Viewing History and Undoing Mistakes

Reading history

git log --oneline --graph --decorate --all   # the whole picture
git log -p app.py                             # every change to one file
git log --author="Ada" --since="2 weeks ago"
git show a1b2c3d                              # one commit in full
git blame app.py                              # who last changed each line
git diff main..feature                        # compare branches

Make the first one an alias: git config --global alias.lg "log --oneline --graph --decorate --all".

Undoing, by situation

revert vs reset

• git revert creates a new commit that undoes an old one. History is preserved, so it is safe on shared branches.
• git reset moves the branch pointer backwards, erasing commits from the branch. Only use it on commits nobody else has.

Rule of thumb: if it has been pushed, revert. If it is only local, reset is fine.

The safety net: reflog

Git records every position your branch has been at, even after a reset:

git reflog
# 9f8e7d6 HEAD@{0}: reset: moving to HEAD~3
# 4c5b6a7 HEAD@{1}: commit: Add payment webhook
git reset --hard 4c5b6a7     # your "lost" commits are back

Commits are very hard to truly lose in Git. Uncommitted work, however, is not protected, so commit often.

Stash: put work aside

git stash push -m "half-done navbar"
git switch main              # fix something urgent
git switch feature
git stash pop                # bring the work back
git stash list

Practice

In a test repository, make three commits, git reset --hard HEAD~2, then recover them with git reflog.

Check yourself

• Which undo command is safe on a branch your team uses?
• How do you recover from an accidental git reset --hard?
• What does git restore --staged do to your edits?