Someone turned me onto a Humble Bundle of O'Reilly Linux/Unix books. $15 gets you 15 books.

https://www.humblebundle.com/books/linux-unix-oreilly-books

Here is the list of filenames, not titles, but I'm sure you can sort it all out.

• bashcookbook
• classicshellscripting
• effectiveawk
• greppocketref
• introducingregularexpressions
• learninggnuemacs_3rdedition
• learningthebashshell_3rdedition
• learningtheviandvimeditors_7thedition
• linuxdevicedrivers
• linuxinanutshell
• linuxpocketguide_3rdedition
• linuxsystemprogramming
• masteringregularexpressions
• sedandawk
• unixpowertools

--
~elb