git-training

Up your Git game.

Basics
Branches
Merging
- Merging from a different branch
Rebase
Other useful commands
- Reset
- Revert
- Stashing
- Patching
Git Workflows
Signing your commits
Resources

Basics

Get the repo:

git clone git@github.com:matusmarcin/git-training.git

Edit something (like this README.md) or create new files:

echo "hello world">hello.txt
mkdir assets
echo "assets will go here">assets/readme.txt
echo "another file">assets/file.txt

Now see the status of your repo:

git status

Make git track files (or directories):

git add hello.txt
git add assets

Now check the status again and see there are changes to be committed and not staged (if you have modified something).

Let's stage those changed files too:

git commit README.md

This will stage one file for commit README.md and open default editor for you to type the commit message.

Often you have many changed files so here you go: -a stands for all:

git commit -a

Let's also get rid of the editor and just type in the message using -m:

git commit -a -m "Fixed that nasty bug."

Now the changes are committed into our repository (locally) so let's push them to remote origin.

git push remote origin

Depeding on your circumstances, a git push might be enough.

Let's what we have done using log.

git log
git log --oneline

We can see our commit so hurray, great job everybody.

Okay, those are the uber-basics. Let's get to the basics now.

Branches

Understand the sh*t out of branches by studying up on this tutorial from Atlassian

You cannot really say you can use git unless you're using branches. Branches in git are really easy to use and often part of your daily workflow.

Inspect the branches on your repo:

git branch

Remembed this show only local branches. Explore the origin using -a:

git branch -a

Probably just master. That's the default. Let's create a branch.

git branch development
git checkout development

We've created a branch called development and then switched to it with another command. This can be done with one just like so:

git checkout -b development

Now you can go ahead and do your branch-specific changes and commit them. When you try to push, you need to set what this branch will be called on the origin repo. This is done with --set-upstream or -u. We use the same name. (Why not?)

git push --u origin development

Now we have multiple branches and when running git branch we can see the current one highlighted with an asterisk.

To switch between existing branches just use git checkout <branch>.

Merging

Make friends with merge in this tutorial by Atlassian.

As soon as you use branches, you need to be able to merge.

Switch to development branch and make changes to development.txt file. Commit your changes. Let's have someone else do the same but also push their changes before you manage to. When you try to push them, git warns you to pull first.

How did I get this far into a tutorial without a git pull? It's the opposite of push. With pull you get changes from the remote repo into your own. Unless there are conflicts, git merges your changes automagically.

git pull

That's it, you don't have to do anything. Unless it fails :-)

When this failes and you have conflict, git leaves the changes in the files. Below HEAD mark are your changes and above the commit hash are changes from the remote repo. Use your smarts to merge this properly or consult with the person that made those changes. Then, commit this to finish the merge:

git commit -a

Merging from a different branch

Now let's assume you've done some development work on that branch and those changes are now ready to be merged back into master. This can be either simple or a bit tricky.

git checkout master
git merge development

This is how we merge development into the master branch. In various cases git cleverly decides the correct strategy and just merges it properly. However, if your work on development took a while and master was changed at the same time, you probably need to... follow your git workflow. Especially if you're going to have conflicts.

Rebase

Rebasing takes a branch and makes it a base for our current branch. It does not directly change the branch but the idea is that we will merge the current branch into that branch in the next step.

Make sense out of rebase with these two tutorials from Atlassian: git rebase and Merging vs. Rebasing

Rebasing can cleanup git history nicely. Rebasing must be used with caution. A good rule is to never use rebase on already published code. So the use case here is, commit some stuff localy, then rebase it into a single commit or nicer commits and push.

Let's start with a new branch for our feature:

git checkout -b some-feature

Do some development... and then rebase:

git rebase master
git checkout master
git merge some-feature

And this is not so bad, we now all commits from some-feature at the top of the master. Perhaps we could've squashed those commits into one, so that the history looks real nice. This can be done with interactive rebase using -i flag.

git rebase -i master

Or let's say we don't want to change all the commits, only last three:

git rebase -i HEAD~3

Anyways, this gives us a text editor with all the commits and options to take them in, change the message, squash them together or leave them out.

reword abfce88 More development
fixup 4acb83d More development
fixup 93f53ee More development

This way we squash the two commits together with the third one - wihout including their commit message (fixup) - and reword the message for the first one. Reword option shows us the editor again to type in a new message.

The other day I have found git merge-base but having never used it, I am just going to tell to read about it by yourself.

Other useful commands

Reset

Don't really do this. Only on your own local unpublished code. It's like a permanent undo.

git reset <commit>

Revert

Revert is a good undo you can use, if you want to fix a screw up. It actually commits a new change that reverts exactly what you wanted to. This prevents git from losing history (so that everybody can know about your screw up) - and that's a good thing.

git revert <commit>

Stashing

Would you ever decide you don't want to commit your work but don't want to loose it stash is the solution.

git stash
git stash apply

git stash list
git stash apply stash@{2}

Or create a branch from your stash!

git stash branch testchanges

Patching

Sometimes you just can't push changes directly to the repository and need to send changes by other channel. One of the ways you can use is creating patch. You can create patch directly from the changes you just made:

git diff > my_cool_changes.patch

or from specific commit:

git format-patch -1 <COMMIT_SHA>

After that, patch can be applied somewhere else. First, let's see what's in there:

git apply --stat my_cool_changes.patch

Next, you can check how troublesome applying is going to be, git allows that by running:

git apply --check my_cool_changes.patch

And if everything looks fine, patch can be applied simply by:

git apply my_cool_changes.patch

If patch was created from commit(s), patch can be even signed as normal comit:

git am --signoff < patch_from_commit.patch

Good reading about patches can be find here.

Git Workflows

Workflows are about how we organise our work in git repo. We already know most of the commands we need for this, we're only going to be using them.

Feature Branch Workflow

This article is a much better resource.

Simply put: Every feature is a new branch.

In reality, you'll probably have to deal with conflicts in case someone else merges their branch before you do, so you're probably better with something like this:

Create a branch (from master) for your new feature
Do your work
Checkout and pull master
Merge master into your branch to resolve conflicts and catch-up
Merge your branch into master

To do a really good job you can use rebase in the step 4. And you really should create a pull request to merge your branch in step 5.

Pull Request (PR)

You can use GitHub to create a pull request (PR). Just find a button somewhere and click it. Then choose base as where you want your stuff to end up and compare as your stuff you want to merge. So the pull request is a request to merge compare into base, i.e. your branch into master or development.

Gitflow Workflow

This is the guy who came up with this and this is another good article on it.

This is arguably the best and most used workflow. It has:

master
development
feature-* branches created from development
hotfix-* branches created from master
release-* branches created from development to be merged into master

Image source

Forking Workflow

Learn about forking workflow here!

This one is different from the others above since the workflow is:

You fork the repository
Implement your changes
Create a PR for a project maintainer to merge your changes

You can and still should use feature branch workflow inside your own repository.

With this workflow you have two remotes where you can call your own origin and the project maintainers upstream.

Signing your commits

It's fairly simple:

Generate a key
Add it to git config
Upload public key to github
git commit -S or set in config

Read here: https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work

Resources

Have fun!