1
general::
Also, know like the back of one's hand or know backwards and forwards. Be extremely familiar with or knowledgeable about; understand perfectly. For example, I know Greg like a book? I'm sure he'll come, or I know this town like the back of my hand, or John knew his part backwards and forwards. The first of these hyperbolic idioms, dating from the early 1800s, has a close cousin in read like a book, which means "to discern someone's intent," as in I can read Greg like a book; Also see under OPEN BOOK. The second (back of hand) dates only from the mid-1900s. Also see BACKWARDS AND FORWARDS, def. 2; INSIDE OUT, def. 2; KNOW ALL THE ANSWERS.
American Heritage Idioms