Two German grocery giants are casting a big shadow in the U.S. Aldi, which has operated here since the late 1970s, says it wants to add about 800 stores to the 1,700 it operates today. Meanwhile, Lidl, another German chain, will open the first of its planned U.S. stores later this week on the East Coast. The hallmark of both chains is a limited selection of items, offered via store brands at steep discounts — a big growth area in groceries right now. 

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