$re = '`^(?:ktm(?:-e|-(?:[^e\W]|e[^d\W])\w*)*-)?abcd(?:-e|-(?:[^e\W]|e[^d\W])\w*)*$`m';
$str = 'abcd-st-ed-qrew
ktm-ewe-abcd-st-ed-qrew
abcd-st-wer-qrew-wabe
ktm-ewe-abcd-st-qrew-qrrt
';
preg_match_all($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