grep Pocket Reference
John Bambenek & Agnieszka Klus
Classic Shell Scripting
Arnold Robbins & Nelson H. F. Beebe
Learning the bash Shell, 3rd Edition
Cameron Newham
Linux System Programming
Robert Love
Linux in a Nutshell
Ellen Siever, Stephen Figgins, Robert Love & Arnold Robbins
UNIX Power Tools, 3rd Edition
Jerry Peek, Shelley Powers, Tim O’Reilly & Mike Loukides