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Git 101: Force-sensitive to Jedi padawan

Git 101: Force-sensitive to Jedi padawan

What is Git? What does it do, how does it work, how does it fit into my workflow?

If you've ever wondered about the answers to any of those things, this session is designed for you, my friend.
Starting with the assumption of no prior knowledge of Git or even of version control, we'll cover the technology at a theoretical level, its manifestation in your projects in the physical level, and your development workflow at the practical level - by which time you'll be ready to step out into the world, secure in your knowledge of what the heck Git is, and ready to use it in your projects - and you'll marvel at how you ever worked without it.

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James Ford

April 11, 2014
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Transcript

  1. git 101: Force sensitive to Jedi Padawan

  2. None
  3. What is git?

  4. What is ‘git’? • Distributed Version Control System • Git

    is version control for files & directories • Runs on the command line / terminal • Stores file versioning information in a hidden folder at the root of the project • Version information exists as (relatively lightweight) difference information between files and file versions
  5. Version Control • Parallel versions • Historical versions

  6. Command Line • Installed system-wide • Runs on the command

    line • Uses SSH Keys (with optional passwords) • You can also use a GUI for the complex stuff
  7. Everything exists locally • Without the .git directory, it can’t

    work • Everyone has a complete* copy of the branches and history of the project • Git is self-sufficient - no remote services needed for branching or commits
  8. Pushing & Remotes • Unless you push your code to

    a remote repository, it won’t leave your machine • You can make peer-to-peer pushes • It’s best to manage sharing and reduce conflicts by pushing to a single designated remote location • Pushing puts all of the historical and branching information into the remote repo
  9. Merges & Conflicts • Most of the time, git can

    auto-merge two (or more) changesets, because they don’t overlap • Conflicts occur when the file data changes overlap
  10. What does git give you? • Complete version history •

    Easy visualisation of changes • Ability to work with multiple developers and effortlessly merge changes • Parallel versions of source code • Ability to switch versions or roll back changes
  11. Are you ready to begin?

  12. Core git commands • commit • push • pull •

    branch • checkout • merge ➔ Save a change ➔ Send changes to a remote ➔ Get changes from a remote ➔ Create a new branch ➔ Switch to a branch or historical version ➔ Combine branches
  13. Getting set up

  14. Setting up a new git repository Existing repository: cd /path/to/my/repo

    git remote add origin ssh://git@bitbucket.org/username/bbreponame.git git push -u origin --all New repository: mkdir /path/to/your/project cd /path/to/your/project git init git remote add origin ssh://git@bitbucket.org/username/bbreponame.git
  15. Saving changes

  16. Simple git workflow 1. Make your change(s) 2. Test it,

    make sure it works, and then: git commit -am “my commit message” git push origin master
  17. git commit -am “my commit message” git push origin master

    If you don’t use -am, git will open VIM, and you don’t want that. your remote location name, the one you gave it when you set up the repository, which is usually ‘origin’ the remote branch name, usually the name of your current branch
  18. Writing Good commit messages A good commit message is one

    that: • Has a short (<50 character) description • Uses the imperative, present tense: “change” not “changed” nor “changes” • Includes motivation for the change and contrasts with previous behavior
  19. Making Good commits • A commit message becomes your only

    referral point in the projects’ history • Your commit must represent a stable point in your source code history - no half-baked commits! • Only include relevant files and changes • Treat every commit as if it were the final release
  20. The GUI is your secret weapon • A GUI (like

    Sourcetree) gives an excellent overview of your repository • It makes it possible to craft your commits on a line-by-line basis • You can also modify your most recent commit (so long as you haven’t pushed it)
  21. Synchronizing with other repositories

  22. your remote location name, the one you gave it when

    you set up the repository, which is usually ‘origin’ the remote branch name, usually the name of your current branch git commit -am “my commit message” git pull git push origin master if you don’t pull changes and merge locally before pushing, your push will likely be rejected
  23. Pulling and Merging • git fetch will retrieve version information

    from a remote, but does nothing with it • If your push is rejected, it’s likely because the remote is more up-to-date than your local branch, and you need to git pull those changes • Pulling changes will automatically merge them if able; but if it can’t, you’ll get conflicts that will need to be resolved manually
  24. Dealing with Conflict

  25. Dealing with conflicts • A conflict occurs when two changesets

    are trying to modify the same lines of code • Resolving conflicts involves manually picking which of the two competing modifications are accepted • Resolving a conflict doesn’t necessarily mean that the code will still work - you’re going to have to figure that bit out yourself and edit the file manually
  26. Resolving conflicts is either: • A yes/no selection between competing

    versions of a line of code • Or manually editing the partial merge result to resolve the conflicts You’re going to need a GUI
  27. Avoiding Conflict • Conflicts occur when you have an overlap,

    so don’t reformat, move or refactor code when there’s a chance someone else has also modified it • Commit little and often • Keep your branches up-to-date: Pull changes frequently • Sort out your crlf settings before you start • Some conflicts can’t be avoided
  28. Branching

  29. Understanding Branches Branches: • Are alternate versions of the working

    copy of your entire project, with their own history • Can be created from, and merged back into other branches • Can be created explicitly, or implicitly when merging two versions of the ‘same’ branch • Allow you to work on features in isolation
  30. Branching strategy • master is the stable release • development

    is for work in progress • Individual features should have their own branch • features are branched from development • Completed features are merged in from development • Stable development versions are merged in from master
  31. None
  32. Branching strategy in practice git checkout -b development // create

    and switch to development git checkout -b feature-one // create and switch to feature-one git commit -am “my awful commit message” // create a commit on feature-one git checkout development // switch back to development git merge feature-one // merge feature-one into development git checkout master // switch to master git merge development // merge development into master git push // push master branch to remote git push -u origin development // push the development branch and set its ‘upstream’
  33. Remote branches • Unless you explicitly push a branch, or

    set an upstream for the branch, it won’t get pushed to the remote repository
  34. Useful tricks

  35. Don’t use fast-forward merges • The default behaviour of a

    merge is to ‘fast forward’ the original when possible • Fast-forwarding branches doesn’t add an extra commit for the merge, which is cleaner but loses some context
  36. Stashing • A ‘stash’ is a representation of the differences

    between your last commit, and your current working copy. • In order to switch branches, your current working copy must not conflict with the branch you’re checking out. • Been working on the wrong branch? Stash changes. Checkout the correct branch. Apply stash. • Got half-finished code but now you’ve got to drop everything to fix a bug? Stash it. Come back later.
  37. Git Reset • So long as you haven’t pushed your

    change to a remote repository, everything is changeable • git reset will make it completely forget your commits • It’s useful if you’ve made changes to the wrong branch • It can be dangerous
  38. Cherry Picking • Merging branches brings across the entire history

    of both branches and mashes them together. • A ‘cherry pick’ takes just the changes from a single commit and can apply them to another branch • It’s useful, but treat it as an indication that you’ve done something wrong if you need to use it.
  39. Golden Rules

  40. Golden Rules • Commit early, commit often (when it’s stable)

    • Commit only one feature and its relevant changes at a time • Write good commit messages • Develop on feature branches • Merge feature branches into development, not the other way around • Push your changes on a regular basis
  41. Remember • Git is your time machine • Git is

    your safety net
  42. That’s all folks

  43. Bonus

  44. git push --force