What is VCS

VCS (Version Revision Control) System

  • A system for managing changes to documents, programs, web pages, etc.
  • Maintains a revision history of changes to the document
  • Maintains multiple versions of a document
  • Enables multiple users to collaborate on a common collection of documents
  • There are many revision control systems available
    • rcs, cvs, subversion, mercurial
    • git

What git is?

Git is a decentralized version control system (VCS) for tracking changes in computer files.

  • Distributed version control
  • Coordinates work between multiple developers
  • Who made what changes and when
  • Revert back at any time
  • Local and Remote repos

Developed by the Linux development community

Inital Goal:

  • Speed
  • Simple design
  • Strong support for non-linear development (thousands of parallel branches)
  • Fully distributed
  • Able to handle large projects like the Linux kernel efficiently (speed and data size)

Git vs Github

  • Git is a high quality version control system
  • Github is a cloud-based hosting service
    • Making VCS distributed (backup and collaboration with people)
    • Remote repositories: copies of your files on other computers
    • Alternative free git servers: gitLab, bitbucket, phabricator, …

Installing git

  • Go to Google : Install git on <your OS>

Basic Commands to work with Local Repository

Initialize Local Git Repository

  • Git Repository contains all the files/folders associated with a project
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git init
  • Begins tracking the directory by creating a .git hidden folder that contains the structures required for version control
  • The file history appears as snapshots in time called commit

Config Name and Email

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git config --global user.name '<your name>'
git config --global user.name '<your email>'

Add File(s) To Index

  • Making git keep track of a file/directory (so-called staging the file/directory)
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git add <file>

Add ALL Files To Index

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git add .

Remove File(s) from Index

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git rm --cached <file>

Check Status of Working Tree (Staging)

  • Gives the status of your git repository
    • Untracked files
    • Changes that are not committed
    • Your current local branch
    • Any unmerged files
    • Changes between the local and the remote branch
    • The remote and the remote branch <remote-name>/ <remote-branch>
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git status

Commit Changes In Index

  • You will need to add a file before committing its changes
  • Git commit is a Lightweight copy-and-paste
  • Only stores the changes (snapshot, not differences!) from one version to another (called delta)
    • each commit has a globally unique name
    • git keeps a history of commits by having them as a linked list
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git commit

This command will bring you to vi interface by default to leave a commit message. To type the commit message, press i to go into insert mode. After finish typing, press Esc to exit insert mode.

Then you can:

  • press :wq to save and quit
  • press :q! to quit without saving

Commit Changes In Index (Add comment here)

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git commit -m '<your commit message>'
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git commit <file> | -a (all files) -m "<message>"

Check your commits

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git log
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git vlog

Branches

  • The commits create a linked list showing one line of history
  • You can create multiple lines of history using branches
    • Branches are essentially pointers to specific commits
    • Can easily be created and deprecated

Listing the existing branches

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git branch

alternatively

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git branch --list
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git branch -l

Create a new branch

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git branch <new branch name>

Note the new branch with have all your files of your main/master branch.

Switch to the branch

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git checkout <branch name>

Try adding some files and switch back to the main/master branch. See the directory and you will found git will only show the files of the current branch in the directory.

Create and switch to a new branch

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git checkout -b <new branch name>

Branch Merge

  • Combining the work from two different branches
  • Merging creates a special commit with two unique parents

Merge a branch to current branch

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git merge <merging branch name>

This command will bring you to vi interface. To type the merge message, press i to go into insert mode. After finish typing, press Esc to exit insert mode.

Then you can:

  • press :wq to save and quit
  • press :q! to quit without saving

Merge conflicts

How it happens?

  • The changes made are auto-merged first.
    • If auto-merge fails, you will need to resolve the conflict manually

Solving Merge conflicts

  • You will need to tell git which version you want to keep
  • Does not affect the merged branch version
  • You can use git mergetool if you want a visual tool for resolving conflicts

Local Git Workflow

  1. Create a local repository (init or clone)
  2. Create a branch (the master branch is for a stable version only—branch early, branch often)
  3. Add the files you want to be tracked by git (typically text- based files—not executables)
  4. Work on your project, make commits (you may create sub- branches)
  5. Merge to master once completed

Work with Remote Repository

Remote Repositories

  • A repository on a remote machine which you have access to
  • The remote repository is shown as <name-of-remote>/<name-of-remote-branch> on your local repository (since last time you synced to the remote)

Note that:

  • The branches on your local repo and remote repo could be different

Basic Commands to work with Remote Repository

Push to Remote Repository

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git remote

Link a remote repository on github

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git remote add <remote name> <url>

First Push to Remote Repository

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git push -u <remote name> <branch name>

Push to Remote Repository

  • Uploads the local branch into the remote branch
    • All people having access to the remote branch can see your changes
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git push

Synchronizing a remote branch with your local branch

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git fetch

Pull Latest From Remote Repository

  • Combining fetching and merging the remote branch into the local branch together (technically the same)
  • there is a remote added to the git once you cloned, so git knows where to fetch from, you can change it
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git pull

Clone Repository Into A New Directory

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git clone <url>

To Clone a local copy of a remote repository without linking a remote manually:

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git clone [—recursive] <username>@<remote address> <name-of-local-directory>
  • ^Requires
    • ssh: uses a ssh-key for authentication or
    • https: asks for username/password on the CLI

what is .gitignore?

.gitignore file basically record the files we want our git to ignore.

Tips of Commits

  • Commit your changes after each unit of work

  • Use appropriate messages for your commits

  • Separate subject from body with a blank line

  • Limit the subject line to 50 characters

  • Capitalize the subject line

  • Do not end the subject line with a period

  • Use the imperative mood in the subject line

  • Wrap the body at 72 characters

  • Use the body to explain what and why vs. how

Tips of Branching

  • Branch early branch often next version to replace (merge into) master
  • branch master or main is only for stable version
    • only stable, well-tested commit

Some common namings of branch

  • dev or develop: development version
    • next version to replace (merge into) master
  • topic : experimental bleeding edge
    • test stuff out before merging into develop

Git Cheatsheet

Interactive Tutorial on GitHub