git create commit from diff between two branches

A simple way to make “the diff from branch_b..branch_a” into a commit is:

1. create and checkout branch tmp at branch_a (git branch tmp branch_a && git checkout tmp) (or git reset --hard branch_a on an existing branch)
2. git reset --soft branch_b
3. git commit

that commit will include all the diff between branch_b and branch_a.

This works because

• 1. causes the files to reflect branch_a. This is the “end result” you want for the branch
• 2. “resets the head to branch_b” but “leaves all your changed files [i.e. branch_a head] as “Changes to be committed”, as git status would put it.” ←(git reset --soft docs, with this example’s branches added)