Get-LocalGroup.ps1

Function Get-LocalGroup {

    [Cmdletbinding()] 
    Param( 
        [Parameter(ValueFromPipeline=$True, ValueFromPipelineByPropertyName=$True)] 
        [String[]]$Computername =  $Env:COMPUTERNAME,
        [parameter()]
        [string[]]$Group
    )

    Begin {
 
        Function ConvertTo-SID {
            Param([byte[]]$BinarySID)
            (New-Object System.Security.Principal.SecurityIdentifier($BinarySID,0)).Value
        }

        Function Get-LocalGroupMember {
            Param ($Group)
            $group.Invoke('members') | ForEach {
            $_.GetType().InvokeMember("Name", 'GetProperty', $null, $_, $null)
            }
        }
    }

    Process {
        ForEach($Computer in $Computername) {
            Try {
                Write-Verbose  "Connecting to $($Computer)"
                $adsi = [ADSI]"WinNT://$Computer"
                If($PSBoundParameters.ContainsKey('Group')) {
                    Write-Verbose "Scanning for groups: $($Group -join ',')"
                    $Groups = ForEach ($item in $group) {                        
                        $adsi.Children.Find($Item, 'Group')
                    }
                } Else {
                    Write-Verbose "Scanning all groups"
                    $groups = $adsi.Children | where {$_.SchemaClassName -eq 'group'}
                }
                If($groups) {
                    $groups | ForEach {
                        [pscustomobject]@{
                            Computername = $Computer
                            Name = $_.Name[0]
                            Members = ((Get-LocalGroupMember -Group $_)) -join ', '
                            SID = (ConvertTo-SID -BinarySID $_.ObjectSID[0])
                        }
                    }
                } Else {
                    Throw "No groups found!"
                }
            } Catch {
                Write-Warning "$($Computer): $_"
            }
        }
    }
}