How branches are just files with hashes in Git - Visual Walkthrough

Process Flow - How branches are just files with hashes

Create branch file

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Write commit hash inside

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Git reads branch file

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Uses hash to find commit

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Checkout or update branch

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Branch points to commit hash

Git stores each branch as a simple file containing the commit hash it points to. Git reads this file to know the current commit of the branch.

Execution Sample

Git

echo abc123 > .git/refs/heads/main
cat .git/refs/heads/main

Create a branch file 'main' with commit hash 'abc123' and read its content.

Process Table

Step	Action	File Affected	Content Written/Read	Result
1	Create branch file	.git/refs/heads/main	abc123	Branch 'main' points to commit abc123
2	Read branch file	.git/refs/heads/main	abc123	Git knows 'main' points to commit abc123
3	Checkout branch	N/A	N/A	Git uses hash abc123 to set HEAD and working directory
4	Update branch	.git/refs/heads/main	def456	Branch 'main' now points to commit def456
5	Read updated branch file	.git/refs/heads/main	def456	Git knows 'main' points to commit def456

💡 Execution stops after branch file content is read and used to point to a commit hash.

Status Tracker

Variable	Start	After Step 1	After Step 4	Final
branch_file_content	empty	abc123	def456	def456

Key Moments - 3 Insights

Why is the branch just a file with a hash inside?

Because Git uses simple files to store the commit hash that the branch points to, as shown in steps 1 and 2 of the execution table.

What happens when the branch file content changes?

Git updates the branch pointer to a new commit hash, as seen in step 4 where the content changes from 'abc123' to 'def456'.

How does Git know which commit a branch points to?

Git reads the branch file content (the commit hash) to find the commit, demonstrated in steps 2 and 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the content of the branch file after step 1?

A def456

B empty

C abc123

D HEAD

💡 Hint

Check the 'Content Written/Read' column at step 1 in the execution table.

At which step does the branch file content change to point to a new commit?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look for the step where the 'Content Written/Read' changes from 'abc123' to 'def456'.

If the branch file was empty, what would Git know about the branch?

A It points to the latest commit

B It points to no commit

C It points to the initial commit

D It points to HEAD

💡 Hint

Refer to the 'branch_file_content' variable in the variable tracker and what an empty value means.

Concept Snapshot

Branches in Git are simple files stored in .git/refs/heads/ directory.
Each branch file contains a commit hash as plain text.
Git reads this hash to know which commit the branch points to.
Updating the branch means changing the hash inside the file.
This simple file-hash system makes branches lightweight and fast.

Full Transcript

In Git, branches are just files that store commit hashes. When you create a branch, Git makes a file named after the branch inside the .git/refs/heads/ folder. This file contains the hash of the commit the branch points to. When Git needs to know the current commit of a branch, it reads this file. Changing the branch means updating the hash inside the file. This simple mechanism allows Git to track branches efficiently.