$re = '/roll (\d+)d(\d+)([\+-]\d+)?$/i';
$str = 'roll 1d10
roll 1d100
roll 1d20
roll 1d1234
roll 1d20+1
roll 1d20-1
roll 1d20*1
roll 1d20a1
';
preg_match_all($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