Git SCM

SCM?
Source Code Management
aka!
!

Version Control System!
aka!
!

Revision Control System

Why?
! collaboration
! because we need to keep track of changes:
when? !
why? !
what was the content? !
who? (very important, right? :))

! centralized SCMs: Subversion, CVS
! distributed SCMs: GIT, Mercurial

Centralized & Distributed
checkout!
commit!
revert!
merge!
tag!
branch!
lock!
conflict resolution.!
...

Centralized vs. Distributed
centralized

distributed

master copy in one
place!

everyone has a full
copy - distributed!

single point of failure!

works offline or
disconnected from a
server!

considers data as a list
of file -based changes
(initial version + deltas) !
a commit operates over
the central repository

saves snapshots of data
it manages !
a commit operates over
the local repository

SVN model
Repository

Client 2

Client 1

Version 1

Version 2

File A

Delta 1

Version 4
Delta 2

Delta 1

File B
File C

Version 3

Client n

Delta 1
Time

Delta 2

GIT model
Central!
Repository
Client 1 !
(mirror)

Client 2!
(mirror)

Client n!
(mirror)

Version 1

Version 2

Version 3

Version 4

File A

File A1

File A1

File A2

File B

File B

File B1

File B2

File C

File C1

File C1

File C1

Time

GIT --history
British slang for "pig headed, think they are always
correct, argumentative"
2005, Linux kernel maintenance (35000 files)!
Linus Torvalds!
written in C
"So I'm sorry, but for something like git, where efficiency was a primary !
objective, the "advantages" of C++ is just a huge mistake. The fact that !
we also piss off people who cannot see that is just a big additional !
advantage." (L.T.)

modern, robust, fast, distributed, great branching
system, complex merges, open source!
available on Mac, Windows, Linux

GIT --philosophy
a git repository is a....graph, Directed Acyclic Graph!
node = commit!
edge = pointers from child nodes to parent node(s)!
nodes are identified by SHA-1 hashes from: content change +
parent(s) commit identifier => speed!
a lot of the work done by git involves moving references
(labels) around => speed

GIT --philosophy
git references = labels assigned to commits !
several types: branch (local/remote), tag, stash!
references are stored in .git/refs/heads ( the SHA-1
identifier of the commit it points to, 41 bytes)!
there are references to references -> HEAD, for example,
which points to the current branch!
references make commits reachable

GIT --philosophy

fast forward merge

GIT --concepts
git manages its content via 3 states: modified, staged,
committed
Workspace

Staging !

Repository

area
stage

commit

unstage

checkout

Local repository

GIT --concepts
Workspace (working directory)
one version of the content, extracted from git database to be
used or modified

GIT --concepts
Staging area (index)
allows you to elect files/content that is going to participate in
the next commit!
you can see how the next snapshot would look like before
actually creating it - avoid mistakes!
allows you to break changes in workspace into more than 1
single commit

GIT --concepts
Repository
where object database and metadata is stored!
the .git folder inside your repository root folder

GIT --concepts
git manages its content via 3 4 states: modified,
staged, committed, stashed!
!

Stash
here you can save changes you want to keep but
not ready to commit yet!
stashes are in fact labeled nodes on the
repository graph

GIT --concepts
Stash
Stash

Workspace

Staging !

Repository

area
create

stage

apply

commit

unstage

checkout

Local repository

GIT --concepts
Remote repository
git repository located on another machine, usually!
the local repository may be a mirror of the remote one!
write into it via push, read from it via pull & fetch

GIT --concepts
Remote repository
Stash

Workspace

Staging !
area

Repository

Remote repository

push

pull/fetch
Stash

Workspace

Staging !
area

Repository

Local repository

GIT --concepts
GIT objects
blobs - contents of a file!
tree - directories of blobs or other trees!
commits - SHA-1 of a tree, parent commit(s), message!
tags (annotated)

GIT --@work
Create a repository
git init
initializes a new, empty repository, inside the current directory

git clone https://stefanprutianu@bitbucket.org/
stefanprutianu/git-scm-remote.git
clones the remote repository on the local machine, inside a
newly created git-scm-remote folder

GIT --@work
Prepare a commit (stage)
git add <file> | <pattern>
marks the file(s) as belonging to the next commit, i.e. changes
are staged

git reset <file>
removes the file from the staging area

GIT --@work
Commit
git commit -m "Commit message"
records the commit in the repository history

git commit --amend
modifies the last commit by adding the staged changes

GIT --@work
Revert
git checkout -- <file>
the <file> contents in working directory is replaced with the
last committed one

git reset --hard <branch/commit/tag>
discards commits until the one pointed to by the reference

git revert <commit>
reverses the specified commit by creating a new one

GIT --@work
Stash
git stash
saves the working directory state and pushes it on the stashes
stack

git stash apply
gets the most recent stash and applies it to the working
directory

GIT --@work
Share changes
publishing changes
git push <server> <branch>
pushes your changes on the specified branch of the remote
repository

git format-patch HEAD --stdout > mypatch.patch
retrieving changes
git fetch <server>
pulls down all the data from the remote repo that you don't
have yet on tracked branches

git pull
does a git pull and merges those on your current branch

GIT --@work
Branch
git branch <branch name>
creates a new branch starting from your last commit

git checkout -b <branch name>
creates a new branch starting from your last commit and
switches to it

git branch -d <branch name>
deletes the specified branch

GIT --@work
Merge
git merge <branch name>
merges the specified branch into the current one

git rebase <branch name>
rebases the specified branch onto the current one

GIT --@work : merge
master

A

E

B
C

D
develop

using merge
master

A

E

B

F
D

C

develop

using rebase
master

A

B

develop

E
C

C'

D

D'

GIT --a branching model
master

develop

hotfix/*

feature/*

tag 1.0.0

tag 1.1.0

tag 1.1.1

tag 1.5.0

http:/
/nvie.com/posts/a-successful-git-branching-model/

GIT --@work
Status
git log
prints out the commit tree from the current HEAD

git status
shows info like: current branch, working directory status,
staged changes

git stash show
shows the most recent stash

git describe
shows where you are in repository history relatively to the latest
tag, i.e a revision number. Eg: v1.0.0-50-g1f8115b

GIT --@work
Status
git diff <commit>
shows the diff between working directory and specified commit

git branch [-r]
lists either local or remote (-r) branches

GIT --@work
Release management
git tag v1.0.0 -m "My first release"
creates a "lightweight" tag, i.e. an immovable reference on the
current head

git tag v1.0.0 -a -m "My first release"
creates an "annotated" tag, i.e. an immovable reference on the
current head + info like: tagger, email, date which are stored in
the git database

GIT --@work
Misc
git cherry-pick <commit>
integrates changes in specified commit into the current branch

git bisect
given a start and an end commit reference it will checkout
commits within that range allowing to find a regression

git blame
annotates each line in a file with that last commit to change it

GIT --repository
.gitignore file to express ignore patterns, can be put in
multiple places!
!

git repos smaller than SVN ones, 30x in case of Mozilla!
!

steep learning curve (debatable)!
!

can't checkout part of a repository!
!

oriented towards content rather than files !
!

for transport it supports: HTTP, SSH, GIT protocols!
!

objects are generally added not deleted, reason for git gc

GIT --how to
latest release http:/
/git-scm.com/downloads!
works from CLI!
good GUI clients:
Github for Mac/Win, free ("optimized" for github.com remotes,
but works with others too)!
SourceTree (Mac & Win), free!
Tower (Mac)

(Em)Powered by GIT
https:/
/github.com/

https:/
/bitbucket.org/

https:/
/www.assembla.com/

GIT SCM
easy branching

local, flexible, fast

reliable history

integrity

non-linear, facilitates collaboration

Thank you!
Questions?

@stefanprutianu

Git SCM

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