在 PowerShell 中使用的 GetType，变量之间的区别

变量 $a和 $b的区别是什么？

$a = (Get-Date).DayOfWeek
$b = Get-Date | Select-Object DayOfWeek

我试着查过了

$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

尽管这些变量的输出看起来不同，但似乎没有什么区别。

452280 次浏览
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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
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最佳答案

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
小开

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.


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