Up and Running with GIT

Atish Goswami

PHP Developer at SANIsoft

What is Git

• Keeps track of your changes Especially text changes Version 1, Version 2, Version 3

• Version Control System (VCS)

• Source Code Management (SCM)

Examples of version control(non-source code)

• File naming (Budget_v4.xls, Logo_v2.gif)

• Microsoft Word's Track Change

• Adobe Photoshop's History

• Wikis

• Undo: control+z(windows), command+z(Mac)

History

• Source Code Control System (SCCS) 1972, closed source, free with Unix

• Revision Control System (RCS) 1982, open source

• Concurrent Versions System (CVS) 1986-1990, open source

• Apache Subversion (SVN) 2000, open source

Turn of Events

• BitKeeper SCM 2000, closed source, proprietary Distributed version control “community version” was free Used for source code of the linux kernel for

2002-2005 Controversial to use proprietary SCM for an

open source project April 2005: the “community version” not free

anymore

Git was born

• April 2005

• Created by Linus Torvalds

• Replacement for BitKeeper to manage Linux kernel source code

What were the features

• Distributed version control

• Open source and free software

• Compatible with Unix-like systems (Linux, Mac Os X, and Solaris) and Windows

• Faster than other SCMs (100x is some cases)

• Better safeguards against data corruption

Git is a hit

• Explosion in popularity

• No official statistics

• Github launched in 2008 to host Git repositories 2009: over 50,000 repos, over 100,000 users 2011: over 2 million repos, over 1 million users

Centralized Version Control

• Popular version controls of the past like RCS, CVS, SVN and SCSS

• All of them use central code repository model One central place where you store the master copy of

the your code Check out a copy of the code from the master repo Work with the code, make changes and submit back to

the master/central repository Other users can also work from that repo, make and

submit there changes Users stay up to date with central code repository by

pulling down and update any changes

Distributed Version Control

• Different users (or teams of users) maintain their own repos, instead if working form a central repository

• Changes are stored as “changes sets” or “patches” Tracks changes, not versions Different from CVS and SVN, which track versions Change sets can be exchanged between repositories

• “merge in change sets” or “apply patches”

Distributed Version Control

• No single master repository; just many working copies Each with their own combination of change

sets• Imagine changes to document as sets A, B, C, D, E, F

Repo 1: A, B, C, D, E, F Repo 2: A, B, C, D Repo 3: A, B, C, E Repo 4: A. B, E, F

Advantages of DVS

• No need to communicate with a central server

Faster No network access required No single failure point

• Encourages participation and “forking” of projects Developers can work independently Submit changes sets for inclusions or rejection

Who should use Git ?

• Anyone wanting to track edits

Reviews a history log of changes made view differences between versions Retrieve old versions

• Anyone needing to share changes with collaborators

• Anyone not afraid of command-line tools

Programmers and Developers

HTML, CSS, JavaScript

PHP, Ruby, Ruby on Rails, Perl, Python, ASP Java, C, C++, C#, Objection-C ActionScript, CoffeeScript, Haskell, Scala,

Shell scripts• Not as Useful for tracking non-text files

Images, movies, music, fonts Word processing files, spreadsheets, PDFs

Git Installation

Where to get Git

Mac

• http://git-scm/download/mac Windows

• http://git-scm/download/windows Linux

• http://git-scm/download/linux

Configuration

System

• /etc/gitconfig• Program Files\Git\etc\gitconfig

User• ~/.gitconfig• $HOME\.gitconfig

Project• my_project/.git/config

Commands to Configuration

System

• git config --system User

• git config --global Project

• git config

Initializing a repository

git init

Process to follow

Make changes

Add the changes • git add [filename/directory]

Commit changes to the repository with message• git commit -m [commit message]

Writing Commit Messages

Commit message best practices

• Short single-line summary (less than 50 characters)

• Optionally followed by a blank line and more complete description

• Keep each lines to less than 72 characters• Write commit messages in preset tense, not

past tense “fix bug” or “fixes bug,” not “fixed bug”

Writing Commit Messages

Commit message best practices

• Bullet points are usually asterisks or hyphens

• Can add “ticket tracking number” form bugs or support requests

• Can develop shorthand for your organization “[css, js]” “bugfix:” “#38456-”

Writing Commit Messages

Commit message best practices

• Be clear and descriptiveBad: “fix typo”Good: “Add missing > in project section

of HTML”Bad: “Update login code”Good: “Changed user authentication to

use Blowfish”Bad: “Updates member report, we should

discuss if this is right next week”

One Good Example

T23094 – Fixes bug in admin logout

When an admin logged out of the admin area, they could not log in to the member area because their session[:userid] was still set to the admin ID. This patch fixes the bug by setting session[:userid] to null when user logs of the any area.

Viewing Commit Logs

git log

commit 330ec85cb900530edbfa0ac73519f29b4150e436Author: Atish Goswami <atishgoswami@gmail.com>

Date: Wed Apr 23 02:15:47 2014 +0530

Fix login page html for responsive view

Advanced Commit Viewing

git log -n [limit]

git log --since=[yyyy-mm-dd]

git log --until=[yyyy-mm-dd]

git log --author=”[name]”

git log --grep=”[pattern]”

Git Concepts and architecture

Two Tree architecture

Three Tree architecture

Three Tree architecture

Git Workflow

Commit Hash Values (SHA-1)

Git generates a checksum for each change set

• checksum algorithms convert data into a simple number

• same data always equals same checksum Data integrity is fundamental

• changing data would change checksum Git uses SHA-1 algorithm to create checksums

• 40-character hexdecimal string (0-9, a-f)• Example:

2da5bdb0d516f69c69f35bde21312ab89cbc3357

Referring to Commits

The HEAD Pointer

pointer to “tip” of current branch in repository

last state of repository, what was last checked out

points to parent of the next commit• where writing commits takes place

Making changes

git add [filename/directory]

git status git diff git diff --staged git rm [filename/directory] git mv [filename-old]<space>[filename-new] git commit git commit -am

Undoing changes

git checkout – [filename]

git reset HEAD [filename] git commit –amend -m “[Message]” git checkout [commit hash] – [filename.txt] git revert [commit hash] git clean -n → Trial run git clean -f → actual action

git reset

--soft

• Does not change staging index or working directory

• git reset –soft [commit hash] --mixed (default)

• changes staging index to match repository• does not change working directory• git reset –mixed [commit hash]

--hard• Changes staging index and working

directory to match repository• git reset –hard [commit hash]

Ignoring Files

Using .gitignore file in the root of the project directory

Project/.gitignore Very basic regular expression

• * ? [aeiou] [0-9] Negate expression with !

• *.php• !index.php

Ignore all files in a directory with trailing slash• asset/video/

Comment lines begin with #, blank lines are skipped

What to ignore

complied source code

packages and compressed files logs and databases operating system generated files user-uploaded assets (images, PDFs, videos) Helpful Links

• https://help.github.com/articles/ignoring-files• https://github.com/github/gitignore

Globally Ignore Files

Ignore files in all repositories

Settings not tracked in repository user-specific instead of repository-specific

git config –global core.excludesfile ~/.gitignore_global

Ignoring Tracked Files

Want it in your working directory

But don't want git track it any more

git rm –cached [filename]

Tracking Empty Directories

• Git doesnot track directories

• Git track files only and keep track of any directory required to track that file

• Add empty or .gitkeep to empty directory

Navigating to a Commit

• Tree-ish

Full SHA-1 hash Short SHA-1 hash

• At least 4 characters• Umambiguous (8-10 characters)

HEAD pointer Branch reference, tag reference ancestry

Ancestory

• Parent commit

HEAD^, acf87504^, master^ HEAD~1, HEAD~

• Grandparent commit

HEAD^^, acf87504^^, master^^ HEAD~2

• HEAD^^^, acf87504^^^, master^^^

• HEAD~3

Tree-ish

• git help ls-tree

• git ls-tree HEAD

• git ls-tree master

• git ls-tree master [directory]

• git ls-tree master^ [directory]

• git ls-tree [object hash]

Getting More From Git Log

• git log --online

• git log –online -[no of commits to show]

• git log –since=”[yyyy-mm-dd]”

• git log –until=”[yyyy-mm-dd]”

• git log –before=”[yyyy-mm-dd]”

• git log –since=”2 weeks ago” --until=”3 days ago”

• git log –since=”2.weeks” --until=”3.days”

Getting More From Git Log

• git log –author=”Atish”

• git log –grep=”temp”

• git log [sha hash from]..[sha hash to] –oneline

• git log [sha hash from]..[leave empty to point HEAD] [filename]

• git log -p -> Git Patch option

• git log -p c4b913e.. index.html

• git log –stat –summary

• git log –format=[oneline|short|medium|full|fuller|email|raw]

• git log –graph

• git log –online –graph –all --decorate

Getting More From Git Log

• git show [sha value]

• git show –format=online HEAD

• git show –format=online HEAD^

• git show –format=online HEAD~2

• git show –format=online HEAD~3

Comparing Commits

• git diff [sha value]

• git diff [sha value]..[sha value till]

• git diff [sha value] filename

• git diff [sha value]..[sha value till] filename

• git diff –stat –summary 1506576..HEAD

• git diff –ignore-space-change or -b

• git diff –ignore-all-change or -w

Git Branching

• Branches are cheap

Try new ideas Isolate features or sections of work

• One working directory

• Fast context switching

Git Branching Commands

• Show branches

git branch• Create branch

git branch [branch name to create]• Switch to a branch

git checkout [branch name]• Create and Switch in a single step

git checkout -b [new branch name]• Branch diff

git diff [branchname]..[other branch name] git diff –color-words new_feature..shorten_title

• Does branch has all changes or not

git branch –merged• Rename a branch

git branch -m [old name] [new name]• Branch Delete

git branch -d [branch to delete]

Merging Branches

• Merge a branch

git merge [branchname to merge]• Fast Forward Merge

• No Fast Forward

git merge –no-ff [branch name]• Only Fast Forward

git merge –ff-only [branch name]

Resolving Conflicts

• Abort merge

git merge --abort• Resolve the conflicts manually

Open files and see for changes to keep git add [files that had merge conflict] git commit → show a auto commit message

• Use a merge tool

Reduce Merge Conflicts

• Keep lines short

• Keep commits small and focused

• Beware stray edits to whitespace

Spaces, tabs, line returns• Merge often

• Track changes to master

Stashing Changes

• It is not like commiting

• Helps keep your experimental files save

• Does add anything to the log history

• Its like a temporary storage space

Stashing Changes

• Adding/Saving a stash change

– git stash save “[message]”• Listing Stashes

– git stash list – stash@{n}: On [branchname]: [message]

• View Stashes Changes

git stash show stash@{n} → diff stat

git stash show -p stash@{n} → patch stat

Stashing Changes

• Applying a stashed change

→ git stash apply [stash@{2}]

→ git stash pop [stash@{2}]

• Deleting Stashed Items

→ git stash drop [stash@{2}]

→ git stash clear

Remotes

Remote Repos

• Viewing remotes

– git remote– git remote -v

• Adding remote to local repo

– git remote [alias] [url]• Removing remote from repo

– git remote rm origin

Remote Repos

• Viewing remotes branches

– git remote -r– git remote -a

• Copying/Cloning Remote Repos

– git clone [url] [folder to create]• Removing remote from repo

– git remote rm origin

Remote Repos

• Pushing Changes

– git push [remote] [branchname]• Syncing Remote with Local

– git fetch [remote]

Good Practices

• Fetch before you work

• Fetch before you push

• Fetch often

Merging Fetched Changes

• Viewing/Comparing Remote with Local

– git diff [remote]/[branchname]..[branchname]

• Merging Changes Into Local

– git merge [remote]/[branchname]• git pull = git fetch + git merge

Working with remote branches

• Checkout a remote branch

– git branch [remote branch name]• Delete a remote branch

– git push [remote] :[remote branch name]– git push origin –delete non_tracking