Get-ChildItem -filter or -include..when, why and how ?

I did a quick PowerShell training and one of the attendees did some question to me about –filter and –include parameters in the  get-childitem. I will reproduce his questions with my answers :

Q – What is the difference between –filter and –include ?

R – The parameter filter is implemented by the Provider and the parameter include by PowerShell.

Q – And……?

R – This means that Include is a “general way” to search in all providers. Filter is unique implemented by the provider and for this reason faster that Include.

Q-Then, I cannot use filter in all drives ?

R – No, just in the drives that have a provider that support the filter.

Q- How can I know what providers have  filter support ?

R – Use the cmdlet Get-PSprovider to get a list of all providers, then in the column Capabilities you will see what this provider supports..or what it can do.  See:

The only provider that accepts Filter is the filesystem provider.

Q – Hummm..then if I wan to find a specific registry  key or a variable, I need to use the include  parameter ?

R – Yes. Lets use the Variable drive that is implemented by the Variable provider. First lets create a variable :

$Jedi = ‘Yoda’

$Sith = ‘Darth Vader’

Then lets connect to the variable drive:

cd variable:  #or set-location variable:

If we try :

Get-ChildItem –filter Jedi –recurse

Get-ChildItem : Cannot call method. The provider does not support the use of filters.
At line:1 char:14
+ Get-ChildItem <<<<  –filter Jedi
    + CategoryInfo          : NotImplemented: (:) [Get-ChildItem], PSNotSupportedException
    + FullyQualifiedErrorId : NotSupported,Microsoft.PowerShell.Commands.GetChildItemCommand

but if we try :

Get-Childitem –include Jedi –recurse

PS Variable:\> Get-Childitem –include Jedi –recurse

Name        Value
—-        —–
Jedi        Yoda

Also –include parameter is a string[] type, then it accepts a string array :

PS Variable:\> Get-Childitem –include Jedi,Sith –recurse

Name   Value
—-   —–
Jedi   Yoda
Sith   Darth Vader

The same with SQLServer provider. It only accepts include. Lets use our Database PowerShell to test it. We have 3 tables called PoshTraining1,PoshTraining2 and PoshTraining3 and 2 stored procedures called sp_PoshTraining1 and sp_PoshTraining2

Lets connect to the SQLServer drive:

cd sqlserver:

Now, in the root lets search for this objects:

get-ChildItem –include *poshtraining* –recurse | format-list schema,name, pspath

By the pspath I know what object it is.

we can also split the select to get the second last value in the pspath , that is the object type :

get-ChildItem –include *poshtraining* –recurse |
select  schema,
        name,
        @{E={($_.pspath -split ‘\\’)[-2]};N= ‘ObjectType’}

Q – There is some property to know the Object Type unless to use the split ?

R – I don’t know, need to check the properties using Get-Member :

get-ChildItem –include *poshtraining* –recurse | Get-Member

Q – Why are you saying that connect to drive and not to the provider ?

See. The provider is a .net program that allow to us use the data as mounted drives. We can connect to the provider mounting  a drive or a PowerShell Provider Drive –PSDrive. If you see in the providers, we have the Variable and FileSystem provider. You can use the Variable provider because PowerShell has a drive called variable implemented in the Variable Provider, then you are connecting at the Variable drive when use cd variable:

If you cannot connect to the provider itself. As you can see in the Filesystem provider, it has its drives : c:\, d: and e:. You only can connect to the drives that are associated with this provide. If you try to connect the FileSystem provider :

PS Variable:\> cd filesystem:
Set-Location : Cannot find drive. A drive with the name ‘filesystem’ does not exist.
At line:1 char:3
+ cd <<<<  filesystem:
    + CategoryInfo          : ObjectNotFound: (filesystem:String) [Set-Location], DriveNotFoundException
    + FullyQualifiedErrorId : DriveNotFound,Microsoft.PowerShell.Commands.SetLocationCommand
 

[UPDATED with Master Jedi Kirk Munro comments. Yes..you can connect to the provider directly . See his comments below] THANKS A LOT Kirk

Q – You told that is faster to use filter than Include (when possible)..so,using this idea,  it is faster to use the parameters rather than where-object ?

R – Exactly. In this case you are avoiding the pipeline streaming that may be slow in some cases. Although knowing how to work with the pipeline and effectively know how to  use it , IMHO  is the main concept to a real programming in PowerShell, there is some cases that avoiding the streaming you will have a higher performance. This is one of this cases.

After these questions, I realized that I need to create a chapter in my training specific to PowerShell Drives and Providers. Not only the mention that I was doing. 

As a friend told me, the better way to learn is  teaching