3 git
TRANSCRIPT
An Introduction to GITVersion Control with Git
Avoid to be the repository manager
Dr. Fabio Fumarola
Agenda• What is Version Control? (and why use it?)• What is Git? (And why Git?)• How git works• Create a repository• Branches• Add remote• How data is stored
2
History• Created by Linus Torvalds for work on the Linux
kernel ~2005• Some of the companies that use git:
3
What is Git?
Git is a
DistributedVersion Control System
OR
Git is a
Content Management System
Git is a
history storage system
Git is a
content tracker
How ever you think about it…
How ever you think about it…
What is a Version Control • Version Control - A system for managing changes made to
documents and other computer files• What kinds of files can we use it with?
– Source code– Documentation– Short stories– Binary files (music and pictures)
• What should we use it for?– Text files– Projects that have lots of revisions (changes)– Collaborating
12
VCS Systems and their Operations
• Lots of different choices available:– CVS– SVN– Perforce– Git– Mercurial (Hg), Bazaar– And more!
• Most follow a repository model (though differ in how the repositories work)
13
So why do we need a VCS?• Our goals
– Share code (or something else) easily– Keep track of any changes we make (and undo them with
ease)– Maintain multiple versions of the same project/code base– Clearly communicate what changes have been made
• There are two type of VCS– Centralized and– Distributed
14
Distributed vs Centralized
Centralized VCS•One central repository•Must be capable of connecting to repo•Need to solve issues with group members making different changes on the same files
Distributed VCS•Everyone has a working repo•Faster•Connectionless•Still need to resolve issues, but it's not an argument against DVCS
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Centralized vs Distributed
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Central ServerRemote Server
Git file lifecycle
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Creating our first repository• Install git• Establish our first repository:
– mkdir git-test– cd git-test– git init
• What do we have here?– git status
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Using our first repository• Add a file
– touch file.txt– git add file.txt– git commit –m “add the first file”
19
Branching• With Git we should embrace
the idea of branching• Branching is the best method
to work with other in a project
20
Branches Illustrated
master
A
> git commit –m ‘my first commit’> git commit –m ‘my first commit’
Branches Illustrated
master
> git commit (x2)> git commit (x2)
A B C
Branches Illustrated
bug123
master
> git checkout –b bug123> git checkout –b bug123
A B C
Branches Illustrated
master
> git commit (x2)> git commit (x2)
A B C
D E
bug123
Branches Illustrated
master
> git checkout master> git checkout master
A B C
D E
bug123
Branches Illustrated
bug123
master
> git merge bug123> git merge bug123
A B C D E
Branches Illustrated
master
> git branch -d bug123> git branch -d bug123
A B C D E
Branches Illustrated
master
A B C D E
F G
bug456
Branches Illustrated
master
A B C D E
F G
bug456
> git checkout master> git checkout master
Branches Illustrated
master
A B C D E
F G
> git merge bug456> git merge bug456
H
bug456
Branches Illustrated
master
A B C D E
F G
> git branch -d bug456> git branch -d bug456
H
Branches Illustrated
master
A B C D E
F G
bug456
Branches Illustrated
master
A B C D E
> git rebase master> git rebase master
F’ G’
bug456
Branches Illustrated
master
A B C D E
> git checkout master> git merge bug456 > git checkout master> git merge bug456
F’ G’
bug456
Branches Review• Branches should be used to create “Features” in our
project• Local branches are very powerful• Rebase is not scary
35
Adding a remoteBut, how we share our code with the other collaborators?
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My Local Repo
Tom’s Repo
Tracey’s Repo
Matt’s Repo
A B C
A B C A B C
A B C
Sharing commits
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My Local Repo
Tom’s Repo
Tracey’s Repo
Matt’s Repo
A B C
A B C A B C
A B C
Remote Repo
AA BB CC
D
D
D
D
DD
Setting up a Remote• We can clone an existing repository– git clone [email protected]:fabiofumarola/akka-tutorial.git
• We can push our changes– git push
• We can pull friends change– git pull
• We can also add a remote to an existing repository– git remote add origin [email protected]:fabiofumarola/akka-
tutorial.git38
Branches with remote
A
master
B C D E
bug123
Branches with remote
A
master
origin/master
B C D E
bug123
Branches with remote
A
BB CC DD EE
master
bug123
origin/master
Branches with remote
A
BB CC DD EE
master
bug123
FF GG
origin/master
origin/masterorigin/master
Branches with remote
A
BB CC DD EE
master
bug123
> git checkout master> git checkout master
origin/master
Branches with remote
A
BB CC DD EE
master
bug123
F G
> git pull origin> git pull origin
origin/master
Pull = Fecth + Merge
Fetch - updates your local copy of the remote branch
Pull essentially does a fetch and then runs the merge in one step.
Branches Illustrated
A
BB CC DD EE
master
bug123
F G
origin/master
Branches Illustrated
A
BB CC DD EE
master
bug123
F G
> git checkout bug123> git checkout bug123
origin/master
Branches Illustrated
A
B’B’ C’C’ D’D’ E’E’
master
bug123
F G
> git rebase master> git rebase master
origin/master
Branches Illustrated
A
B’B’ C’C’ D’D’ E’E’
master
bug123
F G
> git checkout master> git checkout master
origin/master
Branches Illustrated
A
master
bug123
F G
> git merge bug123> git merge bug123
B’B’ C’C’ D’D’ E’E’
origin/master
Branches Illustrated
A
master
F G
> git push origin> git push origin
B’ C’ D’ E’
bug123
origin/master
Push
Pushes your changes upstream
Git will reject pushes if newer changes exist on remote.
Good practice: Pull then Push
Branches Illustrated
A
master
F G B’ C’ D’ E’
bug123
origin/master
Branches Illustrated
A
master
F G
> git branch -d bug123> git branch -d bug123
B’ C’ D’ E’
origin/master
Short vs. Long-Lived Branches• We can use branch to:– Solve bugs (hotfixes)– Create features– Make a release
• In order to simplify the management we can use:– Git Flow: http://danielkummer.github.io/git-flow-
cheatsheet/index.it_IT.html
Branches Illustrated
E
master
origin/master
Branches Illustrated
E
master
origin/master
develop
> git branch develop> git branch develop
Branches Illustrated
E
master
origin/master
develop
> git push origin develop> git push origin develop
origin/develop
Branches Illustrated
E
master
origin/master
develop
> git checkout develop> git checkout develop
origin/develop
Branches Illustrated
E
master
origin/master
FF GG
developorigin/develop
Branches Illustrated
E
master
origin/master
F G
developorigin/develop
> git pull origin develop> git pull origin develop
Branches Illustrated
E
master
origin/master
F G
develop
origin/develop
> git checkout –b idea> git checkout –b idea
idea
Branches Illustrated
E
master
origin/master
F G
developorigin/develop
> git commit> git commit
idea
H
Branches Illustrated
E
origin/master
F G
origin/develop idea
H
II
master
develop
Branches Illustrated
E
origin/master
F G
origin/develop idea
H
master
develop
> git pull (at least daily)> git pull (at least daily)
I
Branches Illustrated
E
origin/master
F G
origin/develop idea
H
master
> git checkout develop> git checkout develop
I
develop
Branches Illustrated
E
origin/master
F G
origin/develop idea
H
master
> git merge idea (fast forward merge)> git merge idea (fast forward merge)
I
develop
Branches Illustrated
E
origin/master
F G
origin/develop
H
master
> git branch –d idea> git branch –d idea
I
develop
Branches Illustrated
E
origin/master
F G
origin/develop
H
master
> git push origin develop> git push origin develop
I
develop
Merge Flow vs. Rebase Flow
E
origin/master
F G
origin/develop
H
master
> git push origin develop> git push origin develop
I
develop
Branches Illustrated – Merge Flow
E
origin/master
F G
origin/develop
H
master
> git checkout master> git checkout master
I
develop
Branches Illustrated – Merge Flow
E
origin/master
F G
origin/develop
H
master
> git merge develop> git merge develop
I
develop
J
Branches Illustrated – Merge Flow
E
origin/master
F G
origin/develop
H
master
> git push origin> git push origin
I
develop
J
Branches Illustrated – Rebase Flow
E
origin/master
F G
origin/develop
H
master
> git checkout master> git checkout master
I
develop
Branches Illustrated – Rebase Flow
E
origin/master
F G
origin/develop
H
master
> git rebase develop> git rebase develop
I’
develop
II
Branches Illustrated – Rebase Flow
E
origin/master
F G
origin/develop
H
master
> git push origin> git push origin
I’
develop
Rebase Flow
E
origin/master
F G
origin/develop
H
master
I’
develop
E
origin/master
F G
origin/develop
H
master
I
develop
J
Merge Flow
How Git stores data• Git stores the content of each file in the tracking history• Each time we do a commit it is made a copy of the file.• However the content of each file is subject to revision for
conflicts (merge).
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Git best practices for code collaboration• When to commit?
– Source of major arguments (big changes vs small change)– Never put broken code on the master branch (test first!)– Try not to break things (don't do two weeks worth of work in one
commit)– Always use a clear, concise commit message– Put more details in lines below, but always make the first line short– Describe the why; the what is clear in the change log
• When making giant changes, consider branches (we'll talk about these in a few slides)
• Oh, and make sure your name and email are right79
Supplemental
SSH• Used to be most common transport for git• Pros
– Allows reads and writes– Authenticated network protocol– Secure: data transfer is encrypted and authenticated– Efficient: makes data as compact as possible
• Cons– No anonymous read-only access
Sidebar: What is SSH?• SSH is a protocol used for secure network
communication Getting files from github• Generate public/private keys (ssh-keygen)• Distribute public keys (add key to github)• Someone (github) sends secure “message” (files) –
they encode with public key• You receive the message/files – decode with
private key (only you know)Putting files on github• Process is reversed to send files to github• You have the github public key (see
github_rsa.pub, in Documents and Settings/Cyndi/.ssh on my machine)
• Use it to encode when sending• github uses their private key to decode