An Overview of Version Control Systems. Guest lecture Juhan Ernits Computer Systems Engineering

Size: px

Start display at page:

Download "An Overview of Version Control Systems. Guest lecture Juhan Ernits Computer Systems Engineering"

Isaac Blair
5 years ago
Views:

1 An Overview of Version Control Systems Guest lecture Juhan Ernits Computer Systems Engineering

2 Prelude: What killed Motorola? Based on The text is an opinion of a person and not a scientific evaluation.

3 Characteristics of Motorola Excellent technology in RF, a pioneer in 3 band mobile phones, a mature company (established in the 1920s) An electronics giant that has been in the firing business for some time now. Why? Software!

4 Moto s Platform 2000 and Synergy UI Synergy user interface in 2002 (images from The Register)

5 Software development at Moto New features to P2K were written in a way that could not be absorbed back into the operating system's mainline source code (GIT terms: master branch). Other phones could not include the features: there was no time to redo what had been hacked together for other hardware. The software forked like crazy. Building a version of the OS for each new phone became a major undertaking. A colour-screen GSM phone with photos in its address book could not pass along this feature to other devices.

6 Moto s solutions Employ more programmers! Results: 1000s of people were developing P2K the platform became less like physics where you know what will happen given a set of inputs The platform became more like biology where you inject a drug and see what happens. No one wanted to make changes fearing what might break. Commission outside manufacturers with their own software No reuse internally possible. Royalties were involved per handset sold

7 Moto s solutions 2 Bought TTPCom with an existing OS for low end handsets called Ajar Tried to merge recent purchase with the existing mess Port Synergy to Ajar Sort summary: failure Tried alternatives Java based solutions Symbian Linux Then all of the above again a couple of times

8 Why is it all relevant today? Managing software and designs/models of hardware well is crucial for success. Most electronic systems involve software so please appreciate the complexity of software management! Managing development is hard. Tools give you time to deal with what is important!

9 End of Prelude!

10 Why version control? There are plenty of tools/methods for distinguising versions of documents: Dropbox And other clouds Unison file sync Windows built-in synchronisation Renaming files etc

11 Main characteristics of versioning systems Backup and Restore Synchronization Short-term undo / Long-term undo Track Changes Track Ownership Sandboxing Branching and merging

12 Local Version Control Old-school version control like RCS Image stolen from which is really good, go read it.

13 Centralized Version Control This is how Subversion works Image stolen from which is really good, go read it.

14 Distributed Version Control This is how Git works Image stolen from which is really good, go read it.

15 Why Do I Care? Because it has been mandated that you care about version control by Prof. Jervan Because you will use version control at every single coding job you get in the real world If your company doesn t have version control in place, that s a huge warning sign Because it will change the way you think about programming, for the better Because it stops you from completely shooting yourselves in the foot the day before an iteration is due

16 Installing Git Please install Git and try some things out! Linux: use your favourite package manager Ubuntu: aptitude install git Windows: use the MSysGit installer Mac: use the OS X installer

17 Learning Git Read Pro Git, it s excellent and free Git is extraordinarily powerful and you ll be a better programmer if you take the time to understand it If in doubt, always use the built in manual Every git command has a --help flag e.g. git cherry-pick --help Seriously go read

18 Getting Started Let s tell Git our name and address It attaches these to any commits we make so people know who to kill for breaking the build an hour before an iteration is due git config --global user.name Your Name git config --global user. you@place.tld --global sets the variable for your OS user --system sets the variable for all users on your machine Omit the --global and --system flags to set a git config variable for just this repository

19 Creating a Repository git init Creates a local, empty git repository in the folder where the command is run Creates a.git folder for the guts of the repository Only one.git folder, at the root of your repository This is way nicer than creating a new.svn folder for every single subfolder in your repository We ll go over how to work with other people on a remote repository soon

20 Anatomy of a Repository Image stolen from which is really good, go read it.

21 Anatomy of a Repository Crazy important! Memorize this! The working directory consists of the actual files and folders on your machine The staging area lets you build commits out of snapshots taken of the files and folders in your working directory. It s kind of a loading bay for your working directory The repository maintains a collection and complete hierarchical history of all commits

22 Oh God, What s Happening? git status Shows you the state of your staging area and of your working directory git log Shows a commit history of your repository git diff Shows changes between commits, your working directory, the staging area, etc. git diff --help to learn more Or you could just go read and you ll be an expert.

23 Adding & Removing Files git add file Adds a snapshot of file to your staging area You can change file and the snapshot will remain as it is git rm file Removes the file snapshot from your staging area and deletes file from your working directory git rm --cached file Removes the file snapshot from your staging area while keeping file in your working directory intact

24 .gitignore Tells Git which files to ignore outright Uses glob syntax for pattern matching There s a decent summary of glob syntax at linux.about.com/library/cmd/blcmdl7_glob.htm Git adds re-inclusion rules with!pattern Include any files matched by pattern, even if they ve been ignored by a previous pattern. There s a sample.gitignore on the website Stack Overflow is a good source of.gitignore files

25 Making Commits git commit -m your message Creates a commit from the contents of your staging area and adds it to the repository -m your message sets the commit message If we keep adding commits we get a linked list that represents the history of our repository gitk --all gives a graphical history of all branches Leaving out the --all shows just this branch And the book at has a whole bunch more information. Read the damn book!

26 GitK Screenshot

27 Branching & Why It Is Awesome Branching allows us to create a tree of commits instead of a linked list Merging will let us turn this into a DAG Easy, painless branching is the most important and powerful feature of Git Give each new feature its own branch, which can be merged back into the main (master) branch after it s been completed and is stable

28 GitK With Branching

29 Creating Branches Git maintains a pointer to the current checked out branch, called HEAD git branch newbranch Creates a new branch starting at the current commit, but does not move the HEAD pointer git checkout newbranch Changes HEAD to point to newbranch Run git branch then git checkout to create and start working from a new branch Shortcut: git checkout -b newbranch

30 Branching Example $ git branch testing $ git checkout testing Images again stolen from which you should read because it s good.

31 Branching Example $ git commit $ git checkout master Images stolen from

32 Branching Example $ git commit At this point, the branch history has diverged We want to branch for new features and merge them back into the master branch This makes your life infinitely easier Images once again stolen from

33 Merge Tools git config --global merge.tool toolname Sets the merge tool for your OS user A merge tool allows you to fix any conflicts that arise from merging two branches Google will give you a list of merge tools Some use p4merge, it s hard to go wrong just choosing a random merge tool and using it git mergetool Run this command if anything goes wrong with a merge, it ll allow you to fix things

34 Merging git merge branchname Allows you to take another branch and merge its changes into the currently checked out branch Git has hyper-intelligent algorithms that track your content, not your files If you move or rename a file and make changes to it, it will still be detected as the same content

35 Image stolen from Merging Example

36 Image stolen from Merging Example

37 Branching & Merging in SVN It s relevant to see how the approach taken by Git differs from that of terrible legacy systems like SVN Subversion doesn t have real branches A branch is just a copy of your repository in a named folder SVN has no concept of branch history and therefore cannot determine common ancestry to help with merging Subversion doesn t have real merging The svn merge command should be called svn diff-andapply-patch because that s all it does If a merge fails, run svn revert and do it by hand. There is no way to tell whether a given set of changes were the result of a merge or were just straight edits

38 Remote Repositories git remote add reponame url Adds an external Git repository called reponame git fetch reponame Fetches updated branches from reponame including all updated data A remote branch shows up as reponame/branchname Your local information about remote repositories isn t updated automatically You need to run git fetch periodically on your remotes to get new branch/commit information

39 Image stolen from Remote Repositories

40 Pushing git push reponame branchname Adds a local branch to a remote Git repository You need to have write access to the remote repository Alternatively, merges your local branch into a remote branch of the same name git push reponame localbranch:remotebranch Explicit syntax for merging your changes from localbranch into remotebranch Always fetch and merge before you push Save yourself grief and error messages

41 Pulling git pull reponame branchname Fetches from reponame then merges the remote branchname into your local branchname git pull reponame localbranch:remotebranch Fetches from reponame then merges reponame/remotebranch into localbranch Syntactic sugar for fetching and merging Your workflow should be git pull; git push

42 Tracking Branches git checkout -b branch remote/otherbranch Gives you a tracking branch that you can work on, that starts where remote/otherbranch is Tracking branches are local branches that have a direct relationship to a remote branch You can just call git push/pull with no arguments and it know which remote branch to change

43 Cloning a Repository git clone url Creates a new local git repository, creates new tracking branches for each branch in the cloned repository, creates and checks out an initial branch that is forked from the remote s active branch Watch out if the remote repository doesn t have any commits yet (really common thing) Cloning will fail, you need to do git init, git remote add origin url, create an initial commit with some content, then run git push origin master

44 And We re Done! There s some stuff I didn t get to cover due to time constraints Look up git stash, git submodule TortoiseGit is a Windows-only frontend for Git It s a knockoff of TortoiseSVN and is really easy to use Go read the Pro Git book because it s short, awesome, free, etc. Reading it will make you taller and more popular with members of your preferred gender Thanks for your time :)

45 Tool summary Centralised version control systems CVS (dead!) Subversion VSS (dead!) Team Foundation Server... Distributed GIT Mercurial Bazaar BitKeeper...

46 Exam Name at least 2 centralised version control tools Name at least 3 distributed version control systems What is staging area for in GIT?

47 Credits Slides about Git are based on a presentation by Eric Lawless

Version Control: Gitting Started

Version Control: Gitting Started ting Started Cai Li October 2014 What is Version Control? Version control is a system that records changes to a file or set of files over time so that you can recall specific versions later. Local Version