In this example, we obtain the diff of commits (revisions) in the source code repositories of OpenStack Nova Project.

1. Clone the repositories.

git clone https://git.openstack.org/openstack/nova

2. Check the patchsets (revisions) of changes. For example, we examine a patchset (change-id = 176805). You will get a list of patchsets of this change.

git ls-remote | grep /176805/

3. Get the revisions and create new branches. Here we create two new branches based on patchset 1 and patchset 2.

git fetch https://review.openstack.org/openstack/nova refs/changes/05/176805/1 
git branch change/176805/1 FETCH_HEAD

git fetch https://review.openstack.org/openstack/nova refs/changes/05/176805/2 
git branch change/176805/2 FETCH_HEAD

4. Compare the diff file. You can also save the diff to local.

git diff change/176805/1 change/176805/2

or

git diff change/176805/1 change/176805/2 > diff-176805-1-2.txt

(Similar shell script to fetch all the diff, please check https://github.com/saper/gerrit-fetch-all/blob/master/gerrit-fetch-all)