PowerShell/Expressions

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This lesson introduces PowerShell expressions.

Objectives and Skills[edit]

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[edit]

  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[edit]

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

Examples[edit]

Arithmetic Operators[edit]

Arithmetic operators calculate values.[1]

$a = 3
$b = 2

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

Assignment Operators[edit]

Assignment operators assign calculated values to variables.[2]

$a = 3
$b = 2

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

Unary Operators[edit]

Unary operators increment or decrement a single variable by one.[3]

$a = 1

$a++    # a = 2
$a--    # a = 0

Comparison Operators[edit]

Comparison operators compare values and test conditions.[4]

$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[edit]

Logical operators compare complex conditions.[5]

$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[edit]

String operators split, join, and concatenate substrings.[6]

$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[edit]

  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[edit]

  • 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.[7]
  • A statement is the smallest standalone element of an imperative programming language which expresses some action to be carried out.[8]
  • 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.[9]
  • 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.[10]
  • The order of operations is exponents and roots, followed by multiplication and division, followed by addition and subtraction.[11]
  • Parentheses are used to explicitly denote precedence by grouping parts of an expression that should be evaluated first.[12]
  • The mnemonic PEMDAS may be used to recall the order of operations of Parentheses, Exponents, Multiplication, Division, Addition, Subtraction.[13]
  • A unary operation is an operation with only one operand.[14]
  • Arithmetic operators calculate values.[15]
  • Assignment operators assign calculated values to variables.[16]
  • Unary operators increment or decrement a single variable by one.[17]
  • Comparison operators compare values and test conditions.[18]
  • Logical operators compare complex conditions.[19]
  • String operators split, join, and concatenate substrings.[20]
  • +, -, *, /, and % are the addition subtraction, multiplication, division, and modulus (remainder) operators.[21]
  • =, +=, -=, *=, /=, and %= are the assignment operators.[22]
  • ++ and -- are the unary increment and decrement operators.[23]
  • -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.[24]
  • -and, -or, -xor, and -not or ! are the and, or, exclusive or, and negation logical operators.[25]
  • -split and -join are the string operators.[26]

Key Terms[edit]

identifier
A name that identifies (that is, labels the identity of) either a unique object or a unique class of objects.[27]
modulo (sometimes called modulus)
The operation that finds the remainder of division of one number by another.[28]
reserved word
A word that cannot be used as an identifier, such as the name of a variable, function, or label.[29]

Review Questions[edit]

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Click on a question to see the answer.
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[edit]

See Also[edit]

References[edit]

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