Using Git

Basics
Adding and Changing Things
Undo Changes and Recover Files
Viewing Commits
Branch and Merge
Commands for Remotes
Favorites
Resources

Note on Paths

In this file, directory paths are written with a forward slash as on MacOS, Linux, and the Windows-Bash shell: /dir1/dir2/somefile.

Basics

1. When using Git locally, what are these? Define each one in a sentence

   • Staging area - Changes are prepared here before they are committed to the repository. It also allows us to selectively choose which change to include in next commit.
   • Working copy - our local directory where we make changes to files.
   • master - The default branch of out git repository. It is the main line of development.
   • HEAD - Pointer that point to the most recent commmit in the current branch represent the curent position within the commit history.

2. When you install git on a new machine (or in a new user account) you should perform these 2 git commands to tell git your name and email. These values are used in commits that you make:

   # Git configuration commands for a new account
   
   git config --global user.name "Your Name"
   
   git config --global user.email "your.email@example.com"
   

3. There are 2 ways to create a local Git repository. Briefly descibe each one:

   • Create from scratch using git init in empty directory.
   • Clone from an existing repository using git clone <repository url>

Adding and Changing Things

Suppose your working copy of a repository contains these files and directories:

README.md
out/
    a.exe
src/a.py
    b.py
    c.py
test/
    test_a.py
    ...

1. Add README.md and everything in the src directory to the git staging area.

   git add README.md src/
   

2. Add test/test_a.py to the staging area (but not any other files).

   git add test/test_a.py
   

3. List the names of files in the staging area.

   git diff --name-only --cached
   

4. Remove README.md from the staging area. This is very useful if you accidentally add something you don't want to commit.

   git reset HEAD README.md
   

5. Commit everything in the staging area to the repository.

   git commit -m "commit message here"
   

6. In any project, there are some files and directories that you should not commit to git.
   For a Python project, name at least files or directories that you should not commit to git:

   • Byte-compiled (__pycache__/)
   • Django stuff (db.sqlite3, *.log)
   • Jupyter Notebook (.ipynb_checkpoints)

7. Command to move all the .py files from the src dir to the top-level directory of this repository. This command moves them in your working copy and in the git repo (when you commit the change):

   git mv src/*.py .
   

8. In this repository, create your own .gitignore file that you can reuse in other Python projects. Add everything that you think is relevant.
   Hint: A good place to start is to create a new repo on Github and during the creation dialog, ask Github to make a .gitignore for Python projects. Then edit it. Don't forget to include pytest output and MacOS junk.

Undo Changes and Recover Files

1. Display the differences between your working copy of a.py and the a.py in the local repository (HEAD revision):

git diff a.py

2. Display the differences between your working copy of a.py and the version in the staging area. (But, if a.py is not in the staging area this will compare working copy to HEAD revision):

   git diff --staged a.py
   

3. View changes to be committed: Display the differences between files in the staging area and the versions in the repository. (You can also specify a file name to compare just one file.)

   git diff --cached
   

4. Undo "git add": If main.py has been added to the staging area (git add main.py), remove it from the staging area:

   git restore --staged main.py
   

5. Recover a file: Command to replace your working copy of a.py with the most recent (HEAD) version in the repository. This also works if you have deleted your working copy of this file.

   git checkout a.py
   

6. Undo a commit: Suppose you want to discard some commit(s) and move both HEAD and "master" to an earlier revision (an earlier commit) Suppose the git commit graph looks like this (aaaa, etc, are the commit ids)

   aaaa ---> bbbb ---> cccc ---> dddd [HEAD -> master]
   

   The command to reset HEAD and master to the commit id bbbb:

   git reset --hard bbbb
   

7. Checkout old code: Using the above example, the command to replace your working copy with the files from commit with id aaaa:

   git checkout aaaa
   

   Note:

   • Git won't let you do this if you have uncommitted changes to any "tracked" files.
   • Untracked files are ignored, so after doing this command they will still be in your working copy.

Viewing Commits

1. Show the history of commits, using one line per commit:

   git log --oneline
   

   Some versions of git have an alias "log1" for this (git log1).

2. Show the history (as above) including all branches in the repository and include a graph connecting the commits:

   git log --oneline --graph --all
   

3. List all the files in the current branch of the repository:

   git ls-tree --name-only -r HEAD
   

   Example output:

   .gitignore
   README.md
   a.py
   b.py
   test/test_a.py
   test/test_b.py
   

Branch and Merge

1. Create a new branch named feature-branch and switch to it:

git checkout -b feature-branch

2. Merge the feature-branch into the master branch:

git checkout master
git merge feature-branch

3. Delete the feature-branch after it has been merged:

git branch -d feature-branch

4. See the list of branches with pending merges.

git branch --merged    # Show merged branches
git branch --no-merged # Show branches with pending merges

Favorites

The git command that I want to remember is the git command that I see on blog A better git log

git log --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit

It add git lg that is other cool way to log commit

---

Resources

• OhMyGit Learn git using game OhMyGit! Nice Learning tool for git!

• Pro Git Online Book Chapters 2 & 3 contain the essentials. Downloadable e-book is available, too.

• Visual Git Reference one page with illustrations of git commands.

• Markdown Cheatsheet summary of Markdown commands.

• Github Markdown some differences in the way Github handles markdown and special Markdown for repos.

Learn Git Visually:

• Learn Git Interactive Tutorial great visual tutorial
• Git Visualizer execute Git commands in a web browser and see the results as a graph.