Gitting It Under (Version) Control

Gitting it under
(version) control

The Plan

• What is Version Control?

• Git Basics

• Workflows

• Other fun stuff

What is Version
Control?
• It’s exactly what it sounds like.
• Sometimes called SCM (source control
management).
• One codebase, one project.
• Lots of people changing it to get things
done at the same time.
• How do we track those changes?

• How do we make sure I don’t step over your toes?

Different Approaches

• Distributed vs. Centralized

• Delta vs. Directed Acyclic Graph (DAG)

Muscle Memory FTW

# 0. Get a copy of the repository
git clone git@github.com:user/repo
# 1. Before you do any work...
git pull
# 2. Do work, edit files, but when you want to share it...
git commit -am "commit message"
# 3. Now send it to everyone else
git push
# GOTO Step 1.

Setting Up

• Download Installer
from http://git-scm.com/

• A few commands you
want to run right away:

git config --global user.name "Ankur Oberoi"
git config --global user.email "aoberoi@gmail.com"
git config --global color.ui true

git commands
• Porcelain (high-level, “nice” for users)
git−add git−commit git−log git−reset
git−branch git−diff git−mv git−status
git−checkout git−fetch git−merge git−push
git−clone git-init git−pull git−tag
git-archive git-bisect git-bundle git-cherry-pick
git-citool git-clean git-describe git-format-patch
... ... ... ...

• Plumbing (low-level, deals with database & filesystem)

git−apply git−checkout−index git−commit−tree git−hash
−object
git−index−pack git−init−db git−merge−index git−mktag
git−mktree git−pack−objects git−prune−packed git−read−tree
git−repo−config git−unpack−objects git−update−index git−write−tree
git−cat−file git−describe git−diff−index git−diff−files
git-diff-index git-diff-tree git-for-each-ref git-ls-files
... ... ... ...

Getting a repository
• One project, one .git (hidden) directory

• Start it from initial code locally

• git init

• Clone it from somewhere else
• git clone URL

Local Repository Operations

Working Directory Staging Area Repository
“Working Tree” “Index” “Database”


Readme.md
* AwesomeProj *

AwesomeProj
does x and y.



git add Readme.md

Readme.md
* AwesomeProj *

AwesomeProj
does x and y.



git add Readme.md git commit -m “commit mess”

Readme.md
* AwesomeProj *

AwesomeProj
does x and y.


git status

# On branch master
nothing to commit (working directory clean)

Readme.md


git status

# On branch master
# Changes not staged for commit:
# (use "git add <file>..." to update what will be committed)
# Readme.md
(use "git checkout -- <file>..." to discard changes in working
Readme.md
directory)
# * AwesomeProj *
# modified: Readme.md
#
no changes added to commit (use "git add" and/or "git commit -a")
AwesomeProj
does x, y and z.


git status

git add Readme.md
# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..."
to unstage)
Readme.md
Readme.md #
# modified: Readme.md
# * AwesomeProj *

AwesomeProj
does x, y and z.



git commit -m “new feat”

Readme.md Readme.md
[master ad9e3bf] new feat
1 files changed, 1 insertions(+), 1 deletions(-)
* AwesomeProj *

AwesomeProj
does x, y and z.





git reset HEAD Readme.md



X
git checkout -- Readme.md

X
git checkout HEAD -- Readme.md
git reset --hard [HEAD]


git reset HEAD Readme.md

Branching & Merging
• What is a commit?

• An object that points to trees/blobs in the .git directory

• addressed by a SHA1 hash (ad9e3b)

• contains info about author/commiter

• also contains pointers to “parent commits”
ad9e3b

Branching & Merging
• What is a branch?
• A pointer to a commit

• logically, a separate concern in development

• What is HEAD?
• A pointer to a branch
ad9e3b master HEAD
• Usually represents whats in the WT *now*

Branching & Merging
git commit -m “new feature”

ad9e3b master HEAD

Branching & Merging
git commit -m “new feature”

ad9e3b

c88da7 master HEAD

Branching & Merging
git branch issue8

ad9e3b

master HEAD

c88da7
issue8

New branch for a separate logical concern

Branching & Merging
git checkout issue8

ad9e3b

master

c88da7
issue8 HEAD

Checkout actually changes the files in your Working
Tree

Branching & Merging
# Make changes in editor, add changes to staging...
git commit -m “redoing data structure”

ad9e3b

master

c88da7

b9711f issue8 HEAD

New commits have pointers to parent(s)

Branching & Merging
git checkout master

ad9e3b

master HEAD

c88da7
b9711f issue8

Checkout actually changes the files in your Working
Tree

Branching & Merging
# Making more commits...

ad9e3b

c88da7 b9711f issue8

f327e3 master HEAD

Branching & Merging
# Now we need to get that fix for issue8 into master
git merge issue8

ad9e3b


f327e3 master HEAD

Branching & Merging
# Now we need to get that fix for issue8 into master
git merge issue8
ad9e3b


f327e3 This is known as a “merge commit”

a77106 master HEAD

Sharing Code with
Remotes
• How do we share code with others?

• git has stored URLs with aliases called “remotes”

• a few operations to move code from your local repository
to and from a remote

• you get local copies of remote branches in your repo

• *branch related operations happen locally

Remotes
• By default, you always get one remote
when you clone, it is called “origin”

• You can add more remotes using:
git remote add github git@github.com:aoberoi/testproj.git

This URL can be ssh:// (most common),
http://, https://, git://, or even file:///

Using Remotes
f327e3 master HEAD

Using Remotes
origin/master HEAD

f327e3

master HEAD

Now what if someone else adds commits to origin?

Using Remotes
master HEAD

f327e3

3602ea origin/master HEAD

This new commit only exists on the server...
git fetch origin

Using Remotes
master HEAD

f327e3


Now we have a local copy.
How do we continue working where the latest
from the server left off?

Using Remotes
master HEAD

f327e3


How do we continue working where the latest
from the server left off?
git merge origin/master

Using Remotes
f327e3 master HEAD


git merge origin/master

Fast-forward merge: my commit is in the history of
what is to be merged in

Using Remotes
f327e3 master HEAD


Pull is a shortcut:
git pull = git fetch + git merge
No need to specify the argument to merge if you are
on a “tracking branch”

Creating a Tracking
Branch

• If theres a new branch available on the
server and you want to participate in
developing on that “logical concern”
git checkout -t origin/next-big-thing

You are not checking out a remote
branch,
you are creating a new one

Pushing Changes

• Pushing can only be fast-forward commits,
this prevents you from abandoning
someone else’s changes
git push origin master

Inspection and History

• git log --pretty=oneline --graph

• git diff [--cached]

• git status

• git remote show

Other Neat Tricks
• git add -u

• git stash

• git push -u origin master

• git push origin :badfeature

• git log feature ^master

• git add -i

Gotchas

• Binary files? Images? Videos? Databases?

• Detached HEAD

• non fast-forward

• git rm / git mv

master is always
deployable
• Good general convention

• Keep actual development on ‘topic’
branches

• When topic is complete and code is
tested → merge (or pull request)
master

issue-8

Local Development
• Common pieces to share:

• unit tests

• graphics

• utility scripts

• Keep your own preferences on your local
machine and don’t commit them

.gitignore

• A file with filename patterns that you
don’t want to become part of your index
(nor your commits)

• See samples for all types of platforms:
https://github.com/github/gitignore/

Mark versions with
Tags
• Tags are like “unmovable” branches

• This makes it a good bookmark to keep
track of code that was released

• “I need to patch a bug that my customer sees, but what
code did I deploy?”

Github Pull-Requests
• You don’t always have access to push if
you are contributing to open source, send a
pull-request

• Pull-requests work from branch to branch

• use this for collaborative development

• code review

• http://www.confreaks.com/videos/706-

Github Forks

• Just a “clone” that you initialize on a
remote server, instead of on your machine

• Holds a little bit of history for the project
so you can track relationships in a
“network”

IDE and GUI Tools
Eclipse Egit

IDE and GUI Tools
• Platform Specific Tools

• Tower for Mac

• TortoiseGit for Windows

• Cross Platform

• gitk

Feeling more “at home”

• Bash Completion

• Merge Tool

• Commit Message Editor

• Aliases

Left as an exercise for
the readers
• cherry-picking
• “rewriting” history
• git-svn
• git modules
• environment variables and $GIT_DIR
• Treeishes by ‘x’spec
• Writing your own git hooks

Resources
• Git Cheatsheet (visual)
http://ndpsoftware.com/git-cheatsheet.html
• Github Help
http://help.github.com/git-cheat-sheets/
• Pro Git
http://progit.org/book/
• Git Community Book
http://book.git-scm.com/
• Google Tech Talk with Linus Torvalds

Erasing any
Preconceived Notions
• If you came from svn, you have a separate
understanding of version control
• commits happen locally (actually almost
everything happens locally)
• version numbers are not monotonically
increasing
• branches are not global (pollution of
namespace?)
• merging is (relatively) cheap, can be done

Why distributed over
centralized?
• Offline development
• Easy to do experimental work
• ... code review
• ... other workflowy specific purposes
(flexibility)
• “commit access” politics are avoided
• backups

Gitting It Under (Version) Control

Recommended

More Related Content

What's hot (20)

Viewers also liked (7)

Similar to Gitting It Under (Version) Control (20)

Recently uploaded (20)

Gitting It Under (Version) Control