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Tips and Tricks

Prof. Powershell: Get Smart and Get -Out
PowerShell cmdlets come well-stocked with common parameters. Let's look at what you can get out of the -OutVariable parameter.

by Jeffery Hicks

Just about all PowerShell cmdlets support a set of common parameters. These parameters are the same across all cmdlets regardless of the cmdlet's primary parameters -- which is to say the ones you use the most, like -computername. One common parameter you might want to use is -outvariable.

Usually you save a cmdlet's output to a variable like this:

PS C:\> $svc = get-service

This is perfectly acceptable because you likely plan on using $svc later. But you could also create $svc this way using -outvariable:

PS C:\> get-service -outvariable svc

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The only difference is this expression will also write the results to the console. But you'll still have a $svc object. Notice that the name of the variable doesn't need the $. This is because the parameter's value is a variable name and not an object. Here's another way you might use it:

PS C:\> get-service -outvariable svc | where 
	{$_.status -eq "stopped"} -outvariable stopped | 
    Sort Displayname | Select DisplayName
PS C:\> $stopped.count
86
PS C:\> $svc.count
159

This one-line PowerShell expression will produce a sorted list of all stopped services' displaynames, with some added benefits. The results of Get-Service have been saved to $svc. The filtered results from the Where-Object expression have been saved to variable $stopped. Now you can reuse the filtered services variable to work with just stopped services, without having to rerun or retype a long PowerShell command, like this:

PS C:\> $svc | export-
clixml stoppedservices.xml

This is an especially useful technique for long-running commands, where you need information parsed in several ways but don't want to have to rerun a command. Or where the original objects will be lost but you might still need them:

PS C:\> dir d:\files -recurse -outvariable myfiles | 
measure-object length -sum -maximum | 
Select Count,Sum,Maximum

If you want to do more with the files all you have to do is use the $myfiles variable. There's no need to rerun the DIR command, unless you want an updated list:

PS C:\> $myfiles | sort extension | 
   group extension | sort Count -descending | format-table Count,
   Name -autosize
PS C:\> ($myfiles | where {$_.extension -match ".doc"} -outvariable 
   docfiles | measure-object length -sum).sum2809966
PS C:\> $docfiles | Select Fullname

Parameters are all about efficiency. Look at the help file about_CommonParameters for more information.

Jeffery Hicks, MCSE, MCSA, is a Microsoft PowerShell MVP and scripting guru for SAPIEN Technologies. Jeff is a 16 year IT veteran who has co-authored and written several books, courseware and training videos on administrative scripting and automation. He is the co-author of Advanced VBScript for Microsoft Windows Administrators (Microsoft Press) and Windows PowerShell:TFM (SAPIEN Press). His latest is WSH and VBSCript Core:TFM (SAPIEN Press). You can contact Jeffery about "Prof. Powershell: Get Smart and Get -Out" at jhicks@sapien.com.