how to use 'dry-run' in powershell

Question

I'm just a starter, dry-run is pretty useful to make a parameter to test, can any body tell me how to use it with an easy way? I googled that but few results on its uses.

Thank you very much

Answer 1

Use on existing cmdlets

Explicitly supply the -WhatIf parameter:

rm foo.txt -WhatIf

Result:

What if: Performing operation "Remove File" on Target "C:\temp\foo.txt".

Use on existing cmdlets within a function or script

SupportsShouldProcess attribute automatically propagates -WhatIf to supported cmdlets:

function do-stuff
{
    [CmdletBinding(SupportsShouldProcess=$True)]
    param([string]$file)
    Remove-Item $file
}

do-stuff foo.txt -WhatIf

Result:

What if: Performing operation "Remove File" on Target "C:\temp\foo.txt".

Use on your own code blocks

Explicitly use ShouldProcess() method to determine whether -WhatIf was passed:

function do-stuff
{
    [CmdletBinding(SupportsShouldProcess=$True)]
    param([string]$file)
    if ($PSCmdlet.ShouldProcess($file)) {
        Write-Host "Deleting file"
        Remove-Item $file
    }
}

do-stuff foo.txt -WhatIf

Result:

What if: Performing operation "do-stuff" on Target "foo.txt".

Use on Nested functions in the same module

SupportsShouldProcess attribute automatically propagates -WhatIf to nested functions:

function do-stuff
{
    [CmdletBinding(SupportsShouldProcess=$True)]
    param([string]$file)
    if ($PSCmdlet.ShouldProcess($file)) {
        Write-Host "Deleting file"
        Remove-Item $file
    }
    inner "text"
}

function inner
{
    [CmdletBinding(SupportsShouldProcess=$True)]
    param([string]$s)
    if ($PSCmdlet.ShouldProcess($s)) {
        Write-Host "Inner task"
    }
    $s | out-file "temp9.txt"
}
do-stuff foo.txt -WhatIf

Result:

What if: Performing operation "do-stuff" on Target "foo.txt".
What if: Performing operation "inner" on Target "text".
What if: Performing operation "Output to File" on Target "temp9.txt".

Use on Nested functions in a different module

Unfortunately, -WhatIf does not propagate automatically to functions defined in a different module. See Powershell: How to get -whatif to propagate to cmdlets in another module for discussion and workaround for this.

Answer 2

You are probably referring to the -WhatIf and -Confirm parameters on cmdlets. You can read up about them in Get-Help about_commonParameters:

Risk Management Parameter Descriptions

-WhatIf[:{$true | $false}]

Displays a message that describes the effect of the command, instead of executing the command.

WhatIf parameter overrides the value of the $WhatIfPreference variable for the current command. Because the default value of the $WhatIfPreference variable is 0 (disabled), WhatIf behavior is not performed without the WhatIf parameter. For more information, type the following command:

get-help about_preference_variables

Valid values:

$true (-WhatIf:$true). Has the same effect as -WhatIf.
$false (-WhatIf:$false). Suppresses the automatic WhatIf behavior that results when the value of the $WhatIfPreference variable is 1.

For example, the following command uses the WhatIf parameter in a Remove-Item command:

PS> remove-item date.csv -whatif

Instead of removing the item, Windows PowerShell lists the operations it would perform and the items that would be affected. This command produces the following output:

What if: Performing operation "Remove File" on
Target "C:\ps-test\date.csv".

-Confirm[:{$true | $false}]

Prompts you for confirmation before executing the command.

The Confirm parameter overrides the value of the $ConfirmPreference variable for the current command. The default value is High. For more information, type the following command:

get-help about_preference_variables

Valid values:

$true (-WhatIf:$true). Has the same effect as -Confirm.
$false (-Confirm:$false). Suppresses automatic confirmation, which occurs when the value of $ConfirmPreference is less than or equal to the estimated risk of the cmdlet.

For example, the following command uses the Confirm parameter with a Remove-Item command. Before removing the item, Windows PowerShell lists the operations it would perform and the items that would be affected, and asks for approval.

PS C:\ps-test> remove-item tmp*.txt -confirm

This command produces the following output:

Confirm
Are you sure you want to perform this action?
Performing operation "Remove File" on Target " C:\ps-test\tmp1.txt
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend
[?] Help (default is "Y"):

Answer 3

I think what you are looking for is actually the module Pester (delivered with Windows 10 since first release) that can perform mock ups. I.e. pretend to run parts of the code for doing real isolated Unit test.

This is a big subject though...

MS Scripting - What is Pester and Why Should I Care?