Git Activity

Section 1 Using Git Locally

This sequence of commands shows how to work using git just by yourself, locally. No github and no collaborators. I'll demo this with the "cs304guest" account.

cd ~/cs304
mkdir personal-project
cd personal-project
git init
echo "My personal project" > README.md
ls
git status
git add README.md
git commit -m 'added README' # this will fail

The last step will fail because it needs to know who we are, etc. Let's fix that.

git config --list
git config user.email "your github username"
git config user.name "your name"
git config --list
git commit -m 'added README' #will succeed

Let's do a bit more, just for practice:

cp -r ~cs304/pub/downloads/flask-starter/* .
ls
git status
git add app.py
git status
git commit -m "first version of the app.py file"
git add templates/*
git status
git commit -m "all the templates"
git status
git add static/*
git commit -m "first CSS file"
git status
git log
ls -A # Note the .git directory

Section 2 Using Branches as alternative versions

The idea here is to see branches as distinct versions

git checkout -b foo # create and switch to branch for feature 'foo'
git branch
echo "this is file foo" > foo.py
ls
git status
git add foo.py
git commit -m 'first version foo.py'
git status
git branch
git checkout master
git branch
ls # no foo.py!
git checkout foo
ls # here it is!
git branch
git checkout master
git merge foo
ls

Section 3 Using Github and remote repositories

Learning how to work with Github, but still without collaborators

home page
repositories
click green "new" button
name it using this form:
click green "create repository" button

Go to Tempest and follow their incantation for "…or push an existing repository from the command line", making sure (for now) to choose the HTTPS method: namely

git remote add origin https://github.com/your-account/your-repo.git
git push -u origin master
you'll have to type in your password. Eventually, we'll fix this.

Go to Github and see the source code by clicking on the link to the repo
Go to Tempest
git push origin --all # push all branches to github
On Github, refresh the page, check the source code and switch between the two branches
return to Tempest
git checkout -b bar # new branch
git status
git branch # confirm we are on branch bar
echo "This is bar" > bar.py
git add bar.py
git commit -m 'v1 of bar.py'
git checkout master
ls
git merge bar
ls
git push origin master # again, you'll have to give your username and password.

Section 4 Collaborators

Here, we'll create a directory for our project and add our teammates as collaborators. Use chat to choose a "captain" for today. The captain will do the following:

cd ~/cs304
mkdir group-project
cd group-project
git init
cp -r ~cs304/pub/downloads/flask-starter/* .
git status
git add *
git status
git commit -m 'starting project' # you'll have to set username and such

Now, go to Github and create a repo and then return to Tempest and do the incantation to push it to Github:

git remote add origin https://github.com/captain-account/your-repo.git
git push -u origin master # have to supply Github username/password

Now, return to Github and add your teammates. Your teammates should have sent their github names (or you can do this later). For this example, I will use my personal github account, scott-anderson:

Go to project settings
Click on "manage access"
give your password
Click on green "invite collaborators" button
add the github names of your collaborators
(optionally) add my work github name: scott-anderson-wc

The teammates should login to github and accept the invitation.

The notification is under the bell in the upper right
click on it the notification
click on the green "accept notification" button
They can see the code on github
They can click the green "clone or download" button and note the https or ssh url. We'll use the https url this time; later we'll replace it with the ssh url.

Now, the teammates can go to their tempest account and copy the repo.

login
cd cs304
mkdir draft
git clone https://github.com/captain-account/your-repo.git
cd into the repository directory

I'll do this in my "anderson" account, as opposed to "cs304guest".

Note that this will work even without inviting collaborators, because your github repo is *public*. (Since it's public, make sure you don't put anything personal or private in it. Just CS 304 project code and such.)

But only collaborators will be able to modify the code, so that's next.

Next, a teammate should make a modification on Tempest. In this example, I'm imagining a team of Harry, Ron and Hermione, with Hermione the captain. So, Ron is a teammate, and he does:

echo "written by Ron" > ron.py
git status
git add ron.py
git config user.email "rweasley@wellesley.edu" # or github name
git config user.name "Ron Weasley"
git commit -m 'first version of ron.py'
git pull origin master
git push origin master # ron will have to give his github username/password

Let's switch back to github on the captain's account or the collaborator's account, and see the upload.

For Ron's teammates to get his contribution (which is on the master branch), they will do:

git pull origin master

I'll demo that with the "cs304guest" account, pulling in the update from me/ron.

Note that because it's a public repo, you'll never have to give a username/password to do a pull, but you'll always have to give one on a push

Section 5 Merge Conflicts

Now, an important issue is a Merge Conflict. In this scenario, Hermione (the captain) and Ron will both edit shared.py but *incompatibly*

Ron does:

git checkout -b ron
ls
cat > shared.py

def foo():

return 5

git add shared.py
git commit -m 'defined foo to return 5'
git checkout master
git pull origin master
git merge ron
git push origin master

Hermione will do the same thing, except she will define her branch with her own name, and her version of foo will return a different value.

git checkout -b her
ls
cat > shared.py

def foo():

return 17

git add shared.py
git commit -m 'my version of foo'
git checkout master
git pull origin master # this pulls in Ron's code
git merge her

When she gets to the git merge, she should see:

Auto-merging draft/shared.py

CONFLICT (add/add): Merge conflict in draft/shared.py

Automatic merge failed; fix conflicts and then commit the result

She should do:

cat shared.py
git status
code shared.py, resolve the conflicts and save
git status
git add shared.py
git commit -m 'resolved conflict, foo should return 88'
git push origin master

Section 6 SSH Keys

Having to give our username/password all the time is a pain. Let's fix that. I'll do these steps as the cs304guest account:

git config user.name "Scott Anderson"
git config user.email scott-anderson-wc # your Git username
ls -l ~/.ssh/ # the before picture
ssh-keygen
ls -l ~/.ssh/ # the after picture
more ~/.ssh/id_rsa.pub

Copy that file to your clipboard, then go to Github, and

Using your icon in the upper right, go to settings
go to SSH and GPG keys
click "new SSH key"
title the key "my account on tempest"
paste the public key.

Go back to tempest and do

echo "does this work" > newfile.py
git add newfile.py
git commit -m 'created newfile.py'
git pull origin master
git push origin master # this will FAIL

That last step will fail because we used HTTPS to clone. How do we know? Look at the remote.origin.url in git config:

git config --list

We can retroactively change the URL like this:

Go to github and Go to the page that allows you to download/clone the repo and grab the SSH url
on Tempest, do:
git remote -v
git remote set-url origin git@github.com:<Username>/<Project>.git # paste here
git remote -v
git push origin master

Now the last step will work and will always from now on.

Section 7 Advice

Each team member should work in their own branch
commit in fine-grained steps, so you can always go back to earlier, working versions
git pull origin master *before* git push origin master
deal with merge conflicts locally

Tutorials and References

https://product.hubspot.com/blog/git-and-github-tutorial-for-beginners

https://www.jquery-az.com/git-push-command/

https://github.com/Kunena/Kunena-Forum/wiki/Create-a-new-branch-with-git-and-manage-branches

https://stackabuse.com/git-merge-branch-into-master/

https://stackoverflow.com/questions/5330145/when-to-delete-branches-in-git

https://swcarpentry.github.io/git-novice/08-collab/index.html

https://help.github.com/en/github/authenticating-to-github/adding-a-new-ssh-key-to-your-github-account

https://stackoverflow.com/questions/14762034/push-to-github-without-password-using-ssh-key

https://linuxize.com/post/how-to-change-git-remote-url/

https://help.github.com/en/github/using-git/setting-your-username-in-git

https://stackoverflow.com/questions/2432764/how-to-change-the-uri-url-for-a-remote-git-repository