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Lesson2b VersionControl
Back To Local Version Control - [[Forward to Python Shell and Variables | Python1-ShellAndVariables]]
Presented By : Katy Huff
GitHub is a site where many people store their open (and closed) source code repositories. It provides tools for browsing, collaborating on and documenting code. It is very similar to the ictp gforge portal. GitHub, much like the ictp gforge portal and other forge hosting services (launchpad, bitbucket, googlecode, [[sourceforge | http://sourceforge.net]] etc.) provides :
- landing page support ([[my research is at cyclus.github.com | http://cyclus.github.com]])
- wiki support
- network graphs and time histories of commits
- code browser with syntax highlighting
- issue (ticket) tracking
- user downloads
- varying permissions for various groups of users
- commit triggered mailing lists
- other service hooks (twitter, etc.)
Setting up github at first requires [[some setup | http://help.github.com/set-up-git-redirect]].
Once you've set up your rsa keys, you need to tell github who you are. Crack open a terminal.
$ git config --global user.name "Firstname Lastname" $ git config --global user.email "your_email@youremail.com"
Unless your name is Firstname Lastname, please don't copy the above lines verbatim. Make the appropriate substitutions.
If you did this properly, you'll have a file in your home (~) directory that's called .gitconfig . It's contents should look like :
[user]
name = Katy Huff
email = southside@gmail.com
This configuration step allows github to properly credit the authorship of changes you make in your repository. For projects with numerous authors, this is essential.
Another configuration step for some will be to set their favorite text editor as git's text editor of choice. This is optional, since vi is usually the default, but can be done with the following command (if you like gedit for example):
$ git config --global core.editor gedit
A key step to interacting with an online repository that you have forked is adding the original as a remote repository. By adding the remote repository, you inform git of a new option for fetching updates and pushing commits.
The git remote command allows you to add, name, rename, list, and delete repositories such as the original one upstream from your fork, others that may be parallel to your fork, and so on.
While you probably already have a copy of the PyTrieste repository, GitHub doesn't know about it yet. You'll need to tell github you want to have an official fork of this repository.
Step 1 : Go to our [[repository | https://github.com/thehackerwithin/PyTrieste/]] from your browser, and click on the Fork button. Choose to fork it to your username rather than any organizations.
Step 2 : Clone it. From your terminal :
$ git clone git@github.com:username/PyTrieste.git $ cd PyTrieste
Step 3 :
$ git remote add upstream git://github.com/thehackerwithin/PyTrieste.git $ git remote -v origin git@github.com:username/PyTrieste.git (fetch) origin git@github.com:username/PyTrieste.git (push) upstream git://github.com/thehackerwithin/PyTrieste.git (fetch) upstream git://github.com/thehackerwithin/PyTrieste.git (push)
All repositories that are clones begin with a remote called origin.
Now that you have alerted your repository to the presence of others, it is able to pull in updates from those repositories. In this case, if you want your master branch to track updates in the original PyTrieste repository, you simply git fetch that repository into the master branch of your current repository.
The fetch command alone merely pulls down information recent changes from the original master (upstream) repository. By itself, the fetch command does not change your local working copy. To update your local working copy to include recent changes in the original (upstream) repository, it is necessary to also merge.
To incorporate upstream changes from the original master repository (in this case thehackerwithin/PyTrieste) into your local working copy, you must both fetch and merge. The process of merging may result in conflicts, so pay attention. This is where version control is both at its most powerful and its most complicated.
Step 1 : Fetch the recent remote repository history
$ git fetch upstream
Step 2 : Make certain you are in the master branch and merge the upstreeam master branch into your master branch
$ git checkout master $ git merge upstream\master
Step 3 : Check out what happened by browsing the directory.
The command git pull is the same as executing git fetch followed by git merge. Though it is not recommened for cases in which there are many branches to consider, the pull command is shorter and simpler than fetching and merging as it automates the branch matching. Specificially, to perform the same task as we did in the previous exercise, the pull command would be :
$ git pull upstream Already up-to-date.
When there have been remote changes, the pull will apply those changes to your local branch, unless there are conflicts with your local changes.
The git push command pushes commits in a local working copy to a remote repository. The syntax is git push [remote] [local branch]. Before pushing, a developer should always pull (or fetch + merge), so that there is an opportunity to resolve conflicts before pushing to the remote.
We'll talk about conflicts later, but first, since we have no conflicts and are up to date, we can make a minor change and send our changes to your fork, the "origin."
$ git push origin master
If you have permission to push to the upstream repository, sending commits to that remote is exactly analagous.
$ git push upstream master
In the case of the PyTrieste code, new developer accounts will not allow this push to succeed. You're welcome to try it though.
This is the trickiest part of version control, so let's take it very carefully.
In the PyTrieste code, you'll find a file called readme.rst. This is a standard documentation file that appears rendered on the landing page for the repository in github. To see the rendered version, visit your fork on github, https://github.com/username/PyTrieste/ .
For illustration, let's imagine that, suddenly, each of the developers on the PyTrieste code would like to welcome visitors in a language other than English. Since we're all from so many different nations and speak so many languages, there will certainly be disagreements about what to say instead of "Welcome."
I, for example, am from Texas, so I'll push (to the upstream repository) my own version of the Welcome on line 2 of readme.rst.
You, however will want to replace the english word Welcome with an equivalent word that you prefer (willkommen, bienvenido, benvenuti, etc.).
You'll want to start a new branch for development. It's a good convention to think of your master branch as the "production branch," typically by keeping that branch clean of your local edits until they are ready for release. Developers typically use the master branch of their local fork to track other developers changes in the remote repository until their own local development branch changes are ready for production.
Step 1 : Make a new branch, edit the readme file in that branch, and commit your changes.
$ git branch development $ git checkout development Switched to branch 'development' $ gedit readme.rst & <edit the readme file and exit gedit> $ git commit -am "Changed the welcome message to ... "
Step 2 : Mirror the remote upstream repository in your master branch by pulling down my changes
$ git checkout master Switched to branch 'master' $ git fetch upstream $ git merge upstream/master Updating 43844ea..3b36a87 Fast-forward README.rst | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
Step 3 : You want to push it to the internet eventually, so you pull updates from the upstream repository, but will experience a conflict.
$ git merge development Auto-merging readme.rst CONFLICT (content): Merge conflict in readme.rst Automatic merge failed; fix conflicts and then commit the result.
Now what?
Git has paused the merge. You can see this with the git status command.
# On branch master # Unmerged paths: # (use "git add/rm <file>..." as appropriate to mark resolution) # # unmerged: readme.rst # no changes added to commit (use "git add" and/or "git commit -a")
The only thing that has changed is the readme.rst file. Opening it, you'll see something like this at the beginning of the file.
===================== <<<<<<< HEAD Howdy ======= Willkommen >>>>>>> development =====================
The intent is for you to edit the file, knowing now that I wanted the Welcome to say Howdy. If you want it to say Willkommen, you should delete the other lines. However, if you want to be inclusive, you may want to change it to read Howdy and Willkommen. Decisions such as this one must be made by a human, and why conflict resolution is not handled more automatically by the version control system.
===================== Howdy and Willkommen =====================
This results in a status To alert git that you have made appropriate alterations,
$ git add readme.rst $ git commit Merge branch 'development' Conflicts: readme.rst # # It looks like you may be committing a MERGE. # If this is not correct, please remove the file # .git/MERGE_HEAD # and try again. # $ git push origin master Counting objects: 10, done. Delta compression using up to 2 threads. Compressing objects: 100% (6/6), done. Writing objects: 100% (6/6), 762 bytes, done. Total 6 (delta 2), reused 0 (delta 0) To git@github.com:username/PyTrieste.git