Git tech talk

Git : Awesome Distributed Version Control SystemGit : Awesome Distributed Version Control System
Presenter : Raza.Z.Sayed

2
History
● Linux kernel project
● Patch emailing system
● Bitkeeper from 2002 to 2005.
● Why the name Git ?
- “I’m an egotistical bastard, and I name all my
projects after myself.First Linux, now git.” – Linus
Torvalds
● First commit message : 'initial version of “git”,the
information manager from hell'-Linus 4/7/05

3
Basic Concepts
●
Git is not like SVN (Subversion) and is fundamentally different . Git tracks
content not changes or deltas
●
Its like a filesystem. Its a collection of tools that implement tree history storage
and directory content management system.
● Non linear development, distributed development and efficient
- Ruby on Rails Git repository is around 13 Mb and Subversion repository of
the same is around 115 Mb !
● Not a binary but a toolkit design in spirit of unix philosophy (Write programs
that do one thing and do it well)

4
Basic Concepts
●
Git Object Database → .git directory
●
Git Object Types → stored in .git/objects
1. Blob
2. Tree
3. Commit
4. Tag
●
Git Data Model
1. Git Object Types
2. References (Branches and Remotes) → stored in .git/refs

5
Basic Git Workflow
● mkdir my_awesome_project
● cd my_awesome_project
● git init
● Create a file e.g. README.txt
● git status (Optional)
● git add README.txt (Add to staging)
● git commit -m “first commit”

6
Basic Git Workflow
● Make some changes to README.txt
● Create a new file e.g. hello.rb
● git status
● git add hello.rb README.txt or git add . or git add --all
● git commit -m “another commit”
● Make changes to hello.rb
● git commit -a -m “added foo method” (Wont add
untracked files to staging. git add them separately)

7
Different ways to add
● git add <list of files> (Add the list of files)
● git add --all (Add all files from the project.)
● git add . (Add all files from the project)
● git add *.txt (Add all txt files in current dir)
● git add “*.txt” (Add all txt files from the project)
● git add docs/*.txt (Add all txt files from docs dir)
● git add docs/ (Add all files from docs dir)

8
Viewing changes
● git diff (Show unstaged changes since last
commit)
● git diff --staged (show staged changes since
last commit)
● git log (show project history)

9
Undo unstaged changes
● git checkout . (Blow away all changes since
last commit)
● git checkout <list of files> (Blow away changes
to specified files since last commit)

10
Unstage changes
● git reset HEAD (Unstage all staged files)
● git reset HEAD <list of files> (Unstage
particular files) e.g. git reset HEAD
README.txt or git reset HEAD README.txt
hello.rb

11
Undo commits
● git reset soft HEAD^ (Undo last commit and move changes
back to staging) or git reset soft HEAD~1
● git reset soft HEAD^^ (Undo last two commits and move
changes back to staging) or git reset soft HEAD~2
● git reset hard HEAD^ (Undo last commit and blow away all
changes) or git reset hard HEAD~1
● git reset hard HEAD^^^ (Undo last three commits and blow
away all changes) or git reset hard HEAD~3
● git commit --amend -m “New commit message” (Change
the last commit message)

12
Sharing and Collaborating
● Lots of different code hosting services to
choose from e.g. Unfuddle, Github, Bitbucket
etc. or setup your own server.
● Create a git repo on the server. This is called a
remote repository.
● Inside your project dir on your local machine :
git remote add <some arbit name for the
remote repo> <path of remote repo>

13
● git remote -v (show remote repositories
associated with the project)
● git push -u <remote repo name> <branch
name> e.g. git push -u origin master
● git pull (Pull changes from the remote repo)
● git remote rm <remote repo name> (Delete a
remote repo from the project)

14
● Types of git repo urls : https://.. (Read only or read
write depending upon permissions) , git://.. (Git read
only), git@.. (SSH read write)
● git clone <remote repo url> or git clone <remote repo
url> [local name]
● git clone does the following three things. 1) Downloads
the entire repo into a new directory 2) Adds origin
remote pointing it to clone url 3) checks out the master
branch i.e. sets local repo HEAD to point to the master
branch

15
Branching
● Need to work on a new feature or fix a bug that
will take time ?. Create a new branch to work on
it.
● git branch <branch name> (Creates the branch)
● git checkout <branch name> (Switch to the
branch)
● git checkout -b <branch name> (Shortcut to
create and switch to a branch in one step)

16
Basic Branching Workflow
● git checkout -b cool_feature
● echo “This is readme for the cool feature” >
README.txt
● git add README.txt
● git commit -m “first commit in cool_feature branch”
● git checkout master
● git merge cool_feature
● git branch -d cool_feature (Delete the branch as were
done with it)

17
Types of Branch Merge
● Fast Forward Merge
● Non Fast Forward Merge (Recursive Merge)
● Recursive Merge creates an extra commit
automatically called a “Merge commit”

18
Conflicts
● Can either arise during git push or while doing a
merge (merge conflict)
● git push conflict scenario. Do a git pull first to fix
● Two cases in which merge conflicts can arise. 1)
During merging a local branch 2) Doing a git pull
● git pull = git fetch+git merge. What is origin/master ?
● Resolving merge conflicts

19
Sharing local branches
●
A wants to create a new branch and share it.
git checkout -b awesome_new_feature
git push origin awesome_new_feature
●
B wants to collaborate on the new branch.
git pull
git checkout awesome_new_feature
●
Listing remote branches : git branch -r
●
Getting detailed information about remote branches : git remote show origin
●
Deleting remote branches.
git push origin :awesome_new_feature
git branch -d awesome_new_feature. If this does not work then,
git branch -D awesome_new_feature
●
Cleaning up local references to deleted remote branches : git remote prune origin

20
Tagging
● What are tags ?
● Listing all tags : git tag
● Creating a new tag : git tag -a v1.0 -m “version
1.0”
● Checkout code at a particular commit : git
checkout v1.0
● Sharing tags : git push --tags

21
Rebase
● What is a rebase and why its better than a merge ?
● Dont do git pull ! . Instead do a fetch + rebase.
● Remote branch rebase workflow
git fetch
git rebase
● Local branch rebase workflow. e.g. To rebase branch new_feature into master
git checkout new_feature
git rebase master
git checkout master
git merge new_feature

22
Ignoring Files
● Only for yourself
Put exclude patterns in .git/info/exclude file
● For everyone
Put exclude patterns in .gitignore file in the
project root directory
● Untracking files
git rm --cached <file name>

23
References
● Git Community Book - http://git-scm.com/book
● Git Branching -
http://pcottle.github.com/learnGitBranching/
● Git for computer scientists -
http://eagain.net/articles/git-for-computer-scientists/
● Visual Git Reference -
http://marklodato.github.com/visual-git-guide/index-

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