Linux -如何在不删除包含字符串的其他模式的情况下替换字符串

I want to replace a string 'abc' with 'xyz', but there are other strings also contains 'abc', for example, 'abcdef'. I want to only replace exact match of 'abc', not 'abc' in 'abcef'. How would I accomplish that in linux?I want to replace a string 'abc' with 'xyz', bu