Unable to diff files in two separate branches in Git

Question

I have FileA in branchA and FileB in branchB.

The problem is that I can access only one file at time. I would like to be able to compare the files by FileMerge or mel

Answer 1

If you're currently checkout out to branchA, for example, you can use the command:

git diff branchB path/to/common/file/between/branches.txt

You can then edit the diff if you want a subset of the changes, or leave it as is, and git apply the diff as a patch. As for a GUI tool that does this, hopefully someone else will have a suggestion there.