5. Bash Syntax and Variables

This chapter begins the scripting sequence by showing how Bash parses commands, expands values, stores data, and combines arithmetic with string operations.

• Syntax: Recognize how Bash separates commands, options, and arguments.

• Quoting: Control when spaces, variables, and special characters are interpreted.

• Variables: Store values and expand them safely in scripts.

• Substitution: Use parameter and command substitution to derive script values.

• String and arithmetic operations: Manipulate text and integer values with Bash syntax.

Chapter Video

What are Variables in Bash (5:57) by Microsoft Developer

Hosted on YouTube; property of its original creator, embedded here for educational reference only.

Learning Objectives

By the end of this chapter, you will be able to:

1. Write Bash commands with correct spacing, quoting, and structure.

2. Explain how quoting, escaping, and word splitting affect command safety.

3. Create and run a first Bash script.

Chapter Flow

1. Syntax & Quoting

2. Your First Bash Script

Glossary

#	Term	Explanation
1	Command	A program, shell builtin, function, or alias invoked by name.
2	Argument	A value passed to a command after its name.
3	Option	An argument that modifies command behavior, often beginning with -.
4	Quoting	Syntax that controls how Bash interprets spaces and special characters.
5	Single quotes	Quotes that preserve text literally, including dollar signs.
6	Double quotes	Quotes that preserve spaces while still allowing selected expansions.
7	Escaping	Using a backslash to give a special character a literal meaning.
8	Variable	A named shell value that can be expanded later.
9	Assignment	Setting a variable with syntax such as name=value.
10	Parameter expansion	Using ${...} or $name to retrieve or transform a parameter.
11	Command substitution	Running a command and inserting its output with $(...).
12	Environment variable	A variable exported to child processes.
13	export	A command that places a variable in the environment of child processes.
14	Positional parameter	A script or function argument referenced as $1, $2, and so on.
15	Default value expansion	A parameter expansion that supplies a fallback when a value is unset or empty.
16	Substring expansion	A parameter expansion that extracts part of a string.
17	Arithmetic expansion	The $((...)) syntax used for integer arithmetic.
18	Word splitting	The shell step that splits unquoted expansion results into separate words.
19	Globbing	Filename pattern expansion performed by the shell.
20	String length	The number of characters in a shell value, available with ${#name}.