Parent/Child scoping of variables and functions can really mess with people starting out with PowerShell (or Bash).

In terms of “Dot-sourcing” a .ps1 file, it is like running the PowerShell script it contains inline in the current scope. Thus when that script finishes, any variables set/updated within it are changed within the current scope.

Let create a .ps1 file that increments the variable $x by one and ‘outputs’ it to the pipe:

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echo "`$x++;`$x;" > inc_x_by_one.ps1

Now assign the variable $x to be 1

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$x=1
$x
1

Now run the inc_x_by_one.ps1 routine:

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.\inc_x_by_one.ps1
2

So we got a result of 2 which is what you wanted right? Well, maybe… Let run the same thing again:

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.\inc_x_by_one.ps1
2
$x
1

What? Why is it not 3(?), and it is still 1!!! Well that is because the $x++ is executing in a child scope. Basically your script is getting a copy of $x, not a reference (pointer) to that variable. Same thing that you experience in passing variables to functions in C, C#, Java, etc…

If your desire is to actually change $x in your shell (the current scope), you can ‘dot-source’ the call.

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. .\inc_x_by_one.ps1
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. .\inc_x_by_one.ps1
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$x
3

This is compariable to the way shell variables work under bash, zsh, … and I’m assuming the PowerShell term borrowed ‘dot sourcing’ in that regard as the syntax if the same: Period Space File.ps1|.sh

Take a few minutes and read the help on scope, it just might save you a headache in the future ;-)

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help scope

Note: In PowerShell, you can assign variables to the global scope and not ‘worry’ about parent/child scoping rules. Normally this is not a preferred way as it create it creates messy code, issues of which function/module is changing it, debugging nightmares, etc…