I use “Linux” almost exclusively when talking about the operating system surrounding the shell, because

• while Bash is available on all the big platforms, as of 2020 Linux is the most popular platform with professional developers

• “GNU/Linux” never caught on, despite the massive importance of the GNU tools

• Linux is the only Unix–like operating system I’ve used in the last few years

PATH may refer to a variable name, and $PATH definitely refers to a variable value. I will use the latter to avoid any confusion between variables and other things.

[…] means that some of the command output was omitted for brevity. This should be more readable than a bunch of cut, head and tail commands.

Throughout this book, you will see the following typographical conventions that indicate different types of information:

In–line code references will look like this: echo "$SHELL".

Blocks of code look like this:

#!/usr/bin/env bash

Shell sessions include:

• The prompt, which is the string printed before the cursor when starting a new command. It’s set as simply PS1='\$ ' to make it stand out while being short.

• The command itself.

• Continuation indicators, which are the strings printed before every line after the first one in a multi–line command. It’s set to the default, PS2='> '.

• Command standard output and standard error.

Example:

$ cat > credentials.json << 'EOF'

> {"username":"jdoe","password":"sec\\ret"}

> EOF

$ jq . credentials.json

{

  "username": "jdoe",

  "password": "sec\\ret"

}

• cat is the first command, spread over three lines and with no terminal output.

• jq is the second command, followed by its output.

$PS0 is empty. $PS3 and $PS4 are not relevant to this book.

When relevant, shell sessions may include a █ character to indicate the position of the cursor after running the last command.

Tips and tricks look like this:

mkdir is short for “make directory.”

Warnings look like this:

Use More Quotes™!