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Lab 2: Git Practice

In this lab, you'll practice using git and GitHub. Git is a collaborative tool, so make sure you form a group of 2-3 people to do this lab together. You'll do the following:

  • practice merging in a Git simulator
  • create a GitHub account
  • create a GitHub repos from scratch and by forking other GitHub repos
  • push changes from a laptop repo directly to a GitHub repo
  • push changes from a loptop repo to a forked repo, before merging those changes into the main repo (this is the very important pull request process)

You can do this lab on your virtual machine, which should already have git installed (and even not, installing git on Ubuntu can be done with a simple apt command, like this: sudo apt install git).

It's probably a good idea to install git on your own laptop at some point. Windows directions: https://git-scm.com/download/win. Mac directions: https://www.ics.uci.edu/~pattis/common/handouts/macmingweclipse/allexperimental/macxcodecommandlinetools.html. You're welcome to do this lab directly on your laptop (not through the virtual machine), though if you run into any tricky issues installing or using git directly on your laptop, we might ask you to switch to using your virtual machine.

Step 1: Practice Git Branching

Let's start by practicing in the Git simulator here. Try to run commands to get to the following state (if you get stuck, check the solution here):

Useful commands for the above problem:

  • git commit: make a new commit
  • git branch bname: create a branch named bname
  • git checkout bname: move HEAD to the commit referenced by the bname
  • git checkout c1: move HEAD to the c1 commit
  • git merge bname: merge changes on the bname branch into the current branch
  • git branch -D bname: delete the branch named bname

Ready for a real challenge? Try to get to this state (no answer to check for this one, so you'll need to work for it!):

Hint: start by creating commits on four branches, b1, b2, b3, and b4. Merge b2 into b1 and b4 into b3. Then merge the two merge commits with a third merge commit.

Step 2: Create GitHub Account

Everybody in your group should go to http://github.com/ and create a GitHub account (choose a name that wouldn't embarrass you on a resume):

Later, running certain git commands will make you type your GitHub password each time, unless you setup an SSH key to use instead of a password (you likely setup an SSH key during the first lab to access your virtual machine). It's recommended (but not required) that you configure GitHub with an SSH key following these directions.

Step 3: Create and Fork/Clone a Repo

Identify one person to be the team leader -- it should be whoever has an upcoming birthday the soonest.

The leader should go to https://github.com/new and create a public repo called "cs320-lab2", initialized with a README (the other people working on the lab will have another role to play):

This should create a repo at https://github.com/tylerharter/cs320-lab2 (with the leader's GitHub name instead of "tylerharter"). All team members should go there and click the "Clone or download" link:

The preferred option for any team member that configured their SSH keys is to click "Use SSH" (the HTTPS option would also work, it but would require frequent typing of your password later):

Everybody should copy that clone address (from the leader's repo), then run the command git clone ADDRESS in the shell, replacing "ADDRESS" with whatever was copied. This will create a new directory to which you can cd and run git status. These three steps should look something like this:

Step 4 [Leader Only]: Making and Pushing a Change

Everybody should read, discuss, and understand this part, but only the team leader will run commands in this section.

We'll pretend that your group is creating some pages for a new company you're starting together. Agree on a company name now for your group.

Leader Only: you should create some initial pages (other team members will later make additions. Type nano README.md from in the cs320-lab2 directory. Type in your company name and a brief description. Save the file by typing CTRL-O (control and "O" keys at same time).

Exit with CTRL-X and edit a team.md file by typing team.md; put in the leader's name, and a note for others to add themselves:

Run git status, and note that README.md and team.md are not staged for commit. Run git add README.md team.md, then run git status again to note the difference:

Run git commit -m "updated company name and team list"

Currently, the repo on your laptop (which was cloned from the GitHub repo) has been updated. The original GitHub repo has not been updated yet.

To sync back to the GitHub repo, run the git push command (you may be asked to configure your name/email before this will work -- just follow the hints git provides).

Go back and visit the repo online at https://github.com/tylerharter/cs320-lab2 (with the leader's GitHub name instead of "tylerharter"). Do you see the changes?

Step 5 [Non-Leaders Only]: Making a Pull Request

These steps are for everybody except the leader, but the leader should read and understand them too.

The leader's changes are now in their laptop's repo and in the GitHub repo, but not in the previously cloned repos of other team members. Try running git log and confirm there is only one commit, not two.

Run git pull from in the cs320-lab2 directory. This will grab the latest changes from the GitHub repo. Not try running git log again. See both the commits?

Now type nano team.md and add yourself to the list, using an alias if you wish:

Then stage your files (git add team.md) and commit (git commit -m "added myself to the team").

Getting your changes back into the leader's repo will trickier for you than it was for the leader. The leader could just run git push, but you cannot push changes directly to the leader's GitHub repo because you aren't configured to have permission to do that.

Instead, what you'll do is create your own GitHub repo that's a copy of the leader's repo -- such a repo copy is called a fork. You can push whatever changes you want to your own fork.

Then, you can create a pull request. A pull request is a message to the leader that basically says: "look at these cool changes in my forked repo -- please consider pulling those changes back into your own GitHub repo."

Go to the leader's GitHub page, and click "Fork" at the top:

You'll now see your own forked copy of the repo. Find and copy the clone address of the fork:

Now, back in the terminal, run the following, replacing PASTEHERE with the clone address you just copied:

git remote add myfork PASTEHERE

We chose "myfork" as a convenient label for your fork -- you could have chosen any name there.

Now, even though we can't push your committed changes directly to the leader's GitHub, you can push them to your own fork by running git push REMOTE BRANCH, replacing REMOTE and BRANCH, something like this:

git push myfork master

It should all look like this:

Go back and refresh the GitHub page for your fork. Do you see the changes to team.md? (you should!).

Ok, now we want to create your pull request, to ask the leader to integrate your changes back to the main repo.

Go to the GitHub page for the leader's repo, select the "Pull requests" tab, and click "New pull request":

Click the "compare across forks" link and configure the dropdowns so that the arrow points from the master branch on your GitHub repo to the master branch on the leader's repo:

Click "Create pull request", write a note, and click "Create pull request" again.

Step 6 [Leader Only]: Merging a Pull Request

The leader should go back to the "Pull requests" tab on the page for their GitHub repo and open the new Pull Request. To accept it (after browsing through the changes), click the "Merge pull request" button:

Confirm the merge, then go back to the main repo page and verify that everybody's changes are part of the main repo.

If you're in a group of 3, the leader will need to repeat these steps twice to merge in the pull requests of both the other team members.

Conclusion

Pull requests are neat -- they give you an easy way to make improvements and recommend them to any public project on GitHub. Even amongst your own team, they provide a great way to get feedback on changes in a fork before those changes become part of the main repository.

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