Ready, Git Set, Go

Ready, Git Set, Go!

Understanding Git

Lindsay Gaudinier at Hook 42

Github Presentation Link

About me

  • Front End Developer at Hook 42
  • Swimming, cats and the internet
  • My first solo talk

Assumptions

  • You have basic command line knowledge
  • You have Git downloaded and configured on your computer (if not, download Git here)
  • You are patient - some words are mentioned before they are defined

Source: xkcd

Why?

  • Because Git is actually pretty awesome
  • Fast -- super fast
  • Working with large projects with lots of people
  • Great for non-linear development
  • Work offline! Local work!
  • Hard to lose information

Photographs

Git takes photographs of your data

When you decide you want to keep a change - you tell Git to take another photo

This photo is called a commit

Commits look like this:

commit b69e6a0d77ff0faa92e209e67398b0077f4961cd

Let's talk about you

Specifically your local computer

This is where you do all your work

It is called your local

You have a code project your local

The code has Git

.git subdirectory

If not - use git init

Deep breath

Three States of Git

These exist on your local

1. Committed:

Data is safely stored on your local
 
2. Modified:

You have changed some data/files but have not recognized these changes
 
3. Staged:

You recognized that changes occurred but you haven't committed these changes to save them

The three states directly relate to...

Three Sections/Trees of A Git Project

We are still only on your local

1. Git Directory (aka Git Repository):

Stores the metadata and object database for your project
 
2. Working Directory:


One single checkout of a version of the project
 
3. Staging Area (aka Index):


File that stores information about what will go in your next commit

Let's tie it together

Git Project Workflow

Step: 1

Git State:
Modify files

Git Section:
Working Directory

Step: 2

Git State:
Stage the Modified Files

Git Section:
Staging Area

Step: 3

Git State:
Commit these Modified Files

Git Section:
Git Directory

Let's get to work!

Check the state of the Git Project (Working Directory, Staging Area, and Git Directory)

git status

Make some changes to a CSS file

In the Working Directory

Add these CSS changes to the Staging Area

git add [filename]

Add a completely new PHP file

Add this new file to the Staging Area

git add [filename]

Must add new files to track them in Git

Git Diff - Comparing Sections/Trees

Difference between your Working Directory with your Staging Area

git diff

Difference between your Staging Area and your Git Directory

git diff --staged

git diff --staged

Git Commit

When the Staging Area is how you like it and you want to move the changes from the Staging Area to the Git Directory

git commit

Git Commit

Records a snapshot of your project that you can revert back to

Commit Message

git commit launches a text editor

Write a good commit message

Good Commit Messages

  • Formatting: first line is 50 characters max, blank line, remaining text wrapped at 72 characters
  • Include a ticket/task number
  • Explain why you are making the commit
  • What is being changed in the commit

Hate Command Line Text Editors?

add the -m flag and avoid the editor

git commit -m["Your message goes here"]

Commit Output

  • Unique SHA-1 Checksum (long mix of numbers and letters)
  • The branch the commit is on (we will get to this)
  • The file changes
  • Stats about the lines added/removed

Removing a file

Remove the file from your Working Directory

git rm [filename]

Run git commit after removing a file

Renaming a file

git mv [old_file_name][new_file_name]

Run git commit after renaming a file

Ignoring a File

.gitignore file - add or modify

Uses glob patterns

Local settings

Viewing the Commit History

git log

This will display the most recent commits first

There is a lot you can do to modify this

Git Log

Another Git Log

Source: coderwall

Undoing Things

Warning

⚠ You cannot always undo your undoes!

Make a commit too early and miss files / Write a bad commit message

git commit --amend

Takes your Staging Area and uses that snapshot for the commit

If there are no file changes - this command will rewrite your previous commit message

git commit -m"Great commit message"

git add forgotten_file

git commit --amend -m["Better commit message goes here"]

git commit --amend

Unstaging A Staged File

You changed two files and added both. But you only want to add one to the commit!

Unstage the file you don't want to commit

git reset HEAD [filename]

Now the file is modified in your Working Directory but NOT in your Staging Area

Unstaging A Staged File

Warning

⚠ If you add options/flags to
git reset HEAD [filename]
things can get dangerous

Unmodifying a Modified File

Did you make some changes, stage those changes and decide you hate them? Undo it!

⚠ Warning: This is an undo that you cannot undo!

git checkout -- [filename]

Unmodifying a Modified File

Git helps teams work together

Remote

A place outside of your local where the code project exists

Git Clone

Receives a full copy of nearly all the data from the remote

git clone [url]

Probably hosted on Acquia, Github, Pantheon, internally, etc

Origin

Default name Git gives the remote server you cloned from

Master

Default name Git gives your local Git project (includes Working Directory, Staging Area, and Git Directory)

List Multiple Remotes

git remote [-v]

The -v flag will provide the url

Get data from a remote

If someone on your team made changes to the remote AFTER you got your code

There are two ways to do this:

1. git fetch [remote-name]

git merge origin/master

OR
2. git pull origin master

Quick Review

  1. Got code from a remote
    git clone [url]
  2. Made changes in your Working Directory
  3. Added these changes to your Staging Area
    git add [filename]
  4. Committed these changes with a message
    git commit -m"Best commit message ever"

Share your commits with your remote!

Git Push

Geting your commits up to the remote is known as pushing upstream

git push [remote-name][branch-name]

Using Git defaults

git push origin master

Git Push Failed!

Output with failed to push some refs to [url]

Someone on your team has updated the remote, and you need to get these changes before you push

Get data from the remote

git pull origin master

Git Branching

Now Git gets super cool

Git Branching

Separate from the main line of development and continue to do work without messing up the main line

Git Branching

When you make a commit, Git stores a commit object that point to content changes included in that commit

A branch is just a lightweight movable pointer associated with one commit

Remember how git clone [url] called your local Git Project master?

The default Git branch is called master

Every branch has its own Working Directory, Staging Area and Git Directory

Branching and Commits

When you start to make commits, you are given a master branch pointing to the last commit made

Every commit made moves the branch forward

Each commit points back to its parent(s)/ancestor(s)

Master branch

Oldest Commit

commit 93ac7
commit a67bf

Newest Commit

commit bf032

HEAD

A special unique pointer called HEAD keeps track of what branch you are on

HEAD only points to the most recent commit on your current local branch

Oldest Commit

commit 93ac7
commit a67bf

Newest Commit

commit bf032
HEAD

Switch Branches

Different branches point to different commits

When you switch branches you move your HEAD

git checkout [branch-name]

Let's take a closer look at branching

Scenario

You are on branch master

You have made several commits

You want to make a new branch to work on a specific feature

Make a branch

git status

Make a branch called feature-branch
git branch feature-branch

Switch your HEAD to that branch
git checkout feature-branch

feature-branch and master are pointing at the same commit

Naming Branches

[id][ticket-number][3-to-5-word-summation-of-issue]

h42-1001-header-navigation-styling

Develop on your Branch

Make a commit on feature-branch

feature-branch has moved forward by one commit

Your Local Git Now Looks Like This

commit 93ac7
commit a67bf
master
commit bf032
commit 7de21
HEAD
feature-branch

If you git checkout master, the HEAD now points to branch master's lastest commit

Your local files revert to match the files of that commit

commit 93ac7
commit a67bf
commit bf032
master
HEAD
commit 7de21
feature-branch

Divergent History

Someone on your team has some work and updated master

Your local master branch is now behind the remote

Update your local with git pull

Both branches no longer point to the same commit ancestor/parent

Divergent History

commit 93ac7
commit a67bf
commit bf032
commit cba52
commit 7de21
feature-branch
master
HEAD
commit f04d8

Merging

We have decided our feature-branch changes are magical

Let's share this magic - get these changes on our local master and then push up to the remote

git checkout[branch-WANTS-the-changes]
git merge [branch-HAS-the-changes]

Merge Commit

We want to be on the master branch and accept the feature-branch changes

git checkout master
git merge feature-branch

Three-Way Merge Commit

Divergent history - Git uses a three-way merge (also called a merge commit)

Git creates a new commit with a new snapshot

This commit has more than one parent

Three-Way Merge Commit

commit 93ac7
commit a67bf
commit bf032
commit cba52
commit 7de21
feature-branch
commit f04d8
master
HEAD
MERGE commit e67a8

Non-Divergent History

git checkout master
git merge feature-branch

Two branches with non-divergent history

Git will create a fast-forward merge

commit 93ac7
commit a67bf
commit bf032
commit cba52
master
HEAD
feature-branch
commit f04d8

Fast Forward Merge

Git simply moves the pointer forward

commit 93ac7
commit a67bf
commit bf032
commit cba52
feature-branch
commit f04d8
master
HEAD

After your three-way merge or your fast-forward merge, push up to your remote and everyone can access your changes

Git Conflict

Unless. It. All. Goes. Horribly. Wrong.

Git Conflict

If the same part of a file is changed on two branches

Appears when you try to merge these two branches

Git pauses the process and tells you there is a conflict

What's Going On?

Git has added conflict markers <<<<<<<, =======, and >>>>>>> in the files

Your HEAD changes appear above the =======

The branch's changes you are trying to merge into your HEAD appears underneath the =======

Fix it!

Solve the conflict by choosing your HEAD changes, the branch changes or select what you want from both

There are a bunch of GUI merge conflict tools

Old school: Edit the file and make sure you remove the conflict markers

Conflict Resolution

After you have resolved the conflict
git add [filename]

Check that you fixed all the file conflicts
git status

Finalize the merge commit
git commit

Avoid Merge Conflicts

  • Communicate with your team!
  • Make sure your master branch is up to date with remote

Merging's Semi-Evil Twin: Rebasing

Integrates changes from one branch into another like merging

Takes all the changes committed on one branch and replays them on another

Makes a cleaner history

Git Log - Rebasing

commit 93ac7
commit a67bf
commit bf032
master
commit cba52
commit df71a
feature-branch

How Rebasing Works

We want to rebase the changes feature-branch onto master
git checkout feature-branch
git rebase master

Now we need to do a fast-forward merge
git checkout master
git merge feature-branch

Rebasing

Branches look linear instead of parallel

commit 93ac7
commit a67bf
commit bf032
commit cba52
feature-branch
commit df71a
master
HEAD

Warning! Warning! Warning!

Rebasing rewrites history

⚠ Do not rebase commits that exist outside of your repository

⚠ Do not rebase commits that others may have based work off of

Cherry-Pick

A cherry-pick is a rebase for a single commit

commit 93ac7
commit a67bf
commit bf032
commit cba52
commit 5d42e
master
commit 45ec9
feature-branch
commit aac871

Cherry-Pick

Pull in the second commit on feature-branch 45ec9 into master

git checkout master
git cherry-pick 45ec9

This creates a new commit

Cherry Pick

commit 93ac7
commit a67bf
commit bf032
commit cba52
commit 5d42e
commit 45ec9
 
feature-branch
commit aac871
CHERRY PICK commit 98bef
master
HEAD

Stashing

Current problem is a work in progress, but need to switch branches for a hotfix

Want to fix the hotfix with a clean Working Directory, but still keep the progress you made

Save the state of modified tracked files and staged changes

git stash

Working directory is now clean

Stashing

Stashing - Files Overwritten By Checkout

Reapply A Saved Stash

List your stashes - most recent stash is first
git stash list

Reapply a stash
git stash apply stash@{1}

Git assumes most recent stash if you don't specify

Create a Branch from a Stash

Use if the stash has been left alone for some time

git stash branch [branch-name] [stash-number]

git stash branch feature-branch stash@{1}

This is just skimming the surface of Git

References

Questions?