An example of normal usage is:
- torvalds@ppc970:~/git> git diff-tree 5319e4......
- *100664->100664 blob ac348b.......->a01513....... git-fsck-objects.c
+ torvalds@ppc970:~/git> git diff-tree --abbrev 5319e4
+ :100664 100664 ac348b... a01513... git-fsck-objects.c
which tells you that the last commit changed just one file (it's from
this one: