Managing Files with GIT

Akshay Mathur

@akshaymathu 2

Ground Rules• Post on FB and Twitter now• Disturb Everyone during the

session– Not by phone rings– Not by local talks– By more information and questions

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Let’s Know Each Other

• Who does not code?• How do you store files?• Have you used VCS?– Which one?– What do you store?– Repository size?– What happens when you are not on network?

• Why are you attending?

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Akshay Mathur

• Founding Team Member of– ShopSocially (Enabling “social” for retailers)– AirTight Neworks (Global leader of WIPS)

• 15+ years in IT industry– Currently Principal Architect at ShopSocially– Mostly worked with Startups• From Conceptualization to Stabilization• At different functions i.e. development, testing, release• With multiple technologies

What is the issue

What if I don’t care?

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Keeping Track of Changes

• Hope you get it right first time• Hope you can remember the changes

• You will actually end up rewriting

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Organizing Backups

• Save the files/directories appending some context (usually dates)– Totally ad-hoc– Only the owner knows where is what– Hard to pick a version to go back to– Prone to error– No tools to help

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Sharing Work

• When many people need to work on same file– Work sequentially– Overwrite other’s changes– Keep track via emails

The Solution

Version Control System (VCS)

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How VCS Help?

• Keeps track of changes– Tells who change what and when

• Merges changes done by different people– Detects and alerts if same thing is changed by

different people• Allows comparing two versions– Shows how information has grown

• Allows going back to previous version

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VCS Terminology

• Repository– Place where VCS stores files and its metadata

• Sandbox– Place where files are available for editing

• Checkout– Process of getting files from repository to sandbox

• Commit– Process of putting files from sandbox to repository

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Storage System

• Non-intrusive– Everything is stored in

different folders/files• Compact– Incremental changes are

stored– Different storage techniques• RCS, BerkleyDB etc.

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Versioning Scheme

• File Versioning– Version number of only changed file is changed

• Repository Versioning– Version number of entire repository changes every

time• Version numbers can be– A serial number– Hash of the content1.1 1.2 1.3 1.4 1.5

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How VCS work

Managing Concurrency Optimistically

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Types of VCS

Where is the repository?

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Centralized

• CVS, SVN etc.• Repository at only one central location– Sandbox on every working machine

• Network is needed for every operation– Can not work offline

• The repository has to be protected and backed up– Work stops if repository goes down

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Centralized VCS

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Centralized VCS Operations

Repository

Server Client

Sandbox

Checkout

Commit

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Distributed

• Mercurial, Bitkeeper etc• Repository on every machine– Sandbox and repository are always together

• Network is needed only for repository sync– Can work offline

• Backups are trivial• Election of central repository by convention

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Distributed VCS

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Distributed VCS Operations

Repository

Remote Local

Sandbox

Pull

Push

Sandbox

Repository

Commit Checkout

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Working with GIT

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GIT

• Free• Open Source• Created by Linus Torvalds (Mr. Linux)• First used for Linux Kernel

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General Info

• Distributed– All repositories hold same data/info

• Compact– Low footprint– Compact Repository

• Fast– Quick operations– Low Data Transfer

• Feature rich yet simple• Intelligent

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Hands on Practice

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Creating Repository

• Init– Initialize a new repository on local machine• Creates a .git directory with subdirectories for objects,

refs/heads, refs/tags, and template files• An initial HEAD file that references the HEAD of the

master branch is also created

git init <repository_name>

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Adding New File

• Add– Adds a new file into the list of tracked files– A list of files (or wildcard) is accepted– Commit is not automatic

git add <file_1> <file_2>git add <file_*>

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Editing the File

• No restriction from GIT• Use your favorite editor– Text files• Vim, Notepad, Textpad, Eclipse, Visual Studio,

Dreamviewer etc.

– Binary Files• Word, Excel, Powerpoint, Photoshop etc.

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Removing Files

• Rm– Removes file from the sandbox– Remember to commit the change

git rm <file_name>

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From Repository to Sandbox

• Checkout– Gets file(s) from repository to sandbox– Local changes of the files go away

git checkout <file_name>

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Switching to Old Version

• Checkout– Gets file(s) from repository to sandbox• Commit ID of old version needs to be provided

– Sandbox gets detached and does not allow commits

– Command fails if local changes are there in the file

git checkout <commitID>

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Checking Current State

• Status– Displays information about current state of sandbox

• Branch name• List of added, removed, modified and conflicted tracked

files• List of untracked files• Ignores files listed in .gitignore

git status

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.gitignore

• A gitignore file specifies intentionally untracked files that git should ignore– Files already tracked by git are not affected

• Each line in a gitignore file specifies a pattern• Wildcard can be used

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Reviewing Changes

• Diff– Shows difference between working copy of a file and the

copy in the repository

git diff• Difftool– Allows to use an external tool for viewing diff

git difftool –y –t xxdiff• Log– Lists all commit logs

git log

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Saving into Repository

• Commit– Stores current content of tracked files from

sandbox into repository• A log message is required• All files can be committed with –a option• Selected files can be committed by providing list of files

git commit –am “<commit message>”git commit –m “<commit message>” <file1>

<file2>

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Commit Object

• Commit creates a commit object with the current state of repository– Author info and timestamp is recorded– A new checkpoint is created– New version number (commit ID) is assigned to

the checkpoint• Commit ID is hash of the content in the commit

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Marking a State of Repository

• Happens automatically with every commit• Name of the state, the commit ID, is tough to

remember– A simple name can be assigned

git tag <tag_name>git tag <tag_name> <commitID>

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Handling Emergencies

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Saving Local Changes

• Stash– Saves all local changes of sandbox– Sandbox goes clean for coding and pushing a

hotfix– Multiple stash can be created

git stash

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Applying Saved Changes

• Stash apply– Applies stashed changes back to the sandbox– You can choose from multiple stashes

git stash apply

Sharing the Work

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Distributed VCS Operations

Repository

Remote Local

Sandbox

Pull

Push

Sandbox

Repository

Commit Checkout

Clone

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Getting Repository

• Clone– Clones an existing remote repository, on local

machine, into a newly created directory• Creates remote-tracking branches for each branch in

the cloned repository• Checks out an initial branch into sandbox• Default name of remote repository is ‘origin’

git clone <path_to_repository>

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Getting Changes

• Pull– Downloads objects and refs from remote

repository– Merges with local repository– Commits automatically

git pullgit pull origin master

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Sending Changes

• Push– Update remote repository with changes in local

repository• Use --tags option for pushing tags• Use –u option to push a new branch

– Uncommitted changes are not updated

git push origin master

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Diverging Streams

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Why Diverging

• For parallel development– A feature requiring long development time

• For experimenting new stuff– Something we are not sure of

• Custom development– For multiple clients from same codebase

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Creating a Branch

• Branch– Creates a new code stream reference in local

repository from specified point• Checkout– Checkout with –b option also creates a new

branch• Latest checkpoint is used for branching by

default• Any older commit ID can be specified

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Branching

git branch <branch-name>git checkout –b <branch_name>

git branch <branch-name> <start_point>

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Branch Facts

• A branch named ‘master’ is always present in the repository

• Name of a branch refers to a moving checkpoint that is the latest commit on the branch– Branch name can be used in place of commit ID in

any command

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Switching Branches

• Checkout– Gets file(s) from repository to sandbox• Branch name needs to be provided

– Command fails if local changes are there in the file that are going to be overwritten• Otherwise changed files remain there as is in sandbox

git checkout <branch_name>

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Folding Back

• Merge– Merges a branch into current branch– Automatically commits, if no conflict– Runs in local repository• Requires push to update changes to remote

git merge <other_branch_name>

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Merging

git merge <other_branch_name>

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Conflicts

• If, at two places, changes are made in same portion of a file– GIT is not able to understand what to keep– Puts both changes in the file• Boundaries are marked in the file• File is marked as conflicted

– Authors need to collaborate and fix• Remember to commit after done

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Moving Branch Point

• Rebase– Forward-port local commits to the updated

upstream head• All local commits in the current branch are saved to a

temporary area• The current branch is reset to upstream• The saved commits are then re-applied to the current

branch, one by one, in order• Rebase stops in the middle in case of conflicts• Rebase can be continued after resolving conflicts

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Rebase

git rebase <upstream_branch_name>

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Best Practices

• Communicate with peers• Write good commit log• Never directly modify files repository directory• Never share files using external means e.g.

email, ftp, ssh etc.– Get the difference as needed

• Do not commit generated files

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Branching Best Practices

• Merge a branch only into its upstream• Keep ‘master’ untouched for hot fixes• Have a branch (say ‘develop’) for out of

‘master’ for system and regression testing• Create feature branches out of ‘develop’

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Working with GUI

• Gui– Launches a Graphical User Interface (GUI) for GIT– Common operations can be performed

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Thanks

@akshaymathu