Advanced `git`

Block 4.1: Advanced features of git

Jan Simson

Amending Commits ⏳️

Modify the last commit
- Modify the commit message
- Modify the commited changes
git commit --amend
VSCode: Possible via GitLens
- Demo

Caution

Never do this if you already pushed the commit, as it will re-write history

Staging Parts Instead of Full Files 🧩

Instead of staging complete files, you can also stage just a section or selection of your changes.

CLI: Interactive Staging
- git add --patch <file>
- git add -p <file>
VSCode: “Stage selected ranges”
- Demo

Tags 🏷️

Background: https://giphy.com/gifs/stop-motion-experience-3oriNYjm7cl8MjpszK

What is a tag? 🏷️

You can tag a single commit in git.

Creates a named reference to this commit
- Useful for versioning / releases e.g. v1.2.3
- also e.g. course material: SS23, WS23
Can be checked out via git checkout <tag>
You can create a specific release for a tag
- Attach changelog or artifacts
Can be useful for deployments if CD is not feasible

Creating a tag

CLI: git tag v1.2.3
VSCode: Commit > Create Tag (GitLens)
- Demo

Note

Tags need to be pushed explicitly via git push --tags

Optional Practicals: Tags

Creating a Release
1. Tag the latest commit in your repository
2. Push the tag to GitHub
  - You do not need to make a new commit
3. Create a new release for the tag you pushed
Go to learngitbranching.js.org
1. Do Section "A Mixed Bag" > #4: Tags

Patches 🩹

Background: https://giphy.com/gifs/VeSvZhPrqgZxx2KpOA

Patches 🩹

Before platforms like GitLab/Hub existed, people collaborated by sending around patches via email.

A patch is essentially a commit exported as a file.

Create: git format-patch <commit/branch>
- Will create .patch files for all commits till target
Apply: git apply <patch-file(s)>

Example Patch

From 265f0c1119113f0f84ebfc047c26ef39f5532e57 Mon Sep 17 00:00:00 2001
From: Jan Simson <git@simson.io>
Date: Wed, 15 Nov 2023 20:10:36 +0100
Subject: [PATCH 1/8] Update slogans

---
 docs/.vuepress/config.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/.vuepress/config.js b/docs/.vuepress/config.js
index 6c61bba..53a76bd 100644
--- a/docs/.vuepress/config.js
+++ b/docs/.vuepress/config.js
@@ -1,6 +1,6 @@
 module.exports = {
-    title: 'GitLab ❤️ VuePress',
-    description: 'Vue-powered static site generator running on GitLab Pages',
+    title: 'Advanced Git & Gitlab',
+    description: 'An interactive course where you get publish your own website',
     base: '/',
     dest: 'public'
 }
\ No newline at end of file
-- 
2.39.2 (Apple Git-143)

Practical: Creating Patches

Navigate to a local git repository of your choice
Get the latest commit hash
Use git format-patch <id> to create a patch for it
Examine the generated patch

Working with Large Files / Data: 🦣 `git lfs`

Git struggles with large binary files.

One possible solution: git lfs (large file storage)
Extension that needs to be installed separately
- Install git lfs
- Initialize once in each repository you want to use it in
- Configure a pattern to specify which files should use it
Useful, but a bit annoying to use & debug
- Alternatives exist: e.g. dvc

Stashing 🗄️

What is Stashing? 🗄️

Stashing allows you to temporarily store changes that are not ready to be committed yet.
Useful when you need to switch branches or perform other operations without committing half-done work.

Illustration of Stashes

How to Use Stashes?

git stash         # Stash changes
git stash list    # List stashes
git stash apply   # Apply the latest stash
git stash pop     # Apply and remove the latest stash

Or in a GUI e.g. VSCode (via GitLens)

Cherry Picking 🍒

Apply a specific commit to your current branch
git cherry-pick <commit-hash>

Cherry Picking 🍒

Apply a specific commit to your current branch
git cherry-pick <commit-hash>

Typically when branches are not merged
Can be useful for e.g. hotfixes 🐛
Should not be overused
- Usually full merges are the preferred solution

Interactive Rebases 🔥

Besides normal rebases, you can also do interactive ones, where you get to decide what happens with each commit.

git rebase -i <target>
Super powerful + super dangerous
- Easy to re-write history
Only use these when necessary or if you have a good backup

Interactive Rebases: Example 🧨

pick f7f3f6d Change my name a bit
pick 310154e Update README formatting and add blame
pick a5f4a0d Add cat-file

# Rebase 710f0f8..a5f4a0d onto 710f0f8
#
# Commands:
# p, pick <commit> = use commit
# r, reword <commit> = use commit, but edit the commit message
# e, edit <commit> = use commit, but stop for amending
# s, squash <commit> = use commit, but meld into previous commit
# f, fixup <commit> = like "squash", but discard this commit's log message
# x, exec <command> = run command (the rest of the line) using shell
# b, break = stop here (continue rebase later with 'git rebase --continue')
# d, drop <commit> = remove commit
# l, label <label> = label current HEAD with a name
# t, reset <label> = reset HEAD to a label
# m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
# .       create a merge commit using the original merge commit's
# .       message (or the oneline, if no original merge commit was
# .       specified). Use -c <commit> to reword the commit message.
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
# However, if you remove everything, the rebase will be aborted.
#
# Note that empty commits are commented out

Taking a Closer Look: git bisect 🧐

You provide two references:
- Last known commit where everything was well
- Earliest commit that has the issue
Automatic search between both points
Great for pinpointing which commit introduced a bug 🐛

Taking a Closer Look: git bisect 🔍️

git bisect start

# Current version is bad
git bisect bad

# 84571cf is known to be good
git bisect good 84571cf

# We get moved to a commit and examine it, it's bad
git bisect bad

# ... repeat with good / bad till we found the culprit ...

# End the git bisect session
git bisect reset

Working Trees 🌲🌳🌴

With git working trees, you can have different different branches from one repository checked out at the same time — each in a different directory

git worktree add <path>

<path> will be automatically checked for a matching branch / commit / tag
- If none is found one is created

# Create a new directory *next* to the repository
# either checkout or create a branch my-feature
git worktree add ../my-feature

Questions?

Optional Practicals: 🍒🔥

Go to https://learngitbranching.js.org/
Complete Section 3: "Moving Work around"
- #1: Cherry Pick
- #2: Interactive Rebase

End of Section 🎉

Any Questions?

[🏡 Back to Overview]

[⏩️ Next Section]

Advanced git

Amending Commits ⏳️

Staging Parts Instead of Full Files 🧩

Tags 🏷️

What is a tag? 🏷️

Creating a tag

Optional Practicals: Tags

Patches 🩹

Patches 🩹

Example Patch

Practical: Creating Patches

Working with Large Files / Data: 🦣 git lfs

Stashing 🗄️

What is Stashing? 🗄️

Illustration of Stashes

How to Use Stashes?

Cherry Picking 🍒

Cherry Picking 🍒

Interactive Rebases 🔥

Interactive Rebases: Example 🧨

Taking a Closer Look: git bisect 🧐

Taking a Closer Look: git bisect 🔍️

Working Trees 🌲🌳🌴

Questions?

Optional Practicals: 🍒🔥

End of Section 🎉

Advanced `git`

Working with Large Files / Data: 🦣 `git lfs`