**NOTE: This slide deck contains many animations. You should download and view in PowerPoint if you can! *** Git (and GitHub) have become pillars in how we manage our code workflow, particularly when we work with large teams. Yet developers tend to be afraid of Git, and only handle but the most basic of operations. This presentation will reveal the magic of Git, and help you understand how and why operations are carried out. After this session, you'll never be afraid of a merge conflict again. Topics covered: * Git under the hood * Git basics * Merging vs Rebasing * Conflict resolution * Triangular Workflow * Common error scenarios and how to solve them * Tips and Tricks

1. Everything you wanted to
know about GIT
(BUT WERE AFRAID TO ASK)

2. ANIMATIONS AHEAD!!!
This deck has plenty of animations to explain
some concepts.
Please view in presentation mode

3. Setting up
 Apple GIT gotchas:
Xcode ships with its custom version of git. You don’t want this:
$ git --version
git version 2.3.2 (Apple Git-55)
$ which git
/usr/bin/git

4. Setting Up
 The right git:
Download and install:
http://git-scm.com/download/mac
Set up:
Modify ~/.profile
export PATH=/usr/local/bin:$PATH
$ git --version
git version 2.4.3

5. Setting Up
 Make life easy for yourself: Autocomplete!
Download: https://raw.githubusercontent.com/git/git/master/contrib/completion/git-completion.bash
Save to -> ~/.git-completion.bash (Note the dot!)
Add to ~/.profile
# Run git autocomplete
source ~/.git-completion.bash
Verify ->
git check<tab> --autocompletes to--> git checkout
PRO TIP: Also autocompletes branch names!

6. Setting Up
 Make life easy for yourself, PART 2: Change your terminal prompt!
Download: https://raw.githubusercontent.com/git/git/master/contrib/completion/git-prompt.sh
Save to -> ~/.git-prompt.sh (Note the dot!)
Add to ~/.profile
# Run git prompt enhancements
source ~/.git-prompt.sh
export GIT_PS1_SHOWDIRTYSTATE=true
export GIT_PS1_SHOWUNTRACKEDFILES=true
export GIT_PS1_SHOWCOLORHINTS=true
export PROMPT_COMMAND='__git_ps1 "w" "$ "'

7. GIT Init
GIT IS MISUNDERSTOOD.
IT JUST WANTS TO BE YOUR
FRIEND

8. Git isn’t magic.
BLOBS TREES COMMITS

9. Git tracks everything. Forever!
 Files (Blobs) are tracked based on content, not on their name.
 Git uses the SHA1 algorithm to create a unique hash (fingerprint) for each file.
foo.txt -> “Hello” -> e965047ad7c57865823c7d992b1d046ea66edf78

10. How is it calculated?
“blob”+space
Do it yourself! printf ”blob 6000Hellon" | shasum
Null char
Length of content File content
b l o b 6 0 0 0 H e l l o n

11. All versions of a file end up as blobs.
E9650
Hello
980a0
Hello World!
53627
Hello World! How are you?
7a27f
Hello World! How are you today?
557db
Hello World

12. Trees organize (and name) sets of files
E9650
Hello
a69b2
557db
Hello World
8984f

13. Commit ec445 Commit bd297
Commits give order to trees
E9650
Hello
Tree: a69b2
Author: lmarkus
Message: First Commit
557db
Hello World
bd297ec445
Tree: 8984f
Parent: ec445
Author: lmarkus
Message: Second Commit

15. Git Recap
 Git saves *everything*
 Git keeps track of what your project looked like at a given time (tree + commit)
 Git keeps a history of the various snapshots as a linked list. (commit -> parent)

16. The world is my
stage!

17. The world is my stage!
HEAD STAGE Work Dir

18. The world is my stage!
HEAD STAGE Work Dir
$ git status
On branch master
nothing to commit, working directory clean

19. The world is my stage!
HEAD STAGE Work Dir

20. The world is my stage!
HEAD STAGE Work Dir
$ git status
On branch master
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)
modified: miner.txt
no changes added to commit (use "git add" and/or "git commit -a")

21. The world is my stage!
HEAD STAGE Work Dir
$ git add miner.txt

22. The world is my stage!
HEAD STAGE Work Dir

23. The world is my stage!
HEAD STAGE Work Dir
$ git status
On branch master
Changes to be committed:
(use "git reset HEAD <file>..." to unstage)
modified: miner.txt

24. The world is my stage!
HEAD STAGE Work Dir

25. The world is my stage!
HEAD STAGE Work Dir

26. The world is my stage!
HEAD STAGE Work Dir
$ git status
On branch master
Changes to be committed:
(use "git reset HEAD <file>..." to unstage)
modified: miner.txt
Untracked files:
(use "git add <file>..." to include in what will be committed)
sun.txt

27. The world is my stage!
HEAD STAGE Work Dir
$ git commit -m “Mining is hard”

28. The world is my stage!
HEAD STAGE Work Dir

29. “Oops…”
moments

30. Git Reset
A B C D E
STAGE WORKING DIR
E E
HEAD

31. Git Reset --soft
A B C D E
STAGE WORKING DIR
E E
HEADgit reset --soft HEAD~1

32. Git Reset --mixed
A B C D E
STAGE WORKING DIR
D E
HEADgit reset --mixed HEAD~1
E

33. Git Reset --hard
A B C D E
STAGE WORKING DIR
D D
HEADgit reset --hard HEAD~1
E E

34. Clean up after
yourself!

35. Git Rebase - Part I
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.

36. Git Rebase - Part I
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
$ git log --oneline
845c2a5 Actually, that wasn't a bug. Reverting
10ae9b3 Oops, fixed a bug
5c68b04 Fixed Another typo
83775b2 Fixed Typo
099d98e Created New Function

37. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
$ git rebase -i HEAD~4
pick 83775b2 Fixed Typo
pick 5c68b04 Fixed Another typo
pick 10ae9b3 Oops, fixed a bug
pick 845c2a5 Actually, that wasn't a bug. Reverting
# Rebase 099d98e..845c2a5 onto 099d98e (4 command(s))
#
# Commands:
# p, pick = use commit
# r, reword = use commit, but edit the commit message
# e, edit = use commit, but stop for amending
# s, squash = use commit, but meld into previous commit
# f, fixup = like "squash", but discard this commit's log message
# x, exec = run command (the rest of the line) using shell
#
# These lines can be re-ordered; they are executed from top to bottom.
# If you remove a line here THAT COMMIT WILL BE LOST.
# However, if you remove everything, the rebase will be aborted.
# Note that empty commits are commented out

38. A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
pick 83775b2 Fixed Typo
pick 5c68b04 Fixed Another typo
pick 10ae9b3 Oops, fixed a bug
pick 845c2a5 Actually, that wasn't a bug. Reverting
squash
Git rebase --interactive

39. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
pick 83775b2 Fixed Typo
squash 5c68b04 Fixed Another typo

40. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
pick 83775b2 Fixed Typo
squash 5c68b04 Fixed Another typo

41. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
# This is a combination of 2 commits.
# The first commit's message is:
Fixed Typo
# This is the 2nd commit message:
Fixed Another typo
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.

42. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
# This is a combination of 2 commits.
# The first commit's message is:
Documentation updates
# This is the 2nd commit message:
# Fixed Another typo
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.

43. Git rebase --interactive
A B C D E
Created
New Function
Fixed typo Fixed
Another typo
Oops!
Fixed a bug.
Actually,
that wasn’t a bug.
Reverting.
$ git log --oneline
779dbd5 Documentation updates
099d98e Created New Function

44. Branching out

45. Branches
A B C
MASTER
 Remember: Your git
history is just a linked list
of commits.
 A branch simply
represents a marker
somewhere in this
history. It points to the
latest commit within a
set.

46. Branches
A B C
MASTER DEVELOP
git checkout -b develop

47. Branches
A B C
MASTER
D E
DEVELOP
git commit -m ”D”
git commit -m ”E”

48. Branches
A B C
MASTER
D E
DEVELOP
git checkout master

49. Branches
A B C
MASTER
D E
DEVELOP
git commit -m “F”
F

50. Rebase Vs Merge
A B C
MASTER
D E
DEVELOP
F

51. Merge
A B C
MASTER
D E
DEVELOP
F M Merge commits have TWO
parents. They represent the
point where to branches
became one
git merge develop
X Y
Work can continue after a merge

52. Rebase
A B C
D E
DEVELOP
MASTER
F
We just re-wrote history!
git rebase develop

53. Rebase Vs Merge - RECAP
A B C
MASTER
D E
DEVELOP
F M
X Y
A B C
MASTER
D* E* F
Merge
 Very explicit, accurate history
 Visually complex
 Easy to roll back
Rebase
 Linear history
 Easy to understand
 Not historically accurate
 Hard to undo.

54. Playing well with
others

55. Forking and Cloning
Develop
Release
Master
Develop
Release
Master
*/Customers-R/activation
* = http://github.paypal.com
*/lmarkus/activation
Develop
Release
Master
originupstream

56. Forking and Cloning
Develop
Release
Master
lmarkus/activation
Develop
Release
Master
origin
Develop
Release
Master
Customers-R/activation
upstream
person1/activation
person2/activation
person3/activation

57. Forking and Cloning
UPSTREAM
ORIGIN
LOCAL
git remote update
git rebase upstream/develop
git push origin develop
DEVELOP BRANCH

58. Forking and Cloning - Common Error #1
UPSTREAM
ORIGIN
LOCAL
git push origin develop
DEVELOP BRANCH
git remote update
git rebase upstream/develop
git push origin develop

59. Forking and Cloning - Common Error #1
$ git push origin develop
To https://github.paypal.com/lmarkus/activation.git
! [rejected] develop -> develop (non-fast-forward)
error: failed to push some refs to
https://github.paypal.com/lmarkus/activation.git
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

60. Forking and Cloning - Common Error #1
UPSTREAM
ORIGIN
LOCAL
DEVELOP BRANCH
Option 1:
git pull origin develop
git push origin master
Solves the problem, but history
gets messy. Doubled up commits

61. Forking and Cloning - Common Error #1
UPSTREAM
ORIGIN
LOCAL
DEVELOP BRANCH
Option 2:
git push origin master --force
The Force has a dark side…
You are overwriting history which
may be shared

62. Resolving merge
conflicts

63. What happens during a merge
Animals.txt
Animals I like:
Dogs!
Animals.txt
Animals I like:
Cats!
Birds!
master feature1
git merge feature1
Animals.txt
Animals I like:
<<<<<<< HEAD
Dogs!
=======
Cats!
Birds!
>>>>>>> feature1

64. What happens during a merge
Animals.txt
Animals I like:
Dogs!
Animals.txt
Animals I like:
Cats!
Birds!
master feature1
Animals.txt
Animals I like:
<<<<<<< HEAD
Dogs!
=======
Cats!
Birds!
>>>>>>> feature1
git add Animals.txt
git commit -m “Dogs Rule”

65. Resolve conflicts the smart way!

66. Resolve conflicts the smart way!
Shortcuts!

67. Resolve conflicts the smart way!