Introduction to Git

Johan Junkka

Git

  • A distributed version control system
  • Created for collaborative coding
  • Full local repository, independent of network
  • Fast and scalable

History

Initaly created by Linus Torvalds in 2005 - now maintained by Junio Hamano.

Google Tech Talk: Linus on Git

Definitions

Working directory

The project directory containing all project files and folders you which to have under version control.

Repository

The .git directory where the history of your project is stored.

Commit

A snapshot containing the state of the project at a certain point.

HEAD

Refers to the commit currently checked out in the working directory.

The Git model

git model 1

The Git model

git model 2 http://www.slideshare.net/lfittl/introduction-to-git-4642204

Set up

Need: git and a GitHub or BitBucket account

Don’t forget: 5 free private repos via GitHub Academic account

Optional: Visual git tool, such as Rstudio, GitHub for Mac

Install

Mac with homebrew brew install git

Linux sudo apt-get install git

Config

git config --global user.name "junkka"
git config --global user.email johan.junkka@gmail.com

git config --global core.editor vim

# check config
git config --list

SSH key

Easiest way to use with a remote server. Instructions

ssh-keygen -t rsa -C "johan.junkka@gmail.com"
cat ~/.ssh/id_rsa.pub

Copy ssh key -> Login to service -> new ssh -> paste ssh key

New local repo

git init
Initialized empty Git repository in /home/johan/rproj/git-pres/.git/
git status
On branch master

Initial commit

Untracked files:
  (use "git add <file>..." to include in what will be committed)

  README.md
  assets/
  index.Rmd
  output/
  render_pres.R

nothing added to commit but untracked files present (use "git add" to track)

First commit

git add README.md
git commit -m "first commit"

Check status

git status
git log

# Overview
git log --stat

.gitignore

Excludes files and directories from git

.gitignore example:

.Rhistory
temp/
echo 'output/' > .gitignore

# Add all files
git add -A
git commit -m "initial all"

# View commit history
git log

# View all currently tracked files
git ls-tree -r master --name-only

Add remote repo

new repo

GitHub

Add remote to local repository

git remote add REMOTE-NAME REMOTE-ADRESS
git remote add origin git@github.com:junkka/git-pres.git

Push

First remote push

push all commits with -all

set remote as main upstream repository with -u

git push -u origin --all

Make changes, commit and push

# Update file

git commit -am "update"
git push origin master

Diff

To view changes between current version and last commited or between versions. Best to use a diff tool. Such as vimdiff, meld, sublimerge etc. Also included in most GUI such as RStudio

For this example we use meld which we set up from the terminal instructions

sudo apt-get install meld

Needs a small startup script

#!/bin/bash
meld "$2" "$5" > /dev/null 2>&1

Add as default diff tool

git config --global diff.tool  /usr/local/bin/git-diff.sh

Now

git difftool filename

Reset, revert or “undo”!

Accidentally pushed half your harddrive to github?

Panic!

  1. Delete public repo on github
  2. remove .git/ folder

Only last commit

Force github to reset!

git reset 93c1d75a8 --hard #commithash 
git push -f origin  # as in force

All together

http://onlywei.github.io/explain-git-with-d3/

More

git clone REPOADRESS = start from an existing project

git checkout -b BRANCH = start a new branch

git merge BRANCH = merge changes from another branch into current

git checkout BRANCH = checkout an existing branch

git checkout HASH = checkout a previous commit

git tag v1.0 = add tag to last commit, easier to find

git push origin --tags = because git doesn’t push tags automatically

Resources

Git official website

GitHub cheat-sheet

GitHub training

Getting Git Right | Atlassian Git Tutorial

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