git for cowards

Tim Duckett 2011

Git for cowards

• I’m a coward - originally an electronics engineer - now freelance: iOS, Ruby, Rails etc - associate lecturer at Sheffield Hallam University - tim@timduckett.co.uk / @timd / adoptioncurve.net

• This is Git - Source code management - Collaboration on shared code - Backup of virtually anything binary

Tim Duckett 2011

What is source control?

• “the management of changes to documents, programs, and other information stored as computer files”

• Also a means of securely storing documents, source code etc

• Also a means of managing changes made by a team of people

Tim Duckett 2011

Why would you use Git?

• Source code management • Collaboration on shared code • Backup of virtually anything binary • It’s social!

Tim Duckett 2011

Git

• A distributed version control system • Originally developed by Linus Torvalds for Linux

kernel development • Key features

- Fast! - Each working directory is a fully-fledged repository - Not dependent on a central server or network access - Open source, and free

• Extensively used in the web and open source community

• Making inroads into corporate life

Tim Duckett 2011

Available for...

• Windows - http://msysgit.googlecode.com/files/Git-1.7.4-preview20110204.exe

• Mac - http://git-osx-installer.googlecode.com/files/git-1.7.4.1-x86_64-leopard.dmg

• Linux: - apt-get install git-core

Tim Duckett 2011

Basic Git concepts

• Places a file can be: - the working directory

the location where you actually work with the files

- the index a “staging area” for files that will be committed to the repository

- the local repository the local database containing all the files in the project that have been committed from the index

- the remote repository a copy of the local repository on a remote system (e.g. Github.com)

Tim Duckett 2011

Basic Git concepts

Tim Duckett 2011

Statuses a file can have

• Untracked - Only in the working directory

• Tracked - Has been added to the index

• Staged - Has been committed to the

repository

• Ignored - Git won’t do anything with it - Has to be listed in

the .gitignore file

Tim Duckett 2011

The working directory

• The place where the work takes place - this is the “normal” working directory,

and is not under Git control - files can be created, modified, and

deleted at will by you - files created and amended in here will

not be touched by Git until they are staged - Git can work out which files haven’t

been staged, but it won’t do it for you

Tim Duckett 2011

The index

• Files which are awaiting commitment to the repository - Only files which are staged in the index

will be committed - Files have to be explicitly copied to the

index by the git add command - Once a file is in the index, it’s

independent from the copy in the working directory

- Changes to the file in the working directory won’t affect the copy in the index

Tim Duckett 2011

The repository

• The database of files which comprise the Git project - Files are added to the repository by

committing the index - Files in the index are copied into the

respository

Tim Duckett 2011

The remote repository

• A copy of the local repository which is stored elsewhere - Can be on another system, or a hosted

service like Github - Commits are pushed from local to

remote - You need to explicitly configure a remote

repository - by default, everything is local

• Git can work completely offline - you don’t necessarily need a remote

repository - you don’t need a network connection

Tim Duckett 2011

(Very) basic Git workflow

Tim Duckett 2011

Git objects - the blob

• Binary Large Object • The contents of a file • Git doesn’t care what is in the file • Each blob has a SHA-1 hash calculated on it

- the SHA1 hash is a 40-digit checksum of the file - you can refer to the hash by the first 4 or 5 digitis

Tim Duckett 2011

Git objects - the tree

• a directory of blobs and commits - also known by a SHA1 hash

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Git objects - the commit

• A pointer to a single tree • Acts as a “snapshot” of the state of

the project. • Contains information about

- the tree it points to - any parent commits it has - the author - the committer - a commit message

Tim Duckett 2011

Git objects - the tag

• A fixed and human-readablelabel for a commit

• Contains - a tag name - the name of the tagger - a message (often the PGP signature

of the tagger)

Tim Duckett 2011

Commits are snapshots over time

Tim Duckett 2011

Commits are snapshots over time- Git “fills-in” the blanks by referring to previous files if they’re

unchanged...

Tim Duckett 2011

Commits are snapshots over time- So each commit is a complete picture of the state of the project

Tim Duckett 2011

Generic Git workflow

Tim Duckett 2011

Initialising the repository

git init

• Creates the repository • “Adopts” the directory as a Git project

Initialized empty repository in /dir/.git/

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Setting up the config

• Git needs to know your name and email address to properly credit your commits

• Set globally using the git config command

git config --global user.name “TimD” git config --global user.email “tim@adoptioncurve.net”

• You can override on a per-repo basis by dropping the --global switch

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Checking files out of the remote repository

• Cloning an existing repo: git clone [repo]

• Adding a remote repo: git remote add [shortname] [url]

• Fetching from a remote: git fetch [remote name]

• Cloning a remote repo: git clone [repo] [branchname]

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Adding files to the index

git add [filename]

or git add [filename] [filename] ...

or git add .

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Check the status of files in the index

•git status

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Adding files to the index

•git add .

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Committing files to the repository

•git commit -am “[message]”

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Pushing files to the remote repository

•git push [repo name] [branch name]

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• Each commit is a snapshot of the project

Branching

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Branching

• A branch is a lightweight movable pointer to a particular commit

• The default branch is called master

• Branching is very cheap... • Branch early, and branch often!

Tim Duckett 2011

Branching

• As you make commits, the branch pointer moves forward automatically

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Branching

• Simple scenario: - You’re working on a project which is going to have a beta

release.

- You make 3 commits, tag the 3rd commit as “beta”, and then deploy:

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Branching

• Simple scenario, continued: - Then after releasing, you create a new branch called “v1.0”:

git branch v1.0

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Branching

• Simple scenario, continued: - Switch to it, start working and make a commit:

- git checkout v1.0

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• Simple scenario, continued: - The master branch stays where it is:

- and the v1.0 branch moves ahead independently

Branching

Tim Duckett 2011

Branching

• Simple scenario, continued: - Git keeps track of your current branch and commit with a label

called “HEAD”

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Branching

• Simple scenario, continued: - You now need to make a tweak to the master branch that’s

been deployed:

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Branching

• Simple scenario, continued: - You switch back to the master branch:

- git checkout master

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• Simple scenario, continued: - Make the fix - commit it - then deploy:

- git add . - git commit -am “Fixed problem”

Branching

Tim Duckett 2011

• Simple scenario, continued: - Then switch back to the v1.0 branch and carry on working

with it:

- git checkout v1.0

Branching

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• Simple scenario, continued: - Then switch back to the v1.0 branch and carry on working

with it:

- git add . - git commit -am “More development”

Branching

Tim Duckett 2011

• Key points: - Changes in the branches are independent - Switching from v1.0 to master ‘resets’ the

working directory

- new files you’ve added to v1.0will ‘disappear’

- files that are in master but not in v1.0 will ‘reappear’ - you can switch between branches at will - you can create a new branch from any existing branch

Branching

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OMFG something went wrong!!!

• Don’t panic! • You can rollback changes with git reset

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OMFG something went wrong!!!

• git reset --hard C3

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• Eventually, you’ll want to bring changes in your working branch back into the the master

Merging

Tim Duckett 2011

Merging

• You merge v1.0 into master

- git checkout master - git merge v1.0

Tim Duckett 2011

A much better workflow

Time

release branches masterdevelop hotfixesfeature

branches

Feature for future

release

Tag 1.0

Major feature for

next release

From this point on, “next release”

means the release after 1.0

Severe bug fixed for

production: hotfix 0.2

Bugfixes from rel. branch

may be continuously merged back into develop

Tag 0.1

Tag 0.2

Incorporate bugfix in develop

Only bugfixes!

Start of release

branch for 1.0

Author: Vincent Driessen Original blog post: http://nvie.com/archives/323 License: Creative Commons

- extends core git with custom workflows - http://nvie.com/posts/a-successful-git-

branching-model/

- https://github.com/nvie/gitflow

Tim Duckett 2011

Merging

• Git will show conflicts between files

everything abovethe line is from HEAD

everything belowthe line is from branch2

this doesn’t clash

Tim Duckett 2011

Merging

• You need to manually select the right modifications, then commit the result

everything abovethe line is from HEAD

everything belowthe line is from branch2

this doesn’t clash

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• github.com - basic accounts are free - Micro accounts are $7pm

(gives you 5 privaterepositories)

- excellent showcase foryour code!

Git hosting at Github.com

Tim Duckett 2011

Git references

• Git Crash Course - http://gitref.org/index.html

• The Git Community Book - http://book.git-scm.com/

• Zack Rusin’s Cheat Sheet - http://zrusin.blogspot.com/2007/09/git-cheat-sheet.html

• Git for Web Designers - http://www.webdesignerdepot.com/2009/03/intro-to-git-for-web-designers/