Git going
with DVCS
mental spoo n bending
50 minutes of
v ia source c ode control
by Matthew McCullough of Ambient Ideas, LLC

What? Why?
Basic Use
GUI
DVCS
Who?
Theory
Sharing
Interop High Points

“ Git
-noun sant or
Slang. an unplea
British
cont emptible per son ” ionar y
-Oxfo rd English Dict

≉

otistical b astard, and
“
I'm an eg
I name all my projects
after myself. Fi rst Linux,
now git. ”
-Lin us Torvalds

darcs
Mercurial
Bazaar
BitKeeper
Subversion
Perforce
Clear
Source Case
Safe
CVS
PVCS
RCS
Folders

t
Source Code Control
Gi

CultureChange

Centralized
VCS =Don’t

Distributed
VCS = Whatever!
Do

Innovate
Experiment
Safely Be Wrong
Drive-by Assist
Crowd Source

Crowd Source

Download binaries

Git Distro Sources
Win Cygwin
Win msysGit
Linux Source
Linux Package manager
Mac MacPorts
Mac git-osx-installer
Any JGit

Put it in your path

Identify yourself

Global Git Settings
git config --global user.name \"Hal Smith\"
git config --global user.email \"hal@bnl.com\"

Use it!

Creating a Repo
mkdir myproj.git
cd myproj.git
git init

Just show it to me!

Certified
Git User

145+ Commands

Follow the
DOTS

Symmetric

subversion server
developer A developer B

ch
ec
ki
n

te
da
up

n
ki
ec
ch

up
da
te

Symmetric

Distributed

developer A developer B

blessed repo
developer A developer B

commit commit
commit
commit commit
commit commit

delete delete

rebase

pu
sh

pu
sh

push

push

pull

pull

Distributed

WorkingOffline

More available connectivity

More demand to work without
connectivity

Offline Anything
Checkin
Add
Branch
List change log
Grep history
Rewrite history
Stash
Merge
Label
Remove
practically everything but push

Cool! Another
commit to my latest OSS
project using Git!
I liked subversion
better...

What? Why?
Basic Use
GUIs
DVCS
Who?
Theory
Sharing
Interop High Points

Who’s Got Git?

GUIs

GitX

GitSafe

GitK

GitGUI

EGit

c i a l !
O f fi
It ’s

UsageModels

Centralized
Central
Repo

Repo
Blessed
Dictatorship

Certified
Integration Managed
Development
Repo Repo

Mirror Mirror
Certified Development
Repo Repo
Mirrored

☚ Private Public ☛
Customized
GitHub
Custom + Public Contrib

Hashes and Git

Index vs Hash
‣ Centralized VCS uses DB
sequential index.

Index vs Hash
‣ Git uses SHA-1 hash.

ght
thou re
I
ashe s we
h
for
wor ds?
p ass

SHA-1 Hash
‣ Different goals.
‣ Hash for the sake of integrity.
‣ Hash for the sake of identity.

40 hex characters

Use as little of it as is unique

Treeish

Shorthand for the hashes

9AB223

9AB223^

9AB223..56CD77

HEAD

HEAD^

HEAD~3

ve b seen
B ut I’
ring new
hea ash
abo ut h
ision s...
coll

49
to m s
rt h a
e a

46
S H A 1

22
s ta rs

20
g ra in s
s an d

19
l is io n
c o l

Hashable Objects
‣ Blob
‣ Tree
‣ Commit
‣ Tag

http://book.git-scm.com/1_the_git_object_model.html

Hash Benefits
Integrity
‣ Identifies damaged repos.
‣ Prevents modification of published history.
‣ Unique to file size and contents.

Hash Benefits
Tags
‣ Cryptographically sign tags by GPG.
‣ Guarantee repo’s state at a point in time.

Storage Mechanics

Typical SCMs use delta storage

CVS / Subversion / darcs / Mercurial

Checkin
ckin
kin
in
Chec
kin
he
ck
ec
C
he
in
in
Ch
C
ck k
C he
h ec
kin C
ec
ec kin
Delta storage gets slower Ch the
Ch
as
history of a file gets longerin
Checkin
Check

Git uses DAG storage

Directed Acyclic Graph

Copy of the entire tree per checkin

cp -r srcfolder srcfolder.prev

Sounds inefficient...

zlib deflates every blob at commit

I’ve had a
400MB Subversion repo
convert to a 70MB Git repo

Speed

git: git
hg: mercurial
bzr: bazaar

Init Add Status Diff
Branch (Cold/Hot)
git hg bzr git hg bzr git hg bzr git hg bzr
Tag Log Commit (Lg) Commit (Sm)
git c git h hg c hg h bzr c bzr h
git hg bzr git hg bzr git hg bzr git hg bzr
data from http://whygitisbetterthanx.com/#git-is-fast

bazaar numbers
subversion = plus
network latency

10
to
100 times
Faster

Location,Location,Location

Three Stage Thinking
of Git

Git
‣ git add
‣ git commit
‣ git push

‣ Commits only what is added to the index.
‣ Opportunity to rewrite history locally.
‣ Provides time to change your mind.
‣ Selectively share with other repos.

Git
‣ git stash
‣ git stash apply

‣ Save work-in-progress temporarily,
but safely.
‣ Merge stashed modifications back in.

Remote
is like a special
Stash
Repo
git clone
git checkout
edit experiment files
git stash
test buggy files
Index git stash apply
Working git add
git commit
git push

repo
git clone git://somedomain/myproj.git B uild
cd myproj.git
dex
pda te in
git checkout master U
echo ‘//Comments’ >> ClassOne.java or king
echo ‘//Thoughts’ >> ClassTwo.java E dit w
to i ndex
git add ClassOne.java Add epo
ave to r
git commit -m’Added comments’ S
st ash
git stash Pus h to

Merge & Rebase

Cheap Branches
git branch newbranch
git checkout -b newer remote/branchnm

Cheap Branches
git show-branch --all
git branch -a

‣Local branch
‣localbranchname
‣Remote branch
‣remote/branchname

Merge Anything
git merge --no-commit <sourcebranch>
git merge --squash <sourcebranch>
git merge <sourcebranch1> <sourcebranch2>

Rebase for Clarity
git checkout myfeaturebranch
git rebase master

Rebase for Clarity
‣Fast forwards the “side” branch.
‣Reposition your feature branch’s start point.
‣See “how trunk will act” before you merge.
‣Makes for simpler merge graphs.
‣Cleaner history than a merge.

ard Bra
d
n e
ta g
a32 n ch
S er
Master/Trunk/MainLatest
d19
M 2e2
e69
8b3
erge
M
9f1

Bra
sing a32
n ch
ba
Master/Trunk/MainLatest
Re 2e2 d19
8b3
e69

Master/Trunk/MainLatest
a32
2e2
8b3
Bra
ch n
d19
e69
Rebase

a32
Master/Trunk/MainLatest
2e2
8b3 Bra
n ch
d19 d19
Me
rg
e
e69 e69

What? Why?
Basic Use
GUIs
DVCS
Who?
Theory
Sharing
Interop High Points

Sharing

Serving It Up
Protocols
‣ GIT
‣ SSH
‣ SCP
‣ Local file system
‣ SAMBA
‣ HTTP
‣ WebDAV
‣ rsync

aem on
git clone git://somehost.org/myproj.git g it d
git clone mccm06@somehost.org:myproj.git SSH
git clone http://somehost.org/myproj.git H TTP
sys tem
git clone ~/work/myproj.git File
rk d rive
Ne two
git clone z:\\someserver\\myproj.git

Serving It Up
‣ git instaweb. Built in, read-only, HTTP.
‣ git daemon. Custom socket language.
‣ gitosis. Easy permissions control.
‣ github. Open source & private repos.
‣ ssh. OS controlled permissions.

SVN Interop

Subversion
git svn clone http://unfurl.com/trunk
git svn dcommit

Subversion
‣ First class compatibility.
‣ Round trip support.
‣ Git commits = svn commits.

Migration
‣ git svn clone

Migration
‣ Power off your Subversion server.

3
reasons

Cherry Pick
❸
‣git cherry-pick a5b2ee
‣Merge in just one commit.

Search History
❷
‣git grep SomeText HEAD^^^
‣Search blob contents history without checkouts.

Bisect Bugs
❶
‣git bisect run mvn test
‣Binary-search for bug.
‣Manual or automated modes.

emerging Control System
Version

Twitter
@matthewmccull Matthew
Blog
http://www.ambientideas.com/blog
sidebar has all my social media links
Email
matthewm@ambientideas.com
GitHub
http://github.com/matthewmccullough

Resources
Git Homepage
http://git-scm.com
Directed Acrylic Graph
http://en.wikipedia.org/wiki/Directed_acyclic_graph
Git for Computer Scientists
http://eagain.net/articles/git-for-computer-scientists/
Git Treeish
http://book.git-scm.com/4_git_treeishes.html

Resources
Git Docs
http://www.kernel.org/pub/software/scm/git/docs/
Git Magic eBook
http://www-cs-students.stanford.edu/~blynn/gitmagic/book.pdf
Linus Torvald’s Git talk at Google
http://www.youtube.com/watch?v=4XpnKHJAok8
CygWin
http://www.cygwin.com

Resources
MSysGit
http://code.google.com/p/msysgit
Git Cheetah
http://code.google.com/p/msysgit/wiki/GitCheetah
Matthew’s Git Bookmarks
http://delicious.com/matthew.mccullough/git
Matthew’s Bash Prompt
http://gist.github.com/47267

Image Credits
‣ http://www.ambientideasphotography.com
‣ http://flickr.com/photos/lenore-m/2903856664/
‣ http://en.wikipedia.org/wiki/Git_(software)
‣ http://flickr.com/photos/karenhorton/1583513014/
‣ http://flickr.com/photos/mashdnart/2545782407/
‣ http://commons.wikimedia.org/wiki/
File:Small_Boy_nuclear_test_1962.jpg
‣ http://www.flickr.com/photos/knmurphy/2506896257/
‣ http://www.flickr.com/photos/albyspace/1022035568/
‣ http://flickr.com/photos/michaelhays/3070238360/
‣ http://flickr.com/photos/d_vdm/509996632/