Objectives:

By the end of this chapter, you should be able to:

• Use git diff to see changes between two commits
• Use a visual diff tool to better examine changes between commits

Seeing commits and changes

Once you have made a commit, you can see the message, author and some additional information using the git log command. When you type this in you will also see the full SHA, which, as we've discussed, is a unique identifier for the commit. To get out of git log you can type q.

As you work on a project by adding and modifying files and committing changes, your commit history will expand and your git log will grow. Sometimes you'll want to compare the history of your code at two different points in time. To do this, we can use the git diff command.

If you want to see differences between your commits you can use the git diff command and specify the SHA to compare. This will compare your code now to your code at that SHA. Here are a few different kinds of diff-s that you can see.

git diff - See changes in the working tree not yet staged for the next commit.

git diff --cached - See Changes between the staging area and your last commit.

git diff HEAD - See all changes in the working directory since your last commit.

git diff ANOTHER_BRANCH - compare with the latest code on another branch

git diff HEAD~1 HEAD - compare with the previous commit (add ~2, ~3 for older commits)

You can read more about git diff here

Try this out with one of your earlier examples, or create a repository from scratch. Build up a commit history of five or so commits, then explore these different ways to compare differences with git diff. It's best if you modify files between commits rather than simply adding or removing files, so that you can begin to appreciate git diff in its full glory!

Using a visual tool

Depending on your operating system, there are a few different visual tools you can use, which give a much nicer interface to compare commits and files than git diff. On OSX, opendiff is a wonderful place to start. If you have XCode installed, you can type opendiff in the terminal and you should not see an error. You can read more about it here, here, and here.