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What does a Version Control System do?

  • Track source code
    • Maintain code history, integrity, atomic change...
  • Coordinate distributed development
    • branch, merge conflicts, tag...

VCS general work flow

VCS Work Flow Categories

Why git is better than X (SVN, CVS, ...)

  • git is super fast
  • Full repository clone
  • Local history: no need to connect to servers when viewing the revision history
  • Cheap branch and easy merge
  • github: social coding2
  • Other things: tidy working directory, better compression, multi work flow support, …

General Advice on Learning git

  • Try git and github
  • Most graphical tool/plug-ins3 SUCK. Please use the command-line git.
  • Read git's prompts, run git help to get help.
  • Find "how-to" on Google, StackOverflow, git book.

Rules of Thumb for git

  • "A clear development flow is worth thousands of VCSs."
  • One repo for one project. Use submodule to organize super projects.
  • Modular design, avoid simultaneous source file editing by different members.
  • Head version at trunk is always ready to deploy.
  • Modification is made on branches, then merged into trunk.
  • Stay on your own branch.
  • Write comment to each commit.

To get started, I will...

  • Illustrate git's various work flows.

  • Explain the most frequently used git commands.

  • Give exercises for self check. Some of the exercises require github access.

git's stand-alone work flow

  • You can use git on a stand-alone computer and easily integrate the code into a more sophisticated work flow (distributed or centralized) at a later time.

gitalone

git's distributed work flow

  • Every collaborator keeps a full clone of the repository.
  • All repositories are peers.
  • Repositories are not necessarily consistent at all time. Use push/pull to exchange changes when necessary.

gitdvcs

git's emulation to the centralized work flow (RECOMMENDED)

  • It's emulation, not real.
  • The statement, "all repositories are peers.", still holds.
  • We pretend that we see the central repo only, unaware of each other's peer repo.

gitcent

Set up git

  • Please follow github's nice tutorials to set up4 git on Windows, Linux or Mac.
  • Must-known things about SSH keys: private key, public key, the pass phrase to access the private key, key fingerprint.
  • Don't forget to set user.name and user.email5 before your very first git commit.

git command

  • help
  • init
  • status
  • add
  • commit
  • diff
  • tag
  • Working with branch
  • Working with remotes
  • submodule
  • Oh, there is a conflict!!!
  • "Time Machine"

help: Get help

git help COMMAND Get help from git.

  • git help add
  • git help commit
  • ...

init: Initialize a local git repo for your project

init command will create a .git dir on the top level of your project.

  1. cd YOUR_PROJ_DIR
  2. git init .

status: Show the status of your repo

git status

  • status tells you how to UNDO the last operation on git
  • File status: untracked, unstaged, staged (indexed), committed6

gitlifecyle

add: A multi-function git command

git add FILES_OR_DIR

  • For untracked files: add them to git's control
  • For unstaged changes: add them to the staged area
  • For conflicted files: add marks them as "resolved"

.gitignore: Ignore files

  • Specify file types to ignore in .gitignore (a normal text file)
    • .tmp (Ignore all *.tmp files)
    • .bak (Ignore all *.bak files)
  • git has an internal .gitignore. You can ask git NOT to ignore some file types in .gitignore
    • !*.o (Don't ignore *.o files)
  • git help gitignore

commit: Store the status (snapshot) permanently

  • git commit -m "YOUR_COMMENT"
    • git commit Stores the STAGED changes only
    • git commit -a Stores all the STAGED and UNSTAGED changes.
  • Please write comment for each of your commit.
  • Each commit is identified by a UNIQUE SHA-1 ID of 40 ASCII characters.
     commit dd5f924c40096b9cda27ffd1cfd1205822ab3c70
     Author: Github Support <me@github.com>
     Date:   Sun Apr 1 19:38:37 2012 +0800

        Restart the git-tutorial project.

diff: Find differences

  • git diff
    • changes between the staged and working files
  • git diff --staged
    • changes between the HEAD and the staged files
  • git diff HEAD
    • changes between the HEAD and the working files
  • git diff COMMIT_ID COMMIT_ID
    • changes between two commits

tag: A milestone version

  • git tag
    • See all the tag
  • git show TAG_NAME
    • See a tag in detail
  • git tag TAG_NAME
    • Add a "lightweight" tag
  • git tag -a TAG_NAME -M YOUR_COMMENT
    • Add an anotated tag
  • git tag -d TAG_NAME
    • Delete a tag

Submodule: Integrate multi git repos

  • git help submodule
  • Repo in Repo
  • Manage other repos as "submodules" in your project

Working with branch: branch, checkout, merge

A branch-based development flow:

  1. Create a branch
  2. Switch to the newly-created branch
  3. Modify and commit on the branch
  4. Merge branch's changes into trunk.

Working with branch: branch, checkout, merge

  • git branch
    • See all the branches
  • git branch BRANCH_NAME
    • Create a branch
  • git branch -d BRANCH_NAME
    • Delete a branch
  • git branch -D BRANCH_NAME
    • Force delete a branch

Working with branch: branch, checkout, merge

  • git checkout BRANCH_NAME
    • Switch to a branch. The working files will change.7
  • git checkout -f BRANCH_NAME
    • Force switch to a branch
  • git checkout master
    • Go back to trunk, named master in git.
  • git checkout -b BRANCH_NAME
    • Create a branch then switch to it.

Working with branch: branch, checkout, merge

  • git merge BRANCH_A BRANCH_B
    • Merge branch_a's and branch_b's changes into current branch
  • git checkout master, git merge master BRANCH_NAME
    • Merge changes into trunk, the master branch.

Working with remotes: clone, remote, push, pull

  • git clone REPO_URL Full clone of a repo.
  • URL can be in forms of local dir (~/proj), git (git://xxx), SSH (ssh://xxx), https (http://xxx)...

Working with remotes: clone, remote, push, pull

  • remote Manages the set of tracked repositories.8
  • git remote
    • Show all the tracked repositories.
  • git remote show REPO_NAME
    • Show the repo's details.
  • git remote add REPO_NAME REPO_URL
    • Add a remote repo to tracked list.
  • git remote rm REPO_NAME
    • Remove a remote repo from the tracked list.
  • git remote rename REPO_OLD REPO_NEW
    • Rename a repo.
  • git help remote
    • Show remote help doc

Working with remotes: clone, remote, push, pull

  • git pull REPO_NAME REMO_BRANCH
    • Merge remote branch's changes into current branch.
  • git push REPO_NAME REMO_BRANCH
    • Push current branch's changes to the remote branch.
  • git push REPO_NAME :REMO_BRANCH
    • Delete a remote branch.

Oh, there is a conflict!!!

  • A conflict looks like:
<div id="footer">contact : email.support@github.com</div>
=======
<div id="footer">
  please contact us at support@github.com
</div>
>>>>>>> iss53:index.html
  • Conflicts arise when git cannot automatically merge changes at merge or pull operations.
  • Don't panic. Conflicts are no big deal, sometimes even inevitable.
  • What you should do: merge the conflicts, mark the files as "resolved", then commit the changes.

Working with conflicts: merge, resolve, commit

  1. You have to edit the conflicted files, merge conflicts MANUALLY. diff command may help you.
  2. git add CONFLICT_FILES Mark the file as resolved.
  3. git commit -m "YOUR_COMM" Commit changes to the repo.

"Time Machine": stash, checkout

stash saves your temporary work and resets the files to HEAD version. You can handle some emergency fix first then continue to hack at a latter time.

  1. git stash
    • Save the temp changes.
  2. git stash list
    • Check the stash list.
  3. EDIT and COMMIT your emergency fix.
  4. git stash pop
    • Continue to hack

"Time Machine": stash, checkout

checkout enable you to go backward and forward in the revision history.

  1. git checkout COMMITID_OR_TAGNAME 9
    • Time Machine starts up.
  2. You are on a unnamed branch with file status dating back. Do anything you want.
  3. git checkout master
    • Come back to master.

Exercise 1: Set up git environment

  1. Set up git on your computer, and sign up a github account.
  2. Initialize a local project as git repo, make your first git.

Exercise 2: git basics

Be familiar with status, add, commit, diff, tag.

Exercise 3: Branch-based development

  1. Create a branch.
  2. Checkout to that branch.
  3. Merge the changes into trunk (master).
  4. Delete the branch.

Exercise 4: Be social on github

  1. Open an issue in GitForBeginners to say hello.
  2. I will add you as a collaborator. Please wait for my message on github before preceeding to next setp.
  3. Clone the GitForBeginners project with Read+Write access.
  4. Write something into the README.mkd (DON'T destroy the description header). add, commit, pull, push.

Exercise 5: Manage remotes

  1. You clone the remote repo GitForBeginners on github. Try git remote.
  2. Copy the REPO_URL to somewhere else.
  3. Delete the remote repo.^[Don't worry. It is just a reference.]
  4. Add the remote repo REPO_URL with a name you prefer, such as myrepo.
  5. Rename the remote repo to its original name -- origin.

Exercise 6: Remote branch

  1. Create a local branch with your full name, such as zhangsan.
  2. Write something into README.mkdg on the branch. add, commit, pull, push to the remote branch.
  3. Leave the branch on github as a mark of "I finish the homework". Please recreate the the remote branch if you've tried the delete remote branch command.

Exercise 7: Handle conflicts

  1. Clone GitForBeginners twice into two seperate projects, namely proj_A and proj_B.
  2. In proj_A, modify README.mkdg. add, commit, pull, push
  3. In proj_B, modify the SAME lines of README.mkdg as you do in proj_A. add, commit, pull
  4. A conflict towards README.mkdg arises in proj_B.
  5. Resolve the conflict, then add, comit, pull, push to github.

Exercise 8: Time Machine

Use stash, checkout to do time travle.

Recommended Materials for Learning git

Acknowledgement

  • The slides are composed with Markdown language, and converted to latex beamer with pandoc.
  • XeTeX is a nice typesetting system. latexmk helps to hide the complexity of compilation.
  • The slides, along with the project, is hosted on github.
  • Feedback is always welcomed. Write me or open an issue on the project homepage.

Footnotes

  1. Distributed VCSs support centralized work flow too. ↩

  2. bitbucket, Google Code support git too, but github in no doubt has more fun. ↩

  3. tortoisegit, gitk, EGit, Snow Octocat... But please, oh please use the command-line tool. ↩

  4. The email you fill in when signing up is used for web login and password reset only. github uses SSH keys for git authentication. Try to clarify the following pass phrases: your email account's pass phrase, your github account's pass phrase, and the pass phrase to access your SSH private key. ↩

  5. Usernames and emails in git's configuration are for identification purpose only, not for sending emails. It is highly recommended that the email in git and SSH keeps the same. ↩

  6. The committed status simply displays nothing when running git status. ↩

  7. Don't confuse git's term checkout here with Subversion's checkout. ↩

  8. Remote repos in git are just references or pointers, so you lose or gain nothing when adding or removing a remote repo. ↩

  9. The full commit ID is 40 characters long. But you may type a short prefix (like 4~6 characters) to refer a commit uniquely. ↩