Git and GitHub

Geoffrey Liu

Follow along!

g-liu.com/git

While we're talking...

Hi, I'm Geoffrey

  • CSE major, music minor, c/o 2016
  • Second time as a 154 TA
  • Past: CDK Global, ASUW
  • Future: Groupon
  • Front-end web dev enthusiast

Life without version control

Have you done any of the following for a project?

  • Emailing copies of files back and forth
  • Working on code through Google Docs
  • Sending code through IM

Life without version control

What if you need to...

  • Go back to an older version of a file?
  • View the history of the project? A file?
  • Manage similar versions of the project?
  • Easily share code with another developer?

Git, conceptually

At the highest level, a Git repository is a series of snapshots of files in a folder.

  • Snapshots formally called commits (more later)
  • You tell Git when to take a snapshot
  • Like a time machine: can view any snapshot whenever you want!

time

Photo credit: gitref.org

Git, conceptually

There are three sections in a Git repository.

  • Repository: all committed files, along with their contents at the time of commit
  • Staging area: all files declared to have been modified (staged), but not yet committed
    • Also known as the index
  • Working directory: all files whose contents have been modified, but not yet staged

Photo credit: Git-scm.com

Git, conceptually

  • Git is what we call a distributed version control system (DVCS)
  • There exists one "master" repo, called the origin
    • ​Usually stored on a server
    • In our case, stored on GitHub
  • Each clone of the origin is called a working copy

Photo credit: CSE 331, UW CSE

One-time setup

Local setup, continued

  1. Log into the GitHub Desktop app with your account
  2. Open up "Git Shell"
  3. In Git Shell, type: git --version
    • You should see "git version 2.X.X"
    • If not, raise your hand or ask your neighbor

Git on PowerShell / cmd

(for Windows users only)

  1. Type %localappdata% in Explorer
  2. Go to GitHub/PortableGit_*/cmd
  3. Copy the filepath, which should look like this:
    C:\Users\name\AppData\Local\GitHub\PortableGit_<uniqueId>\cmd
  4. Add that filepath to your PATH variable

Create the origin repo

  • Go to https://github.com/new
  • Give your repo a name and description
  • (Leave all other settings as default)
  • Click "Create Repository"
  • Copy the Git URL (need this for next step)

Clone your new repository

git clone git_url

  1. Open "Git Shell"
  2. Type the above command into the shell, pasting in the Git URL of your repository
    • Note: May need to use Shift + Insert to paste

Navigate to your local copy

  • git clone creates a new folder with the same name as your repository
  • Type ls to see all files/folders in the current directory
  • Type cd repoName, replacing repoName with the name of your repository, to navigate to your repo

Git basic workflow

Make some changes

Pretend you're working on a project. Maybe you need to:

  • Create a new file/files? touch filename
  • Delete a file/files? rm filename
  • Edit a file? vi filename (or use your favorite editor).
  • What you do here is up to you!

See what's changed

git diff

  • Shows comparison of working tree vs. staging area

git status

  • Shows you a list of files modified

Add changed files

git add pathspec1 pathspec2 ...

  • Stages the files in the working directory that match the given pathspecs
    • Additionally, tracks any untracked files
  • Pathspec: a string that matches zero or more files
    • Like what you can pass into PHP's glob
  • Use git status to list all modified files

Describe the changes made

git commit -m "your commit message"

  • Creates a snapshot of all changes made to staged files
  • Use git status to see the files to be committed
  • Use git log to see all commits made so far

Commit messages

  • #1 rule: A commit message should be descriptive!
    • Concisely describe changes made
    • Pays off in the future
    • Helps other developers understand your changes
  • Git requires every commit to have a message

Good messages

Bad messages

"Upload" the changes

git push

  • Updates origin repo with the latest commit(s) made
  • Makes changes available to other collaborators.
  • Congratulations! You just made your first commit!

Workflow summary

  • For any changes to a repository:
    1. Make changes to necessary file(s)
    2. Add the files with git add files...
    3. Commit the files with git commit -m "message"
    4. Push the files to the origin with git push
  • The quintessential Git workflow; know this if nothing else!

Workflow summary

Undoing things

Reverting file changes

git stash and git stash apply

  • Saves all changes made so far and resets working copy to last commit
  • Use git stash apply to bring back those changes

git checkout -- path1 path2 ...

  • Reverts all changes to the files at the specified path(s)
  • WARNING! Cannot be undone!

git reset --hard

  • Reverts entire repository to the last commit
  • WARNING! Cannot be undone! Use only as last resort!

Undo add

git reset HEAD path1 path2 ...

  • Removes the specified files from the staging area
  • File contents are not changed

git rm --cached path1 path2 ...

  • Removes files from repository
  • Keeps the untracked copy in your working directory

 

Trick: git status tells you which one to use

Undo commit

git commit --amend -m "new message"

  • Changes commit message of the last commit

git reset HEAD~1

  • Undoes last commit, and keeps changes to files

git reset --hard HEAD~1

  • Undoes commit, and discards all changes
  • WARNING! Cannot be undone!

Undo push?

 

Lesson: don't push unless absolutely sure!

Need to peek back?

git checkout SHA

  • Each commit has a unique identifer called an SHA
  • You can find the SHA of each commit with git log
  • Useful for looking at code from a previous commit
    • Can edit and play around with the code
    • Cannot make commits here
  • To go back to current: git checkout master†

†If you were on a different branch, replace "master" with the branch you were on

Need to revert back?

git revert SHA

  • Creates an "anti-commit" to rollback to the commit with the given SHA
  • Push it as a normal commit: git push

Ignoring files

Some files should not be committed:

  • Passwords
  • API tokens
  • Sensitive information / data
  • Compiled code
  • System / OS generated files

 

A file named .gitignore is used to manage this!

The .gitignore file

  • File name starts with a dot (.)
  • May be hidden in your file explorer
  • Create the file in the shell: touch .gitignore
  • Edit with your favorite text editor

.gitignore syntax

# Comments start with hash, and are ignored
# A gitignore file is a list of file-matching patterns

# Ignores any file in any directory with this name. 
passwords.txt

# Ignores any directory with this name
dist/

# Ignores any file with this extension
*.class

# We can combine file-matching patterns
vendor/*.min.js

Read more: https://git-scm.com/docs/gitignore

.gitignore resources

Collaboration

Let's work on code together!

  • "Share" the repository by adding others as collaborators
  1. Find a partner
  2. Exchange GitHub usernames
  3. Follow these instructions to add collaborators

Contribute to each other's repositories

  1. Exchange repository URLs
  2. Go back to your local GitHub folder: cd ..
  3. Clone their repository: git clone their_git_url
  4. Navigate to the cloned repo: cd their_repo_name
  5. Most of the workflow is already familiar:
    • Modify necessary files
    • git add paths...
    • git commit -m "commit message"
    • git push

Keep your copy up to date

git pull

  • Go back to your repo's directory: cd ../yourRepoName
  • Type the above command
    • Fetches the latest changes from upstream
    • Merges changes into your local copy

Git "errors"

  • With many contributors, your local repo can fall behind.
  • Most basic: need to get latest commits with git pull.
  • Even then, what if you and another user change the same file?
  • These are the consequences of collaboration, but are fully justified.
  • Be able to recognize and resolve these common issues

"non-fast-forward"

  • Fancy speak for "your local repo isn't up to date"
  • Usually occurs when git pushing some changes
  • Fix by running git pull, followed by git push

Merge conflicts

  • Happens when two users change the same file
  • File now contains changes from both you and others
  • Need to choose how to resolve conflicts
  • For simple fixes: open text editor, resolve conflicts
  • More complex fixes: git mergetool (may require additional software installation)

Resolving merge conflicts

  1. Open file in text editor
  2. Look for parts of the file that look like this:
<<<<<<< HEAD
    // This is the code that you have written
    ...

=======
    // This is the code that they have written
    ...

>>>>>>> b56a88aab1e13f7c3402fd71a5f890d0368ea3ec

Resolving merge conflicts

  1. Edit each merge conflict accordingly
    • For each conflict, decide which parts to keep
    • When done, all lines with <<<<<, =====, >>>>> should be gone
  2. git add conflicted-file to mark resolution
  3. git commit to conclude merge
  4. git push

Resolution shortcuts

A quick way to say, "their changes are all correct", or "my changes are all correct"

git checkout --theirs file

  • Accept all changes made by other author(s) to file

git checkout --ours file

  • Accept all changes made by you to file

GitHub.com features

Git and GitHub, so far

  • So far, the focus has been on Git
    • ​What is Git, conceptually?
    • How do you use Git commands?
    • What is the basic Git workflow?
  • Now: Focus on GitHub, a "wrapper" around Git
  • Go to your repository on GitHub.com:
    http://github.com/your_username/repo_name

GitHub is a wrapper

Along with hosting your Git repository, GitHub provides the following infrastructure:

Issue tracking

  • Each repository has a built-in issue tracker, at

github.com/username/repo/issues

An issue is a task to accomplish on a project. Examples:

  • Bug report (most common)
  • Feature request
  • Enhancement

Creating an issue

  1. Give the issue a descriptive title
  2. Describe the issue (more to come)
  3. Give the issue a label (recommended)
  4. Give the issue a milestone (optional)
  5. Assign the issue to someone (recommended)

Writing good bug reports

Can't just say "this button doesn't work, plz fix!!"

A good bug report should contain at least:

  • A concise description of the issue
  • The environment on which the bug appeared. Examples:
    • Operating system and version
    • Browser version
    • Application version
    • Hardware info (CPU, screen resolution, etc.)
  • The steps required to reproduce the issue
  • The expected bug-free behavior

Bug report examples

Good:

 

Bad:

Guidelines for issues

  • Each issue should be categorized and assigned to a user
  • Assignees and issue authors should keep the issue progress up to date
  • Referencing issues in commits is a lightweight way to track progress on issues
  • A good project is always closing issues

GitHub issue features

More overhead, but can help keep your project tidy!

  • Reference an issue in another issue
  • Reference a specific commit in an issue
  • Mention user(s) in an issue
  • Close an issue with a single commit

 

See Mastering Issues

Forking

Say you want to contribute to Twitter Bootstrap

  • Problem: You don't have contributor access
  • Solution: Copy of the Bootstrap repo to your account by forking it
    • Make changes to your fork
    • Request those changes to be integrated into the main Bootstrap repo (next slide)

Pull requests

  • Used to tell others about changes you've made to a repository on GitHub.
  • Only contributors with push access can accept pull requests!
  • Read more on Using pull requests

Wikis

  • Like an internal Wikipedia for your project
  • Use it to keep track of information about your project:
    • Installation
    • Known bugs
    • Configuration
    • Software architecture diagrams
    • Detailed documentation
    • Use cases

Stats and graphs

Note about homework code

  • GitHub repos are by default public
  • Homework solutions are for CSE 154 only!
  • In short: don't upload your 154 homeworks to GitHub
  • If you must, make a private repo for homework

What you know now

  • How to set up a repo on GitHub
  • Basic Git workflow
  • Basic Git "debugging"
  • Collaborating with a partner
  • Using GitHub features

What you should do next

Follow me on GitHub!

http://github.com/g-liu

 

I will follow back!

Additional resources

Questions?

Git workshop

By Geoffrey Liu

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Git workshop

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