Automatic variables ($_, $PSVersionTable) in PowerShell - Mini Project: Build & Apply

Explore PowerShell Automatic Variables $_ and $PSVersionTable

📖 Scenario: You are working with PowerShell to process a list of files and want to learn how to use automatic variables to make your scripts simpler and more powerful.

🎯 Goal: Learn to use the automatic variable $_ inside a loop to access the current item, and explore the $PSVersionTable automatic variable to check your PowerShell version.

📋 What You'll Learn

Create an array of file names

Use the automatic variable $_ inside a loop to print each file name

Access the $PSVersionTable automatic variable to display PowerShell version info

Print the results clearly

💡 Why This Matters

🌍 Real World

PowerShell scripts often process lists of files or data items. Using automatic variables like $_ makes it easy to write concise and readable scripts that handle each item automatically.

💼 Career

Understanding automatic variables is essential for system administrators and automation engineers who write PowerShell scripts to manage systems, automate tasks, and gather system information efficiently.

1

Create an array of file names

Create a variable called $files and assign it an array with these exact file names: 'report.docx', 'data.csv', 'image.png', 'notes.txt'.

PowerShell

# Create the $files array with the given file names
# Your code here

Hint

Use @( ... ) to create an array in PowerShell.

2

Set up a loop to process each file

Add a foreach loop that goes through each item in $files using the automatic variable $_ inside the loop body.

PowerShell

$files = @('report.docx', 'data.csv', 'image.png', 'notes.txt')

# Add a foreach loop to process each file using $_
# Your code here

Hint

Use ForEach-Object { ... } and inside the braces, $_ is the current item.

3

Print each file name using $_

Inside the ForEach-Object loop, add a Write-Output command to print the current file name stored in $_.

PowerShell

$files = @('report.docx', 'data.csv', 'image.png', 'notes.txt')

$files | ForEach-Object {
    # Print the current file name using $_
    # Your code here
}

Hint

Use Write-Output $_ to print the current item.

4

Display PowerShell version using $PSVersionTable

Add a line to print the PowerShell version information stored in the automatic variable $PSVersionTable.

PowerShell

$files = @('report.docx', 'data.csv', 'image.png', 'notes.txt')

$files | ForEach-Object {
    Write-Output $_
}

# Print the PowerShell version info using $PSVersionTable
# Your code here

Hint

Use Write-Output $PSVersionTable to show version details.

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