Get-ChildItem -Filter Array

Question

Situation:

1. Get-ChildItem $Path -Filter *.dll works for me

2. This works:

   $Path = "$env:windir\system32\*"
   $GuyArray = @("*.dll", "*.exe")
   
   Get-ChildItem $Path -Include $GuyArray
   

3. But I cannot get this working:

   $Path = "$env:windir\system32\*"
   $GuyArray = @("*.dll", "*.exe")
   
   Get-ChildItem $Path -Filter $GuyArray
   

Error message:

Cannot convert 'System.Object[]' to the type 'System.String' required by parameter 'Filter'. Specified method is not supported.

Questions:

1. Does this mean that -Include supports multiple values, but -Filter only allows one value?
2. If the above explaination is correct, is there a way I could have discovered this from Get-Help gci?

Answer 1

Does this mean that -Include supports multiple values, but -Filter only allows one value?

Yes.

If the above explaination is correct, is there a way I could have discovered this from Get-Help gci?

Yes, but you do not get much information by Get-Help gci -Parameter Filter. But you still can see it is a string, not an array. As for the details, Filter is a provider-specific filter. Get-Help gci cannot tell you anything about implementation in a particular provider. In theory, Get-Help FileSystem (help about this provider) should have explained this.

P.S. Also note that this filter rather uses CMD wildcard rules than PowerShell wilcard rules.

Answer 2

Using Get-Help:

> get-help Get-ChildItem

NAME
    Get-ChildItem

SYNTAX
    Get-ChildItem [[-Path] <string[]>] [[-Filter] <string>] [-Exclude <string[]>] [-Force] [-Include <string[]>] [-Name] [-Recurse] [-UseTransaction] [<CommonParameters>]

The SYNTAX section includes the parameter types, from which you can see that Filter is a string, and Path an array.

Answer 3

Question 1:

Yes. -Filter accepts only [string] as input. -Include accepts [String[]].

Question 2:

Get-help get-childitem -parameter filter gives

-Filter <string>
...explanation...

Get-help get-childitem -parameter include gives

-Include <string[]>
...explanation...