Scripting Games Commentary: IV Whatif
PowerShell cmdlets that change the system state have a –whatif parameter to test what would happen for example
PS> Get-Service sp* | Stop-Service -WhatIf
What if: Performing operation "Stop-Service" on Target "Print Spooler (Spooler)".
What if: Performing operation "Stop-Service" on Target "Software Protection (sppsvc)".
What if: Performing operation "Stop-Service" on Target "SPP Notification Service (sppuinotify)".
I saw a number of entries where people were creating their own functions to supply whatif parameters.
STOP.
This is functionality built into advanced functions
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| function test-whatif {
[CmdletBinding(SupportsShouldProcess=$true)]
param (
[parameter(ValueFromPipeline=$true,
ValueFromPipelineByPropertyName=$true)]
[string]$name
)
PROCESS{
if ($psCmdlet.ShouldProcess("$name", "Stopping Service")) {
"Service $name will be stopped"
}
}#process
} |
The important part is [CmdletBinding(SupportsShouldProcess=$true)] This sets up the use of –whatif. -Confirm we’ll look at another time
This is the working bit
if ($psCmdlet.ShouldProcess("$name", "Stopping Service")) {
"Service $name will be stopped"
}
Check to see if Shouldprocess is called – the parameters are the object the actions is performed on and the action that is being performed respectively (often a cmdlet name) – is it is print the whatif message otherwise perform the normal action
It is used like this
PS> Get-Service sp* | test-whatif
Service Spooler will be stopped
Service sppsvc will be stopped
Service sppuinotify will be stopped
No –whatif parameter so we get the action – in this case just a message
if we supply –whatif
PS> Get-Service sp* | test-whatif -WhatIf
What if: Performing operation "Stopping Service" on Target "Spooler".
What if: Performing operation "Stopping Service" on Target "sppsvc".
What if: Performing operation "Stopping Service" on Target "sppuinotify".
We get a What if:…. message
Huge piece of functionality for practically zero code.