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.

Without any arguments, git diff shows you the differences between your working

directory and your latest commit.

But you can also specify particular commits from your history and git will

ignore the working directory and show you differences between those commits.

First, let me make sure the testing branch is checked out, git checkout testing.

Now I'll look at my history with git log.

I'm going to note the SHA checksums from the commit the master branch points to,

and the commit the testing branch points to.

Now I'll run git diff and give it partial SHA checksums for those two commits.

You should list the earlier commit first, so

I'll give it the checksum from the master branch first.

Git will show you changes for all the commands between the first and

last command you specified.

In this case, all the changes are within the test_decoder.rb file.

But if there are changes in multiple files, it'll show all the files.

If I run git log -p,

you can see the individual changes that went into this combined diff.

There's the commit where we set up the unit test,

followed by a separate commit where we add an additional test.

Being able to show diffs between specific commits like this is occasionally useful.

It's kind of a pain to have to type the commit SHAs though.

So let me run another command that will give me the same result.

git diff master testing.

As we mentioned earlier, a branch is just a pointer to a specific commit.

So git lets you use branch names in place of the commit SHAs.

This lets us get a diff between two branches much more easily.

Git looks up the commits that each branch currently points to,

and gives us a diff between those commits.

You aren't restricted 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.

That shows us that the testing branch doesn't have the letter

translations from the add-letters branch, but it does have the unit test code.

There's one variation on the git diff command that I want to show you.

When you provide only one branch name,

git will compare the contents of the working directory to that branch.

So I can show the differences 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.

The git div tool is always useful, but

it's especially useful when it comes to branches.

Git diff can help you figure out exactly what's on that branch,

whether it was created by you or by a collaborator