This interactions helps students to understand that, whenever they see "command not found", it's very likely that they've typed something incorrectly. Understanding what Unix cannot do is a great first step toward understanding what it can do.
Throughout the 36 chapters of this book, the nature of Unix is built up a few commands and concepts at a time. Interspersed with practical examples, the explanations are both clear and concise. Simple commands, navigating around the file system, experiencing different types of links, grasping relative and absolute paths, looking at portions of files with the less command, understanding key directories, using wildcards, pipes, and filters ... Each lesson is a small step forward with good command examples and just enough explanation to hold the new material together.
Then, in Chapter 7 (Seeing the World as the Shell Sees It), the book steps back and covers the various types of expansion, quoting and escapes. The nature of the Linux command line begins to show itself in increasing dimension.
The book then moves through permissions, identities, the concept of privilege, processes, and performance. It explains the use of ctrl-C, background and foreground tasks, the kill command, and what signals are and how they are used.
By the time readers get through Chapter 10, a great foundation for making sense of the command line has been built up one concept at a time.
By Part 2, readers are ready to move up a level. This part of the book discusses the shell environment and explains important files like .bashrc. Readers soon move to learning vi and customizing their command prompts.
Part 3 ups the ante quite a bit with package management, storage media, networking basics, searching for files, archiving files and making back ups. By this point in the book, our neophyte users are jumping ahead into serious Unix administration.
Readers get to Chapter 19 before hitting regular expressions, the grep command, and anchors. This is the kind of material that, presented too early, intimidates new Unix users. By Chapter 20, the book has moved to text processing -- sorting, pasting, joining and changing text with the likes of cut. Readers are looking at file commonalities and differences with commands like comm and diff. They are using sed and spell checking with aspell. They are formatting output, numbering lines, printing and compiling simple programs.
Part 4 has readers finally writing scripts, adding comments, setting permissions, and using indentation to enhance readability. By this point, the chmod command and the importance of the $PATH variable make total sense. Readers are introduced to good programming techniques, the value of comments, the use of variables and constants.