Bulk update displayname attribute to match cn attribute for all AD groups

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http://serverfault.com – We are setting up ADFS for identity federation with a Microsoft Online service. The documentation states that "Groups without a displayname will NOT get synchronized..." We have over 250 groups that have a blank displayname attribute. Does anyone know of a way to set the displayname attribute to match the cn attribute for all groups where the displayname is blank? (HowTos)