$re = '/\.(?=(.*)\b(?:19[2-9]|20[0-2])\d\b)/m';
$str = 'This.Is.The.Movie.Title.1930.details.of
This.Is.The.Movie.Title.2013.details
This.Is.The.Movie.Title.1919.details.of (year too early)
This.Is.The.Movie.Title.2030.details.of (year too late)
This.Is.The.Movie.Title.201.details.of (too few year digits)
This.Is.The.Movie.Title.20000.details.of (too many year digits)
';
$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