Where-Object for filtering in PowerShell - Mini Project: Build & Apply

Filtering Data with Where-Object in PowerShell

📖 Scenario: You work in a small store and have a list of products with their prices. You want to find which products cost less than $20 to decide what to promote in a sale.

🎯 Goal: Build a PowerShell script that filters a list of products to show only those priced below $20 using Where-Object.

📋 What You'll Learn

Create a list of products with their prices as objects

Set a price limit variable to 20

Use Where-Object to filter products cheaper than the price limit

Display the filtered products

💡 Why This Matters

🌍 Real World

Filtering lists of items by conditions is common in managing inventories, logs, or user data.

💼 Career

Knowing how to filter data with PowerShell helps automate tasks in IT support, system administration, and data processing.

1

Create the product list

Create a variable called products that holds an array of three objects. Each object should have two properties: Name and Price. Use these exact entries: Name = 'Pen', Price = 5, Name = 'Notebook', Price = 15, Name = 'Backpack', Price = 45.

PowerShell

# Your code here

Hint

Use @( ... ) to create an array and @{Name=''; Price=} to create objects.

2

Set the price limit

Create a variable called priceLimit and set it to 20.

PowerShell

$products = @(
    @{Name='Pen'; Price=5},
    @{Name='Notebook'; Price=15},
    @{Name='Backpack'; Price=45}
)
# Your code here

Hint

Just assign the number 20 to $priceLimit.

3

Filter products using Where-Object

Create a variable called cheapProducts that stores the result of filtering $products using Where-Object. Keep only products where Price is less than $priceLimit. Use the syntax: $products | Where-Object { $_.Price -lt $priceLimit }.

PowerShell

$products = @(
    @{Name='Pen'; Price=5},
    @{Name='Notebook'; Price=15},
    @{Name='Backpack'; Price=45}
)
$priceLimit = 20
# Your code here

Hint

Use Where-Object with a script block that checks if Price is less than $priceLimit.

4

Display the filtered products

Use Write-Output to print the $cheapProducts variable.

PowerShell

$products = @(
    @{Name='Pen'; Price=5},
    @{Name='Notebook'; Price=15},
    @{Name='Backpack'; Price=45}
)
$priceLimit = 20
$cheapProducts = $products | Where-Object { $_.Price -lt $priceLimit }
# Your code here

Hint

Just write Write-Output $cheapProducts to show the filtered list.

Practice

1. What does the Where-Object cmdlet do in PowerShell?

easy

A. Filters objects in a collection based on a condition

B. Sorts objects alphabetically

C. Creates new objects from existing ones

D. Deletes objects from a collection

Solution

1. Step 1: Understand the purpose of Where-Object

   Where-Object is used to filter items in a collection by applying a condition to each item.

2. Step 2: Compare options with the purpose

   Only Filters objects in a collection based on a condition correctly describes filtering based on a condition. Sorting, creating, or deleting are different operations.

3. Final Answer:

   Filters objects in a collection based on a condition -> Option A

4. Quick Check:

   Where-Object filters collections = A [OK]

Hint: Where-Object selects items matching a condition [OK]

Common Mistakes:

• Confusing filtering with sorting
• Thinking it creates or deletes objects
• Ignoring the condition part

2. Which of the following is the correct syntax to filter processes with CPU usage greater than 100 using Where-Object?

easy

A. Get-Process | Where-Object { CPU > 100 }

B. Get-Process | Where-Object { $_.CPU -gt 100 }

C. Get-Process | Where-Object CPU -gt 100

D. Get-Process | Where-Object CPU > 100

Solution

1. Step 1: Identify correct use of script block and $_ variable

   Where-Object requires a script block with curly braces and uses $_ to refer to the current object.

2. Step 2: Check each option's syntax

   Get-Process | Where-Object { $_.CPU -gt 100 } correctly uses { $_.CPU -gt 100 }. Versions without the script block braces {} are incorrect. The version with { CPU > 100 } misses $_ before CPU.

3. Final Answer:

   Get-Process | Where-Object { $_.CPU -gt 100 } -> Option B

4. Quick Check:

   { $_.Property -gt value } syntax = D [OK]

Hint: Always use { $_.Property -operator value } inside Where-Object [OK]

Common Mistakes:

• Omitting curly braces {}
• Not using $_ to reference current object
• Writing condition outside script block

3. What will be the output of this command?

1..5 | Where-Object { $_ % 2 -eq 0 }

medium

A. [1, 3, 5]

B. [1, 2, 3, 4, 5]

C. [2, 4]

D. Error: Invalid operator

Solution

1. Step 1: Understand the input and condition

   The input is numbers 1 to 5. The condition filters numbers where remainder when divided by 2 equals 0 (even numbers).

2. Step 2: Apply the condition to each number

   Numbers 2 and 4 satisfy the condition (2 % 2 = 0, 4 % 2 = 0). Others do not.

3. Final Answer:

   [2, 4] -> Option C

4. Quick Check:

   Filter even numbers = [2, 4] [OK]

Hint: Use modulo (%) to filter even numbers [OK]

Common Mistakes:

• Confusing even and odd numbers
• Expecting all numbers as output
• Thinking syntax causes error

4. Identify the error in this command:

Get-Service | Where-Object $_.Status -eq 'Running'

medium

A. Missing curly braces around the condition

B. Incorrect property name 'Status'

C. Wrong operator used for comparison

D. No error, command is correct

Solution

1. Step 1: Check Where-Object syntax

   Where-Object requires the condition inside curly braces {} to form a script block.

2. Step 2: Analyze the given command

   The command misses curly braces around $_.Status -eq 'Running', causing syntax error.

3. Final Answer:

   Missing curly braces around the condition -> Option A

4. Quick Check:

   Where-Object needs { condition } [OK]

Hint: Always wrap condition in { } for Where-Object [OK]

Common Mistakes:

• Omitting curly braces
• Assuming property names are wrong without checking
• Confusing operators

5. You have a list of files with sizes in bytes. Which command filters files larger than 1MB (1048576 bytes) and selects only their names?

Get-ChildItem | Where-Object { $_.Length -gt 1048576 } | ???

What should replace ????

hard

A. Sort-Object Length

B. Where-Object Name

C. Format-Table Length

D. Select-Object Name

Solution

1. Step 1: Understand the filtering part

   Where-Object filters files with Length greater than 1048576 bytes (1MB).

2. Step 2: Identify how to select only file names

   Select-Object Name extracts only the Name property from the filtered files.

3. Final Answer:

   Select-Object Name -> Option D

4. Quick Check:

   Select-Object Name for properties = C [OK]

Hint: Use Select-Object to pick specific properties [OK]

Common Mistakes:

• Using Where-Object instead of Select-Object to pick properties
• Sorting instead of selecting
• Formatting output without selecting needed data