$re = '/(?<!\|\s)(((?:\[x]\s[!]?))\K[^[\n]+)/m';
$str = '- [x] Example task. | Task ends. [x] Another task [x] Another task.
- [x] ! Example task. | This ends. [x] ! Another task.
This is a sentence. [x] Task is here.
Other text. Another [x] ! Task is here.
Must not match in the table.
| | Task name | Plan | Actual | File |
| :---- | :-------------| :---------: | :---------: | :------------: |
| [x] | Task example. | 08:00-08:45 | 08:00-09:00 | [[task-one]] |
| [x] ! | Task example. | 08:00-08:45 | 08:00-09:00 | [[task-one]] |
';
preg_match_all($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