Automatic variables ($_, $PSVersionTable) in PowerShell - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this PowerShell pipeline?

Consider the following PowerShell command:

1..3 | ForEach-Object { $_ * 2 }

What is the output?

PowerShell

1..3 | ForEach-Object { $_ * 2 }

A 1 2 3

B Error: $_ is undefined

C 0 2 4

D 2 4 6

💡 Hint

$_ represents the current item in the pipeline inside ForEach-Object.

In PowerShell, $_ is the automatic variable for the current pipeline object. Multiplying each number 1, 2, 3 by 2 results in 2, 4, 6.

💻 Command Output

intermediate

What does $PSVersionTable.PSVersion.Major return?

If you run this command in PowerShell:

$PSVersionTable.PSVersion.Major

What kind of value will it return?

PowerShell

$PSVersionTable.PSVersion.Major

A A boolean indicating if PowerShell is installed

B A string with the full PowerShell version

C An integer representing the major version number of PowerShell

D An error because $PSVersionTable is undefined

💡 Hint

$PSVersionTable contains version info as properties.

$PSVersionTable is an automatic variable holding version info. PSVersion is a version object, and Major is its major version number as an integer.

📝 Syntax

advanced

Which option correctly uses $_ in a Where-Object filter?

You want to filter numbers greater than 5 from a list using Where-Object. Which of these commands is correct?

A 1..10 | Where-Object { $_ -gt 5 }

B 1..10 | Where-Object { $ -gt 5 }

C 1..10 | Where-Object { $_ > 5 }

D 1..10 | Where-Object { $_ -lt 5 }

💡 Hint

Use the correct comparison operator and variable name.

Option A uses $_ (current object) and the correct PowerShell comparison operator '-gt' for 'greater than'. Option A uses '>' which is invalid in PowerShell filters.

🔧 Debug

advanced

Why does this script fail to filter correctly?

Given this script:

1..5 | ForEach-Object { if ($_ % 2) { $_ } }

It outputs 1 3 5 but you want only even numbers. What is wrong?

PowerShell

1..5 | ForEach-Object { if ($_ % 2) { $_ } }

A The condition '$_ % 2' is true for odd numbers, so it outputs odds instead of evens

B $_ is not defined inside ForEach-Object, causing an error

C The script is missing a closing brace '}'

D The pipeline operator '|' is used incorrectly

💡 Hint

Remember how modulo (%) works with odd and even numbers.

The expression '$_ % 2' returns 1 for odd numbers (true) and 0 for even (false). So the if condition passes for odd numbers, outputting them. To get evens, check for '$_ % 2 -eq 0'.

🚀 Application

expert

How to display PowerShell version in a formatted string?

You want to print the PowerShell version as:

PowerShell version: X.Y.Z

using $PSVersionTable. Which command produces this exact output?

A Write-Output "PowerShell version: $PSVersionTable.PSVersion.Major.$PSVersionTable.PSVersion.Minor.$PSVersionTable.PSVersion.Build"

B Write-Output "PowerShell version: $($PSVersionTable.PSVersion.Major).$($PSVersionTable.PSVersion.Minor).$($PSVersionTable.PSVersion.Build)"

C Write-Output "PowerShell version: $_.PSVersion.Major.$_.PSVersion.Minor.$_.PSVersion.Build"

D Write-Output "PowerShell version: $PSVersionTable[PSVersion][Major].[Minor].[Build]"

💡 Hint

Use subexpressions $() to embed properties inside strings.

Option B correctly uses subexpressions $() to insert each version part inside the string. Option B treats properties as literal text. Option B uses $_ which is undefined here. Option B uses invalid syntax for property access.

Practice

1. What does the automatic variable $_ represent in a PowerShell pipeline?

easy

A. The version of PowerShell installed

B. The current object being processed in the pipeline

C. The last error message generated

D. The total number of commands run

Solution

1. Step 1: Understand the role of $_ in pipelines

   $_ is a special variable that holds the current item being processed in a pipeline command.

2. Step 2: Differentiate from other automatic variables

   $PSVersionTable shows version info, errors use $Error, and command counts are not stored in $_.

3. Final Answer:

   The current object being processed in the pipeline -> Option B

4. Quick Check:

   $_ = current pipeline item [OK]

Hint: Remember: $_ always means current pipeline item [OK]

Common Mistakes:

• Confusing $_ with $PSVersionTable
• Thinking $_ holds error info
• Assuming $_ is a global variable

2. Which of the following is the correct way to display the PowerShell version using $PSVersionTable?

easy

A. Write-Output $PSVersionTable.VersionInfo

B. Write-Output $_.Version

C. Write-Output $PSVersion.VersionTable

D. Write-Output $PSVersionTable.Version

Solution

1. Step 1: Identify the correct property of $PSVersionTable

   The property Version holds the PowerShell version number.

2. Step 2: Confirm the syntax to output the version

   Write-Output $PSVersionTable.Version correctly prints the version; other options use wrong variable names or properties.

3. Final Answer:

   Write-Output $PSVersionTable.Version -> Option D

4. Quick Check:

   $PSVersionTable.Version outputs version [OK]

Hint: Use $PSVersionTable.Version to get PowerShell version [OK]

Common Mistakes:

• Using $_ instead of $PSVersionTable
• Swapping property names incorrectly
• Assuming $PSVersionTable is a method

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

1..3 | ForEach-Object { "Number: $_" }

medium

A. Number: 1 Number: 2 Number: 3

B. Number: $_ Number: $_ Number: $_

C. 1 2 3

D. Error: $_ is undefined

Solution

1. Step 1: Understand the pipeline and $_ usage

   The pipeline sends numbers 1 to 3 one by one to ForEach-Object. Inside the script block, $_ holds the current number.

2. Step 2: Evaluate the output string for each number

   Each iteration outputs "Number: 1", then "Number: 2", then "Number: 3" on separate lines.

3. Final Answer:

   Number: 1 Number: 2 Number: 3 -> Option A

4. Quick Check:

   Pipeline item $_ prints each number [OK]

Hint: $_ holds current pipeline item inside ForEach-Object [OK]

Common Mistakes:

• Thinking $_ is a literal string
• Expecting all output on one line without spaces
• Confusing $_ with a variable outside pipeline

4. Identify the error in this script snippet:

Get-Process | Where-Object { $_.Name -eq 'powershell' } | ForEach-Object { Write-Output $PSVersionTable }

medium

A. The script outputs the entire $PSVersionTable multiple times unnecessarily

B. Using $PSVersionTable inside ForEach-Object is invalid

C. $_ is not defined inside Where-Object script block

D. Get-Process cannot be piped to Where-Object

Solution

1. Step 1: Analyze the pipeline and variable usage

   The pipeline filters processes named 'powershell' and then outputs $PSVersionTable for each matching process.

2. Step 2: Identify inefficiency or error

   $PSVersionTable is a static variable; outputting it inside the loop repeats the same info multiple times unnecessarily.

3. Final Answer:

   The script outputs the entire $PSVersionTable multiple times unnecessarily -> Option A

4. Quick Check:

   Repeated $PSVersionTable output inside loop [OK]

Hint: Avoid repeating static variables inside loops [OK]

Common Mistakes:

• Thinking $PSVersionTable is undefined in pipeline
• Believing $_ is invalid in Where-Object
• Assuming Get-Process can't be piped

5. You want to list all running processes and display their names along with your PowerShell version once at the end. Which script correctly uses $_ and $PSVersionTable to achieve this?

hard

A. Get-Process | ForEach-Object { Write-Output "Process: $PSVersionTable.Version" }; Write-Output "PowerShell Version: $_.Name"

B. Get-Process | ForEach-Object { Write-Output "Process: $_.Name; PowerShell Version: $PSVersionTable.Version" }

C. Get-Process | ForEach-Object { Write-Output "Process: $_.Name" }; Write-Output "PowerShell Version: $PSVersionTable.Version"

D. Write-Output "PowerShell Version: $PSVersionTable.Version"; Get-Process | ForEach-Object { Write-Output "Process: $_.Name" }

Solution

1. Step 1: Understand the requirement to show processes and version separately

   We want to list each process name using $_ inside the pipeline, then show PowerShell version once after.

2. Step 2: Evaluate each option's correctness

   Get-Process | ForEach-Object { Write-Output "Process: $_.Name" }; Write-Output "PowerShell Version: $PSVersionTable.Version" lists processes with $_ correctly, then outputs version once after the loop. Get-Process | ForEach-Object { Write-Output "Process: $_.Name; PowerShell Version: $PSVersionTable.Version" } repeats version for each process. Write-Output "PowerShell Version: $PSVersionTable.Version"; Get-Process | ForEach-Object { Write-Output "Process: $_.Name" } outputs version first, then processes (order reversed). Get-Process | ForEach-Object { Write-Output "Process: $PSVersionTable.Version" }; Write-Output "PowerShell Version: $_.Name" misuses variables inside the loop.

3. Final Answer:

   Get-Process | ForEach-Object { Write-Output "Process: $_.Name" }; Write-Output "PowerShell Version: $PSVersionTable.Version" -> Option C

4. Quick Check:

   List processes with $_, version once after [OK]

Hint: Output static info after pipeline, use $_ inside pipeline [OK]

Common Mistakes:

• Repeating version output inside loop
• Mixing order of outputs
• Using wrong variable names inside pipeline