Expand property values
You can use parenthetical commands to provide parameter input without using the pipeline. In some cases, however, you might have to manipulate the objects produced by a parenthetical command so that the command’s output is of the type that the parameter requires.
For example, you might want to list all the processes that are running on every computer in the domain. In this example, imagine that you have a very small lab domain that contains just a few computers. You can get a list of every computer in the domain by running the following command:
Get-ADComputer –Filter *
However, this command produces objects of the type ADComputer. You couldn't use those objects directly in a parenthetical command such as in the following command:
Get-Process –ComputerName (Get-ADComputer –Filter *)
The –ComputerName parameter expects objects of the type String. However, the parenthetical command doesn't produce String type objects. The –ComputerName parameter only wants a computer name. However, the command provides it an object that contains a name, an operating system version, and several other properties.
You could try the following command:
Get-Process –ComputerName (Get-ADComputer –Filter * | Select-Object –Property Name)
This command selects only the Name property. This property is still a member of a whole ADComputer object. It's the Name property of an object. Although the Name property contains a string, it isn't itself a string. The –ComputerName parameter expects a string, not an object with a property. Therefore, that command doesn't work either.
The following command achieves the goal of passing the computer name as a string to the -ComputerName parameter:
Get-Process –ComputerName (Get-ADComputer –Filter * | Select-Object –ExpandProperty Name)
The –ExpandProperty parameter accepts one, and only one, property name. When you use that parameter, only the contents of the specified property are produced by Select-Object. Some people refer to this feature as extracting the property contents. The official description of the feature is expanding the property contents.
In the preceding command, the result of the parenthetical command is a collection of strings that are passed as individual strings, not an array, and that is what the –ComputerName parameter expects. The command will work correctly; however, it might produce an error if one or more of the computers can't be reached on the network.
Expanding property values also works when piping output. Consider the following example:
Get-ADUser Ty -Properties MemberOf | Get-ADGroup
This command returns an error because Windows PowerShell can't match the MemberOf property to any property of Get-ADGroup.
However, if you expand the value of the MemberOf property, as in the following example, Windows PowerShell can match the resulting output to a value that Get-ADGroup understands as valid input:
Get-ADUser Ty -Properties MemberOf | Select-Object -ExpandProperty MemberOf | Get-ADGroup