OSCON tutorial: Git and GitHub Fundamentals

Oct 28, 2015

Tips for teachers

If you do git init FOLDER, you have to change into that FOLDER to do more git commands.
The only way to truly lose data is with git reset --hard, which will erase only the work in Staging and Working Directory. Nothing in History is lost.

Git config

All is saved in .git/config, which you can edit directly as well.

git config --list
git config user.name "Franciscus Cornelis Donders"
git config user.email f.donders@donders.ru.nl
git config core.editor vim
git config --global push.default simple

Flow of tutorial

git init
git status

Note there's only one hidden folder with all the plumbing in the repository's root. So let's add a text file, called ReadMe.md with any editor you like.

git add ReadMe.md
git commit -m "added a new ReadMe file"

After some more changes, we'll do a git commit without the --m setting. This is why setting the editor to some known one is helpful, because the default editor vim may not be common in your field.

Note that after file editing, git status show the file again in Changes not staged for commit.

INSERT EXPLANATION of Working Directory, Staging Area, and History.

You can select specific hunks from the Working Directory to the Staging Area:

git add -p

If you reject one or more hunks, or change the file after git add, you'll see that in git status in both Staging and not staged for commit.
Git does not work on a file-basis, but on a patch-basis. It does not think about files, but about content.

The differences between

git diff shows difference between Staging and Working
git diff --staged
git diff HEAD

Interacting with a remote repository

git remote add origin URL.git
git push --set-upstream origin master

The option --set-upstream clarifies that the local master branch is tracking the remote master branch.

Websites like GitHub, GitLab, etc. offer simple interfaces to edit files. A nice choice is the Markdown format, which automatically gets rendered nicely. On your local repository, you have to git pull (or more cautiously, git fetch, git merge) the remote changes to your computer.

Here, we had drawings about differences between master, origin/master, and the remote master. Also, origin is just a common alias for the remote location; you could always write the entire URL, but that's annoying.

Branching off and merging again

git branch -vv
git branch BRANCHNAME
git checkout BRANCHNAME
git push --set-upstream origin BRANCHNAME

Again, the use of --set-upstream makes clear that you want to push to the same branch on the remote. Git's old behaviour of pushing was matching, now it's simple. Recommmended best practice:

git config --global push.default simple

Once your branches diverged, git checkout will change the Working Directory, that is, all tracked files' content. Also note that deleting a branch (git branch -d) on one location does not lead to deletion at any other location. Keep in mind that branches are merely pointers to commits.

Easy merging the feature branch with master:

git checkout master
git merge BRANCHNAME

You can use git merge --not-ff to force commit messages for that merge.

Merge conflicts

Option 1: Run away, git merge --abort. Option 2: Dammit, missed it! TODO!

Git log tricks

Git uses SHA-1 hashes to refer to commits. Hashes include the content, the time, and the author of a commit. Thus it created unique enough identifiers without any order; that's a feature in distributed settings with many authors.

git log --online --decorate --all --graph

JoKeyser / oscon-tutorial