$re = '/<!-- message -->([\s\S]*)<!-- \/ message -->/m';
$str = '<!-- message -->
<div><b><font size="6"><font color="Red">Bilim ve Teknik dergisi Mayıs 2019 Sayısı Pdf</font></font></b><br />
<br />
<img src="https://scontent-dus1-1.xx.fbcdn.net/v/t1.0-9/59069640_871111339894885_8805863518755618816_n.jpg?_nc_cat=109&_nc_ht=scontent-dus1-1.xx&oh=2a71d0bc34cda6b45404c30624c75046&oe=5D6C1B30" border="0" alt="" /><br />
<br />
<b><font size="5"><a href="https://yadi.sk/i/oMnXUgBtTqKopg?fbclid=IwAR3KPXInlWCKFXuTKP1AU1VQGdsgvcDLdV9Px6YGOn3aU1tqAFz4Zo2J6PY" target="_blank">https://yadi.sk/i/oMnXUgBtTqKopg?fbc...1tqAFz4Zo2J6PY</a></font></b></div>
<!-- / message -->';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php