Ezine 182 PowerShell -confirm
Which ever version of PowerShell you are using, take the time to learn about -confirm and -whatIf. The benefit is that you can test new commands before you action them, this is particularly useful when contemplating changing settings or deleting objects.
- This Week’s Secret
- This Week’s Mission
- Listing the Environmental Variables
- List Temporary Files
- List of PowerShell Cmdlets in Exchange 2010 Server
- The -confirm Parameter in Action
I feel like an expectant father waiting for the birth of PowerShell v 2.0. Life is on hold, at least as far as this ezine is concerned, because I dare not encourage people to use the CTP (Community Technology Preview) of PowerShell 2.0 on live systems.
The reason I have chosen to feature -confirm this week is because it’s important to get into the habit of testing before you issue complex PowerShell commands. The danger is that when you are under pressure, perhaps we are performing an unfamiliar task and we change something that we later regret. If only we had tested the unfamiliar syntax with -confirm then we could have seen the error in the trial run and thus prevented a disaster.
In a nutshell think of -confirm as putting PowerShell into testing mode. Actually, -confirm has a sister command called -whatIf, this switch truly simulates the command but without making any changes.
This week I have three disparate tasks, however, once I reveal the elements then perhaps you can see how they are linked. What I want to show you is how to delete temporary files, to list the Environmental Variables, and to learn about the -confirm parameter. Naturally, these techniques will work equally well in PowerShell v 2.0.
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For the sake of safety, and for the sake of a smooth learning progression, let us start with a script which merely lists the operating system’s built-in environmental variables.
# PowerShell script to list Environmental variables
get-ChildItem -path Env: |sort-Object name
Note 1: In PowerShell’s the get-ChildItem cmdlet usually involves a drive letter and folder, however, this example accesses the env: namespace.
Note 2: ‘| sort-Object name’ is an optional refinement to order the output of get-ChildItem.
Note 3: Naturally, you should see Tmp and Temp amongst the list of 30+ environmental variables.
Before we issue a command to delete files, let us merely list the temporary files. For this task we employ two additional parameters: -include, which filters the file extension, and -recurse which loops through the files and seeks out any sub-directories.
# PowerShell script to list .tmp files
$Location = "$Env:Temp"
get-ChildItem $Location -include *.tmp -recurse
Note 1: If you don’t get any results, substitute *.* for *.tmp. If you still don’t get any results try a different value for the path controlled by the $Location variable.
Note 2: Confession, when I first ran this script I forgot the dollar sign. Whereas in the previous example -path Env: correctly listed the variables, here $Env:Temp needs the dollar sign to access a specific environmental variable, plain Env:Temp does not work.
Now we are ready to build on the success of the first two scripts. Here is where we unleash remove-Item, which is the PowerShell command to zap stuff. Incidentally there is no delete verb PowerShell consistently uses the pattern ‘remove-Noun’. Now the whole point of this example is to master the safety catch in the form of -confirm. When the script runs, if you are in anyway unsure choose ‘No’ meaning don’t delete anything.
# This script will delete all files in the user’s Temp folder
get-ChildItem $Location -recurse | remove-Item -confirm
Expected result: PowerShell asks you if you want to remove a whole bunch of temporary files. You could respond with ‘No’, or ‘No to All’. Next, you could run the same script again and this time respond with ‘Yes’, or even, ‘Yes to All’.
Challenge 1: Substitute -whatIf for -confirm.
Challenge 2: Research the remove verb with:
get-Command -verb remove
Note: -confirm and -whatIf only work with pure PowerShell commands, I cannot get them to work with WMI syntax. Actually, this is not such a big loss as when scripting WMI one is usually retrieving information and not removing stuff.
Summary of -confirm
If you are coming from scripting languages such as VBScript, you may not be aware that PowerShell has two handy commands for testing before you finally unleash a command. All that you do is append -confirm or -whatIf to the intended code.
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