Linux and the Unix Philosophy
@ https://flylib.com/books/en/2.506.1/
Entire book online covering the thought process behind UNIX systems.
Unix philosophy
@ https://en.wikipedia.org/wiki/Unix_philosophy
Wikipedia entry regarding the UNIX philosophy.
The UNIX programming environment
@ https://www.worldcat.org/title/unix-programming-environment/oclc/10269821
Original book describing the various tools and processes on a UNIX system and how to utilise them.