git 101: Force sensitive to Jedi Padawan

What is git?

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

Version Control

● Parallel versions

● Historical versions

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

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

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

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

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

Are you ready to begin?

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

Getting set up

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

Saving changes

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

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

Writing Good commit messagesA 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

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

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)

Synchronizing with other repositories

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

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

Dealing with Conflict

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

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

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

Branching

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

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

Branching strategy in practicegit 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’

Remote branches

● Unless you explicitly push a branch, or set an upstream for the branch, it won’t get pushed to the remote repository

Useful tricks

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

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.

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

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.

Golden Rules

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

Remember

● Git is your time machine

● Git is your safety net

That’s all folks

Bonus

git push --force