Test if registry value exists

The Carbon PowerShell module has a Test-RegistryKeyValue function that will do this check for you. (Disclosure: I am the owner/maintainer of Carbon.)

You have to check that that the registry key exists, first. You then have to handle if the registry key has no values. Most of the examples here are actually testing the value itself, instead of the existence of the value. This will return false negatives if a value is empty or null. Instead, you have to test if a property for the value actually exists on the object returned by Get-ItemProperty.

Here's the code, as it stands today, from the Carbon module:

function Test-RegistryKeyValue
{
    <#
    .SYNOPSIS
    Tests if a registry value exists.

    .DESCRIPTION
    The usual ways for checking if a registry value exists don't handle when a value simply has an empty or null value.  This function actually checks if a key has a value with a given name.

    .EXAMPLE
    Test-RegistryKeyValue -Path 'hklm:\Software\Carbon\Test' -Name 'Title'

    Returns `True` if `hklm:\Software\Carbon\Test` contains a value named 'Title'.  `False` otherwise.
    #>
    [CmdletBinding()]
    param(
        [Parameter(Mandatory=$true)]
        [string]
        # The path to the registry key where the value should be set.  Will be created if it doesn't exist.
        $Path,

        [Parameter(Mandatory=$true)]
        [string]
        # The name of the value being set.
        $Name
    )

    if( -not (Test-Path -Path $Path -PathType Container) )
    {
        return $false
    }

    $properties = Get-ItemProperty -Path $Path 
    if( -not $properties )
    {
        return $false
    }

    $member = Get-Member -InputObject $properties -Name $Name
    if( $member )
    {
        return $true
    }
    else
    {
        return $false
    }

}

The best way to test if a registry value exists is to do just that - test for its existence. This is a one-liner, even if it's a little hard to read.

(Get-ItemProperty $regkey).PSObject.Properties.Name -contains $name

If you actually look up its data, then you run into the complication of how Powershell interprets 0.

Personally, I do not like test functions having a chance of spitting out errors, so here is what I would do. This function also doubles as a filter that you can use to filter a list of registry keys to only keep the ones that have a certain key.

Function Test-RegistryValue {
    param(
        [Alias("PSPath")]
        [Parameter(Position = 0, Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
        [String]$Path
        ,
        [Parameter(Position = 1, Mandatory = $true)]
        [String]$Name
        ,
        [Switch]$PassThru
    ) 

    process {
        if (Test-Path $Path) {
            $Key = Get-Item -LiteralPath $Path
            if ($Key.GetValue($Name, $null) -ne $null) {
                if ($PassThru) {
                    Get-ItemProperty $Path $Name
                } else {
                    $true
                }
            } else {
                $false
            }
        } else {
            $false
        }
    }
}