Exactly one of the external procedures that is linked into an executable file must specify the main entry point to the program by including the OPTIONS(MAIN) clause on the PROCEDURE statement. This designates that procedure as the main entry point at which execution should begin, after some run-time initialization has been completed. This option must appear even if the entire program is a single procedure contained in a single source file. Failure to specify a main program, or specifying more than one main program, will cause errors to occur during program linkage.
The main procedure is not required to be a PL/I procedure; that is, it can be written in another language.