An article explaining in detail how to write a crawler using PHP

Speaking of crawlers, everyone's first impression will be Python, but not everyone knows Python, so can other languages ​​be used to write crawlers? Of course it is possible. Let’s introduce how to use PHP to write a crawler.

Get the html content of the page

1. Use the function file_get_contents to read the entire file into a string.

file_get_contents(path,include_path,context,start,max_length);
file_get_contents('https://fengkui.net/');

In this way, the html content of the entire page can be read into a string, and then parsed.

2. Use CURL to make a request and obtain the html

/**
 * [curlHtml 获取页面信息]
 * @param  [type] $url [网址]
 * @return [type]      [description]
 */
function curlHtml($url)
{
    $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_URL            => "{$url}",
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_ENCODING       => "",
        CURLOPT_MAXREDIRS      => 10,
        CURLOPT_TIMEOUT        => 30,
        CURLOPT_HTTP_VERSION   => CURL_HTTP_VERSION_1_1,
        CURLOPT_CUSTOMREQUEST  => "GET",
        CURLOPT_HTTPHEADER     => array(
            "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8",
            "Accept-Encoding: gzip, deflate, br",
            "Accept-Language: zh-CN,zh;q=0.9",
            "Cache-Control: no-cache",
            "Connection: keep-alive",
            "Pragma: no-cache",
            "Upgrade-Insecure-Requests: 1",
            "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36",
            "cache-control: no-cache"
        ),
    ));
    curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
    $response = curl_exec($curl);
    $err = curl_error($curl);
    curl_close($curl);
    if ($err) return false;
    else return $response;
}

Using Curl we can perform other operations, such as simulating browser login and other advanced operations.

Parse the page HTML and obtain the required data

1. Regularly obtain the content

/**
 * [get_tag_data 使用正则获取html内容]
 * @param  [type] $html  [爬取的页面内容]
 * @param  [type] $tag   [要查找的标签]
 * @param  [type] $attr  [要查找的属性名]
 * @param  [type] $value [属性名对应的值]
 * @return [type]        [description]
 */
function get_tag_data($html,$tag,$attr,$value){
    $regex = "/<$tag.*?$attr=\".*?$value.*?\".*?>(.*?)<\/$tag>/is";
    preg_match_all($regex,$html,$matches,PREG_PATTERN_ORDER);
    $data = isset($matches[1][0]) ? $matches[1][0] : &#39;&#39;;
    return $data;
}
$str = &#39;<div class="feng">冯奎博客</div>&#39;;
$value = get_tag_data($str, &#39;div&#39;, &#39;class&#39;, &#39;feng&#39;);

2. Use Xpath to parse the data

XPath is the XML path language (XML Path Language), which is a language used to determine the location of certain parts of an XML document. See Baidu Encyclopedia (XPath) for specific usage methods and related introductions. Usage methods:

/**
 * [get_html_data 使用xpath对获取到的html内容进行处理]
 * @param  [type]  $html [爬取的页面内容]
 * @param  [type]  $path [Xpath语句]
 * @param  integer $tag  [类型 0内容 1标签内容 自定义标签]
 * @param  boolean $type [单个 还是多个（默认单个时输出单个）]
 * @return [type]        [description]
 */
function get_html_data($html,$path,$tag=1,$type=true)
{
    $dom = new \DOMDocument();
    @$dom->loadHTML("<?xml encoding=&#39;UTF-8&#39;>" . $html); // 从一个字符串加载HTML并设置UTF8编码
    $dom->normalize(); // 使该HTML规范化
    $xpath = new \DOMXPath($dom); //用DOMXpath加载DOM，用于查询
    $contents = $xpath->query($path); // 获取所有内容
    $data = [];
    foreach ($contents as $value) {
        if ($tag==1) {
            $data[] = $value->nodeValue; // 获取不带标签内容
        } elseif ($tag==2) {
            $data[] = $dom->saveHtml($value);  // 获取带标签内容
        } else {
            $data[] = $value->attributes->getNamedItem($tag)->nodeValue; // 获取attr内容
        }
    }
    if (count($data)==1) {
        $data = $data[0];
    }
    return $data;
}

Recommended learning: "PHP Video Tutorial"

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