JTo see the differences between two branches in a Git reposiory, use:

$ git diff branch_1 branch_2

If you already have a difftool setup (something like Kaleidoscope), you can view the DIFFs using:

$ git difftool branch_1 branch_2

Both commands will produce the diff between the tips of the two branches. The same syntax works for comparing a branch with a tag or a tag with another tag. Note that you can also add a file or folder name after the above two commands.

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