How to branch from a previous commit with Git?

To create a Git branch starting from a previous commit, follow these steps:

1. Find the Commit Hash

Use git log to locate the commit you want to branch from:

git log --oneline  # Shows abbreviated commit hashes and messages
# Example output:
# a1b2c3d (HEAD -> main) Add feature X
# d4e5f6a Fix bug
# 7g8h9i0 Initial commit

2. Create a New Branch from the Commit

Option A: Create and Switch to the Branch

git checkout -b <new-branch-name> <commit-hash>
# Example:
git checkout -b new-feature d4e5f6a

Shortcut with relative references (e.g., HEAD~2 for 2 commits back):

git checkout -b new-feature HEAD~3  # Branches from 3 commits ago

Option B: Create the Branch Without Switching

git branch <new-branch-name> <commit-hash>
# Example:
git branch hotfix a1b2c3d

Then switch to it later:

git checkout hotfix
# Or (Git 2.23+):
git switch hotfix

3. Verify the New Branch

git log --oneline  # Confirm the branch starts at the correct commit

4. Push the Branch to Remote (Optional)

git push -u origin <new-branch-name>

Key Notes

• Commit Hash: Use the full or abbreviated hash (e.g., d4e5f6a).
• Relative Refs: HEAD~n refers to the nth ancestor of the current commit.
• Detached HEAD: If you check out a commit directly (without -b), you’ll enter a detached HEAD state. Create a branch to retain changes.

Example Workflow

1. List recent commits:

   git log --oneline
   # Output:
   # d4e5f6a (main) Update README
   # a1b2c3d Add login feature
   # 7g8h9i0 Initial commit

2. Branch from a1b2c3d:

   git checkout -b login-fixes a1b2c3d

3. Push to remote:

   git push -u origin login-fixes

Why This Works

• Git branches are just pointers to commits. Creating a branch from an older commit lets you develop independently from that point.
• Useful for:
• Fixing bugs in older releases.
• Experimenting without affecting the main branch.
• Isolating features from historical states.