There are several differences between the movie and the book. First of all, the beginning of the movie is different from the book. In the book, is Derek, Outspan and Ray arguing about the name of the group, they were called And And And, but Ray wanted to call the band And And exclamation mark And.
The movie showed Jimmy walking around the city and he met the guys (Outspan and Derek) in a weeding where they were playing. The way the audition for the new band was a bit different too. In the book, the audition is not as important as the fact that Jimmy contact to the rest of the band. But in the movie, the audition part had more emphasis.
I could be forever telling the differences between these two versions (written and film). If I have to choose one, I prefer the book because it gives more details about the band and also gives you freedom to imagine any sight of the story.
For me, the movie was a great musical based on soul hits, as same as in the movie The Blues Brothers, where James Brown actually appeared as a priest. In the movie The Commitments, James Brown was the mentor to follow, mainly for his voice, passion song and lyrics.
Although the fights occurred in different times in the book and songs are different too, the film took them and put them in special places to make sense and to catch the attention of the watcher. However the end is different in the book. In the movie, the group divides and every one follows their own way. They do not end up together or with the idea of get back again as a group. The book does. Jimmy, Outspan, Derek and Mickah were back together and they would include the girls again. Actually the book finishes when they decided the time of the rehearsal.
The author gave us an open ending while the film finished with everyone carried on with his or her life. As I said before I prefer the book to the movie, it has great songs though.
