Tutorial: Git Advanced

Git Advanced

Agenda

Git Commits - Best Practices
Git Stash
Git Ignore
Git Attributes
Git Config
Git Cherry-pick
Git Apply
Git Submodules
Git Worktree
Git Bisect

Git Commits - Best Practices

A commit should be a wrapper for related changes
Don't commit half-done work into public branches
Write good commit messages
- use the imperative style in the subject line
- up to 50 characters, provide detailed information if necessary
  - Good commit message: CMA-5430: Add pulsar icon to the user section
  - Bad commit message: Progress
  - Bad commit message: Add tooltip, fix alignment, delete old config
Use branches
- Branching helps you avoid mixing up different lines of development
Preserve history and traceability

Git Stash

Enables you to save your code without making a commit
git stash - stashes all tracked files
git stash -- #files - stashes the given files
git stash list - displays all stashed changes
git stash apply - reapplies the stashed content
git stash apply stash@{1} - applies selected stash
git stash push -m [message] - creates a stash with a message
git stash drop - drops the stashed content
git stash pop - apply + drop
git stash save - saves the modified file

Git Ignore

.gitignore is a file that tracks ignored files
Each glob pattern is tested relative to the directory containing the .gitignore file

Content:
- dependency cache (node_modules)
- compiled code
- build output directory (bin, build)
- hidden system files
- personal files (IDE config, .env file)

Example: .gitignore for C++

   1  # Prerequisites
   2  *.d
   3  
   4  # Compiled Object files
   5  *.slo
   6  *.lo
   7  *.o
   8  *.obj
   9  
  10  # Precompiled Headers
  11  *.gch
  12  *.pch
  13  
  14  # Compiled Dynamic libraries
  15  *.so
  16  *.dylib
  17  *.dll
  18  
  19  # Compiled Static libraries
  20  *.lai
  21  *.la
  22  *.a
  23  *.lib

Git Attributes

Controls a bunch of Git settings, for instance:
- line endings settings
- LFS settings
- binary/text files handling
*.{bat, [bB][aA][tT]} text eol=crlf - forces to use CRLF so that if a repo is accessed in Windows, the script will work
*.sh text eol=lf - forces bash scripts to always use LF line endings
*.blend binary - will treat blend files as binary files
*.cs text diff=csharp - will treat cs files as text files and uses csharp module for highlighting

.gitattributes example

   1  ###############################################################################
   2  # Set default behavior to automatically normalize line endings.
   3  ###############################################################################
   4  * text=auto
   5  ###############################################################################
   6  # Set default behavior for command prompt diff.
   7  ###############################################################################
   8  *.rs       text diff=rust
   9  ###############################################################################
  10  # Set the merge driver for project and solution files
  11  ###############################################################################
  12  #*.sln       merge=binary
  13  #*.csproj    merge=binary
  14  ###############################################################################
  15  # diff behavior for common document formats
  16  # Don't forget to put the following in .git/config:
  17  # [diff "zip"]
  18  #    textconv = unzip -c -a
  19  ###############################################################################
  20  *.docx diff=zip

Git Config

Contains Git configuration on a global or local project level
Can be accessed by using git config [attributes]
git config --list - displays both configs
git config --global user.name "Dave Dangerous" - sets a global name
git config --global user.email "dave@dangerous.com" - sets a global e-mail
git config --global core.editor "nano -w"~ - sets nano as the default git editor

Example: Local config

   1  [core]
   2  	bare = false
   3  [remote "origin"]
   4  	url = git@gitlab.com:mojo/dojo.git
   5  	fetch = +refs/heads/*:refs/remotes/origin/*
   6  	pushurl = git@gitlab.com:mojo/dojo.git
   7  [branch "myfeature"]
   8  	remote = origin
   9  	merge = refs/heads/myfeature

Don't forget to set up your global name and e-mail!

Git Cherry-pick

git cherry-pick #commit
Takes a commit from any branch and applies it to a different branch
Useful when you made a commit to the wrong branch, and you want to apply it quickly to the right one

Git Apply

Applies a patch of a diff. Used together with git diff > patchfile.patch command

Git Submodules

Keep a git repository as a subdirectory of another git repository
You can incorporate and track version history of external code
Use-cases
- an external component is changing too fast
- you have a component you want to track as a vendor dependency
- you are delegating a piece of the project to a third party
Mapping is managed in a .gitmodules file
git submodule add [url] - transforms a subdirectory into a submodule
Cloning a project with submodules:
1. git clone /url/to/project
2. git submodule init
3. git submodule update

Git Worktree

Alternative for git stash
Creates a linked copy of your git repository under a separate path
You can check out multiple branches at the same time
git worktree add ../myfeature - creates a new worktree
git worktree list - will display the list of worktrees
git worktree remove myfeature - will remove the worktree
Workflow
- Create a worktree
- Do the task that requires it
- Commit the work
- Remove your worktree

Git Bisect

Performs a binary search between two given commits
Can be used to chase down the commit where a bug first appeared
git bisect start - inits the bisect process
git bisect good #hash - marks the good commit
git bisect bad #hash - marks the bad commit
git bisect good - marks the current commit as good
git bisect bad - marks the current commit as bad
git bisect reset - ends the bisect process
git bisect log - shows what has been tested so far
git bisect run #script - runs tests along the way
git bisect start #bad #good - short-hand

Git Bisect Example

Examples

I want to see how the content of myfile.txt looked in the previous commit

   1  git show HEAD~:myfile.txt

Examples

I want to copy-paste a few files from a different branch into my current branch

   1  # Opt 1) for the whole repo
   2  git merge otherbranch --no-commit --no-ff -X theirs
   3  git reset currentbranch
   4  
   5  # Opt 2)
   6  git checkout otherbranch .

Examples

I want to see what has changed in a file over time

   1  git whatchanged -p myfile.txt

Examples

I want to pull a branch that has been rebased and force-pushed on the origin server, without creating a merge request

   1  # Opt 1)
   2  git fetch
   3  git reset origin/master --hard
   4  
   5  # Opt 2)
   6  git pull --rebase

Examples

I want to squash all commits from B to F into one

   1  git reset <commit A>
   2  git add .
   3  git commit -m "BCDEF"

Summary

A commit should be a wrapper for related changes
git stash enables to save your code without making a commit
.gitignore is a file that tracks ignored files
.gitattributes can be used to configure line endings settings
Git config contains Git configuration on a global or local project level
git cherry-pick takes a commit from any branch and applies it to a different branch
git apply applies a patch of a diff
Git submodules keep a git repository as a subdirectory of another git repository
git worktree creates a linked copy of your git repository under a separate path
git bisect performs a binary search between two given commits

1	# Prerequisites
2	*.d
3
4	# Compiled Object files
5	*.slo
6	*.lo
7	*.o
8	*.obj
9
10	# Precompiled Headers
11	*.gch
12	*.pch
13
14	# Compiled Dynamic libraries
15	*.so
16	*.dylib
17	*.dll
18
19	# Compiled Static libraries
20	*.lai
21	*.la
22	*.a
23	*.lib

1	###############################################################################
2	# Set default behavior to automatically normalize line endings.
3	###############################################################################
4	* text=auto
5	###############################################################################
6	# Set default behavior for command prompt diff.
7	###############################################################################
8	*.rs text diff=rust
9	###############################################################################
10	# Set the merge driver for project and solution files
11	###############################################################################
12	#*.sln merge=binary
13	#*.csproj merge=binary
14	###############################################################################
15	# diff behavior for common document formats
16	# Don't forget to put the following in .git/config:
17	# [diff "zip"]
18	# textconv = unzip -c -a
19	###############################################################################
20	*.docx diff=zip

1	[core]
2	bare = false
3	[remote "origin"]
4	url = git@gitlab.com:mojo/dojo.git
5	fetch = +refs/heads/:refs/remotes/origin/
6	pushurl = git@gitlab.com:mojo/dojo.git
7	[branch "myfeature"]
8	remote = origin
9	merge = refs/heads/myfeature

1	# Opt 1) for the whole repo
2	git merge otherbranch --no-commit --no-ff -X theirs
3	git reset currentbranch
4
5	# Opt 2)
6	git checkout otherbranch .

1	# Opt 1)
2	git fetch
3	git reset origin/master --hard
4
5	# Opt 2)
6	git pull --rebase