Take DOM parsing as an example:

$html = new simple_html_dom();
$html->load($output);
$title = $html->find('meta[name=description]', 0)->content;
echo $title;

In the above code, we use the simple_html_dom parsing library to parse the obtained HTML file, find the target tag by using the find() function and CSS selector, and finally, output the obtained Target data (some personal information of the UP owner).

3. Common problems and solutions

In the process of implementing crawlers, you will encounter the following common problems:

1. Website anti-crawling mechanism Resulting in the inability to access or obtain data normally

Common anti-crawling mechanisms include IP blocking, cookie restrictions, User-Agent blocking, etc. In this case, you can consider using proxy IP, automatically obtaining cookies, etc. to avoid the anti-crawling mechanism.

2. The crawling speed is too slow

The crawling speed is too slow usually due to a slow network connection or a bottleneck in the crawling code. You can consider using multi-threaded crawling, using cache and other methods to improve the crawling speed.

3. The target data format is not fixed

When crawling different websites, the format of the target data may be different. For such situations, you can use methods such as conditional statements and regular expressions to deal with it.

4. Summary

This article introduces through examples how to use PHP to implement crawlers and capture data. It also proposes some solutions to some common problems. Of course, there are many other techniques and methods that can be applied to crawlers, which need to be continuously improved through your own practice. Crawler technology is a complex and in-demand skill. I believe this article can help readers get started with crawlers and open up a new field of automated data extraction results.

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