$re = '/https?:\/\/([^\/]*)(?=[0-9\.]*)(.*)\/.*$/m';
$str = 'https://download.virtualbox.org/virtualbox/6.1.36/VirtualBox-6.1.36-152435-Win.exe
https://github.com/notepad-plus-plus/notepad-plus-plus/releases/download/v8.4.4/npp.8.4.4.Installer.x64.exe';
$subst = "$1$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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