Powershell: All new-objects are not created equal?

powershell

Solution

I traced the binding with the object created using `New-Object` and the problem is that `Get-Content` couldn't bind to any properties on the `FileInfo` info object.

You can check this out with this command:

Trace-Command -psHost -Name ParameterBinding {$newFile | gc}
Trace-Command -psHost -Name ParameterBinding {$file | gc}

So when you look at the trace of the one that binds successfully you'll see that Literal path is bound to the property starting with `Microsoft.PowerShell.Core\FileSystem::` which is PsPath. So on closer inspection comparing the object properties when piping to `Get-Member` you'll see the one that works has these note properties where as the one created with `New-Object` does not -

- PSChildName

- PSDrive

- PSIsContainer

- PSParentPath

- PSPath

- PSProvider

Taking a look at the `Get-Content` cmdlet parameters we can see that `LiteralPath` has an alias of `PsPath`:

(Get-Command -Name Get-Content).ParameterSets

  Parameter Name: LiteralPath
    ParameterType = System.String[]
    Position = 0
    IsMandatory = True
    IsDynamic = False
    HelpMessage =
    ValueFromPipeline = False
    ValueFromPipelineByPropertyName = True
    ValueFromRemainingArguments = False
    Aliases = {PSPath}
    Attributes =
      System.Management.Automation.AliasAttribute
      System.Management.Automation.ParameterAttribute

If you add a property to the `New-Object` created `FileInfo` it will work:

$newFile | Add-Member -MemberType NoteProperty -Name PsPath -Value 'Microsoft.PowerShell.Core\FileSystem::C:\temp\jdh.txt'

Problem

I'm working on some short demo scripts for a presentation on powershell and of course one of my own simple demos has me perplexed. The purpose of this demo is to show different ways to create objects in powershell. Here's my code: ``` $file = ls 'C:\temp' | Where-Object {$_.Extension -eq '.txt'} $file.FullName $path = 'C:\temp\jdh.txt' $newfile = New-Object -TypeName System.IO.FileInfo -ArgumentList $path $newfile.FullName $file.GetType() $newfile.GetType() $file $newfile $file | Get-Content | out-null $newfile | Get-Content | out-null ``` Simple right? Create two FileInfo objects via different methods and read them. The output shows the files are identical: ``` C:\temp\jdh.txt C:\temp\jdh.txt IsPublic IsSerial Name BaseType -------- -------- ---- -------- True True FileInfo System.IO.FileSystemInfo True True FileInfo System.IO.FileSystemInfo LastWriteTime : 4/10/2013 3:38:29 PM Length : 46046 Name : jdh.txt LastWriteTime : 4/10/2013 3:38:29 PM Length : 46046 Name : jdh.txt ``` However, when Get-Content tries to read the $newfile object, I get the following error: ``` Get-Content : The input object cannot be bound to any parameters for the command either because the command does not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input. At line:16 char:12 + $newfile | Get-Content | out-null + ~~~~~~~~~~~ + CategoryInfo : InvalidArgument: (C:\temp\jdh.txt:PSObject) [Get-Content], ParameterBindingException + FullyQualifiedErrorId : InputObjectNotBound,Microsoft.PowerShell.Commands.GetContentCommand ``` So I noticed in the error it says PSObject which confuses me because in my ouput it seems $newfile is a FileInfo object. So the next logical thing I figured to do would be to typecast $newfile into type [System.IO.FileInfo]. That yielded the same error, except now instead of PSObject it shows FileInfo as the type. So how is it that I'm getting that error if $file and $newfile appear to be identical and get-content worked on $file? Is there some subtle difference when you use the new-object command?

Original source