How do you support PowerShell's -WhatIf & -Confirm parameters in a Cmdlet that calls other Cmdlets?

Question

I have a PowerShell script cmdlet that supports the -WhatIf & -Confirm parameters.

It does this by calling the $PSCmdlet.ShouldProcess() method before performing the change.
This works as expected.

The problem I have is that my Cmdlet is implemented by calling other Cmdlets and the -WhatIf or -Confirm parameters are not passed along to the Cmdlets I invoke.

How can I pass along the values of -WhatIf and -Confirm to the Cmdlets I call from my Cmdlet?

For example, if my Cmdlet is Stop-CompanyXyzServices and it uses Stop-Service to implement its action.

If -WhatIf is passed to Stop-CompanyXyzServices I want it to also be passed to Stop-Service.

Is this possible?

Answer 1

Passing parameters explicitly

You can pass the -WhatIf and -Confirm parameters with the $WhatIfPreference and $ConfirmPreference variables. The following example achieves this with parameter splatting:

if($ConfirmPreference -eq 'Low') {$conf = @{Confirm = $true}}

StopService MyService -WhatIf:([bool]$WhatIfPreference.IsPresent) @conf

$WhatIfPreference.IsPresent will be True if the -WhatIf switch is used on the containing function. Using the -Confirm switch on the containing function temporarily sets $ConfirmPreference to low.

Passing parameters implicitly

Since the -Confirm and -WhatIf temporarily set the $ConfirmPreference and $WhatIfPreference variables automatically, is it even necessary to pass them?

Consider the example:

function ShouldTestCallee {
    [cmdletBinding(SupportsShouldProcess=$true,ConfirmImpact='Medium')] 
    param($test)

    $PSCmdlet.ShouldProcess($env:COMPUTERNAME,"Confirm?")
}


function ShouldTestCaller {
    [cmdletBinding(SupportsShouldProcess=$true)]
    param($test)

    ShouldTestCallee
}

$ConfirmPreference = 'High'
ShouldTestCaller
ShouldTestCaller -Confirm

ShouldTestCaller results in True from ShouldProcess()

ShouldTestCaller -Confirm results in an confirm prompt even though I didn't pass the switch.

Edit

@manojlds answer made me realize that my solution was always setting $ConfirmPreference to 'Low' or 'High'. I have updated my code to only set the -Confirm switch if the confirm preference is 'Low'.