Prof. Powershell

Out, Out Darn Variable

PowerShell cmdlets come well-stocked with common parameters. Let's look at what you can get out of the -OutVariable parameter.

• By Jeffery Hicks
• 09/10/2008

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

The only difference is that 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 I want to do more with the files all I have to do is use the $myfiles variable. There's no need to rerun the DIR command, unless I 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).sum
2809966
PS C:\> $docfiles | Select Fullname

So, you see ... Parameters are all about efficiency. Look at the help file about_CommonParameters for more information.