The Linux Command Line, 5th Edition
Best Book for Linux Beginners
The Linux Command Line is the work of William Shotts and a number of other contributors from http://linuxcommand.org. Shotts’ pleasant writing style and long experience provide the best possible book for any Linux command line beginner. In fact, it is currently the only Linux book available that covers Bash 4+ including such things as associative arrays. This puts TLCL well beyond established books such as Learning Bash (O’Reilly) which has grown far too out of date to be of any value.
TLCL does, however, contain several glaring flaws that can be summarized best by the fact that it covers nroff. This set of annotations is therefore intended to make up for these flaws without dismissing the book entirely, which unfortunately cannot be fixed because of another major flaw: it’s license, which prevents fixes due to its “no derivative works” clause defeating the main reason for creating open content in the first place.
Eventually TLCL will be replaced with this knowledge app from the RWX community that will eventually cover everything in TLCL without qualifying as a “derivative work” and allow full forks without penalty. The annotations below are not a derivative work and are no different than anyone else’s public notes taken and shared while reading the book.
Introduction
Make sure to read all of the Introduction. It provides an excellent answer to why you should learn the command line.
Chapter 24: Writing Your First Script
Finally we get to write some shell code.
Don’t confuse the term shell code from pentesting with shell script.
Bash is Usually the Default Command Line
Bash has been the default shell for Linux for several decades but was replaced as the system startup scripting language by Dash on most Linux distributions some time ago. But Bash remains the default interactive shell assigned to new users.
What about Zsh?
Don’t use it.
What about Dash?
/bin/sh is symbolically linked /bin/dash, a light-weight, POSIX-compliant shell that runs much more quickly for use in the Linux startup process.
Despite the claim on Dash’s home page that it is the Linux shell. The Arch distro symlinks to /bin/bash instead.
Bash History
Bash code is unlike most other coding languages because it evolved from Bourne Shell which was released in 1979.
Bourne Again Shell has added stuff from lots of shells since that time including primarily Korn Shell, which came out in 1983. The first version of Bash was released in 1989. And the latest significant Bash release (version 5.0) came out on January, 2019. More significantly, however, was the release of Bash 4.0, which came out in February, 2009 and included Bash associative arrays, which are covered by the 5th edition of this book.
This book is the only book available anywhere that covers Bash 4+ associative arrays, which is why it was picked even over Learning Bash from O’Reilly.
Bash is Interpreted
This chapter jumps right into how to use Bash but it is worth understanding that Bash is an interpreted language and that the shebang line tells the operating system to send the script file to the /bin/bash binary command which interprets it into system calls that bash itself executes. There is no intermediary bytecode created.
PATH Environment Variable
These days ~/.local/bin is the preferred place to hide your local bin directory — usually by symlinking to a directory in your personal dotfiles config.
You might consider adding the following script to your ~/.local/bin/ directory or adding the echo line as an alias in ~/.bashrc file in order to simplify reading your PATH.
Script Version
#!/bin/bash
echo -e ${PATH//:/\\n}Bash Alias
alias path="echo -e ${PATH//:/\\n}"