Provider-specific-Filter

Provider specific filters

PowerShell provider specific cmdlets, e.g. *-*Item*, have the parameter Filter. Here is what the help tells for Get-ChildItem

help Get-ChildItem -Parameter Filter

-Filter <String>
    Specifies a filter in the provider's format or language. The value of
    this parameter qualifies the Path parameter. The syntax of the filter,
    including the use of wildcards, depends on the provider. Filters are
    more efficient than other parameters, because the provider applies them
    when retrieving the objects, rather than having Windows PowerShell
    filter the objects after they are retrieved.

Thus, how Filter works completely depends on a provider.

Some providers may not support it at all. For example, Environment. See the script Test-1.Environment.ps1.

Other providers may support Filter expressions with some complex syntax which has nothing to do with wildcards.

FileSystem Filter

The popular provider FileSystem supports Filter which uses some wildcard-like syntax. But its wildcards may work in unexpected ways.

*.* matches all names, not names with a dot

See the script Test-2.1.FileSystem.ps1.

NOTE: In v6.2.0-preview.2 it matches names with a dot, as expected. But v7.0.0-preview.1 works as older v2 - v5.1 again.

*.ext where ext is three characters matches *.ext*

See the script Test-2.2.FileSystem.ps1.

NOTE: Windows 10 seems to work in a more expected way. But results are different on different machines, versions, etc.