Find the Differences Between Two Git Branches

1. Overview

In this tutorial, we’ll discover ways of finding differences between two git branches. We are going to explore the git diff command and use it in branch comparison.

2. Compare Branches in a Single Command

git diff is a useful command that allows us to compare different types of git objects, such as files, commits, branches, and many more. This makes git diff a good choice when we need to compare the differences between two branches.

To compare the branches, we specify both branches’ names after the git diff command:

$ git diff branch1 branch2 
diff --git a/file1.txt b/file1.txt
index 3b18e51..c28f4fa 100644
--- a/file1.txt
+++ b/file1.txt
@@ -1 +1 @@
-hello world
+hello from branch2

Let’s examine the output. The first line diff ‐‐git a/file1.txt b/file1.txt shows which files are different in the branches. In our example, it is the file file1.txt, which is represented as a/file1.txt for branch1, and b/file1.txt is the same file for branch2.

The next line shows index cache numbers for the file1.txt in both the branches. Then, there are several lines that show the file names with added content, and the ones with removed content.

And finally, the most important lines are at the end of the output, where we can see the exact modified lines. We can see that the line “hello world” in the file file1.txt from branch1 was replaced by the line “hello from branch2” in branch2.

3. Showing Only the Names of Files

Although we found the differences between the two branches in the example above, it can be inconvenient to display changes for every single line. Often, we want to see just the names of the changed files.

To display only the names of files that are different between two branches, we use the  ‐‐name-only option in the git diff command:

$ git diff branch1 branch2 --name-only
file1.txt

Now, the output shows just the name of files that are different in both the branches. In our case, it’s just a single file file1.txt.

4. An Alternative Way to Compare Branches

In the examples above, we used a single git diff command to find the differences between the branches. However, we had to specify both branches’ names in this command. Sometimes it feels more intuitive if we do the comparison from within one of the branches.

To check out to a branch, we use the git checkout command. After that, we only need to diff the other branch and see all the changes relative to our current branch.

For example, let’s compare branch1 and branch2 from within branch2:

$ git checkout branch2 
$ git diff branch1

We should now be able to see the same output as earlier.

5. Finding the Differences From a Common Ancestor

So far we were comparing the two branches in regard to their latest states. However, sometimes we need to compare a branch with a common ancestor of another branch.

In other words, we may need to find all differences in the branch compared to another one since they were branched off. For illustration, let’s see the tree below:

---A---B---C---D  <== branch1
        \
         E---F    <== branch2

We’d like to find the differences between branch2 (current commit position F) and branch1 at its commit position B. As we can see, at position B, the two branches are forked out and then they develop separately from each other. In this case, position B is the common ancestor of the two branches.

To find the diff between branch2 and branch1 common ancestor, we need to use three dots between the branch names:

git diff branch1...branch2

The output will be in a similar format as earlier. However, now the comparison is happening between branch2 and a common ancestor of branch1.

6. Finding the Differences Between Commit Hashes

It’s possible to display differences not only between the branches, but also between the commits.

The syntax for this is similar to the branch comparison. However, instead of branches, we need to specify the commit hashes that we want to compare:

git diff b94a88bac17318fb3c3cc881d657c04de9fd7901 73ea8956375c10fe41c669ba8c6f6f9e01490452

The output will be of a similar format to the examples above.

7. Conclusion

In this article, we learned how to find the differences between two git branches using the git diff command.

We first looked at comparing the branches using a single command. Then, we found out how to compare branches from within one of the branches using the git checkout command.

Lastly, we saw how to compare branches to a common ancestor, along with finding the differences between commits.