How to Check If a Git Branch Is Orphaned

Introduction

In this lab, you will learn how to check if a Git branch is orphaned. We will explore the git log command to understand commits without parent commits, which is characteristic of the initial commit in a repository.

Furthermore, you will utilize the git branch --no-merged command to identify branches whose changes have not been integrated into the current branch. Finally, you will test these concepts by creating and examining a new orphan branch.

Skills Graph

Check git log for No Parent Commits

In this step, we will explore the git log command further, specifically looking at how it behaves in a repository with no parent commits. This is the case for the very first commit in a repository.

First, make sure you are in your my-time-machine directory:

cd ~/project/my-time-machine

Now, let's use the git log command with the --pretty=oneline option. This option displays each commit on a single line, which is useful for a concise view of the history. We will also add the --max-count=1 option to only show the most recent commit.

git log --pretty=oneline --max-count=1

You should see output similar to this:

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 (HEAD -> master) Send a message to the future

This output shows the commit hash (the long string of characters), the branch it's on (HEAD -> master), and the commit message.

Now, let's try to see the parent of this commit. Since this is the very first commit, it has no parent. We can use the --no-walk=parent option with git log to attempt to show the parent commit.

git log --no-walk=parent --pretty=oneline --max-count=1

This command will likely produce no output, or an error message indicating that there is no parent commit to display. This is expected behavior for the initial commit.

Understanding that the first commit has no parent is fundamental to understanding how Git builds its history. Each subsequent commit will have one or more parents, forming a chain of changes.

Use git branch --no-merged

In this step, we will learn about the git branch command and specifically the --no-merged option. This option helps us identify branches that contain changes that have not yet been incorporated into the current branch.

First, let's create a new branch. Think of a branch as an alternate timeline where you can work on new features or experiments without affecting the main timeline (master).

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

cd ~/project/my-time-machine

Now, create a new branch called experiment:

git branch experiment

This command creates the new branch, but it doesn't switch you to it. You are still on the master branch.

Let's list all the branches in our repository using the git branch command:

git branch

You should see output similar to this:

  experiment
* master

The asterisk (*) indicates the branch you are currently on, which is master.

Now, let's use the git branch --no-merged command. This command lists branches that have not been merged into the current branch (master).

git branch --no-merged

You should see:

  experiment

This output tells us that the experiment branch contains changes that are not present in the master branch. In this case, since we just created the experiment branch from master and haven't made any changes on it yet, this might seem counterintuitive. However, the --no-merged option is designed to show branches whose tip commit is not reachable from the tip of the current branch. Since experiment points to the same commit as master currently, but master hasn't "merged" experiment (which doesn't make sense in this context), it still lists experiment.

In a real-world scenario, you would typically create a new branch, make some commits on it, and then use git branch --no-merged from your main branch (like master) to see which feature branches are ready to be merged.

Test with New Orphan Branch

In this step, we will create a new "orphan" branch. An orphan branch is a branch that starts with no history from previous branches. It's like starting a completely new timeline in your time machine. This is useful for things like documentation branches or gh-pages branches for websites, where you don't want the history of your main code to be included.

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

cd ~/project/my-time-machine

Now, let's create a new orphan branch called new-start:

git checkout --orphan new-start

You should see output similar to this:

Switched to a new branch 'new-start'

We have now switched to the new-start branch. Notice that the files from the master branch are still present in your working directory. This is because git checkout --orphan prepares your working directory and index for a new root commit, but it doesn't remove the existing files.

Let's check the status:

git status

You should see something like this:

On branch new-start

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        message.txt

nothing added to commit but untracked files present (use "git add" to track)

Git sees message.txt as an untracked file because the history of the new-start branch is completely separate from master.

To truly start fresh on this orphan branch, we typically remove the old files and then add the new content for this branch. Let's remove the message.txt file:

rm message.txt

Now, let's check the status again:

git status

You should see:

On branch new-start

No commits yet

nothing to commit (create/copy files and use "git add" to track)

The working directory is now clean, and we are ready to create the first commit on our new, independent timeline.

Let's create a new file specific to this branch:

echo "This is a fresh start!" > readme.md

Add the new file to the staging area:

git add readme.md

And finally, create the first commit on the new-start branch:

git commit -m "Initial commit for new-start branch"

You should see output similar to this:

[new-start (root-commit) a1b2c3d] Initial commit for new-start branch
 1 file changed, 1 insertion(+)
 create mode 100644 readme.md

Notice that this commit is also a "(root-commit)", just like the first commit on the master branch. This confirms that it has no parent and is the beginning of a new history.

Now, let's look at the log for this branch:

git log --pretty=oneline

You should see only the single commit we just made:

a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 (HEAD -> new-start) Initial commit for new-start branch

This demonstrates that the new-start branch has its own independent history, separate from the master branch.

Summary

In this lab, we learned how to check if a Git branch is orphaned. We started by exploring the git log command, specifically how to identify the absence of a parent commit for the initial commit in a repository using --no-walk=parent. This demonstrated the fundamental concept of Git history where the first commit has no parent.

Next, we were introduced to the git branch --no-merged command. This command is used to list branches that have not been merged into the current branch, which is a key technique for identifying branches that might be orphaned or contain unintegrated changes. The lab also included a step to test these concepts by creating and examining a new orphan branch.