Powershell Join-Path showing 2 dirs in result inst

Question

I am constructing incremental directory structures, and for some reason Join-Path is showing 2 dirs. When I later join that with a file I'm sending to copy-item, it causes an error, as shown below. I have shown in the comment for the $to_loc_finalDT1 line, where I first see these two dirs:

Copy-Item : Cannot find path '\\T2\DisasterBackup\Loc_2019-03-08\Privileges\Privileges_HH_Bak.csv \\T2\DisasterBackup\Loc_2019-03-08\Privileges\Privileges_HH_Bak.csv' because it does not exist

So this is the pertinent powershell script:

$T2 = "\\T2\DisasterBackup\Loc" 
$toLocParentDT2 = CreateDatedFolder $parentDirBaseNameDT2 
$to_loc_finalDT2 = Join-Path -Path $toLocParentDT2 -ChildPath "Privileges" 
#create sub-folder location 
if(-Not (Test-Path $to_loc_finalDT2 )) 
{
   write-output  " Creating folder $to_loc_finalDT2 because it does not exist " 
   New-Item -ItemType directory -Path $to_loc_finalDT2 -force 
}


#second dir save files to
$parentDirBaseNameDT1 = "\\T1\DisasterBackup\Loc" 
$toLocParentDT1 = CreateDatedFolder $parentDirBaseNameDT1 
$to_loc_finalDT1 = Join-Path -Path $toLocParentDT1 -ChildPath "Privileges" #shows 2 dirs here in debugger: \\T2\DisasterBackup\Loc_2019-03-08\Privileges \\T2\DisasterBackup\Loc_2019-03-08\Privileges
#create sub-folder location 
if(-Not (Test-Path $to_loc_finalDT1 )) 
{
   write-output  " Creating folder $to_loc_finalDT1 because it does not exist " 
   New-Item -ItemType directory -Path $to_loc_finalDT1 -force 
}

I'm not sure how to get Join_path to just have the one dir, as it should. Right now, I think it's being treated as an array, which is not correct.

I tried searching for related issues, but didn't see anything similar.

Update

Here's the code for CreateDatedFolder:

#create dated folder to put backup files in 
function CreateDatedFolder([string]$name){
   $datedDir = ""
   $datedDir = "$name" + "_" + "$((Get-Date).ToString('yyyy-MM-dd'))"
   New-Item -ItemType Directory -Path $datedDir -force
   return $datedDir
}

The output for that looks fine when it's returned. It appends the date onto the \T2\DisasterBackup\Loc, but the debugger only shows one dir there, not an array or 2 dirs that are separate strings.

Answer 1

As T-Me correctly inferred before you posted the CreateDatedFolder source, the problem is that the function inadvertently outputs 2 objects, and Join-Path accepts an array of parent paths to each join with the child path.

Specifically, it is the New-Item call that accidentally creates an additional output object, just before your return $datedDir call.

New-Item outputs a [System.IO.DirectoryInfo] instance representing the newly created directory and, due to PowerShell's implicit output behavior, that instance becomes part of what the function outputs too - any command or expression inside a script / function that returns a value that isn't captured or redirected becomes part of the output.

To prevent that, suppress the output:

$null = New-Item -ItemType Directory -Path $datedDir -force

Note that you never need return in PowerShell in order to output a result - but you may need it for flow control, to exit a function prematurely:

return $datedDir 

is syntactic sugar for:

$datedDir # Implicitly output the value of $datedDir.
          # While you could also use `Write-Output $datedDir`,
          # that is rarely needed and actually slows things down.
return    # return from the function - flow control only

For more information about PowerShell's implicit output behavior, see this answer.