Well it sounds like you are ready to storm out of the gates and get your hands dirty. That is great. I have been playing around for years and I have not come across one book that covers all of the bases well. But I can think two books that I have found very useful, one for system administration functions and another that goes into much greater depth on shell scripting.
UNIX system administration handbook
I am using the third edition, I believe that it has been updated since then, also a version that is exclusively for linux has come out from the same group, called of all things:
LINUX system administration handbook
I believe the primary author for the above is Evi Nemeth.
If you are interested only in Linux, I would take a strong look at the Linux text, it covers networking, file systems, how to config for devices. The UNIX version is similar, but it goes over how to accomplish task in solaris and hp-ux as well as linux.
For shell scripting I would recommend:
UNIX shell programming by Stephen Kochan
My version is rather old, but I have found it to be very useful. I beleive that the current version is the 3rd edition, which although I do not have, I have heard very good things about.
A few quick weblinks that you might find useful:
An introduction to unix shell environment
linux system administration (pay attention to the links at the bottom)