perhaps but it's not clear cut.
the bourne shell was quite tidy, but as with many hand-written
recursive descent implementations, it did cheat a few times.
i did do a yacc grammar for its language for a clone, based originally
on the BSTJ paper without sight of the code, but that grammar had to
be weakened in several places, with help from the scanner as i recall,
in order to handle `real' bourne shell scripts when i finally
had access to the bourne implementation and enough real shell scripts.
i'd be more precise but it must be a good 25 years or so
later, and i can't remember the details; not least because
i've moved on and i've got plenty of non-70's things to remember.
(that isn't to suggest that earlier things weren't much better
than some current `inventions', but that's perhaps not so
much a commendation of the old as
a condemnation of the self-styled `new'.