How to Check If a File Is Part of a Specific Branch

Introduction

In this lab, you will learn how to check if a specific file exists within a particular Git branch without needing to switch to that branch. We will explore two primary methods: using the git ls-tree command to inspect the contents of a branch's tree object and utilizing the git log command to view the commit history of a file on a specific branch. You will practice these techniques by creating a new branch, adding a file, and then verifying its presence from a different branch. Finally, you will apply these methods to test for files in other branches.

Skills Graph

Run git ls-tree Branch File

In this step, we will explore how to view the contents of a specific branch and file within your Git repository using the git ls-tree command. This command is useful for inspecting the state of your project at a particular point in history or on a different branch without actually checking out that branch.

First, let's make sure we are in our project directory.

cd ~/project/my-time-machine

Now, let's create a new branch called feature-branch and switch to it. We'll add a new file there.

git branch feature-branch
git checkout feature-branch
echo "This is a new feature." > feature.txt
git add feature.txt
git commit -m "Add new feature file"

You should see output similar to this after the commit:

[feature-branch a1b2c3d] Add new feature file
 1 file changed, 1 insertion(+)
 create mode 100644 feature.txt

Now we have a new branch feature-branch with a file feature.txt that does not exist on the master branch.

Let's switch back to the master branch.

git checkout master

You should see output indicating you switched branches:

Switched to branch 'master'

Notice that the feature.txt file is no longer visible in your current directory because you are on the master branch.

Now, let's use git ls-tree to see the contents of the feature-branch and specifically the feature.txt file from the master branch without switching back.

The basic syntax for git ls-tree is git ls-tree <tree-ish> <path>. <tree-ish> can be a branch name, a commit hash, or a tag. <path> is the path to the file or directory you want to inspect.

To view the contents of the feature-branch's root directory, you can use:

git ls-tree feature-branch

You should see output similar to this, showing the files in the root of feature-branch:

100644 blob a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9	feature.txt
100644 blob f9e8d7c6b5a4938271605f4e3d2c1b0a98765432	message.txt

This output shows the file mode, object type (blob for file), the object hash, and the filename.

To view the details of a specific file, like feature.txt, on the feature-branch, you can use:

git ls-tree feature-branch feature.txt

You should see output similar to this, specifically for feature.txt:

100644 blob a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9	feature.txt

This command allows you to peek into other branches or past commits to see the state of specific files without changing your current working directory. This is incredibly useful for comparing files between branches or inspecting historical versions.

Use git log Branch -- File

In this step, we will learn how to view the commit history of a specific file on a particular branch using the git log command with the -- separator. This is incredibly useful when you want to see how a single file has changed over time, regardless of which branch you are currently on.

Make sure you are still in your project directory:

cd ~/project/my-time-machine

We are currently on the master branch. Let's view the commit history for the message.txt file on this branch.

git log -- message.txt

You should see the commit history for message.txt. Since we only made one commit that included this file on the master branch (the initial commit), the output will look similar to this:

commit a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 (HEAD -> master)
Author: Your Name <[email protected]>
Date:   Mon Aug 7 10:00:00 2023 +0000

    Send a message to the future

Press q to exit the log view.

Now, let's view the commit history for the feature.txt file on the feature-branch. Remember, we are still on the master branch, but we can inspect the history of a file on another branch.

The syntax is git log <branch-name> -- <file-path>.

git log feature-branch -- feature.txt

You should see the commit history for feature.txt on the feature-branch. This will show the commit where you added the feature.txt file:

commit a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 (feature-branch)
Author: Your Name <[email protected]>
Date:   Mon Aug 7 10:05:00 2023 +0000

    Add new feature file

Press q to exit the log view.

The -- separator is important. It tells Git that the arguments that follow are file paths, not branches or other references. This allows you to specify exactly which file's history you want to see.

This command is incredibly powerful for understanding the evolution of specific parts of your project. If you're trying to figure out when a particular line of code was added or changed, git log -- <file> is your best friend. You can even add options like -p to see the actual changes made in each commit for that file.

Test Files in Other Branches

In this step, we will practice accessing and viewing the content of files from different branches without switching our current branch. This is a very common task when you need to compare versions of a file or quickly check something in another branch.

Ensure you are in your project directory:

cd ~/project/my-time-machine

We are currently on the master branch. Let's confirm this:

git branch

The output should show * master, indicating you are on the master branch.

  feature-branch
* master

Now, let's try to view the content of feature.txt which exists only on the feature-branch. We can use the git show command for this. The git show command is typically used to show various types of objects in Git, including the content of files at a specific commit or branch.

The syntax to view a file from another branch is git show <branch-name>:<file-path>.

git show feature-branch:feature.txt

You should see the content of the feature.txt file from the feature-branch:

This is a new feature.

This is very convenient! You didn't have to switch branches to see the file's content.

Now, let's try to view the content of message.txt from the feature-branch. This file exists on both branches, but its content might be different if we had modified it on feature-branch. In our case, the content is the same as on master.

git show feature-branch:message.txt

You should see the content of message.txt from the feature-branch:

Hello, Future Me

This demonstrates how you can use git show to access files from any branch or commit in your repository. This is a powerful technique for comparing file versions, debugging issues by looking at past states, or simply inspecting code in other branches without disrupting your current work.

Being able to quickly inspect files in other branches or commits is a valuable skill that saves you time and helps you understand the history and state of your project more effectively.

Summary

In this lab, we learned how to check if a file is part of a specific branch in Git. We started by using the git ls-tree command to view the contents of a branch and a specific file within that branch without checking out the branch. This involved creating a new branch, adding a file to it, switching back to the original branch, and then using git ls-tree with the branch name and file path to inspect the file's presence and details on the other branch. This method provides a quick way to see if a file exists on a different branch and its associated blob hash.