英文:
Check if a variable is a string list/array?
问题
以下代码返回True。在PowerShell中正确检查类型的方式是什么？
$e = @(1,2)
$e -ne $null -and $e.GetType() -eq (@("")).GetType()
更新：
以下代码将返回False。预期结果应为True。
$e = @('1','2')
$e -is [string[]]
英文:
The following code returns True. What's the correct way to check the type in PowerShell?
$e = @(1,2)
$e -ne $null -and $e.GetType() -eq (@("")).GetType()
Update:
The following code will return false. It's expected to be true.
$e = @('1','2')
$e -is [string[]]
答案1
得分: 3
您可以使用-is运算符来检查类型，以确定它是否为数组：
$arr = 1, 2
$arr -is [array]
然而，更加谨慎的方法可能是检查对象是否实现了IEnumerable接口，因为有许多集合类型不一定是数组，但是可以进行迭代：
$arr = 1, 2
$arr -is [System.Collections.IEnumerable]
还请注意，如果将cmdlet/function的结果分配给一个变量，该结果可以返回多个元素，但默认情况下，如果返回的集合只包含一个元素，它将被解开并分配为单个值。您可以使用以下技巧之一来强制返回的集合被评估/分配为一个数组（以Get-Process作为示例）：
$arr = @( Get-Process iexplore ) # 强制返回值作为集合的一部分，即使只返回单个进程。
$arr -is [System.Collections.IEnumerable] # true
或者，您还可以使用,符号来强制返回的值被评估为集合（在这种情况下，您需要在cmdlet/function调用中使用子表达式）：
$arr = , ( Get-Process iexplore )
$arr -is [System.Collections.IEnumerable]
如果您要检查一个泛型集合（其类型定义在System.Collections.Generic命名空间中），您还可以使用System.Collections.Generic.IEnumerable[T]来检查与集合相关联的类型，其中T是数组中允许的元素类型。例如：
$list = New-Object System.Collections.Generic.List[string]
$list -is [System.Collections.Generic.IEnumerable[string]] # true
英文:
You can use the -is operator to check the type to check if it's an array:
$arr = 1, 2
$arr -is [array]
However, it is probably more prudent to check that the object implements IEnumerable, since there are many collection types that are not specifically arrays but are iterable:
$arr = 1, 2
$arr -is [System.Collections.IEnumerable]
Also note that if you assign the result of a cmdlet/function to a variable that can return more than one element, but it only returns a collection with a single element, by default it will be unrolled and assigned as a single value. You can force a returned collection to be evaluated/assigned as an array with one of the following techniques (using Get-Process as an example of this):
$arr = @( Get-Process iexplore ) # ===========> Forces the returned value to be part of a collection,
# even if only a single process is returned.
$arr -is [System.Collections.IEnumerable] # ==> true
or you can use the , notation to force the returned values to be evaluated as a collection as well (you will need to sub-express your cmdlet/function call in this case):
$arr = , ( Get-Process iexplore )
$arr -is [System.Collections.IEnumerable]
If you are checking a generic collection (a collection whose type is defined within the System.Collections.Generic namespace), you can also check against the collection's associated type using System.Collections.Generic.IEnumerable[T] instead, where T is the type of element allowed in the array. For example:
$list = New-Object System.Collections.Generic.List[string]
$list -is [System.Collections.Generic.IEnumerable[string] # ==> true
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