$re = '/[!"]+([^!"]+)[!"]/m';
$str = '!img2.png|width=83.33333333333334%!
"!robot (f05f0216-caf4-4543-a630-99c2477849d5).png|width=400,height=400!"
"!abc.pdf|width=200!"
"!dfe.xlx"
!"dfe.xlx!"
';
preg_match_all($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