I'm going to respectfully disagree with you folks complaining. The OP was kind enough to share a link that has several books useful to BSD admins.
Ok I have little more stamina so here are few books I recommend so that you see where I am comming from.
Every study of UNIX should start by reading Kernihan and Pike's master peace
The Unix Programming Environment also available on-line in PDF form
http://cs2.ist.unomaha.edu/~stanw/162/csci4500/UNIXProgrammingEnvironment.pdf
Once you have read through that book you should sit in front a computer running an old fashion UNIX (OpenBSD comes to my mind) and start playing with examples from the book. The natural progress would be reading man pages. UNIX-es typically come with stellar man pages (Solaris and OpenBSD come to mind). My biggest grouch with novice users comes from the fact that they start surfing web from some random information instead of reading man pages. People read man pages! Learn how to use
apropos
command
From there one can expend by picking a specialized books which expands on each chapter of the Kernihan's and Pike's book. For example logical expansion for Chapter 3 which talks about shell programming would be reading
UNIX Shell Programming, Revised Edition
Dec 1, 1989
by
Stephen G. Kochan and
Patrick H. Wood
(stick with older edition to avoid Linux non-sense). Then graduate with something like
The New KornShell Command And Programming Language (2nd Edition)
by
Morris I. Bolsky David G. Korn (Author)
Fourth chapter of Rob Pike's book talks about filters. The basic example of a filter is surprisingly editor ed. Your FreeBSD box should just like mine OpenBSD come with
http://www.verticalsysadmin.com/vi/a_tutorial_introduction_to_the_unix_text_editor.pdf
Read ed man pages. Read ex man pages. Read vi man pages. Then get the following second to none book about vi.
Ultimate Guide to the VI and EX Text Editors
OP listed very nice book for sed
sed & awk (Nutshell Handbooks) 1st edition by Dougherty
Again avoid 2nd edition because for Linux-isims. Also don't learn AWK from that book. Get the best programming book every written.
The AWK Programming language by Al Aho.
At that point one should realize that studying regular expressions is must.
Mastering Regular Expressions 3rd Edition
by
Jeffrey E. F. Friedl (Author) has everything in it from the point of view of a Perl Guru.
I am not sure where I am going with this post as OP wanted essentially advise on the whole UNIX universe. I have to finish somewhere so this is final. If you are system admin no reading is complete without reading one of older non Linux versions of
UNIX and Linux System Administration Handbook
by Evi Nemeth and Garth Snyder
make sure you understand filters and pipes in particular.
If you are kernel hacker Design and Implementation of BSD 4.4 and Bach's
The Design of the UNIX Operating System
Jun 6, 1986
by
Maurice J. Bach
are must