Prof. Powershell

Get-Unique -- Same But Different

I still prefer the Select-Object cmdlet, but Get-Unique has a way of weeding out the dupes that's, well, different.

• By Jeffery Hicks
• 12/17/2008

PS C:\> get-wmiobject win32_service | select startname | sort startname | get-unique -AsString

While this works, it is not as efficient as using Select-Object, and it's not something I would use for returning unique properties. Get-Unique is really designed to return unique objects from a collection. Here's a very simple illustration:

PS C:\> 6,1,3,3,2,5,5,5,5,6 | sort | get-unique
1
2
3
5
6

The array of integers is sorted (you should sort objects before you pipe them to Get-Unique for best results) and then piped to Get-Unique. Here's another example. It's not uncommon to have multiple processes with the same name and this expression weeds out the duplicates:

PS C:\> get-process | sort-object | select processname | get-unique -AsString

This will return a unique list of process names. The AsString parameter instructs Get-Unique to treat the incoming the data as string. The cmdlet's default behavior is to treat incoming data as an object as I showed in the earlier example. You can explicitly tell Get-Unique to treat data as an object using the OnType parameter:

PS C:\> 1,"a","b",3,4.5 | sort | get-unique -ontype
1
4.5
a

I've piped an array with a few different types of objects, sorted them and then used Get-Unique to return unique objects based on type.

Most cmdlets return objects of the same type so often Get-Unique isn't very useful. But if you have an array you've created with a variety of different object types, as I did in my last example, then Get-Unique can weed out the duplicate objects.