Why does setting string variable type add spaces to result?

Question

I have the below function:

Function Get-MsiProperty
{
    [CmdletBinding()]
    Param
    (
        [Parameter(Mandatory=$true)]
        [ValidateScript({$_ | Test-Path -PathType Leaf})]
        [string]$Path,

        [Parameter(Mandatory=$true)]
        [string]$Property
    )

    Begin
    {       
        $GetProperty = {
            Param
            (
                $Object,
                $PropertyName,
                [object[]]$ArgumentList
            )
            Return $Object.GetType().InvokeMember($PropertyName, 'Public, Instance, GetProperty', $null, $Object, $ArgumentList)
        }

        $InvokeMethod = {
            Param
            (
                $Object,
                $MethodName,
                $ArgumentList
            )
            Return $Object.GetType().InvokeMember($MethodName, 'Public, Instance, InvokeMethod', $null, $Object, $ArgumentList)
        }

        ${CmdletName} = $PSCmdlet.MyInvocation.MyCommand.Name
        $PSParameters = $PSBoundParameters | Format-Table -Auto | Out-String
    }
    Process
    {
        Try
        {
            Set-StrictMode -Version Latest

            # http://msdn.microsoft.com/en-us/library/aa369432(v=vs.85).aspx
            $msiOpenDatabaseModeReadOnly = 0
            $Installer = New-Object -ComObject WindowsInstaller.Installer -ErrorAction 'Stop'

            $Database = &$InvokeMethod -Object $Installer -MethodName OpenDatabase -ArgumentList @($Path, $msiOpenDatabaseModeReadOnly)

            $View = &$InvokeMethod -Object $Database -MethodName OpenView -ArgumentList @("SELECT Value FROM Property WHERE Property='$Property'")

            &$InvokeMethod -Object $View -MethodName Execute | Out-Null

            $MSIProperty = $null
            $Record = &$InvokeMethod -Object $View -MethodName Fetch
            If ($Record)
            {
                $MSIProperty = &$GetProperty -Object $Record -PropertyName StringData -ArgumentList 1
            }
            Write-Output $MSIProperty
        }
        Catch
        {
            Write-Host -Message "Failed to get the MSI property [$Property]"
        }
        Finally
        {
             &$InvokeMethod -Object $View -MethodName Close -ArgumentList @() | Out-Null
        }
    }
}

If I call the function as below, I get the correct result:

$ProductCode = Get-MsiProperty -Path "ConfigMgrTools.msi" -Property 'ProductCode'

If I call the function as below, the result has a space before and after the result. Why does this happen? I have used Get-Member to analyze the variable it shows up as a 'system.string' both times.

[string]$ProductCode = Get-MsiProperty -Path "ConfigMgrTools.msi" -Property 'ProductCode'

Maybe Execute and Close return $null? Try assigning the result of those calls to $null, e.g. $null = &$InvokeMethod -Object $View -MethodName Close -ArgumentList @() — Jason Shirk
– Jason Shirk, Commented Aug 29, 2014 at 2:18
That was exactly it. You sir are a genius. I've dealt with this type of issue when executing C# code in PowerShell but it just never crossed my mind that might be the case here. If you post it as an answer, I'll mark it answered. — user1367200
– user1367200, Commented Aug 29, 2014 at 3:20
Original post has been edited to send the problematic line of code to Out-Null as Jason Shirk suggested above. — user1367200
– user1367200, Commented Aug 29, 2014 at 11:58

Jason Shirk · Accepted Answer · 2014-08-29 15:35:26Z

The original unedited code was unintentionally writing out $null in two places.

When $ProductCode is untyped, the result is an array, and when formatting the array, the $null values in the array are ignored.

When $ProductCode is typed as a string, the $null values are formatted with a space, e.g.

PS> "__{0}__" -f ([string]@($null, "abc", $null))
__ abc __

Compare that with untyped (using Out-String -Stream to convert the array to a string instead of a type cast):

PS> "_{0}_" -f (@($null, "abc", $null) | out-string -Stream)
_abc_

The $null values typically come from .Net method calls, or in this case, COM method calls. I usually assign the result of method calls like this to $null because that has the best performance in all versions of PowerShell, but piping to Out-Null or casting to [void] both work equivalently so you can choose whichever you prefer.

Collectives™ on Stack Overflow

Why does setting string variable type add spaces to result?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related