Versioning with git. Moritz August Git/Bash/Python-Course for MPE. Moritz August Versioning with Git

Transcription

1 Versioning with git Moritz August Git/Bash/Python-Course for MPE 1

2 Agenda What s git and why is it good? The general concept of git It s a graph! What is a commit? The different levels Remote repositories The most important commands git add, git commit, git reset git checkout, git merge git fetch, git pull, git push Some references 2

3 What s git and why is it good? 3

4 What s git and why is it good? git is a versioning tool for anything from dissertations to software projects In contrast to other tools like Subversion it is distributed No central server everything is local No internet connection required to do versioning Even syncing with remote could be done without internet access You always have a full copy of the project and its history 4

5 What s git and why is it good? git is based on a distributed graph model Most operations merely move around labels/pointers to the nodes That makes git pretty lightweight and fast You can have local branches that are never synced to anything else Checksums are used to guarantee data/history integrity git allows you to not commit all changes at once 5

6 What s git and why is it good? Data from Google Trends Interest in versioning tools 6

7 The general concept of git 7

8 The general concept of git: it s a graph! git stores the history of a project as a graph In fact it s a directed acyclic graph (DAG) Every node is a snapshot of the project The nodes point to their parents The individual nodes are called commits Commits are uniquely identified by their parents and content J K L A B C D E F G H M N O 8

9 The general concept of git: it s a graph! git commands create and delete references to commits Every branch has/is a reference to its latest commit HEAD points to the current branch Tags can be created to denote versions Test 1 HEAD J K L Master A B C D E F G H V0.1 M N O Test 2 9

10 The general concept of git: what is a commit? A commit refers to a (compressed) snapshot of the project It points to zero or more parents It also points to the compressed project data The commit itself contains a commit message and dat about the author Every commit is (content) addressable via its SHA-1 hash Hashed are the pointers to parents and data + message and author 234jk6kj678h90234j This is one awesome commit! hkh562jkh702nf732 Oops, found a tiny bug 4m2334kn29ks4nld2 Well, maybe not so awesome after all Data Directory trees and BLOBs Data Directory trees and BLOBs Data Directory trees and BLOBs 10

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12 The general concept of git: the different levels When working with git one encounters three levels 1. The working directory 2. The index or staging area 3. The history as introduced above git commands copy files between these levels This structure yields much freedom in what to change when git reset git checkout History Index Working Directory git commit git add 12

13 The general concept of git: remote repositories Local git repositories CAN be linked to remote repositories Every branch can be individually set up to track a remote version Copies of the remote branches are stored and updated locally These copies can not be modified Merging with local branches if desired The local version can be copied to the remote repository git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 13

14 The most important commands 14

15 The most important commands: git init and git clone How to set up a repository? Create a local repository git init sets up git in a directory Can be set to track remote repo with git remote add <name> <url> Branches can be configured to follow remote branches Clone a remote repository git clone <user>@<url>:<repository> clones a repository from remote Automatically creates local version of active remote branch All other branches can be tracked as well Many ways to get a remote git repository 15

16 The most important commands: git add git add updates the index with the files in the working directory git add * adds everything in the working directory git add <files> adds specific files git rm <files> to remove files from index and working directory git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 16

17 The most important commands: git checkout git checkout copies files from the index or a commit to the wd git checkout <files> updates files in the wd from the stage Can also be used to switch to/create a branch git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 17

18 The most important commands: git checkout git checkout <branch> updates index and wd from a branch git checkout b <branch> creates a new branch and switches to it --track can be used to follow a remote branch HEAD HEAD Test 1 Master A B C D E Index Working Directory 18

19 The most important commands: git commit git commit creates a new commit from the index or the wd git commit m <message> creates a commit with message git commit a creates a commit from wd and updates stage git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 19

20 The most important commands: git commit git commit creates the new commit and moves the current branch to it HEAD is also moved forward HEAD HEAD Test 1 Master Master A B C D E F Index Working Directory if -a 20

21 The most important commands: git commit git commit creates the new commit and moves the current branch to it HEAD is also moved forward HEAD HEAD Test 1 Test 1 G Master A B C D E F Index Working Directory 21

22 The most important commands: git reset git reset <commit> <files> resets <files> in index from <commit> git reset <commit> resets current branch to <commit> Working directory can also be updated git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 22

23 The most important commands: git reset git reset <commit> <files> [--hard] copies from commit to index HEAD Test 1 Master A B C D E Index Working Directory (if --hard) 23

24 The most important commands: git reset git reset [--hard/--soft] <commit> sets the branch to previous commit If not reachable anymore following commits are deleted HEAD HEAD Test 1 Master Master A B C D E (if not --soft) Index Working Directory (if --hard) 24

25 The most important commands: git merge git merge <branch> merges the current branch with <branch> The easiest case is if HEAD is an ancestor of <branch> This case is called a fast-forward merge HEAD Test 1 Master HEAD A B C D E Test 1 Index Working Directory 25

26 The most important commands: git merge git merge <branch> merges the current branch with <branch> Merging two arbitrary branches is a bit more involved Test 1 HEAD HEAD F Master Master A B C D E G 3-way merge (if no conflict) Working Directory Index 26

27 The most important commands: git merge A conflict occurs if git can not decide automatically what to keep Multiple overlapping modifications of a file Occurences are marked in the respective files Format: <<<<<<<<<<<< <Own version> ============ <Other version> >>>>>>>>>>>> git mergetool can be used to resolve conflicts GUIs normally also have a merge tool When all conflicts are resolved, the result can be committed 27

28 The most important commands: git push git push <remote> updates remote references and sends data By default only current branch is pushed If no fast-forward is possible, push is normally denied Remote repository can be specified or deduced from config files git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 28

29 The most important commands: git fetch git fetch <remote> updates all the locally stored remote branches Stores the required data and updates references git merge can be used to merge remote branches with local ones Remote branches are named like <remote>/<branch> git fetch git reset git checkout Remote History Index Working Directory git push git commit git add 29

30 The most important commands: git pull git pull <remote> is simply git fetch + git merge Convenient shortcut for standard updates Costs some flexibility as user has no way to examine merged content git fetch/pull git reset git checkout Remote History Index Working Directory git push git commit git add 30

31 The most important commands This was only a brief overview, many more things exist Cherry picking Rebasing Some more useful commands: git diff to show differences between working tree and commits etc. git status to show the working tree status git log [--graph] to show history of the repository git show to have a look at individual objects Git also has a very nice reference and lots of tutorials (see literature) 31

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33 Some references - The git documentation - The git book - Simple git guide - Udacity course on git - - Generally, there are tons of nice blog posts and forum discussions. Searching Stackoverflow will help in almost any case. 33