🌿 Git Branches - Named References to Commits

🎯 Branches Are Just Pointers!

A branch is nothing more than a file containing a 40-character commit SHA. That's it!

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📺 Video Reference

Resource	Link
🎬 Video	Git Branches
📄 Transcript	03-git-branches.txt

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🧠 What We Think Branches Are

"We usually think about branches as a sequence of changes related to each other"

We think of branches as separate lines of development...

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🔍 What Branches ACTUALLY Are

"Under the hood, a branch is just a named reference to a commit"

The Reality

❌ What Branches Are NOT

• Separate copies of code
• Folders or directories
• Complex data structures
• Heavy objects to create

✅ What Branches ARE

• A simple text file
• Contains a 40-char SHA
• Located in .git/refs/heads/
• ~41 bytes total!

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📁 Branch Storage Location

.git/
├── HEAD                    ← Points to current branch
├── refs/
│   ├── heads/
│   │   ├── main           ← File containing: a1b2c3d4e5f6...
│   │   ├── feature        ← File containing: 9x8y7z6w5v4u...
│   │   └── bugfix         ← File containing: 1a2b3c4d5e6f...
│   └── tags/
│       └── v1.0           ← File containing: deadbeef1234...

Let's Look Inside

# What's in the main branch file?
cat .git/refs/heads/main
# Output: a1b2c3d4e5f6789012345678901234567890abcd

# That's it! Just 40 characters (+ newline)
wc -c .git/refs/heads/main
# Output: 41 .git/refs/heads/main

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👆 Understanding HEAD

Definition

HEAD = A special pointer that tells Git which branch (or commit) you're currently on.

HEAD Points to a Branch

What's Inside HEAD?

# When on a branch:
cat .git/HEAD
# Output: ref: refs/heads/main

# HEAD contains a REFERENCE to a branch, not a commit SHA directly

Detached HEAD State

Sometimes HEAD points directly to a commit (not a branch):

# In detached HEAD state:
cat .git/HEAD
# Output: a1b2c3d4e5f6789012345678901234567890abcd

# Direct SHA instead of branch reference!

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🔀 How Branch Operations Work

Creating a Branch: git branch test

What Actually Happens:

# Git creates a new file:
echo "a1b2c3d4e5f6789012345678901234567890abcd" > .git/refs/heads/test

# That's ALL that happens! Just a new file with the same commit SHA

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Switching Branches: git checkout test

What Actually Happens:

# Git changes HEAD to point to test:
echo "ref: refs/heads/test" > .git/HEAD

# Plus updates the working directory to match that commit's tree

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Making a Commit on a Branch

What Actually Happens:

1. Git creates a new commit object
2. Git updates the branch file with the new commit SHA:

   echo "b2c3d4e5f6789012345678901234567890abcdef" > .git/refs/heads/test

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Switching Back: git checkout main

Now main and test point to different commits!

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Committing on Main (Divergence)

Now we have diverged branches! Both main and test have commits that the other doesn't.

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🧪 Hands-On Lab: Exploring Branches

See Branch as Files

# List all local branches
ls -la .git/refs/heads/

# See contents of main branch
cat .git/refs/heads/main

# Compare with git branch
git branch -v

See HEAD

# What does HEAD contain?
cat .git/HEAD

# If on main branch:
# Output: ref: refs/heads/main

Create Branch Manually

# Get current commit SHA
git rev-parse HEAD
# Output: a1b2c3d4e5f6789012345678901234567890abcd

# Create branch manually (same as git branch manual-branch)
echo "a1b2c3d4e5f6789012345678901234567890abcd" > .git/refs/heads/manual-branch

# Verify it exists
git branch
# Output: 
#   main
# * manual-branch

Switch Branch Manually

# Switch to new branch (same as git checkout manual-branch)
echo "ref: refs/heads/manual-branch" > .git/HEAD

# Verify
git branch
# Shows manual-branch with asterisk

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📊 Branch Commands vs What Actually Happens

Command	What It Does Under the Hood
git branch test	Creates .git/refs/heads/test with current commit SHA
git checkout test	Writes ref: refs/heads/test to .git/HEAD
git checkout -b test	Both of the above
git commit	Creates commit, updates current branch file with new SHA
git branch -d test	Deletes .git/refs/heads/test file
git merge test	Creates merge commit, updates current branch file

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🎯 Key Takeaways

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🎯 Branches Summary

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🧠 Quiz: Test Your Understanding

1. Where is the 'main' branch stored?

📁 .git/refs/heads/main

It's just a text file containing the SHA of the commit it points to.

2. What does HEAD contain when you're on the main branch?

ref: refs/heads/main

It's a symbolic reference to the branch, not the commit SHA directly.

3. What happens when you create a new branch?

Git creates a new file in .git/refs/heads/ with the current commit's SHA. That's it!

4. Why are branches "cheap" in Git?

Because they're just 41-byte files! Creating a branch doesn't copy any code or create any large data structures.

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🚀 What's Next?

🔧 Next: Creating a Repository From Scratch (Lesson 04a)

Now that you understand objects and branches, let's put it all together! We'll create a complete Git repository without using git init, git add, or git commit.

Continue to Lesson 04a →

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📝 Summary

Concept	Reality
Branch	A file in .git/refs/heads/ containing a commit SHA
HEAD	A file (.git/HEAD) pointing to current branch or commit
Creating branch	Creating a 41-byte file
Switching branch	Updating HEAD file
Committing	Creating commit object + updating branch file

Branches are just pointers. That's the secret! 🎉