You can also add commands to the prototype file of the form !PARAM=value. Commands of this form define variables in the current environment. If you have multiple prototype files, the scope of this command is local to the prototype file where it is defined.
The variable PARAM can begin with either a lowercase or uppercase letter, but its value must be known at build time, or the pkgmk command will abort with an error. For more information on the difference between build and install variables, see Package Environment Variables.