Getting the difference between two repositories
In repo_a:
git remote add -f b path/to/repo_b.git
git remote update
git diff master remotes/b/master
git remote rm b
Meld can compare directories:
meld directory1 directory2
Just use the directories of the two git repos and you will get a nice graphical comparison:
When you click on one of the blue items, you can see what changed.
You can add other repo first as a remote to your current repo:
git remote add other_name PATH_TO_OTHER_REPO
then fetch brach from that remote:
git fetch other_name branch_name:branch_name
this creates that branch as a new branch in your current repo, then you can diff that branch with any of your branches, for example, to compare current branch against new branch(branch_name):
git diff branch_name