The film is generally faithful to the Stephen King novella. Here are some of the differences:
The novella specifies that Andy smuggled $100 into the prison in his rectum; exactly how he pays Red the agreed-upon price of $10 for the rock hammer is never made clear in the film.
Andy orders a second rock hammer from Red in the novella, after the first wears down. This does not occur in the film.
Multiple wardens oversee the prison in the novella. They are combined in the Norton of the film. For example, the warden who agrees to mail Andy's letters and the warden who treats him so harshly at the end are not the same person in the novella.
In addition to Red being a white Irishman, the novella also gives details of his crime that the film doesn't.
Tommy's story is slightly different. He tells Andy that his old cell mate bragged that the double-murder he committed was pinned on a lawyer, rather than a banker, and Andy latches onto the idea that the two professions were commonly confused at that time.
Tommy is also not killed in the novella; after agreeing not to testify on Andy's behalf, he is sent to another prison.
The ending received perhaps the most significant changes. When Red is released from Shawshank Prison, he finds a package Andy left for him in a hayfield. In the film, he simply goes directly to it, while in the novella, his hunt for the appropriate hayfield is a fairly substantial piece of the plot. The final scene of Andy sanding a boat on the beach as Red meets him again is not present in the novella; that ends with Red on his way south to meet Andy, the matter of whether they found each other again left ambiguous.|