$php -r '$foo = get_defined_constants(); var_dump($foo);' array(370) {["E_ERROR"]= int(1) ["E_WARNING"]= int(2) ["E_PARSE"]= int(4) ["E_NOTICE"]= int(8) ["E_CORE_ERROR"]= [...]
This option allows execution of PHP right from within the command line. The PHP start and end tags (?php and?) are not needed and will cause a parser error if present.