The PROCEDURE statement for the main procedure can have a parameter list. Such parameters require no special considerations in PL/I. However, you must be aware of any requirements of the invoking program (for example, when not to use such a parameter as the target of an assignment).
When the invoking program is the operating system and when compiled with the SYSTEM(MVS) compiler option:
Tom: proc (Param) options (main);
dcl Param char(100) varying;
storage is allocated only for the current length of the argument.