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Viewing Differences Between Branches

3:05 with Jay McGavren

We only recently created the `testing` branch, so you probably remember what's on it. But suppose you've gotten pulled away for a week to work on a higher-priority project. Or suppose it's not even your branch, but one created by a collaborator. As we'll see later, branches can be transferred to other repositories, and you're going to need a convenient way to see what's on those branches.

  • git diff can show you the differences between two branches. For example: git diff master testing
    • Git looks up the commits that each branch currently points to, and gives us a diff between those commits.
  • You aren't resricted to the branch that's currently checked out, either.
    • If we want to see the differences between the add-letters and testing branches, you can run this command: git diff add-letters testing
  • When you provide only one branch name, Git will compare the contents of the working directory to that branch.
    • I can show the difference between my files and the master branch by running: git diff master
    • If you have modified files in your working directory that haven't been committed yet, this version of the git diff command will show you those changes.
    • If everything is committed, then it will look the same as comparing two branches.

We only recently created the testing branch, so 0:01
you probably remember what's on it. 0:03
But suppose you've gotten pulled away for 0:05
a week to work on a higher priority project. 0:07
Or suppose it's not even your branch, but one created by a collaborator. 0:10
As we'll see later, branches can be transferred to other repositories, and 0:15
you're going to need a convenient way to see what's on those branches. 0:19
Without any arguments, git diff shows you the differences between your working 0:22
directory and your latest commit. 0:26
But you can also specify particular commits from your history and git will 0:29
ignore the working directory and show you differences between those commits. 0:32
First, let me make sure the testing branch is checked out, git checkout testing. 0:37
Now I'll look at my history with git log. 0:44
I'm going to note the SHA checksums from the commit the master branch points to, 0:47
and the commit the testing branch points to. 0:51
Now I'll run git diff and give it partial SHA checksums for those two commits. 0:54
You should list the earlier commit first, so 0:58
I'll give it the checksum from the master branch first. 1:01
Git will show you changes for all the commands between the first and 1:04
last command you specified. 1:07
In this case, all the changes are within the test_decoder.rb file. 1:10
But if there are changes in multiple files, it'll show all the files. 1:13
If I run git log -p, 1:18
you can see the individual changes that went into this combined diff. 1:19
There's the commit where we set up the unit test, 1:23
followed by a separate commit where we add an additional test. 1:25
Being able to show diffs between specific commits like this is occasionally useful. 1:29
It's kind of a pain to have to type the commit SHAs though. 1:34
So let me run another command that will give me the same result. 1:37
git diff master testing. 1:40
As we mentioned earlier, a branch is just a pointer to a specific commit. 1:46
So git lets you use branch names in place of the commit SHAs. 1:51
This lets us get a diff between two branches much more easily. 1:54
Git looks up the commits that each branch currently points to, 1:59
and gives us a diff between those commits. 2:02
You aren't restricted to the branch that's currently checked out either. 2:05
If we want to see the differences between the add-letters and testing branches, 2:08
you can run this command, git diff add-letters testing. 2:12
That shows us that the testing branch doesn't have the letter 2:18
translations from the add-letters branch, but it does have the unit test code. 2:21
There's one variation on the git diff command that I want to show you. 2:26
When you provide only one branch name, 2:30
git will compare the contents of the working directory to that branch. 2:32
So I can show the differences between my files and 2:36
the master branch by running git diff master. 2:39
If you have modified files in your working directory that haven't been committed yet, 2:42
this version of the git diff command will show you those changes. 2:46
If everything is committed, then it will look the same as comparing two branches. 2:50
The git div tool is always useful, but 2:54
it's especially useful when it comes to branches. 2:56
Git diff can help you figure out exactly what's on that branch, 2:59
whether it was created by you or by a collaborator 3:02

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