git

MOST OF THE THINGS ABOUT A TRENDING DVCS

ISURU WIMALASUNDERA

VERSION CONTROL

▸ version control , revision control & source control are referring to the same…

▸ version control systems are to manage the changes done on software programs, documents and any collection of information .

▸ Centralized version control systems (CVCS) and Distributed version (DVCS)

▸ CVCS - CVS , Subversion (SVN) , Perforce

DVCS …▸ Mercurial, Git and Bazaar

▸ Has a central repository But ….

▸ Do not rely on that central repo to store all the versions of a project.

▸ every developer “clones” a copy of the central repository.

▸ The “clone” copy has the full history and all meta-data of the original.

▸ “pull” to get new change, “push” to add new change.

ADVANTAGES & DISADVANTAGES OF DVCS

▸ pushing and pulling changes are fast , as it is not accessing a remote server but your own hard drive.

▸ offline commit of changes.

▸ can commit a set of changes without affecting others.

▸ Others can refer ones local repository and check changes.

▸ If the main repo is very large and has long history it can consume large amount of space and lot of time to download.

"I'M AN EGOTISTICAL BASTARD, AND I NAME ALL MY PROJECTS AFTER MYSELF. FIRST 'LINUX', NOW 'GIT'."

Linus Torvalds

GIT - HOW IT ALL BEGINS▸ founded by Linus Torvalds and the

Linux Kernel team

▸ From 1991 to 2002 modifications to linux kernel was kept in file system as patches.

▸ Linux moved to BitKeeper a proprietary DVCS in 2002.

▸ BitKeeper revoked the free usage for linux team, and Linux Kernel team started writing their own DVCS.

▸ so came the git , and the rest is history….

GIT COMMANDS ▸

INSTALLING GIT …

▸ Installing git - enough references are there in Google

▸ Installation methods are platform specific.

UNDERSTANDING GIT CORE

▸ git is a content-addressable filesystem, bit like Unix.

▸ means that at the core of Git is a simple key-value data store.

▸ The key is a 40-character checksum hash.

▸ value can be different types of git objects.

▸ git Object types

▸ Tree Objects, Blob Objects, Commit Objects & Tag Objects

UNDERSTANDING GIT CORE (CONTD.)▸ Tree Objects represent the

repository. (similar to a folder/directory in a file system)

▸ Blob objects are the leafs , any file in the repository. (similar to files in a file system)

▸ Commit Objects the functional object of repository current status.

▸ Tag Objects categorise a commit object by naming it.

▸ A good reference

▸ https://git-scm.com/book/en/v2/Git-Internals-Git-Objects

CREATE YOUR GIT REPOSITORY▸ Configure your git

▸ git config --global user.name "Your Name"

▸ git config --global user.email you@example.com

▸ Go in to your project and initialise a git repository.

▸ git init

▸ Add all the project directories and files to repository.

▸ git add .

▸ Now Commit all the added directories and files to git.

▸ git commit -m “<commit-message>”

WHERE IS THE GIT REPOSITORY ?▸ Its there along with the project files, look for a hidden file

“.git” , a single folder , in the project root.

▸ The git repository contains

▸ Head file

▸ Objects

▸ branches

▸ logs and many more

WHAT HAPPENS WHEN YOU ADD TO GIT ?▸ Git Three Tree

USEFUL GIT COMMANDS AT THIS STAGE▸ git log - shows a log of all commits starting from HEAD

back to the initial commit.

▸ git status - shows which files have changed between the current project state and HEAD.

▸ git diff - shows the diff between HEAD and the current project state.

▸ git mv and git rm - mark files to be moved (rename) and removed, respectively, much like git add.

HOW DOES GIT COMMIT WORKS ? ▸ git commit is the current status of repository.

▸ Represented by the Commit Object, the commit object contains follows.

▸ The set of files currently available (changed/unchanged).

▸ Reference to parent commit (the SHA1 key of parent commit).

▸ The SHA1 name.

▸ git add will add files to the commit object, current versions of changed files, previous version of unchanged / un-added files.

HOW DOES GIT COMMIT WORKS ? (CONTD.)▸ git commit will submit the commit object, a commit is a

snapshot of the repository.

▸ Now the “new commit object” is the current status of the git repository.

GIT BRANCHING

▸ Manage drastic changes, new features.

▸ Manage a different copy of the “master” within same repository. which means another commit object.

▸ create a branch.

▸ git branch <name>

▸ Point HEAD to the new branch.

▸ git checkout <branch_name>

▸ Better to manage “trunk” & “branch” practice.

GIT MERGING

▸ If we are merging the branch to master, set HEAD to master. And then merge

▸ git checkout master

▸ git merge <branch_name>

▸ Then do a new git commit.

CONFLICT RESOLUTION

▸ At the point of merging , if master repository has changed from the ancestor commit, then conflicts can happen at the point of merging.

▸ Git will add conflict messages at exact points.

▸ Manually edit those locations and commit.

COLLABORATIVE DEVELOPMENT▸ Get someones git repository ,

▸ git clone <repo_url>

▸ Create a remote repo reference named as “origin”.

▸ Then new heads will get created pointing to the header of remote repo, known as “remote heads”

▸ origin/master - for the master head

▸ origin/<branch> - for the branches

COLLABORATIVE DEVELOPMENT (CONTD.)▸ create your own branch to work on the remote repository

branch.

▸ git branch --track [new-local-branch] [remote-branch]

▸ get updates from remote branch.

▸ git fetch origin

▸ Now update your local “master” and branches with the updates.

▸ git pull origin <master/branch_name>

COLLABORATIVE DEVELOPMENT (CONTD.)

▸ To push your changes to remote repository “master” or branches.

▸ git push origin <master/branch_name>

CUSTOMERS OF GIT

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GIT SERVICES

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ANY QUESTIONS ?