Get-IsGroupMember.ps1

<#
.SYNOPSIS
    Check if user belongs to an active directory group. 
.DESCRIPTION
    The Get-IsGroupMember.ps1 function will check if a user belongs
    to a specified group.
.EXAMPLE
    .\Get-IsGroupMember.ps1 -user johnsmith -group accounting
#>

Param(
    #User
    [Parameter( Mandatory=$True, HelpMessage="user", Position=0 )]
    [ValidateNotNullOrEmpty()][string]$user
,   #Group
    [Parameter( HelpMessage="Group Name", Position=1 )]
    [ValidateNotNullOrEmpty()][string]$group

)
function Get-IsGroupMember{
    $user = $user.ToLower()

    Write-Output "------            Variable Values             ------"
    Write-Output "`$user:      $user"
    Write-Output "`$group:     $group"


    $strFilter = "(&(objectClass=Group)(name=" + $group +"))"

    Write-Output "`$strFilter:     $strFilter"

    $objDomain = New-Object System.DirectoryServices.DirectoryEntry

    $objSearcher = New-Object System.DirectoryServices.DirectorySearcher
    $objSearcher.SearchRoot = $objDomain
    $objSearcher.Filter = $strFilter
    $objSearcher.PageSize = 500
    $objSearcher.SearchScope = "Subtree"

    $objItem = $objSearcher.FindOne().Properties

    return ([string]$objItem.member).contains($user)
}
Get-IsGroupMember