How to pipe objects to a specific parameter - powershell

Question

I want to list all my PowerShell functions from one directory. The following command works:
Get-ChildItem -Path ($env:USERPROFILE + "\somewhere\*.psm1") -Recurse | ForEach-Object {Get-Command -Module $_.BaseName}
Now I tried to pipe the output from Get-ChildItem directly to the cmdlet Get-Command. Something like this, which does not work:
Get-ChildItem -Path ($env:USERPROFILE + "\somewhere\*.psm1") -Recurse | Get-Command -Module {$_.BaseName}
Obviously, I do not really understand how to pipe the object from Get-ChildItem in the correct way to the parameter -Module in Get-Command.
I have two questions:
Do you have a hint how to pipe correctly?
Is it possible to pipe to a specific parameter like -Module or is the object always handed over to one default parameter?

Answer 1

Parameters can be bound in four different ways:
By location in the argument list, e.g., Get-ChildItem C:\ (only certain parameters)
By name in the argument list, e.g. Get-ChildItem -Path C:\
By value from the pipeline, e.g. 1..5 | Get-Random (only certain parameters)
By name from the pipeline, e.g. 'C:\Windows' | Get-ChildItem (only certain parameters)
You can inspect the various ways of parameter binding via Get-Help <command> -Parameter *. You can then see that Get-Command allows the Module parameter to be bound only by property name:
-Module [<String[]>]
Specifies an array of modules. ...
Required? false
Position? named
Default value none
Accept pipeline input? True (ByPropertyName)
Accept wildcard characters? false
So the input has to be an object that has a Module property, to allow binding. In your case you thus need an additional step in between:
Get-ChildItem -Path ($env:USERPROFILE + "\somewhere\*.psm1") -Recurse |
Select-Object #{l='Module';e={$_.Basename}} |
Get-Command
Now, this instance here is something that's a bit annoying, since the Module parameter is bound by property name, but most things don't give you an object with a Module property. Heck, even Get-Module doesn't have that, since the returned object uses Name as the property name, so you can't even do
Get-Module | Get-Command
However, in many other places (notably concerning paths) work very well automatically. And if you can control your input objects, e.g. when reading from CSV or other data sources, you can end up with rather nice and concise code.
EDIT: Ansgar Wiechers notes that, while this should work, it doesn't, actually. This may be a shortfall of PowerShell's parameter binding algorithm (which is quite complex, as seen above, and we never got it to work correctly in Pash either), or maybe the Get-Command cmdlet has parameters described in a way that simply cannot allow binding because of reasons.