What is the difference between variables $a and $b?
$a = (Get-Date).DayOfWeek
$b = Get-Date | Select-Object DayOfWeek
I tried to check
$a.GetType
$b.GetType
MemberType : Method
OverloadDefinitions : {type GetType()}
TypeNameOfValue : System.Management.Automation.PSMethod
Value : type GetType()
Name : GetType
IsInstance : True
MemberType : Method
OverloadDefinitions : {type GetType()}
TypeNameOfValue : System.Management.Automation.PSMethod
Value : type GetType()
Name : GetType
IsInstance : True
But there seems to be no difference although the output of these variables looks different.
3 Answers
First of all, you lack parentheses to call GetType. What you see is the MethodInfo describing the GetType method on [DayOfWeek]. To actually call GetType, you should do:
$a.GetType();
$b.GetType();
You should see that $a is a [DayOfWeek], and $b is a custom object generated by the Select-Object cmdlet to capture only the DayOfWeek property of a data object. Hence, it's an object with a DayOfWeek property only:
C:\> $b.DayOfWeek -eq $a
True
Select-Object creates a new psobject and copies the properties you requested to it. You can verify this with GetType():
PS > $a.GetType().fullname
System.DayOfWeek
PS > $b.GetType().fullname
System.Management.Automation.PSCustomObject
Select-Object returns a custom PSObject with just the properties specified. Even with a single property, you don't get the ACTUAL variable; it is wrapped inside the PSObject.
Instead, do:
Get-Date | Select-Object -ExpandProperty DayOfWeek
That will get you the same result as:
(Get-Date).DayOfWeek
The difference is that if Get-Date returns multiple objects, the pipeline way works better than the parenthetical way as (Get-ChildItem), for example, is an array of items. This has changed in PowerShell v3 and (Get-ChildItem).FullPath works as expected and returns an array of just the full paths.
