Automatic variables ($_, $PSVersionTable) in PowerShell - Step-by-Step Execution

Concept Flow - Automatic variables ($_, $PSVersionTable)

Start Script

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Use $_ in pipeline

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$_ holds current item

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Process item

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Repeat for each item

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Use $PSVersionTable

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Display PowerShell version info

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End Script

The script processes each item in a pipeline using $_ as the current item, then accesses $PSVersionTable to show PowerShell version details.

Execution Sample

PowerShell

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

This code prints each number from 1 to 3 with a label, then shows the PowerShell version.

Execution Table

Step	Pipeline Item ($_)	Action	Output
1	1	Print "Number: 1"	Number: 1
2	2	Print "Number: 2"	Number: 2
3	3	Print "Number: 3"	Number: 3
4	N/A	Access $PSVersionTable.PSVersion	Major.Minor.Build.Revision (e.g., 7.3.4.0)
5	N/A	End of script	No more output

💡 All pipeline items processed; script ends after displaying PowerShell version.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
$_	N/A	1	2	3	N/A
$PSVersionTable.PSVersion	N/A	N/A	N/A	N/A	7.3.4.0

Key Moments - 2 Insights

Why does $_ change inside the ForEach-Object loop?

Because $_ automatically holds the current item from the pipeline during each loop iteration, as shown in execution_table steps 1 to 3.

What is $PSVersionTable and why is it accessed after the loop?

$PSVersionTable is an automatic variable holding PowerShell version info; it is accessed after the loop to display version details, as in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $_ at step 2?

A 1

B 3

C 2

D N/A

💡 Hint

Check the 'Pipeline Item ($_)' column at step 2 in the execution_table.

At which step does the script display the PowerShell version?

A Step 3

B Step 4

C Step 5

D Step 1

💡 Hint

Look for the action 'Access $PSVersionTable.PSVersion' in the execution_table.

If the pipeline was 1..2 instead of 1..3, how many times would $_ change?

A 2 times

B 3 times

C 1 time

D 0 times

💡 Hint

Refer to variable_tracker for $_ changes per iteration.

Concept Snapshot

Automatic variables in PowerShell:
- $_ holds the current pipeline item inside loops.
- Use $_ to refer to each item during ForEach-Object.
- $PSVersionTable stores PowerShell version info.
- Access $PSVersionTable.PSVersion to see version details.
- $_ changes each iteration; $PSVersionTable is static.

Full Transcript

This example shows how PowerShell uses automatic variables. The variable $_ holds the current item in a pipeline during a ForEach-Object loop. For each number from 1 to 3, the script prints 'Number: ' followed by the current number stored in $_. After processing all items, the script accesses $PSVersionTable.PSVersion to display the PowerShell version. The execution table traces each step, showing $_ changing from 1 to 3, and then the version info being displayed. The variable tracker confirms $_ updates each iteration, while $PSVersionTable remains constant. Key moments clarify why $_ changes and what $PSVersionTable represents. The quiz tests understanding of $_ values at specific steps and when the version info is shown.