Chapter 9 is a continuation of chapter 8: shell scripting tools.
It also talks about regular expressions, grep, sed and awk.
Nothing that different from Unix.

The chapter ends with examples of file servers.
File server for archives (tarfs) is very interesting. And plan9's regular interface for archiving commands (compared to the multitude of interfaces of zip(1), tar(1), gzip(1), etc of UNIX) is something I miss on Unix.
I actually use plan9port's zip(1) and tar(1) on my OpenBSD rather than the default ones.

The tenth chapter begins by introducing the concepts of locks, critical region, mutual exclusion, etc.
Most of the chapter is about the theory of synchronization and locking (which is expected for a book for a uni course on operating systems).

The chapter ends by introducing how to implement semaphores in Plan 9.