Deep dive into git

This is the demo repo for a hands-on lab for working with git from the command line.

Before you start

Check yor git installation

Make sure git is installed and the version is > 2.23:

$ git --version
> git version 2.35.1

If not, download and install git.

Check your git config

1. Check your name and email address:

$ git config --global user.name
$ git config --global user.email

If this does not return the desired values, set the config using these commands:

$ git config --global user.name '<your_name>'
$ git config --global user.email '<your_email_address>'

2. Set the default branch to main:

$ git config --global init.defaultBranch main

3. Check your default editor

Check your default editor (i.e. by running git config --global --edit). If you like the editor, then you are good. If your stuck in vim (click ESC : q ! Enter to exit), then configure the editor of your choice - for example CSCode:

$ git config --global core.editor 'code --wait'

Exercise 1: Understanding git

Set-up:

Create a local file/folder:

mkdir UnderstandingGit
cd UnderstandingGit
mkdir folder;
for d in {1..6}; do echo  "Line ${d}" >> folder/file.txt; done;

Powershell:

mkdir UnderstandingGit
cd UnderstandingGit
mkdir folder
for ($d=1; $d -le 6; $d++) { Out-File file$d.md; git add file$d.md; git commit -m "adding file$d.md"; }

Exercise

1. Modify the file and verify its SHA value (git hash-object)
2. Initialize the git repo (git init) and check the changes in your folder.
3. Add file to index (git add).
4. Commit file and check in your .git folder what a commit is (git cat-file and git ls-tree).
5. Add another commit and verify how the two commits are connected.
6. Create a sinple tag and an annotated tag (git tag and git tag -a).

Important commands for this exercise:

$ git hash-object folder/file.txt
$ git init
$ git add
$ git commit
$ git ls-tree
$ git cat-file [-p | -t]
$ cat
$ git tag [-a]

A commit is a tree of blobs and trees:

graph BT;
    Tree==>Commit;
    Blob==>Tree;
    Blob2==>Tree;
    Tree2==>Tree;
    Blob3==>Tree2;
    Blob4==>Tree2;
    Tree3==>Tree2;
    Blob5==>Tree3;

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The commits are connected to their parent commits (DAG):

graph RL;
    96a85==>49c01;
    7e536==>96a85;
    1e542==>7e536;
    b7e6b==>1e542;
    main-.->b7e6b;
    HEAD-->main;
    5a053==>7e536;
    55805==>5a053;
    branch-.->55805;
    tag-.->55805;

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Working with patches:

1. Check how git generates diffs (git diff).
2. Create patches for your two commits (git format-patch).
3. Undo your changes (git reset).
4. Apply the patches (git apply and git am).

Important commands for this exercise:

$ git diff
$ git format-patch HEAD~2..HEAD
$ git reset --hard HEAD~2
$ git apply
$ git am

Exercise 2: Merge conflicts

Set-up

echo "Solving merge conflicts in git is easy" > Merge.txt
git add Merge.txt
git commit -m "Base commit"
git switch -c experiment
echo "Solving merge conflicts is easy in git" > Merge.txt
git commit -am "Modify Merge.txt in experiment"
git switch main
echo "Solving merge conflicts in git is very easy" > Merge.txt
git commit -am "Modify Merge.txt in main"
git switch experiment

Exercise

Create a merge conflict with git merge main and resolve it.

Important commands for this exercise:

$ git config --global merge.conflictStyle diff3
$ git merge --abort
$ git diff
$ git log --merge –p <filename>
$ git show :1:<filename> (common anchestor)
$ git show :2:<filename> (HEAD)
$ git show :3:<filename> (MERGE_HEAD)

$ git add <filename>
$ git merge --continue

Exercise 3: Working with your local history

Set-up:

Create a local history:

mkdir WorkingWithYourHistory
cd WorkingWithYourHistory
git init
for d in {1..6}; do touch "file${d}.md"; git add "file${d}.md"; git commit -m "adding file ${d}"; done

Look at you history. Create a git alias so that you don't have to type the long command all the time.

$ git log --oneline --graph --decorate --all
$ git config --global alias.lol 'log --oneline --graph --decorate --all'

Exercise

1. Add another file (File7.md) and ammend it to te last commit.
2. Reset the last two commits and commit them together as a new commit (git reset --soft).
3. Reset the last commit and create three commits out of it (git reset --mixed).
4. Undo the last three commit (git reset --hard).
5. Cherry pick the changes from the reflog.
6. Do an interactive rebase. Reword commit 2 and edit commit 3.

Important commands for this exercise:

$ git commit --amend
$ git reset [--hard | --soft | --mixed]
$ git reflog
$ git cherry-pick
$ git rebase [-i]

Exercise 3: Branches, tags, finding bugs, and adding patches

Set-up:

$ git clone https://github.com/wulfland/DeepDive.git DeepDive
$ cd DeepDive

Exercise

1. Create a branch fix-bug to fix the bug (git switch -c)
2. Switch to main and search in the history for the bug (inde.html instead of index.html) using git bisect.
3. Modify Readme.md and commit to main.
4. Switch to fix-bug and rename inde.html to index.html.
5. Rebase the branch onto main.
6. Create a branch slow-down.
7. Modify line 9 of index.html and change the background URL to images/texture.jpg.
8. Modify line 78 of index.html and change the timing for the game to speed it up or slow it down.
9. Move texture.jpg to a new folder images.
10. Create seperate commits for refactoring and logic changes (git add -p).
11. Squash the changes into main

Important commands for this exercise:

$ git switch [-c]
$ git bisect start 
$ git bisect good <SHA>
$ git bisect bad <SHA>
$ git bisect start <GOOD> <BAD>
$ git bisect run ls index.html
$ git add -p
$ git merge [--squash | --rebase]