If status is a string, this function prints the status just before exiting.
If status is an integer, that value will also be used as the exit status. Exit statuses should be in the range 0 to 254, the exit status 255 is reserved by PHP and shall not be used. The status 0 is used to terminate the program successfully.
PHP >= 4.2.0 does NOT print the status if it is an integer.
$filename = '/path/to/data-file';
$file = fopen($filename, 'r')
or exit("unable to open file ($filename)");
//exit program normally
//exit with an error code
Because this is a language construct and not a function, it cannot be called using variable functions
This language construct is equivalent to die().