Marcus Oh asked me in IM today how he could tell if an object is an array. I could think of a couple of ways, but one is “more better”.

The first way is to check for the presence of the count property.

PS C:\> $a = 1,2,3
PS C:\> $a.Count
3
PS C:\> $b = "test"
PS C:\> $b.count
PS C:\>

This works, but it’s probably not the best way to do it. There could be other object types which do have a count property.

Here’s a better way:

PS C:\> $a.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

PS C:\> $b.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     String                                   System.Object

You can check the BaseType of an object to see if it is “System.Array”. So what’s the best way to check for this in a script? You can use the –Is operator to validate object types, that’s what its for.

PS C:\> $a -is [system.array]
True

Here’s a short function to use in a script:

PS C:\> function Test-Array { if ( $Args[0] -is [system.array] ) { $true } }
PS C:\> test-array $a
True
PS C:\> test-array $b

Note that you can’t easily do this in a pipeline, because PowerShell will unwrap the array and send each element to a function or script. There are ways to handle this, but we can talk about that another time.