PowerShell/Expressions
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This lesson introduces PowerShell expressions.
Objectives and Skills
[edit | edit source]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 | edit source]- Wikipedia: Expression (computer science)
- Wikipedia: Statement (computer science)
- Wikipedia: Order of operations
- Wikipedia: Unary operation
- Microsoft TechNet: about_Operators
Multimedia
[edit | edit source]- YouTube: Windows PowerShell Fundamentals Chapter 14 - More Operators
- YouTube: PowerShell - How To - Operators
Examples
[edit | edit source]Arithmetic Operators
[edit | edit source]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 | edit source]Assignment operators assign calculated values to variables.[2]
$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
[edit | edit source]Unary operators increment or decrement a single variable by one.[3]
$a = 1
$a++ # a = 2
$a-- # a = 1
Comparison Operators
[edit | edit source]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 | edit source]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 | edit source]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 | edit source]- 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.
- 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.
- 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.
- 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 | edit source]- 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 | edit source]- 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 | edit source]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 | edit source]- Flashcards: Quizlet: Windows PowerShell - Expressions
- Quiz: Quizlet: Windows PowerShell - Expressions
See Also
[edit | edit source]References
[edit | edit source]- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Wikipedia: Expression (computer science)
- ↑ Wikipedia: Statement (computer science)
- ↑ Wikipedia: Statement (computer science)
- ↑ Wikipedia: Order of operations
- ↑ Wikipedia: Order of operations
- ↑ Wikipedia: Order of operations
- ↑ Wikipedia: Order of operations
- ↑ Wikipedia: Unary operation
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Microsoft TechNet: about_Operators
- ↑ Wikipedia: Identifier
- ↑ Wikipedia: Modulo operation
- ↑ Wikipedia: Reserved word