Introduction to Git

Introduction to Git
10/2/2013
Rick Umali
rickumali@gmail.com
@rickumali
http://tech.rickumali.com/
This presentation is on Google Drive at:
http://sn.im/git-talk-2013
There you can read the 'speaker notes' for this
presentation.

What is Source Control?
Source code control is the most important
practice a coding professional can do.
A mechanism to track changes in source code.
Used for version history, auditing, and
recovery.

Revision Control Example: Wiki

Revision Control Example: Git
You’ll learn how to make a repository like this.

Git
Git is an open source, distributed version
control system designed for speed and
efficiency.
Freedom
No "server" required
Unique architecture

Our Example: A Basic Drupal Module

Creating a Repository
% cd web/sites/all/modules
% mkdir dumpstamp
% cd dumpstamp
% git init
"git init" creates the entire Git repository.
No server interaction required!

Committing Your First File
To 'commit' means 'to save the state' of your
work. You must first 'add' this change to the
'staging area'.
% vi README.txt
% git add README.txt
% git commit -m "First commit. README file."
Commit often!

Looking at the Repository History
% git log
% gitk

Adding More Files
% vi dumpstamp.info dumpstamp.module
% git status
% git add .
% git commit
or
% git commit -a -m “My commit message.”
Learn the shortcuts by reading Git docs.

Examining Changes to Files
% vi dumpstamp.module
% git status
% git diff
% git add dumpstamp.module
% git commit
% git log
Become familiar with Git status and diff
output.
Make your commit messages meaningful!

Looking at the Log Again
The history can be examined different ways.
% git log --format=short
% git log --format=oneline
% git log --oneline

Revisiting History
You can 'revisit' any point of your history.
% git checkout SHA_ID
Checkout makes the working directory match
the state of the specific SHA_ID.
This is a time machine!

Returning to the Present
At all times, Git retains a pointer to the
‘present’.
% git checkout master

Branching and Merging Next, But...
What we have covered so far is probably 70-
80% of what you will do with git.
Adding and committing files are the heart of
git (and any version control system).

Git encourages experimentation, by making
branching very easy!
Branching

Branching: git branch
% git branch BRANCH
% git checkout BRANCH
This makes a branch from “where you
currently are”, and then “switches” (checks
out) the branch.
“git branch” tells you what branch you’re on.

Branching: Starting State
SHA 1Amaster
NOTE: 'master' is a branch that's created 'by default'.

Branching: Make Some Changes
SHA 1A
SHA 2Bmaster
git commit

Branching: Making a Branch
SHA 1A
SHA 2Bmaster branch1
git branch branch1
git checkout branch1
OR git checkout -b branch1

Branching: Changes on the Branch
SHA 1A
SHA 2Bmaster
SHA 3C
(Make changes in "branch1".)
git commit
branch1

Branching: Making a New Branch
SHA 1A
SHA 2Bmaster
SHA 3C
git checkout master
git checkout -b branch2
branch1
branch2

Branching: Changes on another
Branch
SHA 1A
SHA 2Bmaster
branch2SHA 4D
(Make changes in "branch2".)
git commit
branch1 SHA 3C

Merging
Bringing two branches together.
First 'checkout' the branch you want to merge
into (typically master), then 'merge' in branch.
% git checkout master
% git merge BRANCH

Merging: Starting State
SHA 1A
SHA 2Bmaster
branch2SHA 4Dbranch1 SHA 3C

Merging: Fast-Forward Merge
git checkout master
git merge branch1
SHA 1A
SHA 2B
branch2SHA 4Cmaster, branch1 SHA 3C

Merging: Resolving Conflicts
git merge branch2
SHA 1A
SHA 2B
branch2SHA 4Cbranch1 SHA 3C
SHA 5 master

Merging: The Hard Part
Manual 'merging' may be required.

Using Git “Remotely”
You can upload your local Git repository to a
public Git repository. These repositories are
known as remotes.
Using “remotes” is the key to collaborating.

Visualizing Remotes
Your Repo Bob Repo
GitHub Repo

Uploading New Code to GitHub
Create a repository (on GitHub).
Add a 'remote' (via git remote add).
Upload your code (via git push).

Creating a Repository
git init

Adding a Remote
git remote adds a name for a repo at a
specific URL
git remote add origin git@github.com:rickumali/DumpStamp.
git
Your Repo GitHub Repo
(origin)
Dumpstamp.git
This is just a naming step!

Push Your Repo to the Remote
% git push -u origin master

Visualizing the Push
git push uploads the repository to the remote
Your Repo GitHub Repo
(origin)

Visualizing Remotes (cloning)
Your Repo Bob Repo
GitHub Repo
(origin)
Now Bob can ‘clone’ your repository
clone

The Cycle with Remotes
Your Repo Bob Repo
GitHub Repo
(origin)
You Push, Bob “Pulls” (or Fetches/Merges)
pullpush

You Saw and Learned A Lot About Git
Typical Git Commands
Add, Commit, Log, Diff, Status
Branch and Merging
Git Remote Repositories

Next Steps
Install Git
Commit frequently and log verbosely
Experiment (branch) often

Resources
http://sethrobertson.github.io/GitBestPractices/
Great list of Git best practices.
http://git-scm.org/
Both "Pro Git" book, and Git reference
http://gitref.org/
A "quicker" Git reference
http://www-cs-students.stanford.edu/~blynn/gitmagic/
"Friendlier" Git walk-through (git magic).
http://www.mail-archive.com/dri-devel@lists.
sourceforge.net/msg39091.html
Linus on "clean history."

Resources
http://www.youtube.com/watch?v=4XpnKHJAok8
Linus Torvalds (Git creator) (May '07)
http://www.youtube.com/watch?v=8dhZ9BXQgc4
Randal Schwartz (Perl expert and Git old-timer) (Oct
'07)
http://www.youtube.com/watch?v=ZDR433b0HJY
Scott Chacon (Pro Git author) (July '11)

Introduction to Git

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