01 Git Basics

Git is a version control system based on a tree of hashed patches called commits. This helps understand the evolution of your code, undo mistakes, and collaborate with others. Let's demo a few of the things you can do with git.

Work with branches

A branch is a named series of commits. You often have one primary branch (e.g. main), with short-lived branches to work on features and functionality. Some projects also use branches as a way to version their releases.

Check out an existing branch

Run git branch. It will show all the repo's branches, with an asterisk next to your currently-checked-out branch. Make sure it has an asterisk next to lab/01-git-basics. If not, run the following to check it out:

git checkout lab/01-git-basics

Create a new branch

You can also create a new branch. By default, it will be based on the current branch (i.e. lab/01-git-basics).

git checkout -b lab/01-git-basics-demooo

Rename a branch

Sometimes you need to rename a branch. You can do this with the -m option.

git branch -m lab/01-git-basics-demo

Work with commits

A commit is an atomic set of patches to your code. Commits tell a story about how the code evolved. Let's try making some commits.

Commit a modification

Git is all about tracking modifications to your code. Let's try that out:

macOSWindows

# Make a dummy change to the README
echo "DukeHacker was here!" >> README.md

# Commit it
git commit -a -m "Says hi to the README."

# Open README.md in your favorite text editor and add "DukeHacker was here!" 
# to the end of the file. Save and exit.

# Commit it
git commit -a -m "Says hi to the README."

The -a tells git to include all modifications. The -m tells git you're going to pass a commit-message directly on the command-line. Without -m it will open your shell's default text editor to draft the message instead. Usually this is vim on Unix-based systems.

Warning

If you end up in vim and are not familiar it, then you can type a to go into append mode to edit content, followed by ESC to exit append mode, plus :wq followed by ENTER to write your changes and quit editing.

Commit a new file

Above we modified an existing file. Git avoids tracking new files unless you explicitly ask it to. So, let's try adding a new file.

cp README.md new_file.md

# Observe that git is aware of the untracked file
git status

# Add and commit the file
git add .  # Adds all new files at or under the current directory (.)
git commit -m "Adds new file."

Note that we omitted -a on the commit because we explicitly added the change on the prior line.

Revert some changes

Sometimes you realize you made a mistake and want to back it out. Git allows you to do this by reverting commits. This essentially creates a new commit with the opposite changes of the one you would like to back out. There are two ways we can do this.

If you want to revert your most recent change(s), you can ask git to roll back relative to the HEAD commit (i.e. your most recent commit). Let's revert the second most-recent commit where we modified the README.

git revert --no-edit HEAD~1

The --no-edit option tells git to use a canned commit-message for the revert commit.

You can also revert commits by their exact hash (e.g. if it's older and using offsets is inconvenient).

git log  # find the "Adds new file." commit hash
git revert --no-edit {hash from above}

# Finally, go back to the main branch
git checkout main