ETC5513: Collaborative and Reproducible Practices

Workshop 6

Author

Michael Lydeamore

Published

20 May 2025

🔄 Git Undo Workshop: git revert and git reset

Mistakes happen — that’s why Git gives us powerful tools to undo changes. In this workshop, you’ll learn two of the most useful commands for fixing things:

  • git revert: Undo a commit by creating a new commit that cancels it out
  • git reset: Move your branch pointer to a previous commit (⚠️ this can rewrite history!)

🛠️ What You’ll Learn

  • The difference between revert and reset
  • How to safely undo changes
  • When to use which command

🧑‍💻 1. Create a New Repository on GitHub

  1. Go to https://github.com and log in
  2. Click + → New repository
  3. Name it something like git-undo-demo
  4. ✅ Check Add a README file
  5. Click Create repository
  6. Click the green Code button → Select SSH → Copy the URL

💻 2. Clone the Repository Locally

Open your terminal and run:

git clone git@github.com:your-username/git-undo-demo.git
cd git-undo-demo

✍️ 3. Add Content to the README

We’ll simulate a few commits by editing the README.md file.

  1. Open README.md in RStudio or your preferred text editor
  2. Add a line at the bottom like:
Line 1: Initial test message
  1. Save the file, then run:
git add README.md
git commit -m "Add line 1"
  1. Repeat the process three more times, adding different lines like:
Line 2: More changes
Line 3: Experimental note
Line 4: Oops! Maybe not needed

Each time, save the file, then:

git add README.md
git commit -m "Add line X"

✅ You should now have 4 commits, each adding a line to README.md.

Check your commit history:

git log --oneline

🧪 Part 1: git revert (Safe Undo)

Let’s say you want to undo the “Add line 3” commit — but without changing the history.

  1. Find the commit hash:
git log --oneline

Copy the hash for “Add line 3”, then:

git revert <hash>

Git will create a new commit that undoes the changes from that commit.

✅ This is a safe way to undo changes — especially useful on shared branches like main.

🧪 Part 2: git reset (Rewriting History)

Now let’s try using reset to go back in time.

⚠️ Warning

reset actually moves your branch pointer and can remove commits — so it’s best used on branches that only you are working on (like feature branches).

🧹 1. Soft Reset

This keeps your changes, but undoes the last commit:

git reset --soft HEAD~1

You can now edit or recommit with a new message.

🧼 2. Mixed Reset (default)

This keeps the file changes but unstages them:

git reset HEAD~1

Run git status to see your changes — they’re back in the working directory.

🔥 3. Hard Reset (Be Careful!)

This discards the last commit and any changes:

git reset --hard HEAD~1

✅ Your repo is now rolled back one commit — as if it never happened.

💡 Summary: When to Use What

Command Does What? Safe for Shared Branches?
git revert Creates a new commit to undo a change ✅ Yes
git reset --soft Moves HEAD, keeps changes staged ⚠️ Not recommended
git reset Moves HEAD, keeps changes unstaged ⚠️ Not recommended
git reset --hard DANGEROUS: Deletes changes + commits ❌ Never on shared branches

📦 Using git stash

Sometimes you make changes in your working directory, but you’re not ready to commit them — and you need to switch branches or pull updates. git stash lets you save your changes temporarily without committing.

🛠️ Goal

Learn how to: - Save changes using git stash - Switch branches safely - Reapply your stashed work

🧪 Step-by-Step Instructions

  1. Make sure you’re inside a Git-tracked project (any project will do).

  2. Open a file and make some changes — but don’t commit yet.

  3. Check your Git status:

git status

You should see the file listed as modified.

📦 1. Stash Your Changes

Run:

git stash

✅ This saves your changes and returns your working directory to a clean state.

🔄 2. Switch Branches (or Pull)

Now try switching to another branch:

git checkout main

Or do a pull:

git pull

✅ Your working directory stays clean — no conflicts!

♻️ 3. Reapply the Stash

When you’re ready to bring back your changes:

git stash apply

✅ Your edits will be restored to the files you changed.

🗑️ 4. (Optional) Clear the Stash

After applying, you can remove the stash:

git stash drop

Or, to both apply and drop in one step:

git stash pop

🎉 You’ve learned how to pause your work safely and come back to it later!