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.
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.
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.
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).
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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?'
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
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'.
If you like this page then please share it with your friends
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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