Mit dieser Function kann man (externe) HTML Seiten einlesen

//function to get the remote data
function url_get_contents ($url) {
    if (function_exists('curl_exec')){ 
        $conn = curl_init($url);
        curl_setopt($conn, CURLOPT_SSL_VERIFYPEER, true);
        curl_setopt($conn, CURLOPT_FRESH_CONNECT,  true);
        curl_setopt($conn, CURLOPT_RETURNTRANSFER, 1);
        $url_get_contents_data = (curl_exec($conn));
        curl_close($conn);
    }elseif(function_exists('file_get_contents')){
        $url_get_contents_data = file_get_contents($url);
    }elseif(function_exists('fopen') && function_exists('stream_get_contents')){
        $handle = fopen ($url, "r");
        $url_get_contents_data = stream_get_contents($handle);
    }else{
        $url_get_contents_data = false;
    }
return $url_get_contents_data;
} 

So sieht es dann in Aktion aus:

$data = url_get_contents("http://www.google.com");
if($data){
//Do Something....
}

eingelesenen HTML Quelltext anzeigen lassen:

echo "<pre>".htmlentities($data)."</pre>";

<?php
// to retrieve selected html data, try these DomXPath examples:
 
$file = $DOCUMENT_ROOT. "test.html";
$doc = new DOMDocument();
$doc->loadHTMLFile($file);
 
$xpath = new DOMXpath($doc);
 
// example 1: for everything with an id
//$elements = $xpath->query("//*[@id]");
 
// example 2: for node data in a selected id
//$elements = $xpath->query("/html/body/div[@id='yourTagIdHere']");
 
// example 3: same as above with wildcard
$elements = $xpath->query("*/div[@id='yourTagIdHere']");
 
if (!is_null($elements)) {
  foreach ($elements as $element) {
    echo "<br/>[". $element->nodeName. "]";
 
    $nodes = $element->childNodes;
    foreach ($nodes as $node) {
      echo $node->nodeValue. "\n";
    }
  }
}
?>

Hier noch mal ein Link zu einer Diskussion über das Thema:
https://www.php.de/forum/webentwicklung/php-einsteiger/1560550-wert-von-bis-innerhalb-eines-tags-aus-einer-textdatei-auslesen