Introduction to PowerShell Scripting -WhatIf and -Confirm
PowerShell’s WhatIf and confirm are two great commands for testing complicated scripts without risking the code running amok. For example, if you decide to delete files by using a script containing wildcards, there could be all manner of unexpected side effects. By employing PowerShell, and appending the -WhatIf switch, you get a preview of would happen without risking any damage.
PowerShell WhatIf and -Confirm Commands
- Mission to Delete Files
- PowerShell -WhatIf Example
- PowerShell -Confirm Example
- PowerShell Cmdlets Containing -Confirm and -WhatIf
Mission to Delete Files
Let us take a real life example, we wish to delete files, but because we are using wildcards we are concerned about deleting the wrong type of file. Instead of gung-ho Guy deleting the files – ready or not, we will take the cautious approach and append -WhatIf. The result is PowerShell completes the command and shows us the result, but does not delete any files. Incidentally, I cannot find a delete verb in PowerShell, there is however, a remove verb.
PowerShell -WhatIf Example
By adding -WhatIf at the end of the command we are saying to PowerShell: ‘Just test, don’t actually make any permanent changes’. Please note, there could be serious consequences if you don’t use the -WhatIf switch. If you don’t understand what you are doing, you could delete all your .txt files.
# PowerShell -WhatIf safety parameter
Clear-Host
Get-Childitem C:\SomeFile\*.txt -Recurse | Remove-Item -WhatIf
Note 1: For safety I chose a fictitious folder, just in case the script ran amok.
A breakdown of what the above script achieves
Get-Childitem (Rather like dir)
C:\SomeFile (Location to start)
-Include *.txt (The pattern to look for)
-Recurse (Search subdirectories)
| Remove-Item (The equivalent of Delete)
-WhatIf (PowerShell please test, but don’t actually complete the operation, in this case, just show me which files with a .txt extension would be deleted if I removed the -WhatIf).
Another example of the -WhatIf switch
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PowerShell -Confirm Example
Here is another PowerShell parameter that you append to a ‘normal’ script – confirm. It really is a case of confirm by name, and confirm by nature. PowerShell says to you: ‘Do you really want to do this?’
# PowerShell -Confirm parameter
Get-Childitem C:\Dzxocs\*.* -Include *.txt -Recurse | Remove-Item -Confirm
Note 2: For safety I chose a fictitious folder, just in case the script went wrong.
The result of -Confirm is that PowerShell presents you with choices, however, remember this is now ‘live’ therefore if you press [Y] or [A] then files will be deleted.
[Y] Yes [A] Yes to all [N] No [L] No to all [S] Suspend
PowerShell -Confirm:$False
I stumbled upon the $False commands for unattended scripts. What I am thinking is that if you are running scripts which require a response, then you could try appending -Confirm:False (do remember that colon).
# PowerShell -Confirm for unattended machines
Restart-Service Bits -Confirm:$False
Get Help About Variable Preferences »
How To Research PowerShell Cmdlets Containing -Confirm and -WhatIf
My idea behind this research is to list the PowerShell cmdlets that contain ‘confirm’ in their parameters.
# Research PowerShell parameters for 'Confirm'
Get-Command | where { $_.parameters.keys -Contains "Confirm"}
Refine Get-Command with -CommandType
# PowerShell Confirm cmdlets
Get-Command -commandType cmdlet `
| where { $_.parameters.keys -Contains "Confirm"} | Format-Table Name
Note 3: You could substitute ‘WhatIf’ for ‘Confirm’.
Summary of PowerShell -WhatIf and -Confirm Commands
PowerShell’s WhatIf switch is hand if you need a dry run of your script. Once you have used PowerShell’s -Confirm, or -WhatIf commands you will think, ‘Why don’t all scripting languages have these safety features’.
See more examples of PowerShell syntax
• PowerShell Tutorials • Syntax • PowerShell functions • Plist • RegEx • -Com
• PowerShell -confirm • WhatIf • -Match • -Like • -Online • Where • Free WMI Monitor
• -ErrorAction • -Replace • Windows PowerShell • PowerShell module directory
Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.
