PowerShell/Expressions

This lesson introduces PowerShell expressions.

Objectives and Skills

After completing this lesson, you will be able to:

• Describe the operators used in PowerShell scripts.
• Explain order of operation.
• Create PowerShell scripts to perform calculations based on user input.

Readings

1. Wikipedia: Expression (computer science)
2. Wikipedia: Statement (computer science)
3. Wikipedia: Order of operations
4. Wikipedia: Unary operation
5. Microsoft TechNet: about_Operators

Multimedia

1. YouTube: Windows PowerShell Fundamentals Chapter 14 - More Operators
2. YouTube: PowerShell - How To - Operators

Examples

Arithmetic Operators

Arithmetic operators calculate values.

$a = 3
$b = 2

$a + $b    # 5
$a - $b    # 1
$a * $b    # 6
$a / $b    # 1.5
$a % $b    # 1
-$a        # -3

Assignment Operators

Assignment operators assign calculated values to variables.

$a = 3
$b = 2

$a += $b    # a = 5
$a -= $b    # a = 3
$a *= $b    # a = 6
$a /= $b    # a = 3
$a %= $b    # a = 1

Unary Operators

Unary operators increment or decrement a single variable by one.

$a = 1

$a++    # a = 2
$a--    # a = 1

Comparison Operators

Comparison operators compare values and test conditions.

$a = 3
$b = 2

$a -eq $b    # False
$a -ne $b    # True
$a -lt $b    # False
$a -gt $b    # True
$a -le $b    # False
$a -ge $b    # True

Logical Operators

Logical operators compare complex conditions.

$a = 3
$b = 2

$a -lt $b -and $b -lt $a    # False
$a -lt $b -or $b -lt $a     # True
$a -lt $b                   # False
-not ($a -lt $b)            # True

String Operators

String operators split, join, and concatenate substrings.

$a = 'Cat,Dog,Fish,Hamster'
$a -split ','                           # Cat
                                        # Dog
                                        # Fish
                                        # Hamster

$b = @('Cat','Dog','Fish','Hamster')
$b -join ','                            # Cat,Dog,Fish,Hamster

'Cat' + 'Dog' + 'Fish' + 'Hamster'      # CatDogFishHamster

Activities

1. Review Microsoft TechNet: about_Operators. Experiment with different arithmetic operators to ensure you understand how they work. Then review Microsoft TechNet: about_Operator_Precedence and MathsIsFun: Order of Operations. Create a script that demonstrates the order of operations for PowerShell operators.
2. Create a script that asks the user how old they are in years, and then calculate and display their approximate age in months, days, hours, and seconds.
3. Review MathsIsFun: Conversion of Temperature. Create a script that asks the user for a Fahrenheit temperature and then calculate and display the corresponding Celsius temperature or ask the user for a Celsius temperature and then calculate and display the corresponding Fahrenheit temperature.
4. Review MathsIsFun: Area of Plane Shapes. Create a script that asks the user for the dimensions of different shapes and then calculate and display the area of the shapes.

Lesson Summary

• An expression is a combination of explicit values, constants, variables, operators, and functions that are interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then produces another value.
• A statement is the smallest standalone element of an imperative programming language which expresses some action to be carried out.
• In most languages, statements contrast with expressions in that statements do not return results and are executed solely for their side effects, while expressions always return a result and often do not have side effects at all.
• The order of operations (sometimes called operator precedence) is a rule used to clarify which procedures should be performed first in a given mathematical expression.
• The order of operations is exponents and roots, followed by multiplication and division, followed by addition and subtraction.
• Parentheses are used to explicitly denote precedence by grouping parts of an expression that should be evaluated first.
• The mnemonic PEMDAS may be used to recall the order of operations of Parentheses, Exponents, Multiplication, Division, Addition, Subtraction.
• A unary operation is an operation with only one operand.
• Arithmetic operators calculate values.
• Assignment operators assign calculated values to variables.
• Unary operators increment or decrement a single variable by one.
• Comparison operators compare values and test conditions.
• Logical operators compare complex conditions.
• String operators split, join, and concatenate substrings.
• +, -, *, /, and % are the addition subtraction, multiplication, division, and modulus (remainder) operators.
• =, +=, -=, *=, /=, and %= are the assignment operators.
• ++ and -- are the unary increment and decrement operators.
• -eq, -ne, -gt, -lt, -le, and -ge are the equal, not equal, greater than, less than, less than or equal, and greater than or equal comparison operators.
• -and, -or, -xor, and -not or ! are the and, or, exclusive or, and negation logical operators.
• -split and -join are the string operators.

Key Terms

identifier

A name that identifies (that is, labels the identity of) either a unique object or a unique class of objects.

modulo (sometimes called modulus)

The operation that finds the remainder of division of one number by another.

reserved word

A word that cannot be used as an identifier, such as the name of a variable, function, or label.

Review Questions

1. An expression is _____.

An expression is a combination of explicit values, constants, variables, operators, and functions that are interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then produces another value.

2. A statement is _____.

A statement is the smallest standalone element of an imperative programming language which expresses some action to be carried out.

3. In most languages, statements contrast with expressions in that statements _____, while expressions _____.

In most languages, statements contrast with expressions in that statements do not return results and are executed solely for their side effects, while expressions always return a result and often do not have side effects at all.

4. The order of operations (sometimes called operator precedence) is a rule used to _____.

The order of operations (sometimes called operator precedence) is a rule used to clarify which procedures should be performed first in a given mathematical expression.

5. The order of operations is _____.

The order of operations is exponents and roots, followed by multiplication and division, followed by addition and subtraction.

6. Parentheses are used to _____.

Parentheses are used to explicitly denote precedence by grouping parts of an expression that should be evaluated first.

7. The mnemonic PEMDAS may be used to _____.

The mnemonic PEMDAS may be used to recall the order of operations of Parentheses, Exponents, Multiplication, Division, Addition, Subtraction.

8. A unary operation is _____.

A unary operation is an operation with only one operand.

9. Arithmetic operators _____.

Arithmetic operators calculate values.

10. Assignment operators _____.

Assignment operators assign calculated values to variables.

11. Unary operators _____.

Unary operators increment or decrement a single variable by one.

12. Comparison operators _____.

Comparison operators compare values and test conditions.

13. Logical operators _____.

Logical operators compare complex conditions.

14. String operators _____.

String operators split, join, and concatenate substrings.

15. +, -, *, /, and % are _____.

+, -, *, /, and % are the addition subtraction, multiplication, division, and modulus (remainder) operators.

17. ++ and -- are _____.

++ and -- are the unary increment and decrement operators.

18. -eq, -ne, -gt, -lt, -le, and -ge are _____.

-eq, -ne, -gt, -lt, -le, and -ge are the equal, not equal, greater than, less than, less than or equal, and greater than or equal comparison operators.

19. -and, -or, -xor, and -not or ! are _____.

-and, -or, -xor, and -not or ! are the and, or, exclusive or, and negation logical operators.

20. -split and -join are _____.

-split and -join are string operators.

Assessments

• Flashcards: Quizlet: Windows PowerShell - Expressions
• Quiz: Quizlet: Windows PowerShell - Expressions

References

Type classification: this is a lesson resource.

Completion status: this resource is considered to be complete.

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