$re = '/(?m)(ERROR[^\n]*)?(?:.|\n)*?(\d{1,3}%),.*?ETA\s(\d\d.)/m';
$str = '1ERROR and a description
Complete: 77%, and ETA 10s';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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