这两个null指出，我们不想改变这一文件的最后访问时间或者创建时间。

The two nulls indicate that we do not want to change the last access time or creation time for this file.

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times选项保持每个文件的访问权限、创建和最后修改时间。

The -times option preserves the access, creation, and last modified time of each file.

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times选项保持每个文件的访问权限、创建和最后修改时间。

The -times option preserves the access, creation, and last modified time of each file.

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