$re = '/(?m)^\[([^]]*)\](.*\n?(?!^\[))*/';
$str = '[My Custom Exe][2018-05-24 11:03:01] Starting Process
[My Custom Exe][2018-05-24 11:03:01] Getting config
[My Custom Exe][2018-05-24 11:03:02] Beginning operation
[My Custom Exe][2018-05-24 11:03:02] Could not complete this operation, invalid inputs
[My Custom Exe][2018-05-24 11:03:02] Available inputs are:
- 1: Mode 1
- 2: Mode 2
- 3: Mode 3
- 4: Mode 4
- 5: Mode 5
[My Custom Exe][2018-05-24 11:03:02] Exiting Program';
preg_match_all($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