$re = '/^(\d+).([^:]+):([^:]+):(.*?)(?:\n\n|\Z)/ms';
$str = '1. Food : Cake : Baked sweet food made from flour, sugar and other ingredients.
2. Electronics : Computer : A machine to carry out a computer programming operation.
Computers mainly consists of a CPU, monitor, keyboard and a mouse.
3. Automobile : Car : Car is a four wheeled motor vehicle used for transportation.';
preg_match_all($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