How to Check If a Git Branch Is Ahead of the Remote Branch

Introduction

In this lab, we will learn how to check if your local Git branch is ahead of its corresponding remote branch. This is a crucial skill for understanding the state of your repository before pushing changes. We will explore two primary methods: using git status to see the "ahead" status and using git log with the @{u}..HEAD syntax to view the specific commits that are ahead.

Through hands-on exercises, we will simulate making local commits and then use these commands to observe how Git indicates that our local branch has diverged from the remote. Finally, we will test these methods with synced branches to see the expected output when no commits are ahead.

Skills Graph

Check git status for Ahead Status

In this step, we will learn how to check the status of our Git repository, specifically focusing on how Git tells us if our local branch is "ahead" of a remote branch. This is a common scenario when you've made commits locally but haven't pushed them to a remote repository yet.

First, let's make sure we are in our project directory. Open your terminal and navigate to the my-time-machine directory:

cd ~/project/my-time-machine

Now, let's create a new file and add some content to it. We'll simulate making a change that we will eventually commit.

echo "Another message for the future" >> message.txt

This command appends the text "Another message for the future" to our existing message.txt file.

Next, let's stage this change using git add:

git add message.txt

Now, let's create a new commit with a message describing the change:

git commit -m "Add another message"

You should see output similar to this, indicating that a new commit has been created:

[master 1a2b3c4] Add another message
 1 file changed, 1 insertion(+)

Great! We have now made a new commit on our local master branch. However, this commit only exists locally. If we had a remote repository (like on GitHub or GitLab), this commit would not be there yet.

Let's check the status of our repository again using git status:

git status

This time, the output will be slightly different. You should see something like this:

On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)

nothing to commit, working tree clean

Notice the line Your branch is ahead of 'origin/master' by 1 commit.. This is Git telling us that our local master branch has one commit that is not present on the origin/master branch (which represents the master branch on a hypothetical remote repository named origin).

This "ahead" status is a key indicator that you have local changes that need to be pushed to the remote repository to be shared with others or to back them up remotely. Understanding this status is crucial for collaborating with others and keeping your local and remote repositories in sync.

Use git log @{u}..HEAD for Ahead Commits

In the previous step, we saw that git status told us our local branch was "ahead" of the remote tracking branch. But how can we see which commits are ahead? Git provides a powerful way to compare branches using git log.

The syntax @{u}..HEAD is a shorthand in Git. @{u} refers to the upstream branch (the remote tracking branch your current branch is configured to track, like origin/master), and HEAD refers to the tip of your current local branch. So, @{u}..HEAD means "show me the commits that are on my current branch (HEAD) but not on the upstream branch (@{u})".

Let's try this command in our terminal. Make sure you are still in the ~/project/my-time-machine directory:

cd ~/project/my-time-machine
git log @{u}..HEAD

You should see the log entry for the commit we just made in the previous step:

commit 1a2b3c4d5e6f7g8h9i0j1k2l3m4n5o6p7q8r9s0 (HEAD -> master, origin/master)
Author: Jane Doe <[email protected]>
Date:   Mon Aug 7 10:00:00 2023 +0000

    Add another message

(Note: The commit hash and date will be different in your output, but the commit message should be the same.)

This command is incredibly useful for seeing exactly what changes you are about to push to a remote repository. It helps you review your work and ensure you are only pushing the intended commits.

The @{u}..HEAD syntax is a specific example of Git's range notation for git log. You can use similar syntax to compare any two commits or branches. For example, branch1..branch2 shows commits on branch2 that are not on branch1.

Understanding how to use git log with range notation gives you fine-grained control over viewing your project's history and comparing different states of your repository.

Press q to exit the log view and return to the command line.

Test with Synced Branches

In the previous steps, we saw what happens when our local branch is ahead of the remote tracking branch. Now, let's see what git status and git log @{u}..HEAD show when our local branch is in sync with the remote tracking branch.

Since we don't have a real remote repository in this lab environment, we can simulate being in sync by removing the commit we just made. In a real scenario, being in sync would mean you have pushed your local commits to the remote repository.

We can use git reset to move our local branch pointer back to the previous commit. Be careful with git reset in real projects, as it can discard changes! For this lab, it's safe because we are just simulating a state.

Make sure you are in the ~/project/my-time-machine directory:

cd ~/project/my-time-machine

Now, let's reset our branch to the commit before the last one. We can use HEAD~1 to refer to the commit before the current HEAD.

git reset --hard HEAD~1

You should see output similar to this, indicating that the HEAD has been moved back and the working directory has been updated:

HEAD is now at a1b2c3d Send a message to the future

(Note: The commit hash will match the hash of your first commit.)

Now that we have reset our local branch to the state of the first commit, let's check the status again:

git status

This time, the output should indicate that your branch is up to date with the remote tracking branch:

On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean

The message Your branch is up to date with 'origin/master'. tells us that our local master branch is in sync with the remote tracking branch.

Finally, let's use git log @{u}..HEAD again to see if there are any commits ahead:

git log @{u}..HEAD

This command should produce no output, because there are no commits on our local branch (HEAD) that are not also on the upstream branch (@{u}).

This confirms that our local branch is now in sync with the remote tracking branch. Understanding the output of git status and using git log @{u}..HEAD are essential skills for managing your Git workflow and collaborating effectively.

Summary

In this lab, we learned how to check if a local Git branch is ahead of its corresponding remote branch. We started by making a local commit and then used git status to observe the "ahead" status message, which indicates that the local branch contains commits not yet present on the remote.

We also explored using git log @{u}..HEAD to specifically list the commits that are ahead of the remote tracking branch, providing a more detailed view of the differences. Finally, we tested the behavior with synced branches to confirm that git status reports the branches as up to date when there are no local commits ahead of the remote.