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