function arasini_al($bas = "", $son = "", $icerik){
    $icerik = ' ' . $icerik;
    $ini = strpos($icerik, $bas);
    if ($ini == 0) return '';
    $ini += strlen($bas);
    $uzunluk = strpos($icerik, $son, $ini) - $ini;
    return substr($icerik, $ini, $uzunluk);
}
    
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://siteadresi");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
$sonuc = curl_exec($ch);
curl_close($ch);

$istenilen_tag = arasini_al('<istenilen_tag_ac>', '</istenilen_tag_kapa>', $sonuc);
echo $istenilen_tag;