What is the difference between The Big Sleep the movie and the book?

The writers who adapted Chandler’s novel for the screen decided they wanted to have Eddie Mars killed rather than leaving him alive and continuing to pose a threat to the General and his two daughters. The final scene is entirely invented by the screen writers, who included the famous William Faulkner. In order to make it plausible that Eddie could be machine-gunned by his own men, who are waiting to kill Marlowe, expecting him to exit Geiger’s house first, the writers called for a thick fog. They also wrote in several mini-scenes in which Mars’s two main thugs are made to look stupid by Marlowe, played by Humphrey Bogart. The whole idea of having Marlowe arrange to meet Mars at Geiger’s house at the end of the film was invented by the screen writers. In Chandler’s novel, Marlowe simply tells Vivian he will go and have a talk with Mars and warn him against using his knowledge of Carmen’s killing Rusty Regan for blackmail purposes. Evidently the screen writers didn’t like leaving loose ends such as that. They didn’t see what Marlowe could say to Mars that would positively silence him indefinitely; and they also probably thought they could make a more interesting cinematic finale out of having Eddie Mars gunned down and permanently disposed of as a threat. However, they didn’t want Marlowe killing Mars the way he had killed Canino. Why not? For one thing, it would seem too repetitious of the shootout with Canino. Also, it might involve Marlowe in a whole lot of interviews with the cops and the D.A. and therefore would not provide the neat closure they wanted for the end of the film.