7. Operators and Expressions

This chapter shows how Bash represents calculations, comparisons, tests, and logical expressions that scripts can use to make decisions.

• Arithmetic: Use Bash integer operators for counters, offsets, and status checks.

• Comparison: Choose numeric and string operators for the kind of value being tested.

• File tests: Ask precise questions about files before acting on them.

• Logic: Combine tests with AND, OR, and NOT.

• Conditionals: Place expressions inside if, case, and short-circuit command patterns.

Chapter Video

What are Conditional Statements in Bash (5:02) 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. Use arithmetic operators and arithmetic expansion.

2. Choose numeric, string, and file-test operators correctly.

3. Combine tests with logical operators.

4. Use expressions safely inside conditional logic.

Chapter Flow

1. Arithmetic

2. Comparison & Logic

3. String & File Tests

4. Expressions in Conditionals

Glossary

#	Term	Explanation
1	Operator	A symbol or keyword that performs a comparison, calculation, or logical operation.
2	Expression	A combination of values and operators evaluated by Bash.
3	Arithmetic expansion	The $((...)) form used to evaluate integer arithmetic.
4	Integer division	Division that discards any fractional result.
5	Modulo	The remainder operator %, often used for divisibility tests.
6	Numeric comparison	A test using operators such as -eq, -ne, -lt, and -gt.
7	String comparison	A test comparing text values with operators such as =, !=, <, or >.
8	Logical AND	A condition that succeeds only when both parts succeed.
9	Logical OR	A condition that succeeds when either part succeeds.
10	Logical NOT	A condition that reverses success and failure.
11	test	A command that evaluates expressions, also written as [ ... ].
12	Double brackets	The Bash [[ ... ]] conditional expression syntax.
13	File test	A test such as -e, -f, or -d that checks file properties.
14	Exit status	A numeric result where 0 means success and nonzero usually means failure.
15	Short-circuit evaluation	Evaluation that skips later commands when the result is already determined.
16	Unary test	A test with one operand, such as -z string.
17	Binary test	A test comparing two operands.
18	Pattern matching	Matching text against shell-style patterns inside conditionals.
19	Readable test	The -r file test, which checks read permission.
20	Executable test	The -x file test, which checks execute permission.