* causes OSCLI to handle the rest of the line. Dot was an abbreviation for Cat, short for catalogue, IOW ls(1). P. is presumably at the BASIC prompt; it abbreviated the PRINT keyword. OPT had the filing system set some options stored on the current disk; 4 was how to handle the !Boot file. 0, do nothing; 1, load; 2, run; 3, exec, i.e. pretend it had been typed.