Git Training

Dan Hyun

Topics

Introduction
Git Now
Git Fundamentals
Git Commands
Everyday Git
Best Practices
Resources

What is Git?

Cross platform, distributed
source control management system.

Brief Background

Created in 2005 by Linus Torvalds
Named after Linus Torvalds
Used to maintain the Linux Kernel

Motivations for Git

Performance	fast, reliable file integrity
Simplicity	no separate admin binaries
Flexibility	supports multiple protocols, methods of contributions, etc.

Git in action

Figure 1. As of 2015-03-03

Git Now

Create a new git repository

$ git init demo
Initialized empty Git repository in /home/vagrant/demo/.git/

Add a file

$ echo 'public class Hello { public static void main(String[] args) { System.out.println("Hello, World!"); } }' > Hello.java
$ javac Hello.java
$ java Hello
Hello, World!
$ git add Hello.java

Save it forever

$ git commit -m "Add important Hello.java file"
[master (root-commit) bf94b34] Add important Hello.java file
 1 file changed, 1 insertion(+)
 create mode 100644 Hello.java

Congratulations!

Now you know git!

Fundamental concepts

Objects
References
State
Distributed Nature

Objects

Every file is an object
Every commit is an object
These objects form a tree

Objects

References

HEAD is a reference
Branches are references
Tags are references
Remotes are references

References

State

A given file can be in one of these four states:

Untracked
Tracked - not modified
Tracked - staged for commit
Committed

State

Distributed

No central server or authority
Most actions performed locally
Eliminates issues (politics) around commit access

Distribution

Git vs CVS/SVN

Attribute	Git	CVS/SVN
Tracking changes	Snapshot of all files	Per file
History storage	Compressed binary objects with SHA1 checksum	Diff per file in .cvs/.svn directories
Source of truth	Distributed	Centralized

Attribute

Git

CVS/SVN

Tracking changes

Snapshot of all files

Per file

History storage

Compressed binary objects with SHA1 checksum

Diff per file in .cvs/.svn directories

Source of truth

Distributed

Centralized

Git commands

Git config

Used to set and get configuration properties

Sample Truncated Config

$ git config --list
user.name=Dan Hyun
user.email=dan@hyunlabs.com

Config locations

Table 1. Locations and corresponding flags
Level	Config Location	Git flag
Project	`${project}/.git/config`	`--local`
User	`~/.gitconfig`	`--global`
System	`/etc/gitconfig`	`--system`

Who am I?

$ git config --global user.email "dan@hyunlabs.com"
$ git config --global user.name "Dan Hyun"

INFO: This information goes into your commits

git init

Create a new Git repository

$ git init demo
Initialized empty Git repository in /home/vagrant/demo/.git/

`init`

.git
├── branches
├── config (1)
├── description
├── HEAD (2)
├── hooks
│   ├── applypatch-msg.sample
│   ├── commit-msg.sample
│   ├── post-update.sample
│   ├── pre-applypatch.sample
│   ├── pre-commit.sample
│   ├── prepare-commit-msg.sample
│   ├── pre-push.sample
│   ├── pre-rebase.sample
│   └── update.sample
├── info
│   └── exclude
├── objects (3)
│   ├── info
│   └── pack
└── refs (4)
    ├── heads
    └── tags

1	Project level config file
2	Current branch reference
3	Blob storage
4	Reference locations

git add

Stages the given file(s) as is to the index

$ git add <file or path>

`add`

$ touch hello
$ git add hello
$ git status
On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

        new file:   hello

git objects

$ find .git/objects/ -type f
.git/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391

git commit

Commit all staged objects to local repository

$ git commit [-m <message>]

`commit`

$ git commit -m "Initial commit"
[master (root-commit) d400d55] Initial commit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 hello

git objects

$ find .git/objects -type f
.git/objects/e6/9de29bb2d1d6434b8b29ae775ad8c2e48c5391 (1)
.git/objects/f9/66952d7e0715683ee935d201cd4ab22736c831 (2)
.git/objects/d4/00d55d841364e0bdf479c5e172210954ae3d5c (3)

1	Our `hello` file as a blob
2	Tree object containing fileset for commit
3	Commit object containing author and tree object

tree object

git cat-file -p allows us
to inspect git objects

$ git cat-file -p f966952d7e0715683ee935d201cd4ab22736c831
100644 blob e69de29bb2d1d6434b8b29ae775ad8c2e48c5391    hello (1)

1	File mode object type object hash

Differentiating git object types

Object types?

$ git cat-file -t e69de
blob
$ git cat-file -t f9669
tree
$ git cat-file -t d400d
commit

HEAD master

$ find .git/refs/ -type f
.git/refs/heads/master (1)

1	New reference `master` added

git references

$ cat .git/refs/heads/master
d400d55d841364e0bdf479c5e172210954ae3d5c (1)

1	The hash of the commit object

I know Kung-fu

Everyday git

`git add everything`

$ git add .
$ git commit -m "#yolo"
[master (root-commit) e96454d] #yolo
 2 files changed, 1 insertion(+)
 create mode 100644 Hello.class
 create mode 100644 Hello.java

NO

create mode 100644 Hello.class

Removing files

$ git rm Hello.class
rm 'Hello.class'
$ git status
On branch master
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

        deleted:    Hello.class

Removing Files

Don’t forget to commit

$ git commit -m "Remove generated files"
[master c36a69a] Remove generated files
 1 file changed, 0 insertions(+), 0 deletions(-)
 delete mode 100644 Hello.class

.gitignore

.gitignore lives at the root of the repository

# ignore generated files
*.class
# ignore maven output
target/
# ignore gradle output
build/

Branching

$ git branch neato-feature
$ git checkout neato-branch
Switched to branch 'neato-branch'

`git branch`

$ git branch -v
  master       c36a69a Remove generated files
* neato-branch c36a69a Remove generated files

Working on a branch

$ echo "Hello is very important" > README
$ git add README
$ git commit -m README
[neato-branch 1f1f2ae] README
 1 file changed, 1 insertion(+)
 create mode 100644 README

Git branch

$ git branch -v
  master       c36a69a Remove generated files
* neato-branch 1f1f2ae README

Gitk

$ gitk

Merging

$ git checkout master
Switched to branch 'master'

$ git merge neato-branch
Updating c36a69a..1f1f2ae
Fast-forward
 README | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 README

Merged

$ git branch -v
* master       1f1f2ae README
  neato-branch 1f1f2ae README

Collaboration

$ git remote add origin <URL> (1)

1	Any valid URL

git push

$ git push origin master
Counting objects: 9, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (7/7), done.
Writing objects: 100% (9/9), 1.09 KiB | 0 bytes/s, done.
Total 9 (delta 0), reused 0 (delta 0)
To ../demo-remote
 * [new branch]      master -> master

Updating from remotes

$ git fetch
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../demo-remote
   1f1f2ae..ecf757d  master     -> origin/master

Merge from origin/master

$ git merge origin/master
Updating 1f1f2ae..ecf757d
Fast-forward
 Hello.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

All in one go

$ git pull origin master
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../demo-remote
 * branch            master     -> FETCH_HEAD
   1f1f2ae..ecf757d  master     -> origin/master
Updating 1f1f2ae..ecf757d
Fast-forward
 Hello.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Git push

What happens when
code changes?

$ git push origin master
To ../demo-remote
 ! [rejected]        master -> master (fetch first)
error: failed to push some refs to '../demo-remote'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

Conflict

$ git pull origin master
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 3 (delta 1), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../demo-remote
 * branch            master     -> FETCH_HEAD
   ecf757d..fd10976  master     -> origin/master
Auto-merging Hello.java
CONFLICT (content): Merge conflict in Hello.java
Automatic merge failed; fix conflicts and then commit the result.

Resolving Conflict

$ cat Hello.java
<<<<<<< HEAD
public class Hello { public static void main(String[] args) { System.out.println("Hallo, Welt again!"); } }
=======
public class Hello { public static void main(String[] args) { System.out.println("Hello, World again!"); } }
>>>>>>> fd10976633568cd872f2d1aa64d97429957d73bb

Commit

$ git commit -am "resolve conflict"
[master b0ae7d5] resolve conflict

Push

$ git push origin master
Counting objects: 8, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 514 bytes | 0 bytes/s, done.
Total 4 (delta 1), reused 0 (delta 0)
To ../demo-remote
   fd10976..b0ae7d5  master -> master

Final product

Best practices

Use commandline exclusively in the beginning
Adhere to your team’s work flow
Branch from your team’s canonical branch

Commit messages

Use consistent messaging
Use present tense and one line summary < 50 chars
Add paragraph with more details if needed

Example

Reads like a log file:

Fixes duplicate entry issue

Update schema to use primary key
Update DAO to accept additional param

Use ssh

$ git clone https://chucknorris.com/roundhouse.git
Cloning into 'roundhouse'...
Password for 'https://chucknorris.com':

LAME

Ssh setup

Generate an ssh key pair
Add public key to central server
Enjoy not typing passwords

Generate ssh key

$ ssh-keygen -t rsa -C "dan@hyunlabs.com"

ssh-keygen output

Generating public/private rsa key pair.
Enter file in which to save the key (/home/vagrant/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/vagrant/.ssh/id_rsa.
Your public key has been saved in /home/vagrant/.ssh/id_rsa.pub.
The key fingerprint is:
64:59:65:dc:ad:81:85:26:9e:ad:dd:d7:7a:21:75:e9 dan@hyunlabs.com
The key's randomart image is:
+--[ RSA 2048]----+
|          .oo=.. |
|         o..= o .|
|        +. =   o.|
|       o  o . .o.|
|        S  o .o o|
|          . ...Eo|
|              .o.|
|              . .|
|               . |
+-----------------+

Upload public key

Setup ssh config

~/.ssh/config

Host *
        PreferredAuthentications publickey,keyboard-interactive
        ServerAliveInterval 120
        ServerAliveCountMax 30
        IdentityFile ~/.ssh/id_rsa
Host stash
        User git
        Hostname chucknorris.com
        Port 7999

Enjoy

$ git clone stash:/roundhouse.git

Workflows

Develop → Staging → Master
Commit to Master

Multibranch process

Maintain two canonical branches (master, develop)
Master represents what is on production (always "deployable")
Develop is coordination branch

Multibranch process

Branch from develop
Do some work
Merge from origin/develop if updated
Submit Pull Request*

Multibranch process

Resources

Git Flow: Blog article by Scott Chacon about a workflow
Pro Git: Free ebook by Scott Chacon (Github) and Ben Straub
Git Immersion: Series of labs to learn git fundamentals

Resources continued

Linus Torvalds on git: Video - Linus talks about git
Interactive git cheat sheet: Interactive git command cheat sheet
Suggested git branching model: A popular git branching model

Resources continued

Vicinio’s git process

Git Training

Topics

What is Git?

Brief Background

Motivations for Git

Git in action

Git Now

Add a file

Save it forever

Congratulations!

Fundamental concepts

Objects

Objects

References

References

State

State

Distributed

Distribution

Git vs CVS/SVN

Git commands

Git config

Config locations

Who am I?

git init

init

git add

add

git objects

git commit

commit

git objects

tree object

Differentiating git object types

HEAD master

git references

I know Kung-fu

Everyday git

git add everything

NO

Removing files

Removing Files

.gitignore

Branching

git branch

Working on a branch

Git branch

Gitk

Merging

Merged

Collaboration

git push

Updating from remotes

Merge from origin/master

All in one go

Git push

Conflict

Resolving Conflict

Commit

Push

Final product

Best practices

Commit messages

Example

Use ssh

LAME

Ssh setup

Generate ssh key

ssh-keygen output

Upload public key

Setup ssh config

Enjoy

Workflows

Multibranch process

Multibranch process

Multibranch process

Resources

Resources continued

Resources continued

Questions?

`init`

`add`

`commit`

`git add everything`

`git branch`