How do you fix a bad merge, and replay your good commits onto a fixed merge?

Question

I accidentally committed an unwanted file (filename.orig while resolving a merge) to my repository several commits ago, without me noticing it until now. I want

Answer 1

If it's the latest commit you want to clean up, I tried with git version 2.14.3 (Apple Git-98):

touch empty
git init
git add empty
git commit -m init

# 92K   .git
du -hs .git

dd if=/dev/random of=./random bs=1m count=5
git add random
git commit -m mistake

# 5.1M  .git
du -hs .git

git reset --hard HEAD^
git reflog expire --expire=now --all
git gc --prune=now

# 92K   .git
du -hs .git