Git

Statement

Some of the content and pictures in this article are excerpted from the CS-Notes. If there is infringement, please inform to delete

Common Commands

1. See more from the cheat sheet

Command	Object	Description
git add	filename	Add files to the staging area
git commit -m	filename	Submit files in staging area to the repository
git commit –amend		Modify the last submission (use “shift+zz” to exit; use “q!” to exit without saving)
git mv	original new	Modify the name of a file
git rm	filename	Delete files in both working directory and staging area (use “-f” to force delete)
git rm –cached	filename	Delete files in the staging area only

git pull		Fetch from and integrate with another repository or a local branch
git push		Update remote refs along with associated objects

git log		View submission logs
git reflog		Show referentiable history versions

git reset	version	Roll back the version to the staging area
git reset	HEAD~n	Move the HEAD pointer to the first “n” objects and roll back the objects to staging area
git reset –soft	HEAD~n	Move the HEAD pointer to the first “n” objects only
git reset –hard	HAED~n	Further restore the staging area files to working directory (overwrite the source code)

git diff		Compare files in working directory and staging area
git diff	version	Compare files in working directory and repository
git diff	version1 version2	Compare 2 files in a repository
git diff –cached	version	Compare files in staging area and repository (only files in repository have “version”)

git branch	branch name	Create a branch
git checkout	branch name	Switch to a branch
git merge	branch name	Merge changes from another branch
git branch -d	branch name	Delete a branch

Centralized & Distributed

1. Git is a distributed version control system, while SVN is centralized

2. Comparison between centralized and distributed:

	Centralized	Distributed
The copy of code	Only the central server	Everyone’s computer
Work without central server	×	√
Networking required	√	×
Create and merge	Slow (copy a complete code)	Fast

Central Server

1. The central server is used to exchange the changes of each user. Git can work without it, but the central server can run continuously which makes exchanges easier

For example, the Github is a central server

Workflow

1. After creating a new repository, the current directory becomes the workspace

2. There is a hidden directory “.git” in the workspace, which belongs to the Git version library

The Git version library includes a staging area called “Stage” and the latest “History” version library. “History” stores all branches’ information and uses a HEAD pointer to point to the current branch

Branch

1. Implement

Use the pointer to connect each submission into a timeline, and the HEAD pointer points to the current branch pointer

2. New

Create a new pointer to the last node of the timeline, and make the HEAD pointer point to the new branch, indicating that the new branch becomes the current branch

3. Commit

Each commit will only move the current branch pointer forward, while other pointers stay fixed

4. Merge

Simply change the pointer

Conflict

1. When two branches modify the same line of the same file, conflicts will occur during merging:

2. Git will use “<<<<<<<, =======, >>>>>>>” to identify contents of different branches. We only need to modify the conflicting parts to be the same to resolve the conflict

<<<<<<< HEAD
Creating a new branch is quick & simple.
=======
Creating a new branch is quick AND simple.
>>>>>>> feature1

Stashing

1. After operating on a branch, switch to another branch before the changes are committed, the changes can also be seen on the other branch. This is because all branches share a same workspace

2. We can use git stash to store the changes of the current branch

At this time, all the changes of the current workspace will be stored in the stack to keep the current workspace clean. As there are no uncommitted changes, we can safely switch to other branches

$ git stash
Saved working directory and index state \ "WIP on master: 049d078 added the index file"
HEAD is now at 049d078 added the index file (To restore them type "git stash apply")

3. Stashing can be used to implement the “bug branch”

If you are currently developing on the “dev branch”, but there is a bug on the “master branch”, and the development on the “dev branch” is incomplete to be submitted immediately. Before creating and switching to a new bug branch, you need to use git stash to store the uncommitted changes of “dev branch”