How to Checkout/Clone a Git Repository from a Specific Commit ID (SHA)

When working with Git, you may need to clone or check out a specific commit to review the code at that point. Every commit in Git has a unique identifier called a SHA. This SHA acts as a snapshot of the project’s state at that time.

By checking out a commit using its SHA, you can view or work with the code as it was during that commit. This process doesn’t affect the main branch. It’s useful for debugging or reviewing past versions of the code.

In this tutorial, we’ll explore how to checkout or clone a repository from a specific Git commit ID (SHA).

What is a Commit ID?

A commit ID, also known as a SHA (Secure Hash Algorithm), is a unique identifier that Git generates for each commit. This SHA is a 40-character string that ensures the integrity and uniqueness of each commit in the repository. It helps track changes, navigate the project’s history, and manage different codebase versions.

Why Use a Specific Commit ID?

There are several reasons you might want to checkout or clone a repository from a specific commit ID:

• Debugging: You can pinpoint when a bug was introduced by checking out the code as it was at various points in history.
• Code Review: Reviewing the code as it was at a particular commit can help understand changes and their impacts.
• Stable Versions: Sometimes, a specific commit represents a stable version of the code that you need to replicate or build upon.

How to Check Out a Specific Commit?

To check out a specific commit in Git, you use the git checkout command with the commit hash (SHA). Below is a step-by-step guide on how to do it:

1. Open your terminal and navigate to the directory of your repository:

 # cd your-repository

2. Ensure your local repository is up to date with all the commits from the remote repository:

 # git fetch --all

3. If you don’t know the commit SHA, you can get it from the log:

 # git log

Output:

commit a1b2c3d4e5f6g7h8i9j0 (HEAD -> main, origin/main)
Author: Your Name <[email protected]>
Date:   Mon Jun 24 14:00:00 2024 +0000

    Initial commit

4. Copy any commit (SHA) ID from the above output and use the git checkout command followed by the commit ID (SHA) to checkout the specific commit:

 # git checkout commit-id

For example:

 # git checkout a1b2c3d4e5f6g7h8i9j0

Output:

Note: checking out 'a1b2c3d4e5f6g7h8i9j0'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b new-branch-name

5. After checking out a specific commit, your repository enters a “detached HEAD” state. This means you are not on any branch. You can still make changes and create new commits in this state. However, these changes won’t be linked to any branch.

To save your work,  create a new branch using the below command:

 # git checkout -b new-branch-name commit-id

6. Verify that you have checked out the specific commit by looking at the commit log.

 # git log -1

This will display the latest commit, matching the commit ID you checked out.

commit a1b2c3d4e5f6g7h8i9j0 (HEAD -> my-new-branch)
Author: Your Name [email protected]
Date:   Mon Jun 24 14:00:00 2024 +0000

    Initial commit

How to Clone a Repository from a Specific Commit?

Cloning a Git repository from a specific commit allows you to work with the codebase at that exact point in history. Follow the below steps to clone a repository from a specific commit:

1. First, clone the repository as usual:

 # git clone repository-url

For example:

 # git clone https://github.com/user/repo.git

2. Change the directory to the newly cloned repository:

 # cd repo

3. Use the git reset –hard command to reset your working directory to the specific commit. Replace COMMIT-SHA-ID with the actual commit hash.

 # git reset --hard COMMIT-SHA-ID

For example:

 # git reset --hard a1b2c3d4e5f6g7h8i9j0

Output:

HEAD is now at a1b2c3d4e5f6g7h8i9j0 Initial commit

4. After resetting to the specific commit, you can pull the latest changes to update your references.

 # git pull

5. Perform another hard reset to the specific commit to ensure your working directory and index are in the exact state of that commit.

 # git reset --hard a1b2c3d4e5f6g7h8i9j0

Output:

HEAD is now at a1b2c3d4e5f6g7h8i9j0 Initial commit

Conclusion

This article covered the basics of checking out and cloning a repository using a specific Git commit ID (SHA). We explained what a commit ID is and why it’s useful. We also provided step-by-step instructions to help you complete the task.

FAQs

1. Can I make changes after checking out a specific commit?

Yes, you can make changes and commit them, but these commits will not belong to any branch unless you create a new branch.

2. What does 'git reset --hard' do?

This command resets the working directory and the index to match a specific commit. Be cautious, any uncommitted changes will be lost.

3. Can I push changes from a specific commit checkout?

Yes, but only if you create a branch from that commit. Otherwise, the changes are in a detached HEAD state and can’t be pushed.

4. How do I get back to the latest commit after checking out a previous one?

You can switch back to the latest commit by checking out your branch again using git checkout main command.