$re = '/(?:\G(?<!\A)\||(?:\[x]\s[?!]?\s*\|?))\K([^|\n]*)/m';
$str = '
- [x] Example of a completed task.
- [x] ! Example of a completed task.
- [x] ? Example of a completed task.
| | Task name | Plan | Actual | File |
| :---- | :-------------------------------------- | :---------: | :---------: | :------------: |
| [x] | Task one with a reasonably long name. | 08:00-08:45 | 08:00-09:00 | [[task-one]] |
| [x] ! | Task two with a reasonably long name. | 09:00-09:30 | | [[task-two]] |
| [x] ? | Task three with a reasonably long name. | 11:00-13:00 | | [[task-three]] |
';
preg_match_all($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