Scripting PowerShell -WhatIf and -Confirm

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

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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

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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'.

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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.

 

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