Colin,

the first few chapters of "MPE/iX Shell and Utilities User's Guide"
provide a fairly reasonable intro to Posix Shell and utils (make sure
to pick the User's Guide, not the Reference Manual).

Unfortunately I cannot find a copy at http://docs.hp.com at present.
You might want to check yourself or use the feedback button there.

I also recall having seen intro/tutorial papers on Posix-for-MPE-ers
at http://www.smga3000.com/papers&articles.html (-> technical papers)
as well as http://www.robelle.com/library/tutorials/ (-> scroll down
to HP-UX for MPE Users).

Lars.