Advance Git

by scmGalaxy.com

About Me !

History

Source Code Control Systems (SCCS)

- 1972, Closed Source, free with Unix

Revision Control System (RCS)

- 1982, Open Source

Concurrent Version System (CVS)

- 1986-1990, open source

Apache Subversion (SVN)

- 2000, Open Source

BitKeeper SCM

- 2000, closed source, proprietry

- Distributed version control

- "community version" was free

- used for source code of the Linux Kernal from 2002-2005

- Controversial to use proprietary SCM for an open source project

- April - 2005 - The community version not free any more

Git is born

April 2005
Created by Linus Torvalds
Replacement for bitKeeper to manage Linux Kernal source code

Git is Popular

Distributed Version Control
Open source and free software
Compatible with Unix-like Systems (Linux, Mac OSX, and Solaris) and Windows
Faster than other SCMs (100x in some cases)

Git is a hit

Explosion in Popularity
No official statics
GitHub is launched in 2008 to host Git repositories

- 2009: over 50,000 repositories, over 100,000 users

- 2011: over 2 million repository's, over 1 million users

Programmers and Developers

HTML, CSS, JavaScript

- PHP, Ruby, Ruby on railes, Perl Python, ASP

- Java, C, C++, C#, Objective C

- Action Script, Coffee Script, Haskell, Scala, Shell Scripts

Not as useful for tracking non-text files

- Image, movies, music, fonts

- Word processing files, spreadsheets, PDFs

The Git Repository

.git directory

- Config - Repo private configuration file (.ini style)

- Description - Repo description

- Hooks/* - hooking scripts

- Objects/* - The object repository

- Refs/heads/* - branches (like "master")

- Refs/tags/* - tags

- Refs/remotes/* - tracking others

- Logs/* - logs

- Index - changes to commit

- HEAD - points to one of the branches (the "current branch", where commits go)

Objects

Every object has a SHA1 to uniquely identify it
Objects consist of 4 types:

- Blobs (the contents of a file)

- Trees (directories of blobs or other trees)

- Commits

A Tree
Plus zero or more parent commits

- Tags

An object (usually a commit)

A SHA-1 hash value is typically rendered as a hexadecimal number, 40 digits long.SHA-1 produces a 160-bit (20-byte) hash value

Configuring Git

System

- /etc/gitconfig

- Program file\git\etc\gotconfig

User

- ~/.gitconfig

- $HOME\.gitconfig

Project

- my_project/.git/config

Configuring Git ...

System

- git config --system

User

- git config --global

Project

- git config

Configuring Git ...

git config -- global user.name "rajesh kumar"
git config -- global user.email someon@nowehre.com
git config -- list

more .gitconfig
git config -- global core.editor "vim"
git config -- global color.ui true

Configuring Git...

git config -- list
git config -- global section.key
git config -- global section.subsection.key
git config -- global user.name "rajesh kumar"
git config -- global user.email
git config -- global core.editor "vim"
git config -- global color.ui true

git Config Priorities

Lowest /etc/gitconfig

~/.gitconfig

.git/config

git workflow

Working with local repos

-- git init

Creates a .git in the current dir

Adds all files (except .git)

Commits the changes (in this case initial commit)
Creates a branch named master
HEAD points at master

Working with Remote Repos

-- git clone

Creates a git repo from an existing repo
All remote branches are tracked
Remote HEAD branch checked out as your initial master branch as well

git workflow

Head

Pointer to "tip" of the current branch in repository
Last state of repository, what was last checked out
Points to parent next commit

SCM Operations

Bootstrap

Init

Checkout

Switch branch

Modify

Add, delete, rename

Commit

Information

Status

Diff

Log

Reference

- Tag

- Branch

Collaborate

- Clone

- Pull, fetch

- push

Git Help

git help (list of common commands)

git <command> -h

Manual page

man git <command>

git help <command>

git <command> --help

git add .

git add . only adds what is there, not what has been deleted (if tracked).

git add .

git add -A would take care of both steps...

Referring to commits

When we submit any changes to the repository,

Git generate a checksum for each change set

- Checksum algorithm convert data into a simple number

Data Integrity is fundamental
Git uses SHA-1 hash algorithm to create checksums

- Example: 1837f0b7056c64cef103210b07539b6313612ba3

Referring to commits

Commit Message best practices

Short single-line summary (less than 50 characters)
Optionally followed by a blank line and a more complete description
Keep each line to less than 72 characters
Write a commit messages in present tense, not past tense

Commit Message best practices

Bullets points are usually asterisks or hypens
Can add "ticket tracking numbers" from bugs or support requests
Can develop shorthand for your organization

-- "[css,js] "

-- "bugfix: "

-- "#24223 - "

Commit Message best practices

Be clear and descriptive

Bad: "Fix typo"
Good: "Add missing > in project section of HTML
Bad: "Update login code"
Good: "Change user authentication to use Blowfish"
Bad: "Updates member report, we should discuss if this is right next week"

git log

commit 1837f0b7056c64cef103210b07539b6313612ba3

Author: rajesh kumar <someon@nowehre.com>

Date: Thu Dec 6 01:16:03 2012 -0800

first commit

git log --oneline

git log --oneline --graph

git log --format=short == git shortlog

git log file1 file2 dir3

Show changes only for listed files or subdirs

git log

git log -n 1/2/3/0
git log --since=2012-05-05
git log --until=2012-04-23
git log --grep="init"

See the log pof remote repos
git fetch origin
git log origin/master
Eq. to
git log HEAD..origin/master

Head

Pointer to "tip" of the current branch in repository
Last state of repository, what was last checked out
Points to parent next commit

HEAD

HEAD Commands

git log HEAD

- shows all the commits reachable from the current HEAD

git show

- The git show command reports the changes introduced by the most recent commit:

git show HEAD~

git show HEAD~2
Behind The Scenes: Where Is The HEAD?

- The contents of the git HEAD variable is stored in a text file in the .git/HEAD:

cat .git/HEAD

- ref: refs/heads/master

That is telling us that we need to look at the file refs/heads/master in the .git directory to find out where HEAD points:

Undoing the changes

git checkout
git revert - Undo the commits with new commits.
git clean - removes untracked files from your working directory.
git reset - It modifies the index (the so-called "staging area") Or it changes which commit a branch head is currently pointing at.

git checkout

The git checkout command serves three distinct functions:

checking out files,
checking out commits, and
checking out branches.

git checkout

git checkout <commit> <file>

Check out a previous version of a file. This turns the <file> that resides in the working directory into an exact copy of the one from and adds it to the staging area.

git checkout

> git checkout <commit>

Update all files in the working directory to match the specified commit.

git checkout

> git checkout master

git revert

The git revert command undoes a committed snapshot. But, instead of removing the commit from the project history, it figures out how to undo the changes introduced by the commit and appends a new commit with the resulting content.

This prevents Git from losing history, which is important for the integrity of your revision history and for reliable collaboration.

git clean

> git clean -n

- Perform a "dry run" of git clean.

> git clean -f

- Remove untracked files from the current directory.

> git clean -df

- Remove untracked files and untracked directories from the current directory.

git reset

git revert is a "safe" way to undo changes, whereas git reset as the dangerous method. When you undo with git reset(and the commits are no longer referenced by any ref or the reflog), there is no way to retrieve the original copy- it is a permanent undo.

In Practice

It can be used to remove committed snapshots, although it's more often used to undo changes in the staging area and the working directory. In either case, it should only be used to undo local changes- you should never reset snapshots that have been shared with other developers.

git reset

> git reset <file>

Remove the specified file from the staging area, but leave the working directory unchanged. This unstages a file without overwriting any changes.

git reset

> git reset

Reset the staging area to match the most recent commit, but leave the working directory unchanged. This unstages all files without overwriting any changes, giving you the opportunity to re-build the staged snapshot from scratch.

git reset

> git reset --hard

Reset the staging area and the working directory to match the most recent commit. In addition to unstaging changes, the --hard flag tells Git to overwrite all changes in the working directory, too.

git reset A dangerous method

Three kinds of reset

soft

- Moves the head

- git reset --soft 34dghsd

Mixed

- Changes HEAD and Staging Index

- git reset --mixed eb45juh

Hard

- Reverts completely back to commit

- git reset --hard fg4533df

SOFT RESET

MIXED RESET (Default)

HARD Reset

Renaming the file

> git mv

> git commit -m"renaming file"

Deleting the file

git rm file1.txt

git commit -m "remove file1.txt"

git diff

git diff SHA1...SHA2
git diff HEAD~1..HEAD
git diff HEAD~1..
git diff branch1 branch2
git diff anotherbranch
git diff --staged

git branching

git checkout -b
git branch <branchname>
Find .git/refs - To knw the branches
Delete Branch

git branching

git checkout -b = git branch + git checkout

git merge

> git merge <branch>

Working with remote repository

Scenario 1 - Start from Local repository
Scenario 2 - Start from Remote repository
Scenario 3 - Mixed approach

Remotes Repository

git remote - List of remotes connections
git remove -v "
git remote add <alias> <url>
git remote rm <alias>
git remote rename <old-name> <new-name>

Start from Existing repository

git init
git remote add <name> url
git push

Start from Remote repository

git clone
git push
git pull (or git fetch + git merge)

Mixed approach

git init
git remote add <name> url
git pull (or git fetch + git merge)
git push

get fetch

git-fetch - Download objects and refs from another repository

Fetch before work
Fetch before you push
Fetch often

git fetch
git fecth origin

git pull

== git fetch + git merge

Pull Vs Clone

Clone: Get a working copy of the remote repository.
Pull: I am working on this, please get me the new changes that may be updated by others and merge it.