Git & Github#

Author: Fu Yin
Update: July 27, 2022
Reading: 60 min

Introduction#

Git consists of three parts: Working Directory(工作区), Index(暂存区) and Repository(版本库):

Working Directory: the directory that you can see on your computer
Index: also called the Stage, it is usually stored in the .git/index file.
Repository: the workspace has a hidden directory, the .git, which is the repository. It usually consists of a branch and Head, with the Head pointing to the result of your last submission.

GitHub is the single largest host for Git repositories, and we can host Git repositories on GitHub. The interaction between Git and Github is showing in figure below:

../_images/Git-Github-1.jpeg — Fig. 3 Project and Github#

Install#

MacOS uses Xcode’s Command Line Tools to install Git in /usr/bin/git directory. However, Xcode usually comes with a lower version of Git, so you need brew to upgrade. After installation, remember to add the environment variable.

# install
brew install git

# add path
vim ~/.zshrc
> export GIT=/usr/local/Cellar/git/2.37.1
> export PATH=$GIT/bin:$PATH
source ~/.zshrc

# check version
git --version

After the successful installation , we need to configure git.

username and email

git config --global user.name "Your Name"
git config --global user.email "email@example.com"

color ui and git log

# let Git show different colors
git config --global color.ui true

# configure log command --> git lg
git config --global alias.lg "log --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit"

master to main

Manually modify the ~/.gitconfig file and set defaultBranch = main. Or use the git config command for git version > v2.28:

git config --global init.defaultBranch main

My complete ~/.gitconfig file showing below:

[user]
	name = OUCyf
	email = oucyinfu@gmail.com
[color]
	ui = true
[alias]
	lg = log --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit
[init]
	defaultBranch = main

SSH keys for Github#

Imagine the scenario that you have a remote repository on GitHub, and one computer at home and one computer at the office all be needed to submit codes using SSH keys, and both the SSH public keys are needed to be stored in the GitHub Setting.

../_images/Git-Github-2.jpg — Fig. 4 SSH keys in Github#

Then check git SSH status

ssh -T git@github.com

Github IP in China#

We can update the IP address manually or automatically

Manually update IP

Query the latest IP address of GitHub

usually query the following four domain names in ipaddress website.

Or you can connect the IP address with the ipaddress website to query directly:

Change the /etc/hosts file

After querying the IP, map the IP with the website address, and add the mapping relationship to the /etc/hosts file with sudo permission. For example:

vim /etc/hosts

# output with mapping format:  [ip] [domainName]
199.232.69.194 github.global.ssl.Fastly.net
140.82.114.4 GitHub.com
185.199.108.153 assets-cdn.Github.com
140.82.114.9 codeload.Github.com

Refresh the /etc/hosts file

sudo killall -HUP mDNSResponder

Automatically update IP

GitHub520 is a project that can real-time update the IP resolution of GitHub domain, the project server’s mirror website is HelloGitHub 镜像站. Run the following python code, then the IP resolution provided by GitHub520 will be obtained in real time, and the /etc/hosts file is automatically modified. The code is as follows:

"""
Created on Tue Feb 22 20:51:03 2022

@author: yinfu
"""

"""
##############################
##  origin /etc/hosts file  ##
##############################
#
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1       localhost
255.255.255.255 broadcasthost
::1             localhost
"""

from shutil import copyfile
import datetime
import os
import requests
import sys

class GithubHost:
    winHostsPath='C:\Windows\System32\drivers\etc\hosts'
    macHostsPath='/etc/hosts'

    hostsDic = {'win32':winHostsPath, 'darwin':macHostsPath}
    dnsRefreshDic = {'win32':'ipconfig /flushdns', 'darwin':''}

    githubHostUrl='https://raw.hellogithub.com/hosts'
    googleHostUrl=''

    def refreshHosts(self):
        # 备份原hosts文件
        hosts=self.hostsDic[sys.platform]
        self.backUpHosts(srcfile=hosts)
        
        # 获取并更新github新host内容
        self.updateHosts(hosts, self.githubHostUrl, '# GitHub520 Host Start', '# GitHub520 Host End')

        # 获取并更新google新host内容
        # self.refreshHosts(hosts, self.googleHostUrl, '', '')

        # 刷新
        refreshCmd=self.dnsRefreshDic[sys.platform]
        os.system(refreshCmd)


    def updateHosts(self, hosts, hosturl, beginRowStr, endRowStr):
        # 删除原有内容
        self.removePartOfFile(hosts, beginRowStr, endRowStr)
        self.addHostsFromURL(hosts, hosturl)


    def removePartOfFile(self, file, beginRowStr, endRowStr):
        lines = []
        with open(file, 'r') as oldhosts:
            lineInRange = False
            for line in oldhosts:
                # 如果在beginRowStr 与 endRowStr 之间的，就不记录在新文件中
                if line.strip() == beginRowStr.strip():
                    lineInRange = True
                if not lineInRange and line.strip() != '': # 删除空行
                    lines.append(line)
                if line.strip() == endRowStr.strip():
                    lineInRange = False

        with open(file, 'w') as newHosts:
            for line in lines:
                if len(line) != 0 and line is not os.linesep:
                    newHosts.write(line)
        

    def backUpHosts(self, srcfile):
        dstfile = srcfile + datetime.datetime.now().strftime('%Y-%m-%d-%H-%M-%S')
        copyfile(src=srcfile, dst=dstfile)

    def addHostsFromURL(self, hostfile, hostsurl):
        '''从github项目地址：读取最新的github的IP记录'''
        with open(hostfile, 'a+') as fw:
            # 字符串给出当前平台使用的行终止符。例如，Windows使用'\r\n'，Linux使用'\n'而Mac使用'\r'。
            # fw.write(os.linesep)
            fw.write(requests.get(hostsurl).text.strip())

if __name__ == '__main__':
    GithubHost().refreshHosts()

Note

sudo permission is required to modify /etc/hosts. Make sure to back up the original /etc/hosts. The script will update the content between the line from # GitHub520 Host Start to # GitHub520 Host End, without deleting or modifying anything else.

The following is an example of a modified /etc/hosts file:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
0.0.1	localhost
255.255.255	broadcasthost
::1             localhost
# MacWk.com Hosts Start
# Macs Fan Control
0.0.1 crystalidea.com
0.0.1 www.crystalidea.com
0.0.1 v3pro.crystalidea.com
# MacWk.com Hosts End
# GitHub520 Host Start
82.113.4                  alive.github.com
82.113.4                  live.github.com
232.140.192                github.githubassets.com
82.113.4                  central.github.com
201.249.207                desktop.githubusercontent.com
82.113.4                  assets-cdn.github.com
206.232.135                camo.githubusercontent.com
101.1.6                   github.map.fastly.net
101.1.6                   github.global.ssl.fastly.net
82.113.4                  gist.github.com
199.108.153               github.io
82.113.4                  github.com
0.66.2                    github.blog
82.113.4                  api.github.com
204.44.248                 raw.githubusercontent.com
163.208.41                 user-images.githubusercontent.com
204.67.163                 favicons.githubusercontent.com
192.65.19                  avatars5.githubusercontent.com
208.135.184                avatars4.githubusercontent.com
175.3.163                  avatars3.githubusercontent.com
239.50.191                  avatars2.githubusercontent.com
87.18.202                  avatars1.githubusercontent.com
197.52.125                 avatars0.githubusercontent.com
236.14.33                   avatars.githubusercontent.com
82.113.4                  codeload.github.com
21.206.80                  github-cloud.s3.amazonaws.com
21.206.80                  github-com.s3.amazonaws.com
21.206.80                  github-production-release-asset-2e65be.s3.amazonaws.com
21.206.80                  github-production-user-asset-6210df.s3.amazonaws.com
21.206.80                  github-production-repository-file-5c1aeb.s3.amazonaws.com
199.108.153               githubstatus.com
71.144.211                 github.community
100.27.125                 github.dev
82.113.4                  collector.github.com
72.161.117                pipelines.actions.githubusercontent.com
193.198.252                media.githubusercontent.com
196.61.168                 cloud.githubusercontent.com
236.14.33                   objects.githubusercontent.com
107.213.51                 vscode.dev


# Update time: 2022-07-15T22:10:03+08:00
# Update url: https://raw.hellogithub.com/hosts
# Star me: https://github.com/521xueweihan/GitHub520
# GitHub520 Host End

Note

The IP address of the Github changes frequently, and we should update /etc/hosts file when it slows down again.

Manual#

creating a repository#

Init Locally

Init Remotely

Assuming you have created a remote repository on GitHub, you can use ssh for git clone, which is fast than https in China.

git clone git@github.com:your_Github_name/reop_name.git

Init Submodule

If your code needs to use other package, which is located on GitHub. You need to use git to initialize and update. git submodule init xxx will download some info provided by .gitmodules file to fill .git/config. Then use git update to clone those code. Here is an example refer to https://www.codenong.com/44366417/.

For example a .gitmodules file contains three submodules to use:

[submodule "pygments-style-algforopt"]
    path = style
    url = https://github.com/sisl/pygments-style-algforopt.git
    branch = master
[submodule "pygments-julia"]
    path = lexer
    url = https://github.com/sisl/pygments-julia.git
    branch = master
[submodule "juliaplots.sty"]
    path = juliaplots.sty
    url = https://github.com/sisl/juliaplots.sty.git
    branch = master

If we only need to use the pygments-julia and juliaplots.sty code, which means that do not require clone and checkout pygments-style-algforopt, we can use

git submodule init pygments-julia juliaplots.sty

Then run the following command to clone and check them

git submodule update

add, commit and push#

Add changes to the local repository.

# Add the changes to the Index
git add <filename>

# Add all changes at once
git add .

# check status
git status

# Add the changes from Index to local Repository
git commit -m "your comment"

Push the last changes in the Local Repository to the Remote Repository in github.

git push origin main

If you need to connect your local repository to a remote repository, use the following command

git remote add origin <server>

branch, merge and diff#

Create a new branch and switch to it

# new branch's name is feature
git switch -c feature_x   # or: git checkout -b feature_x 
 
# create the dev branch of the remote origin to the local
git checkout -b dev origin/dev

# switch to main branch
git switch main   # or: git checkout main

Delete a branch

# delete a local branch
git branch -d <branch-name>

# delete a remote branch
git push origin --delete <branch-name>

Compare 2 branches

# show a file list with difference between 2 branches
git diff branch1 branch2 --stat

# show detailed differences for the specified file
git diff branch1 branch2 /path/to/file

# show the detailed differences of all the different files between 2 branches
git diff branch1 branch2

Merge 2 branches

# merge the contents of the dev branch under the main branch
git merge dev

# the '--no-ff' option disables fast-forward mode, and '-m' records the merge as a commit
git merge --no-ff -m "merge dev --add new blog-1" dev

pull = fetch + merge#

If the team is developing on the dev branch and a teammate commits a new commit to dev, we need to pull the commit from GitHub to our local dev branch before developing

# specify the link between the local dev branch and the remote origin's dev branch
git branch --set-upstream-to=origin/dev dev

# pull code
git pull

Note

git pull = git fetch + git merge, and git fetch will only pull remote code to local repo and do not merge it.

tag#

# tag the current branch with v1.0
git tag v1.0

# show all the tags
git tag

# show the tag v0.9's information
git show v0.9

# tag a previous commit，f52c633 is the 'commit id'
git tag v0.9 f52c633

# create a tag with instructions，'-a' add tga  ，'-m' add instructions
git tag -a v0.1 -m "version 0.1 released" 1094adb

# delete a tag
git tag -d v0.1

# push the tag to remote
git push origin v1.0

# Push all local tags that have not been pushed to the remote at one time
git push origin --tags

# delete a remote tag (make sure that you have deleted the local tag before)
git push origin :refs/tags/v0.9

log#

git log --graph --pretty=oneline --abbrev-commit
git log --pretty=oneline --abbrev-commit
git log --pretty=oneline

# check the latest commit
git log -1

delete files#

delete one file

# delete test.txt from repo and commit
git rm test.txt
git commit -m "remove test.txt"

# use 'rm' delete，then 'git add' and 'git commit'
rm text.txt
git add .
git commit -m "remove test.txt"

delete untracked files from .gitignore

# delete untracked files
git clean -f

# delete untracked files and their directory
git clean -fd

# ? cautious
git clean -xfd

it is highly recommended to add the -n parameter to see which files will be deleted first to prevent the deletion of important files by mistake

git clean -nxfd
git clean -nf
git clean -nfd

版本回退 (working…)#

Warning

最新版本的git已经使用git restore 代替了原来的reset和checkout命令了

在 Git 中，用HEAD表示当前版本, 上一个版本是HEAD^，上上一个版本是HEAD^^，往上100个版本HEAD~100。但推荐使用commit id来退回版本：

# 退回到上一个版本
git reset --hard HEAD^

# 首先查看历史 commit 的 id
git log

# 例如发现 id 是 1094a，退回到该版本
git reset --hard 1094a

Note

Git的版本回退速度非常快，因为Git在内部有个指向当前版本的HEAD指针，当你回退版本的时候，Git仅仅是把HEAD从指向append GPL

现在退回到过去的版本了，想回到未来的版本：

# 要重返未来，用'git reflog'查看命令历史，以便确定要回到未来的哪个版本
git reflog

# 例如发现未来的 id 是 1094a，退回到该版本
git reset --hard 1094a

撤销修改 (working…)#

Warning

需要替换成最新版本的 git restore

git checkout -- xx.txt 

figure#

Link from git-tips project.

Programming Notebook

Git & Github

Contents

Git & Github#

Introduction#

Install#

SSH keys for Github#

Github IP in China#

Manual#

creating a repository#

add, commit and push#

branch, merge and diff#

pull = fetch + merge#

tag#

log#

delete files#

版本回退 (working…)#

撤销修改 (working…)#

figure#

Reference#