PowerShell Returns Inaccurate Results for Installed Software When Run In x86 Context

Your problem is that to a 32-bit process, the following key paths refer to the same location, namely the registry view for 32-bit applications:

# To both 64- and 32-bit processes: The registry view for 32-bit applications.
HKLM:\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall

# To 32-bit processes: same as above
# To 64-bit processes: the 64-bit view of the registry.
HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*

In other words: your code, when run in a 32-bit process, does the same thing twice.

Using just a registry key path won't allow a 32-bit process to see the 64-bit registry.

However, there are workarounds:

• Call the 64-bit instance of PowerShell as an external process, via directory $env:WinDir\SysNative - see below.

• Use .NET types directly, as shown in this answer.

• Call the standard reg.exe utility, which has /reg:32 and /reg:64 parameters for targeting the bitness-specific hives. However, you'll lose PowerShell's rich data-type support with this approach and you'll have to parse the results as text.

Calling 64-bit PowerShell from (32-bit) PowerShell with a script block { ... } automatically serializes the 64-bit instance's output objects in CLIXML format, which makes the calling instance automatically deserialize them with reasonable fidelity^[1], so that your original filtering commands should work:

# Works only in a 32-bit process.
& $env:WINDIR\SysNative\WindowsPowerShell\v1.0\powershell.exe {
  Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*
} | 
  Where-Object {$_.DisplayName -like $appName} | 
    Select-Object @{Expression={$_.DisplayName + "|" + $_.DisplayVersion +"|x64"}} |
      Sort-Object -Unique

To determine whether your script is being run in a 32-bit process, use this:

# PowerShell v3 and above.
$is32Bit = [Environment]::Is64BitProcess

# PowerShell version 2 alternative
$is32Bit = ${env:ProgramFiles(x86)} -eq ${env:ProgramFiles} -or 
             -not ${env:ProgramFiles(x86)}

The -or -not ${env:ProgramFiles(x86)} part detects the case of running on a pure 32-bit Windows version, but note that, obviously, no 64-bit definitions exist there.

In PowerShell v3 and above you can easily test whether the OS (Windows installation) is 64-bit or not with [Environment]::Is64BitOperatingSystem

Theo's helpful answer provides a helper function that determines both the process and the OS bitness in a backward-compatible fashion.

^{[1] Except for a few well-known types, input objects are deserialized as [PSCustomObject] instances with static properties reflecting the original object's property values - see this answer for details.}

To add to @mklement0's correct answer, maybe a small test function can help to determine the Windows bitness as opposed to the current PowerShell process bitness:

function Get-Architecture {
    # What architecture does Windows use
    $windowsBitness = switch ([Environment]::Is64BitOperatingSystem) {   # needs .NET 4
        $true  { 64; break }
        $false { 32; break }   
        default { 
            (Get-WmiObject -Class Win32_OperatingSystem).OSArchitecture -replace '\D+', '' 
            # Or do any of these:
            # ((Get-WmiObject -Class Win32_ComputerSystem).SystemType -replace '\D+', '') -replace '86', '32'
            # (Get-WmiObject -Class Win32_Processor).AddressWidth   # slow...
        }
    }

    # What architecture does this PowerShell process use
    $processBitness = [IntPtr]::Size * 8
    # Or do any of these:
    # $processBitness = ($env:PROCESSOR_ARCHITECTURE -replace '\D+]', '') -replace '86', '32'
    # $processBitness = if ([Environment]::Is64BitProcess) { 64 } else { 32 }

    # Return the info as object
    return New-Object -TypeName PSObject -Property @{
        'ProcessArchitecture' = "{0}-bit" -f $processBitness
        'WindowsArchitecture' = "{0}-bit" -f $windowsBitness
    }
}

Possible returns are:

64-bit PowerShell on 64-bit Windows

ProcessArchitecture WindowsArchitecture
------------------- -------------------
64-bit              64-bit

32-bit PowerShell on 64-bit Windows

ProcessArchitecture WindowsArchitecture
------------------- -------------------
32-bit              64-bit

32-bit PowerShell on 32-bit Windows

ProcessArchitecture WindowsArchitecture
------------------- -------------------
32-bit              32-bit

There's always get-package (5.1 only). It seems to work as both 64 & 32 bit (hello Kace client). There's both programs and msi provider listings, so I'm limiting it to programs. Only one entry appears in add/remove programs. Piping to format-table -autosize to get the full name to display. Pipe to format-list to see all the other properties, including $_.metadata['uninstallstring']. The msi version could be piped to uninstall-package.

get-package '*Microsoft Office Professional*' -provider programs | ft -a

Name                                    Version        Source ProviderName
----                                    -------        ------ ------------
Microsoft Office Professional Plus 2016 16.0.4266.1001        Programs

get-package '*Microsoft Office Professional*' -provider programs | 
  % {$_.metadata['uninstallstring']}

"C:\Program Files\Common Files\Microsoft Shared\OFFICE16\Office Setup Controller\setup.exe" /uninstall PROPLUS /dll OSETUP.DLL