ForEach loop in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a ForEach loop with array modification

What is the output of this PowerShell script?

PowerShell

$arr = 1,2,3,4
foreach ($i in $arr) {
  $i = $i * 2
  Write-Output $i
}
Write-Output $arr

A

1
2
3
4
1 2 3 4

B

2
4
6
8
2 4 6 8

C

2
4
6
8
1 2 3 4

D

2 4 6 8
2 4 6 8

💡 Hint

Remember that modifying the loop variable inside a ForEach does not change the original array elements.

The loop variable $i is a copy of each element, so changing $i does not affect the original array $arr. The Write-Output inside the loop prints doubled values, but the original array remains unchanged.

📝 Syntax

intermediate

Identify the syntax error in this ForEach loop

Which option contains a syntax error in the ForEach loop?

PowerShell

foreach ($item in $list) {
  Write-Output $item
}

A foreach $item in $list { Write-Output $item }

B foreach ($item in $list) { Write-Output $item }

C } meti$ tuptuO-etirW { )tsil$ ni meti$( hcaerof

D foreach ($item in $list) Write-Output $item

💡 Hint

Check the parentheses around the loop variable.

Option A is missing parentheses around the loop variable and collection, which is required syntax in PowerShell ForEach loops.

🔧 Debug

advanced

Why does this ForEach loop not output anything?

Given this script, why is there no output?

PowerShell

$numbers = 1..5
foreach ($num in $numbers) {
  $num * 2
}

A Because the array $numbers is empty.

B Because the multiplication operator * is invalid in PowerShell.

C Because the foreach loop syntax is incorrect.

D Because the loop variable $num is not being output explicitly.

💡 Hint

In PowerShell, expressions inside loops need to be output explicitly to display.

The expression $num * 2 calculates the value but does not output it. You need to use Write-Output or just place the expression alone to output it.

🚀 Application

advanced

Using ForEach to modify a list of objects

You have a list of objects with a property 'Name'. You want to append '-done' to each Name. Which script correctly updates the objects?

PowerShell

$items = @(
  [PSCustomObject]@{Name='Task1'},
  [PSCustomObject]@{Name='Task2'}
)
foreach ($item in $items) {
  # update Name here
}

A foreach ($item in $items) { $item.Name = $item.Name + '-done' }

B foreach ($item in $items) { $item = $item.Name + '-done' }

C foreach ($item in $items) { $item.Name = $item.Name - '-done' }

D foreach ($item in $items) { $item.Name += '-done' }

💡 Hint

Remember to assign the new string back to the property.

Option A correctly concatenates the string and assigns it back to the Name property. Option A uses += which works but is less clear. Option A replaces the whole object with a string, losing the object structure. Option A uses an invalid operator '-' for strings.

🧠 Conceptual

expert

Understanding pipeline ForEach-Object vs ForEach loop

Which statement about PowerShell's ForEach-Object cmdlet and ForEach loop is TRUE?

A ForEach loop can only process arrays, but ForEach-Object can process any collection.

B ForEach-Object processes items one at a time as they come through the pipeline, while ForEach loop processes all items after the collection is fully available.

C ForEach-Object is faster than ForEach loop because it uses parallel processing by default.

D ForEach loop can be used in pipelines directly, but ForEach-Object cannot.

💡 Hint

Think about how pipeline processing works in PowerShell.

ForEach-Object processes each item as it passes through the pipeline, allowing streaming processing. ForEach loop requires the entire collection before starting the loop.

Practice

1. What does the foreach loop do in PowerShell?

easy

A. Creates a new collection from scratch

B. Runs code only once regardless of the collection

C. Repeats a block of code for each item in a collection

D. Stops the script immediately

Solution

1. Step 1: Understand the foreach loop purpose

   The foreach loop is designed to repeat actions for every item in a list or collection.

2. Step 2: Compare options to this purpose

   Only Repeats a block of code for each item in a collection correctly describes repeating code for each item in a collection.

3. Final Answer:

   Repeats a block of code for each item in a collection -> Option C

4. Quick Check:

   foreach = repeat for each item [OK]

Hint: Think: foreach means 'for each item' repeat [OK]

Common Mistakes:

• Confusing foreach with a one-time action
• Thinking foreach creates new collections
• Believing foreach stops the script

2. Which of the following is the correct syntax for a foreach loop in PowerShell?

easy

A. foreach ($item in $list) { Write-Output $item }

B. foreach $item in $list { Write-Output $item }

C. foreach ($item : $list) { Write-Output $item }

D. foreach ($item; $list) { Write-Output $item }

Solution

1. Step 1: Recall correct foreach syntax

   PowerShell foreach loops use: foreach ($var in $collection) { ... }

2. Step 2: Match options to syntax

   Only foreach ($item in $list) { Write-Output $item } uses the correct 'in' keyword and parentheses.

3. Final Answer:

   foreach ($item in $list) { Write-Output $item } -> Option A

4. Quick Check:

   Syntax uses 'in' keyword inside parentheses [OK]

Hint: Look for 'foreach ($var in $collection)' pattern [OK]

Common Mistakes:

• Omitting parentheses around variable and collection
• Using ':' or ';' instead of 'in'
• Missing the 'in' keyword

3. What will be the output of this PowerShell script?

foreach ($num in 1..3) { Write-Output ($num * 2) }

medium

A. 2 4 6

B. 1 2 3

C. 3 6 9

D. Error: Invalid syntax

Solution

1. Step 1: Understand the loop range

   The loop runs for numbers 1, 2, and 3.

2. Step 2: Calculate output for each iteration

   Each number is multiplied by 2, so outputs are 2, 4, and 6.

3. Final Answer:

   2 4 6 -> Option A

4. Quick Check:

   1*2=2, 2*2=4, 3*2=6 [OK]

Hint: Multiply each loop number by 2 mentally [OK]

Common Mistakes:

• Confusing the range operator '..'
• Thinking output is original numbers
• Expecting syntax error

4. Identify the error in this PowerShell foreach loop:

foreach $item in $array { Write-Output $item }

medium

A. No error, code is correct

B. Missing parentheses around the loop variable and collection

C. Using $item instead of $i as loop variable

D. Incorrect use of Write-Output

Solution

1. Step 1: Check foreach syntax

   PowerShell requires parentheses around the variable and collection in foreach loops.

2. Step 2: Identify missing parentheses

   The code lacks parentheses: it should be foreach ($item in $array) { ... }

3. Final Answer:

   Missing parentheses around the loop variable and collection -> Option B

4. Quick Check:

   foreach needs parentheses [OK]

Hint: Always use parentheses in foreach syntax [OK]

Common Mistakes:

• Omitting parentheses
• Confusing variable names
• Thinking Write-Output causes error

5. You have a list of filenames stored in $files. You want to print only those filenames that end with '.txt' using a foreach loop. Which script correctly does this?

hard

A. foreach ($file in $files) { if ($file -eq '*.txt') { Write-Output $file } }

B. foreach ($file in $files) { if ($file contains '.txt') { Write-Output $file } }

C. foreach ($file in $files) { Write-Output $file -match '.txt' }

D. foreach ($file in $files) { if ($file -like '*.txt') { Write-Output $file } }

Solution

1. Step 1: Understand filtering condition

   To check if a filename ends with '.txt', use the '-like' operator with '*.txt' pattern.

2. Step 2: Verify foreach loop and condition

   foreach ($file in $files) { if ($file -like '*.txt') { Write-Output $file } } correctly uses foreach with an if condition checking '-like "*.txt"' and outputs matching files.

3. Final Answer:

   foreach ($file in $files) { if ($file -like '*.txt') { Write-Output $file } } -> Option D

4. Quick Check:

   Use '-like' with wildcard for pattern match [OK]

Hint: Use '-like "*.txt"' inside if in foreach [OK]

Common Mistakes:

• Using '-eq' instead of '-like' for pattern matching
• Misusing '-match' without if condition
• Using 'contains' which is invalid here