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This repository should be forked as part of the collaborative Git exercises.


This focuses on slightly-more-advanced-than-an-introduction features of git. If you're new to git, consider checking out our introduction presentation and then come back and give this a try!

The examples and situations are specifically arranged to result in certain issues that will naturally come up in collaborative environments. Please avoid working ahead to prevent troubleshooting issues at unexpected times.


For this activity, find a person nearby who you can work with. Ideally, you will want to be in teams of two; however, teams of 3 will probably work out fine. Assign a number (1..n where n is the number of people on the team) to each person on your team. All futher instructions will assume teams of 2, but can be easily adjusted.


Person 1 from each team needs to fork the upstream UUG repo. To fork a repository, click the "Fork" button in the upper-right corner of the page. If prompted, fork the repository to your personal GitHub account.

Person 1 should add all others as collaborators on the repository. On the GitHub website for Person 1's fork, Person 1 should go to Settings, then Collaborators, then add all other team members as collaborators. The other team members should accept the invite.


To clone the repository, run git clone$USERNAME/git-201. Replace $USERNAME with Person 1's GitHub username. Then type cd git-201.

Set up

If you haven't done this at some point in the past, run the following two commands

git config --global "$YOURNAME"
git config --global "$EMAILADDRESS"

Replace $YOURNAME with your first and last name and $EMAILADDRESS with the email address you used to sign up for GitHub. Leave the quotation marks in.


The year is 1609 and Shakespeare has just written his Sonnet #18. He is about to publish it; however, he got his copy of Microsoft Word from TPB and instead of having malware added, it simply has the spell checker removed. Instead of lecturing him on how he should have just used LibreOffice, you decide to lend him a hand. Now because it's 1609 you don't have spellcheck either, so the spelling errors will need to be corrected mostly one-at a time manually. Also because it's 1609, there's a good chance you're illiterate, so not all of the changes that will be made in this exercise are actually fixes.

Sonnet 18 can be found in the CHANGEME.txt file.

Making the first fix

The first issue found is by Person 1 on Line 11. The apostrophe in "untrimm'd" needs to be replaced with an "e". After saving the file, add the changes to the stage with git add CHANGEME.txt. Once that is done, commit the changes with git commit

Writing a commit message

Much like there are style guides for code, commits have style guides as well. The general style is an introductory line less than 50 characters written in the present imperative tense, which means that all commit messages should start with something like

Fix the spelling of untrimmed

And not

I fixed the spelling of untrimmed

After writing a summary, you can continue to write paragraphs explaining the details of your change. Each line should wrap at 72 characters and each paragraph should be separated by a single line. For example, this commit might get a commit message like:

Fix the spelling of untrimmed

Spelling is hard. It seemed like a good choice at first to replace vowels that we weren't sure about with apostrophes, but that adds a bunch of weird symbols to the text. Replace the symbols with actual letters.

There are five vowels in the English alphabet. "E" seems like a good choice here.

Once you've got a good commit message and assuming git kindly dropped you in vim to write the message, press the Esc key and then type ":wq" and press Enter.

Pushing the commit

Now that the commit has been written, it's time to share it with the world. Person 1, type git push -u origin main.

Sidenote: The -u origin main is only necessary the first time you push to a repository. It tells git that you want to track the remote named origin and the branch named main.

A second fix

Person 2 can now fix the issue on line 9. It's very similar, again an apostrophe needs to be replaced with the letter "E". Make the change in the file, add the file to the stage with git add CHANGEME.txt, then git commit. Write a commit message.

Now type git push -u origin main.

How to fix the error

Git has now given Person 2 a fairly helpful error message. You can't push because someone else (Person 1) has pushed changes that you don't have. There are two ways to fix this. We can do either of:

  • Merge the changes into your branch
  • Rebase your changes atop the remote changes

Both merging and rebasing mean different things. Merging means that you take two different histories of a project and smush them together and you get a merge commit which represents all the changes from the alternate history.

Rebasing means that you take the known history and replay all the commits from the alternate history on top of the known.

In this example, Person 2 has the alternate history (not a real git word), and the stuff on GitHub is the real history

Here, we will rebase. Run the command git pull --rebase.

Now look at the output of git log and see that Person 2's change exists in the log on top of Person 1's change. At this point, Person 2 should git push and it should work successfully. Person 1 should now run git pull to get the latest changes.

More fixes!

Person 1 and 2 both notice different issues on line 14. Person 1 should change "Death" to "death" and Person 2 should change "wander'st" to "wanders". Person 2 should commit and push their changes then Person 1 should attempt to do the same. Person 1 will get an error when pushing, just like they did before. This time, Person 1 should just do a git pull because it's easier to type.

Merge conflicts

Person 1 should open CHANGEME.txt in their favorite text editor and look around Line 14. It should look something like:

<<<<<<< HEAD
Nor shall death brag thou wander’st in his shade,
Nor shall Death brag thou wanders in his shade,
>>>>>>> abunchoflettersandnumbershere

Person 1 should resolve this in any way that seems acceptable. It is important to remove the lines that Git added. Make any modifications to the changed line as necessary. In a real project, this merge conflict may span several lines; just change the lines as needed and remove the ones with >>>, ===, and <<<.

After making the changes to the file, tell git that you're done resolving the conflict by running git add CHANGEME.txt. Then run git merge --continue.

Person 1 will now need to create a merge commit. Just leave the message as the default. Person 1 should git push and Person 2 should git pull.


Clearly this whole mess of every person having to communicate every single change they want to push and making everyone else git pull. This can be minimized with using branches. Generally branches that are made for the purpose of fixing a particular issue are referred to as topic branches.

git checkout is a tool to switch between branches and when passed the -b flag, it will create the branch if it doesn't exist.

We will play around with these and how to turn them into Pull Requests.


An introduction to using git with other people






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