4. Using Git

Most of the Land Surface Dynamics group’s code is under the version control of subverion, and housed within the sourceEd. respositories.

However it can be advantageous to distribute code for open development on the Git platform and distributing the code via Github.

In this document we detail how to use Git on the Edinburgh servers.

4.1. Getting started with Git

Git is already installed on our servers. You can call it with:

$ git

Much of what I will descrbe below is also described in the Git book.

The first thing you want to do is set the username and email for the session:

$ git config --global user.name "John Doe"
$ git config --global user.email johndoe@example.com

I’m not acutally sure if this will affect other users, as it is sitting on the GeoScience server. So you might choose to not use the –global flag, and so the name and email will only apply to the specific project you are working on that session:

$ git config user.name "John Doe"
$ git config user.email johndoe@example.com

After trying this, I get an error:

error: could not lock config file .git/config: No such file or directory

So so much for that.

I’ll try something else. First, I’ll navigate to the directory that holds my prospective git repository:

smudd@burn OneD_hillslope $ pwd
/home/smudd/SMMDataStore/Git_projects/OneD_hillslope
smudd@burn OneD_hillslope $ ls
branches  tags  trunk

Now I’ll initiate git here:

smudd@burn OneD_hillslope $ git init
Initialized empty Git repository in /exports/csce/datastore/geos/users/smudd/Git_projects/OneD_hillslope/.git/

Great! That seemed to work. Lets try that local configuration again:

smudd@burn OneD_hillslope $ git config --local user.name simon.m.mudd
smudd@burn OneD_hillslope $ git config user.name
simon.m.mudd

Excellent!! Things are moving nicely along now! I then set up some other config options:

smudd@burn OneD_hillslope $ git config --local merge.tool vimdiff
smudd@burn OneD_hillslope $ git config --local core.editor emacs

You can check all your options with:

smudd@burn OneD_hillslope $ git config --list
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true
core.editor=emacs
user.name=simon.m.mudd
user.email=Mudd.Pile@pileofmudd.mudd
merge.tool=vimdiff

4.2. Adding files and directories to the repository

So now you gave run git init in some folder to initiate a repository. You will now want to add files with the add command:

smudd@burn OneD_hillslope $ ls
branches  tags  trunk
smudd@burn OneD_hillslope $ git add tags
smudd@burn OneD_hillslope $ git add trunk

So a few things here

• I think that the branches folder is redundant since git does this implicitly
• Git adds all files in a folder, including all the files in a named subdirectoy.

If you want to add a specific file(s), you can do something like this:

smudd@burn OneD_hillslope $ git add trunk/*.hpp

4.3. Committing to the repository

This works much the same as svn:

mudd@burn OneD_hillslope $ git commit -m "Initial project version" .

Where the . indicates you want everything in the current directory including subfolders.

4.4. Pushing your repository to Github

Github is a resource that hosts git repositories. It is a popular place to put open source code.

To host a repository on Github, you will need to set up the repository before synching your local repository with the github repository.

You can place your repository on Github by using the push command:

smudd@burn OneD_hillslope $ git remote add origin https://github.com/simon-m-mudd/OneD_hillslope.git
smudd@burn OneD_hillslope $ git push -u origin master
Counting objects: 36, done.
Delta compression using up to 64 threads.
Compressing objects: 100% (33/33), done.
Writing objects: 100% (36/36), 46.31 KiB, done.
Total 36 (delta 8), reused 0 (delta 0)
To https://github.com/simon-m-mudd/OneD_hillslope.git
* [new branch]      master -> master
Branch master set up to track remote branch master from origin.

Once you have uploaded an inital copy, you will need to keep it in sync with local copies. You can push things to github with:

git push -u origin master

but if things are out of sync (I did this by modifying a readme on the github site) you will get this error message:

To https://github.com/simon-m-mudd/OneD_hillslope.git
! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'https://github.com/simon-m-mudd/OneD_hillslope.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Merge the remote changes (e.g. 'git pull')
hint: before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

I fixed this by running:

git pull origin

It seemed to be happy after that.

4.5. Problems with Setting up repos on github

Git is not quite as intuitive as subversions, so I’ve found quite a number of problems in setting up github repos. Here are some examples and (hopefully) their fixes.

4.5.1. Creating local repo and then Github repository

I made a local github repository using:

git init

And then tried to push to a github repo, but the first error message is you need to make a repository on github first. I added a readme file on Github, but this seemed to lead to errors:

Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Merge the remote changes (e.g. 'git pull')

So what I did to fix this was:

1. On the local repo, I used:

   touch README.md
   git add README.md
   git commit -m "Trying to add readme" .

2. Then I pulled from the master:

   git pull origin master

3. Then I pushed to the master. That seemed to fix things:

   git push -u origin master