PSMonday #9: Monday, June 27, 2016

Topic: Less Used Variable Properties Continued I

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

As was mentioned last week, variables have some properties we don’t often use, and many of us, may not even know about them. Last week we briefly learned about the Description property of a variable, and today, we’ll start to learn about the Options property.

While a variable’s Options property is set to None by default, there’s at least two other possibilities, and one of them, is ReadOnly. The first example uses New-Variable to create a new, read-only variable named String3, and Get-Variable and Select-Object to return all the variable’s properties.

New-Variable -Name String3 -Value 'A new week; another Monday.' -Option ReadOnly

Get-Variable -Name String3 | Select-Object *

Name        : String3
Description :
Value       : A new week; another Monday.
Visibility  : Public
Module      :
ModuleName  :
Options     : ReadOnly
Attributes  : {}

Now, what does it mean that it’s read-only? It means that we can’t change the value that’s stored by the variable, as is indicated below.

Set-Variable -Name String3 -Value 'A new week; another Friday!'

Set-Variable : Cannot overwrite variable String3 because it is read-only or constant.

Notice in the error message that it indicates we can’t overwrite the variable because the variable is read-only or constant. It turns out that we actually can change the value stored in a read-only variable, if we use the -Force parameter.

Set-Variable -Name String3 -Value 'We Want Friday!' -Force

Get-Variable -Name String3 | Select-Object *

Name        : String3
Description :
Value       : We Want Friday!
Visibility  : Public
Module      :
ModuleName  :
Options     : ReadOnly
Attributes  : {}

So, in the end, a read-only variable can be overwritten if absolutely necessary. Keep this read-only option in mind as you create variables in Windows PowerShell. There may be times you create variables and want to mostly protect the original, stored value. In that case, you can choose to make them read-only.

If we already have a variable created, how do we then make it read-only? We have to use Set-Variable, whether we created the variable with New-Variable, or the standard way, as is used below.

$String4 = 'Last variable for today.'
$String4

Last variable for today.

(Get-Variable -Name String4).Options
None

Get-Variable -Name String4 | Set-Variable -Option ReadOnly

(Get-Variable -Name String4).Options
ReadOnly

To clear a variable’s value (to continue to allow a variable to exist, but to remove the value it stored), we have to use the -Force parameter. Same goes for removing the entire variable; that will also require the -Force parameter if it’s a read-only variable.

Clear-Variable -Name String3 -Force

Remove-Variable -Name String4 -Force

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