$re = '/^(\d+\s?(years|year|months|month|weeks|week|days|day|hours|hour|minutes|minute|min|mins|seconds|second|sec|secs|y|M|w|d|h|m|s)\s?)+$/i';
$str = '1y 5M 3w 5d 23h 59m 50s';
preg_match($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