Creating a git diff from nothing

If you want the full diff from nothing to a particular commit, there is an easier way than in the accepted answer:

empty_tree=$(git hash-object -t tree /dev/null) 
git diff-tree -p ${empty_tree} $MY_COMMIT [${files}...]

The value of ${empty_tree} is always 4b825dc642cb6eb9a060e54bf8d69288fbee4904 but I prefer not to have the magic number in there.

If you want to get diff for your initial commit (maybe I misunderstood your question), you can display it using

git show COMMIT

Alternatively to get it as file:

git format-patch -1 COMMIT

Where COMMIT is revision of this commit. If this is your current commit as well, you don't have to specify it at all.

However if your commit is not initial and you want to get full diff for your history, you need to create empty branch first:

git checkout --orphan empty         # Create orphaned branch
git read-tree --empty               # Remove all files from index
git commit --allow-empty -m 'Empty' # Initial commit

Now you can do full diff against empty branch:

git diff empty..master