$re = '/(nazwa.*rozmiar\n)([\s\w\n]*)([-]{26})/m';
$str = 'nazwa plik rozmiar
progra exe 3560k
obraz gif 500k
obraz1 gif 500k
obraz2 gif 1500k
obraz3 gif 2500k
obraz4 gif 3500k
tekst txt 20k
--------------------------';
$subst = "$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