PHP Linux script operation practice: web crawler development guide

PHP Linux Script Operation Practice: Web Crawler Development Guide

Introduction:
With the rapid development of the Internet, information has exploded, and people are acquiring information. The demand is also growing. As an automated tool, web crawlers can help us obtain the required information from the Internet quickly and efficiently, and have received widespread attention and application. This article will introduce how to use PHP and Linux script operations to develop web crawlers, and provide specific code examples to help readers quickly get started with the development of web crawlers.

1. Environment preparation:
Before starting the development of web crawlers, we need to prepare the following environment:

1. A server with a Linux operating system installed;
2. For PHP environment, you can check whether it has been installed by entering "php -v" in the terminal. If it is not installed, you can install it through "apt-get install php";
3. To install the curl extension, you can install it through "apt-get install php-curl";
4. Install the wget tool, It can be installed via "apt-get install wget".

2. Crawl web page content:
To develop a web crawler, the most basic task is to obtain content from a specified web page. The following is a simple example to obtain the content of a specified web page through PHP's curl extension:

<?php
// 创建一个curl句柄
$ch = curl_init();

// 设置curl的参数
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

// 执行请求并获取返回的内容
$result = curl_exec($ch);

// 关闭curl句柄
curl_close($ch);

// 输出获取到的内容
echo $result;
?>

In the above code, first use the curl_init() function to create a curl handle, and then use the curl_setopt() function to set it The web page address that needs to be accessed and the format of the returned content. Finally, use the curl_exec() function to execute the request and obtain the returned content. Finally, use the curl_close() function to close the curl handle. Finally, the obtained content is output through the echo statement.

3. Parse the content of the web page:
Obtaining the content of the web page is only the first step. Next, we need to extract the data we need from it. Normally, we can use regular expressions to extract data. Here is a simple example:

<?php
// 获取网页内容
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
curl_close($ch);

// 使用正则表达式提取标题
preg_match("/<title>(.*?)</title>/", $result, $matches);
$title = $matches[1];

// 使用正则表达式提取正文内容
preg_match("/<div class="content">(.*?)</div>/", $result, $matches);
$content = $matches[1];

// 输出提取到的标题和正文内容
echo "标题：".$title."
";
echo "正文内容：".$content."
";
?>

In the above code, we use curl to obtain the content of the web page and extract it separately through regular expressions. The title and text content. Finally, the extracted data is output through the echo statement.

4. Save data:
After obtaining the data, we usually save it to a database or file for subsequent analysis and use. The following is an example of saving crawled data to a file:

<?php
// 获取网页内容
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://www.example.com/");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result = curl_exec($ch);
curl_close($ch);

// 使用正则表达式提取标题
preg_match("/<title>(.*?)</title>/", $result, $matches);
$title = $matches[1];

// 使用正则表达式提取正文内容
preg_match("/<div class="content">(.*?)</div>/", $result, $matches);
$content = $matches[1];

// 将数据保存到文件中
$file = fopen("data.txt", "w");
fwrite($file, "标题：".$title."
");
fwrite($file, "正文内容：".$content."
");
fclose($file);

echo "数据已保存到文件 data.txt 中
";
?>

In the above code, we created a file named data.txt and wrote the extracted data through the fwrite() function. into the file, and finally close the file through the fclose() function. Finally, a prompt of successful saving is output through the echo statement.

Summary:
Through the introduction of this article, we learned how to use PHP and Linux scripts to develop web crawlers. First, we learned how to use curl extension to obtain the content of a specified web page; then, we learned to use regular expressions to extract the required data from the web page content; finally, we learned how to save the crawled data to a file middle. I believe that through the practice of these sample codes, readers can master basic web crawler development skills and further in-depth learning and exploration.

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