Split-DN

function Split-DN {
    [CmdletBinding(DefaultParameterSetName = 'Parent')][OutputType([string])]
    param (
        [Parameter(Mandatory, Position = 0, ValueFromPipeline, ValueFromPipelineByPropertyName)][AllowNull()][AllowEmptyString()][AllowEmptyCollection()][Alias('DN')][string[]]$DistinguishedName,
        [Parameter(ParameterSetName = 'Parent')][switch]$Parent = $true,
        [Parameter(ParameterSetName = 'Leaf')][switch]$Leaf
    )
    Process {
        switch ($PSCmdlet.ParameterSetName) {
            'Leaf' {
                $DistinguishedName -replace '\A((:?CN|OU|DC)=.*?),(CN|OU|DC)=.*', '$1'
                break
            }
            default {
                $DistinguishedName -replace '\A.*?,(CN|OU|DC)=', '$1='
            }
        }
    }
}