Learn Git & GitHub

A note about learning Git.

Git

Git is a popular version control system.

Get started

Install

add-apt-repository ppa:git-core/ppa
sudo apt-get install git

Check the Git version

git --version

Configure git

git config --global user.name "Your Name"
git config --global user.email "email@example.com"

Note: --global will set the name and email for every repository on this computer.
You can remove --global to set the information just for this repository.

Create a git folder

mkdir myproject
cd myproject

Initialize git

git init

Note: Git creates a hidden folder called .git in the root directory of the repository to keep track of changes.

Add new files to git

• First, create a new file.

git status

Now git is aware of the file, but has not added it to our repository.

• Tracked: files have been added to your repository.
• Untracked: files that are in your working directory, but not added to your repository.

git status --short can display the changes in a more compact way.

?? Untracked files.
A Files add to stage.
M Modified files.
D Deleted files.

Use git diff <filename> to show the differences.

Git staging environment

git add <filename>
git status

Use git add -a to add all files.

Git commit

git commit -m "<message>"

• Use git commit -a -m "<message>" to commit without stage(don’t recommend).
• Use git log to view the historu of commits.

Git help

• git commit --help – See all the available options for the specific command.
  • Use --help to open the relevant Git manual page.
• git help --all – See all possible commands.
  • SHIFT + g to the end of the list, q to exit.

Git branch

A branch is a new version of the main repository’s codebase.

To add some new features to the firstfile.cpp, create a new branch.

git branch newbranch

git branch can display all the branches.

git checkout newbranch can move our current workspace from the main branch to the new branch.

git checkout -b newbranch will create a new branch and move to it if it doesn’t exist.

Make some changes to a file and add a new file.

git status – To check the status of the current branch.

git add --all – Add files to the staging environment.

Now, git checkout main and ls, you’ll find that the file created just now is no longer exist.

Emergency branch

Imagine you are not yet done with the new branch, but we need to fix an error on main.

We can create a new branch called bugFix to deal with it without messing the two branches.

Make some changes, git add and git commit, now we should merge two branches.

Git merge

Merge branches

Now git checkout main and git merge bugFix.

git merge bugFix

After merging, this branch is useless, so we want to delete it.

git branch -d bugFix

Merge conflicts

Now we return to our newbranch to finish our work, make some changes to the firstfile.cpp.

Then git checkout main and git merge newbranch to apply new changes.

We failed, then use git status to check the status.

Unmerged paths:
  (use "git add <file>..." to mark resolution)
        both modified:   firstfile.cpp

Open the firstfile.cpp you’ll find there’s something new.

Adjust the file to what you want, then git add and git commit -m “merged changes”.

Delete the newbranch, then finish this part of work.

Git and Github

Get started

Go to Github to sign up for an account and creat a new repository.

Remember to use the same e-mail adress you used in the git config.

Push local repository to GitHub

Copy the link of the repository paste the following command.

Search for how to configure ssh.

git remote add origin git@github.com:lzlcs/learngit.git

Now, push out main branch to the origin url, and set it as the default remote branch.

git push --set-upstream origin main

-u is the same as --set-upstream.

Edit files in Github

It’s simple, follow the instructions.

Git pull from github

Use pull to get the most recent changes to your local copy.
pull is a combination of 2 different commands: fetch and merge.

Git fetch

fetch gets all the change history of a tracked branch.
Now check our status.

On branch main
Your branch is behind 'origin/main' by 1 commit, and can be fast-forwarded.
  (use "git pull" to update your local branch)

nothing to commit, working tree clean

We are behind the origin/main by 1 commit, let’s double check by viewing the log.
Also use git diff to show the differences between our local main and origin/main.

So we can safely merge.

Git merge

git merge origin/main
git status

Everything is done.

Git pull

Make another change to the README.md.

git pull origin

Push to Github

Try making some changes to our local git and pushing them to Github.

git commit -m "xxxx"
git push origin
git status

Go to Github to confirm that the repository has a new commmit.

Github branch

Create a branch beta on Github and make some changes.

git pull origin
git status
git branch -a

Use git branch -a to show all local and remote branches.
Use git branch -r to show remote branches only.

git checkout beta and git pull to check if it is all up to date.

Now you can see the changes you made recently on branch beta.

Push a branch to Github

git checkout -b branch2

Make some changes.

git status
git add 
git commit -m "..."
git push origin branch2

In Github, we can see the changes and merge them into the branch master if we approve it.

Github flow

1. Create a new branch
2. Make changes and add commits
3. Open a pull request
4. Review
5. Deploy
6. Merge

Create a new branch

If you want to try something new, you create a new branch.
Branching gives you an environment where you can make changes without affecting the main branch.

When you make a new branch, you will always want to make it from the main branch.

Using descriptive names for new branches, so everyone can understand what is happening.

Make changes and add commits

When you reach a small milestone, add the changes into your branch by commit.

Commit message are very important.

Open a pull request

A Pull Request notifies people you have changes ready for them to consider or review.

Review

When a Pull Request is made, it can be reviewed by whoever has the proper access to the branch.

Deploy

GitHub allows you to deploy from a branch for final testing in production before merging with the master branch.

Merge

After exhaustive testing, you can merge the code into the master branch!

Git contribute

Github fork

Fork a repository

Click the fork.

Git clone

Clone a fork from Github

Move back to the origin repository.

git clone ....
cd ....
git status
git log
git remote -v 

Raname: git remote rename origin upstream.

Then fetch the URL of our own fork: git remote add origin ...

• origin: we can read and write.
• upstream wo can read only.

Github send pull request

Make some changes.

git add .
git commit -m ""
git push origin

Now go to Github and pull request.

Git ignore

When sharing your code with others, there are often files or parts of your project, you do not want to share.

Create .gitignore

touch .gitignore

It is also possible to have additional .gitignore files in subdirectories.
These only apply to files or folders within that directory.

Git security

ssh-keygen -t rsa -b 4096 -C "...@...com"
ssh-add ~/.ssh/id_rsa
clip < ~/.ssh/id_rsa.pub

Add ssh to Github.

ssh -T git@github.com
git remote set-url remote-name git@github.com:username/repository.git

Git undo

Git revert

When we want to take a previous commit and add it as a new commit, keeping the log intact.

git log --oneline
git revert HEAD --no-edit

Use --no-edit to skip the commit message editor (getting the default revert message).

Git reset

• Use git log --pretty=oneline to show the commit history.
• Use git reset --hard HEAD^ to be the last version.
  • HEAD is the current version, HEAD^ is the previous version.
  • HEAD~n is the previous n version
• Use git reflog to show your commands, you can find the version number to estoppel.

Git amend

commit --amend is used to modify the most recent commit.

git commit -m "Adding plines to reddme"
git commit --amend -m "Added lines to README.md"

You should avoid making changes that rewrite history to remote repositories,
especially if others are working with them.