Working with GIT

Working with GIT - presented at ONF Member Workdays
By Brian O'Connor, ON.Lab

Transcript

1. Brian O'Connor
   Open Networking Lab
   2/11/2015
   Working with
   

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2. What this talk will cover
   Git Basics
   - Getting started
   - Basic workflow and commands
   GitHub
   - Getting started
   - Anatomy of a project
   - How to contribute
   

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3. Disclaimer
   This will be a bit of a whirlwind tour,
   and I will borrow some of the materials from
   git-scm.com and github.com
   There are plenty of in-depth (and better)
   tutorials and videos that get into a lot of the
   details that I may gloss over.
   

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4. Why Version Control?
   ● For Version History
   ○ Allows you to go back and revert changes and
   recover or compare against old version
   ○ Makes experimentation easier (using branches)
   ● To Facilitate Collaboration
   ○ Allows you to make modifications to files in parallel
   as a team and merge the result
   

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5. What is Git?
   vs.
   CVS, Subversion, Perforce Git, Mercurial, Bazaar
   

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6. How do I start?
   ● A brand new project
   ○ git init # in the project's top level directory
   ● An existing project (more common)
   ○ git clone [URL]
   ○ git clone https://github.com/mininet/mininet.git
   Note: Projects will contain a .git directory that will track will contain all
   changes and metadata. Also, if you don't have git installed, do this first:
   https://help.github.com/articles/set-up-git/
   

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7. Branching
   ● master
   ○ default branch when you check out a project
   ○ usually "stable" and "deployable"
   ● topic branches
   ○ best practice for changes
   ○ local only, unless you push them somewhere
   git checkout -b my-feature master # to create
   git checkout master # to switch branches
   

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8. Committing Changes
   1. Make a change to a file
   2. Look at what's changed (optional)
   ○ git status
   3. Stage your files for commit
   ○ git add [file name]
   4. Commit!
   ○ git commit # opens the default editor
   Shortcut: git commit -a -m"Commit Message"
   

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9. Anatomy of a commit
   commit ea9ae214f9bca97537378f205910d62b7aa4be47
   tree de130618eaf06592df72b43b06e88ea87160d8b6
   parent 0cc189e6814cb0bf5af049fd6074212a2599a571
   Author: Brian O'Connor
   Date: Fri Feb 6 16:41:49 2015 -0800
   Using CommandSession console instead of System.*
   in AbstractShellCommand print and error
   fixes ONOS-986
   diff --git a/cli/src/main/java/org/onosproject/cli/AbstractShellCommand.java
   b/cli/src/main/java/org/onosproject/cli/AbstractShellCommand.java
   index e6a62d0..b404db6 100644
   --- a/cli/src/main/java/org/onosproject/cli/AbstractShellCommand.java
   +++ b/cli/src/main/java/org/onosproject/cli/AbstractShellCommand.java
   @@ -62,7 +62,7 @@ public abstract class AbstractShellCommand extends OsgiCommandSupport
   {
   * @param args arguments
   */
   public void print(String format, Object... args) {
   - System.out.println(String.format(format, args));
   + session.getConsole().println(String.format(format, args));
   }
   /**
   commit hash (SHA1)
   author information
   commit message
   commit diff
   git show [commit hash | branch | HEAD]
   

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10. Looking at the past
    git log [branch | commit hash]
    git log --oneline --graph --decorate=short
    * 0094997 (tag: 2.2.0b3) fixing install-mininet-vm.sh
    * 7a411b6 Merge pull request #453 from cdburkard/master
    |\
    | * c2341cd update examples README with new examples
    |/
    * 4219b22 (tag: 2.2.0b2) 2.2.0b2
    * 08ab7e8 Merge pull request #452 from mininet/nat-cmd
    |\
    | * ab97dfa (origin/nat-cmd, nat-cmd) fixing no --nat issue
    | * af1ccf9 Updating NAT class to use gateway interface
    * | 3ef6bcf Additional info about --nat and LinuxRouter
    |/
    * 015cd9e Merge pull request #443 from cdburkard/devel/cluster
    |\
    | * bbf94cd use rcmd instead of quietRun when shutting down remote nodes
    * | 3d44bcd MiniNet -> Mininet
    * | 1817cbc Pass pyflakes
    * | e0bf8ec Minor code cleanup
    

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11. : the social network for code
    

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12. Getting Started on GitHub
    ● Create an Account
    ● Add your public key (strongly recommended)
    ○ makes pushing changes easier
    Get started @ https://github.com/
    

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13. Anatomy of a project page
    repository
    viewer
    commit
    log
    project forks
    issue tracker
    pending
    contributions
    project wiki
    download
    URL
    

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14. Pulling the latest changes
    ● git clone [URL]
    ○ create a new repository with the latest code
    ● git pull [remote] [branch]
    ○ gets the latest code for the specified branch on the
    remote and merges it into your current local branch
    ● git fetch [remote]
    ○ updates your local metadata with the latest
    information about the remote repository
    

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15. Dealing with merge conflicts
    ● Happens when two people change the same
    file in a conflicting way
    ○ Usually manifest themselves when you do git pull
    ● What you'll see
    ○ CONFLICT (modify/delete): ...
    # Automatic merge failed; fix conflicts and then commit the result.
    ● How to fix it
    ○ Update the offending file(s)
    ○ Stage the changes using git add [filename]
    ○ Commit using git commit
    

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16. Forking a project
    ● Your own copy of someone else's project
    ● Somewhere to push your local changes
    ○ And collaborate with others on them, too!
    ● Push your changes to GitHub
    ○ git push origin [branch name]
    ● To fork, click the "Fork" button on the
    upstream project page in GitHub
    ○ Creates a clone of the upstream in GitHub
    

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17. Keeping your fork up to date
    ● Set up remote
    ○ git remote add upstream [upstream URL]
    1. Fetch the latest from the remote
    ○ git fetch upstream
    2. Checkout your local master
    ○ git checkout master
    3. Merge the upstream changes
    ○ git merge upstream/master
    4. Push the changes to GitHub
    ○ git push origin master
    

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18. Pull requests
    ● Push the latest changes to your topic branch
    to GitHub
    ○ git push origin [branch]
    ● Click the "Compare & pull request" button
    on your fork's project page:
    

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19. Issue tracking and GitHub wiki
    ● Automatically built-in
    ● Issue tracker
    ○ Useful for reporting bugs, tracking new features, etc.
    ○ Automatically integrated using commit messages
    e.g. "Closes #843"
    ● Wiki
    ○ Great place to put project documentation
    e.g. installation instructions, tutorials, etc.
    ○ Editable by anyone with a GitHub account
    ○ Versioned
    

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20. Live Demo
    ● Fork a project
    ● Make a change and commit
    ● Pull and Merge conflicts
    ● Push to remote
    ● Create a pull request
    

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21. Other Topics
    ● .gitignore file
    ○ Tells git to ignore certain files or patterns, like build
    artifacts
    ● git stash
    ○ Useful for quickly stashing local changes while
    pulling/updating code
    ● git rebase
    ○ Replay your branch from a new parent
    ○ NEVER rebase code that's been pushed*
    ○ Used heavily in Gerrit workflow
    

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22. Merge vs. Rebase
    Note: NEVER rebase public (i.e. pushed to remote) branches
    Exception: Okay to rebase pending changes/commits in Gerrit
    Images from: https://www.atlassian.com/git/tutorials/merging-vs-rebasing/workflow-walkthrough
    git merge master git rebase master
    Feature Branch
    

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23. Resources
    Cheat Sheet
    https://training.github.com/kit/downloads/github-git-cheat-sheet.pdf
    Collection of Tutorials
    https://help.github.com/articles/good-resources-for-learning-git-and-
    github/
    Fantastic (free!) eBook
    http://git-scm.com/book/en/v2
    Tons more easily found via Google
    

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