Square brackets tags

Hi All, I need to write a PHP extension or a PHP template system (this is the question) to parse some commands enclosed in square brackets inside web pages. Please note that the commands are in the form [command1] and not <?php [command1] ?>. I want use PHP because these commands needs to be remapped with a "web oriented" language. Is it technically possible to remap these square brackets tags to php? And if yes, what is the best way? A custom template system or a C PHP extension? Thanks a lot. Best regards, Marco Bambini Italy