Git tips

Git Tips
by Arthur Shvetsov
CoreValue/MalkosUA

Agenda
● Git common principles and design goals
● Merging vs. Rebasing
● How to rewrite history?
● A successful Git branching model

What is Git?
● Git is a distributed revision control and source code
management (SCM) system with an emphasis on
speed, data integrity, and support for distributed, non-
linear workflows.
● Git was initially designed and developed by Linus
Torvalds for Linux kernel development in 2005, and has
since become the most widely adopted version control
system for software development.

Git design goals
● Speed
● Simple design
● Strong support for thousands of parallel branches
● Fully distributed
o full local repository
o offline commits
o full size repository
● Able to handle large projects like Linux kernel effectively
● Ensure integrity

Git drawbacks
● Big committed files will be in every clone of
repository
● No partial checkout
● No lock
● No support of empty directories

Git philosophy
● Commit early, commit often
● One commit represents one idea or one
change
o Make it easy to read patches
o Easy to revert unwanted changes later
● Your working directory, index and local
repository are your scratch pads

Nearly Every Operation Is Local

Snapshots, Not Differences
The major difference between Git and any
other VCS (Subversion and friends included) is
the way Git thinks about its data.

Tracking changes (most VCS)
Storing data as changes to a base version of each file

Tracking changes (the Git way)
Storing data as snapshots of the project over time

The Staging Area
The staging area is a buffer between the
working directory and the project repository.

What happens when you create a
commit ?

What happens when you create a
new branch?
$ git branch testing

How does Git know what branch
you’re currently on?

What happens when you switch a
branch?
$ git checkout testing

Merging vs. Rebasing
git rebase and git merge - both of these
commands are designed to solve the same
problem - integrate changes from one branch
into another branch — they just do it in very
different ways.

A forked commit history
To incorporate the new commits into your feature branch,
you have two options: merging or rebasing.

Merging master into feature branch
$ git checkout feature
$ git merge master

Pros
● Simple to use and understand
● Merging is a non-destructive operation
● The existing branches are not changed in any way
Cons
● The feature branch will have an extraneous merge
commit every time you need to incorporate changes
● Visual charts of repository can have non-informative
branch lines
Git merge pros and cons

The Rebase Option
$ git rebase master

Pros
● Much cleaned project history
● Eliminates the unnecessary merge commits required by git merge
● A perfectly linear project history
Cons
● Re-writing project history can be potentially catastrophic for your
collaboration workflow
● Rebasing loses the context provided by a merge commit - you can’t
see when upstream changes were incorporated into the feature
Git rebase pros and cons

Git rebase golden rule
Never use git rebase on public branches. Only rebase
local branches

When you rebase pushed branch, you’re
abandoning existing commits and creating
new ones that are similar but different

Interactive Rebase
$ git rebase -i master

Pros
● Eliminating insignificant commits like this makes
your feature’s history much easier to understand.
This is something that git merge simply cannot do
Interactive rebase pros, no cons :)

Force Pushing
$ git push -f origin feature

Integrating an Approved Feature

Integrating an Approved Feature.
“Fast forward” effect

Rebasing a temporary branch
git checkout feature
git checkout -b temporary-branch
git rebase -i master
git checkout master
git merge temporary-branch

Git pull --rebase
By default, the git pull command performs a
merge, but you can force it to integrate the
remote branch with a rebase by passing it the --
rebase option.
$ git config branch.autosetuprebase always

Git revert
Reverting undoes a commit by creating a new
commit. This is a safe way to undo changes, as
it has no chance of re-writing the commit
history.

$ git checkout hotfix
$ git revert HEAD~2

Git reset
Git reset as the dangerous method. When you
undo with git reset, there is no way to retrieve
the original copy—it is a permanent undo.

$ git checkout hotfix
$ git reset HEAD~2

git checkout
● checking out branches
● checking out commits - makes the entire
working directory match that commit
● checking out files - lets you see an old
version of that particular file, leaving the rest
of your working directory untouched

“Detached HEAD” state
$ git checkout HEAD~2

Multiple ways how to rewrite
history?
● $ git reset
● $ git rebase

Git cherry-pick
Applies the changes introduced by some
existing commits to specific branch
$ git checkout feature-branch
$ git cherry-pick <commit hash>

Stashing
Records the current state of the working
directory and the index, and cleans up the
working directory
$ git stash

Submodules
Submodule allows you to keep another Git
repository in a subdirectory of your repository
$ git submodule

A successful Git branching model

The main branches
● master
o contains production ready code
● develop
o an integration branch
o contains the latest changes
o used for nightly builds
o getting a production release
when merging with master

Supporting branches
● Feature branches
● Release branches
● Hotfix branches

Feature branches (topic branches)
● May branch off from:
o develop
● May merge back into:
o develop
● Branching name convention:
o anything except master, develop,
release-* or hotfix-*

Creating a feature branch
$ git checkout -b myfeature develop
Switched to a new branch “myfeature”
Incorporating a finished feature on develop
$ git checkout develop
Switched to branch 'develop'
$ git merge myfeature
Updating ea1b82a..05e9557 (Summary of changes)
$ git branch -d myfeature
Deleted branch myfeature (was 05e9557).
$ git push origin develop

Release branches
o develop
● Must merge back into:
o develop and master
● Branch naming convention:
o release-*
● Used for preparation of a new production release
● Allow minor bug-fixes

Creating a release branch
$ git checkout -b release-1.2 develop
Switched to a new branch "release-1.2"

Finishing a release branch
$ git checkout master
Switched to branch 'master'
$ git merge release-1.2
Merge made by recursive. (Summary of changes)
$ git tag -a 1.2
$ git merge release-1.2
$ git branch -d release-1.2
Deleted branch release-1.2 (was ff452fe).

Hotfix branches
o master
● Must merge back into:
o develop and master
● Branch naming convention:
o hotfix-*

Creating a hotfix branch
$ git checkout -b hotfix-1.2.1 master
Switched to a new branch "hotfix-1.2.1"
$ git commit -m "Fixed severe production problem"
[hotfix-1.2.1 abbe5d6] Fixed severe production problem 5
files changed, 32 insertions(+), 17 deletions(-)

Finishing a hotfix branch
$ git checkout master
Switched to branch 'master'
$ git merge hotfix-1.2.1
$ git tag -a 1.2.1
$ git merge hotfix-1.2.1
$ git branch -d hotfix-1.2.1
Deleted branch hotfix-1.2.1 (was abbe5d6).

Links and Literature
● Pro Git
● A successful Git branching model
● https://www.atlassian.com/git/tutorials/
● https://help.github.com/

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