$re = '`\bkey="((?:ktm(?:-e|-(?:[^e\W]|e[^d\W])\w*)*-)?abcd(?:-e|-(?:[^e\W]|e[^d\W])\w*)*)"`m';
$str = ' 1. object{one="ab-vwxc",two="value1",key="abcd-eest-ed-xyz-bnn",four="obsoleteValues"}
2. object{one="ab-vwxc",two="value1",key="abcd-eest-xyz-bnn",four="obsoleteValues"}
3. object{one="ab-vwxc",two="value1",key="abcd-eest-xyz-bnn-ed",four="obsoleteValues"}
4. object{one="ab-vwxc",two="value1",key="abcd-e-xyz-bnn",four="obsoleteValues"}
5. object{one="ab-vwxc",two="value1",key="ktm-bb-abcd-e-xyz-bnn",four="obsoleteValues"}
6. object{one="ab-vwxc",two="value1",key="ktm-bb-abcd-ed-xyz-bnn",four="obsoleteValues"}
';
preg_match_all($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