## Group filter
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$groupname = (Get-ADGroup 'group1').DistinguishedName
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## SearchBase filter
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$OUs = "OU=OU1,DC=domain,DC=local","OU=OU2,DC=domain,DC=local"
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## Users filter
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$newmembers = Foreach ($OU in $OUs) { Get-ADUser -Filter {-not (memberof -eq $groupname)} -SearchBase $OU }
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## Add users to group
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Add-ADGroupMember -Identity $groupname -Members $newmembers