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58. Using ShouldProcess

Note

The below information is extensively based in information taken from the PowerShell® Notes for Professionals book. I plan to extend this information based on my day to day usage of the language.

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Parameter Details
Target The resource being changed.
Action The operation being performed. Defaults to the name of the cmdlet.

58.1: Full Usage Example

Other examples couldn't clearly explain to me how to trigger the conditional logic.

This example also shows that underlying commands will also listen to the -Confirm flag!

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<#
    Restart-Win32Computer
#>
function Restart-Win32Computer
{
  [CmdletBinding(SupportsShouldProcess = $true,ConfirmImpact = 'High')]
  param (
    [parameter(Mandatory = $true,ValueFromPipeline = $true,ValueFromPipelineByPropertyName = $true)]
    [string[]]$computerName,
    [parameter(Mandatory = $true)]
    [string][ValidateSet('Restart','LogOff','Shutdown','PowerOff')] $action,
    [boolean]$force = $false
  )
  BEGIN {
    # translate action to numeric value required by the method
    switch($action) {
      'Restart'
      {
        $_action = 2
        break
      }
      'LogOff'
      {
        $_action = 0
        break
      }
      'Shutdown'
      {
        $_action = 2
        break
      }
      'PowerOff'
      {
        $_action = 8
        break
      }
    }
    # to force, add 4 to the value
    if($force)
    {
      $_action += 4
    }
    Write-Verbose -Message "Action set to $action"
  }
  PROCESS {
    Write-Verbose -Message "Attempting to connect to $computerName"
    # this is how we support -whatif and -confirm
    # which are enabled by the SupportsShouldProcess
    # parameter in the cmdlet bindnig
    if($pscmdlet.ShouldProcess($computerName)) 
    {
      Get-WmiObject -Class win32_operatingsystem -ComputerName $computerName | Invoke-WmiMethod -Name
      Win32Shutdown -argumentlist $_action
    }
  }
}
#Usage:
#This will only output a description of the actions that this command would execute if -WhatIf is removed.
'localhost', 'server1'| Restart-Win32Computer -action LogOff -whatif

#This will request the permission of the caller to continue with this item.
#Attention: in this example you will get two confirmation request because all cmdlets called by this cmdlet that also support ShouldProcess, will ask for their own confirmations...
'localhost', 'server1'| Restart-Win32Computer -action LogOff -Confirm

58.2: Adding -WhatIf and -Confirm support to your cmdlet

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function Invoke-MyCmdlet {
  [CmdletBinding(SupportsShouldProcess = $true)]
  param()
  # ...
}

58.3: Using ShouldProcess() with one argument

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if ($PSCmdlet.ShouldProcess("Target of action")) {
 # Do the thing
}

When using -WhatIf :

What if: Performing the action "Invoke-MyCmdlet" on target "Target of action"

When using -Confirm :

Are you sure you want to perform this action? Performing operation "Invoke-MyCmdlet" on target "Target of action"

[Y] Yes [A] Yes to All [N] No [L] No to All [S] Suspend [?] Help (default is "Y"):