Version Control Systems: git
(title TBD)

Andrei Mustață

  • Software Engineer, etc
  • Love me some git

This talk

  • What VCS are
  • Benefits of using one
  • Basic `git`

Version Control System

  • ... version control
  • "Records changes to a [...] set of files"1
  • "recall specific versions later"1

What is it?

Version Control System

  • CTRL+Z has its limits
  • Creates a safe environment for work
  • Encourages innovation

Why bother?

Version Control System

  • Google Docs
  • ?

Examples

Version Control System

  • What?
  • Why?

Intro - wrap-up

Version Control System

  • Local
  • Centralised
  • Distributed

Types

Version Control System

  • Copy files to separate directories
  • Timestamp in filenames
  • Error-prone

Local - manual

Version Control System

  • The Revision Control System2
  • Old af, released in 1982!
  • Automates some of the tasks
  • Mitigates some of the issues of manually doing this

Local - RCS

Version Control System

  • File versioning is handled, which is nice
  • HDD corruption
  • What about collaboration?

Local - Issues?

Version Control System

  • Versioned files are on a single server
  • More people can access it
  • Teamwork makes the dreamwork
  • Examples: CVS, SVN, Perforce

Centralised (CVCS)

Version Control System

  • Concurrent Versions System3
  • Older than you are :P
  • Initially a set of shell scripts

Centralised (CVCS) - CVS

Version Control System

  • Subversion4
  • Came to replace `CVS`

Centralised (CVCS) - SVN

Version Control System

  • Files are still versioned
  • Collaboration is allowed
  • ?
  • Single-point of failure
  • HDD corruption

Centralised (CVCS) - Issues?

Version Control System

  • More arrows
  • Clients fully mirror the repo
  • Server dies, client repos can serve as backups
  • Allows for different workflows
  • Examples: git, Mercurial, Bazaar

Distributed (DVCS)

Version Control System

Distributed (DVCS) - git

  • Created by Linus Torvalds for the Linux kernel
  • After BitKeeper was no longer free of charge
  • Great for large projects
  • Great for branching

Version Control System

Distributed (DVCS) - Issues?

  • ?
  • Surely there are some

Version Control System

Types - wrap-up

  • Local - manual
  • Local - using tools
  • Centralised - server-client
  • Distributed - server-client-like, but not necessarily

git

  • How it works

  • Installation, setup

  • Most used commands

git

How it works

  • Snapshots
  • Most operations are local
  • Check-sums
  • Fear of the data-loss
  • Three states

git

Everything (almost) is local

  • Most operations are done on the local file system
  • No network overhead = offline work
  • Differences in files between now and 7 days ago
  • Commit away

git

Everything is check-summed

  • Before storing files, git always check-sums it
  • Can't change stuff without git knowing about it
  • SHA-1, based on file content

git

Everything is (pretty) safe

  • Once the commit has been made, it's pretty safe
  • It's hard to get git to do things that are not undoable
  • Freedom to try new things without losing the initial state

git

The three states

  • Working directory
  • Staging area
  • Repository (local .git directory)

git

Basic workflow

  1. Modify files on your machine
  2. Stage the files
  3. Commit

git

Basics - wrap-up

  • Safety-net
  • Three states: working, staging, repository
  • Check-sums
  • Three states, pls
  • Modify-Stage-Commit

git

Setup

  • Install - cmd or GUI
  • Configure user.name, user.email
  • on you go!

git

Local repository

  • Create your own
  • Clone an existing one

git

Create local repository

$ mkdir hello-world-git
$ cd hello-world-git
$ git init
$ ls -la

git

Clone remote repository

$ rm hello-world-git
$ git clone https://bitbucket.org/andreimic/hello-world-git.git
$ cd hello-world-git
$ ls -la
  • git clone downloads a full copy of the repository
  • access to the whole public history of the project

git

Recording changes

  • staging files
  • committing files

git

Staging files

$ date >>README.md

$ git stage README.md

git

Committing changes

$ git commit

git

Recording changes

  • modify (hacky thingy changy)
  • stage (git stage <filename>)
  • commit (git commit)
  • you're done, go home

git

Status

  • what the repository status is
$ git status

git

Status of a file

  1. Untracked - new file, not added anywhere yet
  2. Staged - file in git staging area
  3. Unmodified - ...
  4. Modified - file is tracked by git; changed

git

Diff

  • differences
$ git diff

git

Branches

  • at least one branch, default master
  • add stuff without interfering with the main branch
  • allows for experimenting without fear of breaking
$ git branch my-feature

git

Merge

  • bring changes from a branch into another branch
$ git merge my-feature-branch

git

Push

  • don't keep changes to yourself
  • push to the common git server (remote)
$ # git push <remote> <branch>
$   git push  origin   master

git

Less important stuff

  • ignoring files
  • hm

but important still

git

Ignoring files

*.class

# Mobile Tools for Java (J2ME)
.mtj.tmp/

# Package Files #
*.jar
*.war
*.ear

# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
hs_err_pid*

git

Commit early

  • pls
  • made some progress? commit!

Reading material

References

  1. Chacon, Scott, and Ben Straub. Pro git. Apress, 2014.
  2. https://www.gnu.org/software/rcs/
  3. CVS 
  4. Subversion 

Danke

Version Control Systems: git

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Version Control Systems: git

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