$re = '/^-{2}\b[a-z][a-z\d]{2,}\b(-{1}[a-z\d]+)*$/m';
$str = '--valid
--th1s-is-also-val1d
--match-this-option-as-well
--9this-is-invalid-because-of-the-leading-digit
--this--is--invalid--because--of--word--wrapping--by--multiple--hyphens
--this-should-also-fail-because-of-the-trailing-hyphen-
-A -g -1 -Ag1 --valid --th1s-is-also-val1d --match-this-option-as-well --9this-is-invalid-because-of-the-leading-digit --this--is--invalid--because--of--word--wrapping--by--multiple--hyphens --this-should-also-fail-because-of-the-trailing-hyphen- --load-file="ReAdMe2.TxT"';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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