* 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.

Was P. shorthand for PRINT .? No idea what the other two commands do I think *OPT was for addressing a serial port or the screen but my memory is very hazy.

BBC BASIC on the original RISC PC was my first experience writing code. I think that machine is still in my parents' garage along with the 6 volume BBC BASIC reference manual.

Yes, in BASIC you could enter keywords abbreviated with a . to save typing. The tokeniser would turn it into the byte or two representing PRINT ready for it to be interpreted.

I think you're thinking of the four volume RISC OS Programmers' Manual, plus slim index, that came in a big white cardboard sleeve. Augmented later by a Volume 5 of changes with later OS versions to save re-printing costs. BASIC itself was introduced in the User Guide that came with the machine IIRC and had a one-volume reference manual of its own at additional cost.

Further to other comments, you would never see P. in the output of LIST. It would be expanded automatically to PRINT.

Strictly speaking, it wasn't P. being expanded to PRINT at the time of LIST but the byte representing the tokenised PRINT being expanded then. The P. was turned into that byte earlier.