class: center, middle # Learn Git ## HackMIT 2015 ### Anish Athalye --- # Agenda 1. Why use a version control system 2. Why Git 3. Teaching philosophy 4. Repository model 5. Using git (the command-line tool) 6. Beyond the basics 7. Resources 8. Questions / Workshop <br> If you have questions, feel free to interrupt me at any time! Slides available online at https://go.hackmit.org/git ??? * If you have a question, there are probably others who have the same question as you * If the presentation is going too fast or slow, tell me --- # Prereqs * Know Unix command line basics * Using a shell, `ls`, `cd`, etc. * Check if you have Git installed * Run `git --version` * Download using a package manager (Homebrew, APT, etc.) * Or get it from https://git-scm.com/download * Windows users: installer also gives you Git BASH ??? * If you don't have it installed, download it now --- # Why use a version control system (VCS)? * Keep track of changes in code * Enable good local workflows * Enable collaboration --- # Keeping version history without a VCS .center[  ] ??? * Keep history with copies of project directory * How many people have done this before? --- # Branching without a VCS .center[  ] ??? * Make branches with copies of project directory * How many people have done this before? --- # Collaborating without a VCS .center[  ] ??? * Collaborate by sending email attachments * Most painful * How many people have done this before? --- # Why Git? * Popular * Used for Linux kernel, Android, Bootstrap, Angular.js, D3, Meteor, Rails, React, ... * Fast, simple, and robust * Distributed * Enables non-linear workflows * GitHub * Social coding site * Lots of popular projects hosted here ??? * You're convinced that a manual workflow is painful * Want a tool to make everything nicer * Git is simple and robust * Designed by Linus Torvalds * Simple implementation, fairly clean interface * Fast * GitHub is a social coding site * Super popular, lots of big projects are there, lots more are migrating there * There are other version control systems * Mercurial, SVN, ... * You can read about the differences online, there are lots of blog posts on this topic --- # Teaching philosophy * Can't teach Git in an hour * It's not just about using the git command-line tool, it's about learning good practices and learning how to collaborate with others * Can learn the fundamentals in an hour * Figure out the rest by playing around with git and reading the documentation * Learn implementation before interface --- # Repository model * Snapshots of state (files, directory structure) * "Commit" * In a way, like making a copy of the entire directory * Store how commits are related to each other * Commit has "parents", revision(s) that preceded it * Directed acyclic graph * References * Pointers to commits * Branches - mutable * Tags - immutable --- # Repository model .center[  ] ??? * Does not track deltas like other VCSs --- # Object model * Surprisingly simple * Content-addressed file system .center[  ] * Learn more: https://git-scm.com/book/en/v1/Git-Internals --- # Learn Git * Follow along with the slides * But this is just an introduction to some of the git subcommands * You'll have time to play with Git later, and we'll be around to help you * Do all this in a new directory * Don't do this with an existing project (yet) * Think about how command line operations affect the history DAG * If you know what you want to do, but don't know what command to run, search on Google or Stack Overflow --- # Configuration * Initial setup ```bash git config --global user.name "Alyssa P. Hacker" git config --global user.email hacker@hackmit.org ``` * Settings in `~/.gitconfig` * Other useful bits ```bash git config --global ui.color auto git config --global alias.graph "log --graph --decorate --all" ``` * Getting help: `git help <subcommand>` * Like `git help config` * Run `git help` for a list for a list of commonly used commands --- # Initializing a repository ```bash git init ``` ``` Initialized empty Git repository in /src/repo/.git/ ``` --- # Initial commit ```bash echo "blah" > blah.txt git add :/ git status ``` ``` On branch master Initial commit Changes to be committed: (use "git rm --cached <file>..." to unstage) new file: blah.txt ``` ```bash git commit -m "Initial commit" ``` ``` [master (root-commit) bdf98f2] Initial commit 1 file changed, 1 insertion(+) create mode 100644 blah.txt ``` ??? * Staging area * What does "On branch master" mean? --- # Making changes ```bash echo "more stuff" >> blah.txt git diff ``` ``` diff --git i/blah.txt w/blah.txt index 907b308..82471e8 100644 --- i/blah.txt +++ w/blah.txt @@ -1 +1,2 @@ blah +more stuff ``` --- ```bash git add :/ && git commit -m "Add more stuff" git graph ``` ``` * commit c61e4c53da0a2c5142252d0d194d7b2cf6d0b4bd (HEAD, master) | Author: Anish Athalye <me@anishathalye.com> | Date: Thu Sep 10 20:29:49 2015 -0400 | | Add more stuff | * commit bdf98f24631baa22063d01ad7e8bb8a7424c736a Author: Anish Athalye <me@anishathalye.com> Date: Thu Sep 10 20:24:56 2015 -0400 Initial commit ``` * `git graph` is the single most important command (alias) to remember * It will be super helpful in understanding what is going on * Use it often ??? * Commit messages * Commit hashes * Branches / HEAD * Graph / parents --- # Branching and Merging * Used to work on different topics concurrently (among other stuff) ```bash git checkout -b optimization # do stuff, editing files and making commits git checkout master # do some work on master, editing files and making commits # when ready to merge in changes from optimization: git merge optimization ``` * Dealing with merge conflicts --- # Remotes * Interact with other Git repositories ```bash git remote add origin https://github.com/username/reponame ``` * Push changes ```bash git push origin master ``` * Fetch changes ```bash git fetch ``` * Fetch changes and merge ```bash git pull ``` --- # Cloning * Getting code from a remote ```bash git clone https://github.com/git/git ``` ??? * Try it --- # Organizing version history * Best way to learn how to organize version history and have good workflows? * See how other people do it! * https://github.com/git/git * Things can get pretty complicated - visualize as a graph! .center[  ] --- # Beyond the basics * Customizing Git * `~/.gitconfig` * See https://go.hackmit.org/gitconfig as an example * Git status in your shell prompt * Learning `git mergetool` * Nice tools for handling merge conflicts like Vimdiff * Open-source workflows * Merging, rebasing, tagging * Using GitHub * Issues, Pull Requests, Wiki, ... --- # If something goes wrong * `git reflog` * Read about it online * Google / StackOverflow * Other people have probably had the same issue --- # Resources * `git help <subcommand>` * https://git-scm.com/doc * Awesome resource, covers everything from basics to Git internals * **Highly recommended** that you read this at some point, at least chapters 1-4 * http://pcottle.github.io/learnGitBranching/ * Really cool browser-based game * https://go.hackmit.org/git * These slides --- # Questions / Workshop * Play with Git, ask us questions! * This stuff can be pretty confusing! * Ideas * Make and switch between branches * Play the "Learn Git Branching" game * Interact with remotes * Clone code from GitHub, explore version history * https://github.com/git/git * Customize your `~/.gitconfig` * Put git status in your shell prompt * Create a GitHub account * Find a bug in a project and submit a Pull Request <br> Slides at https://go.hackmit.org/git