Version Control with Git

Collaborating

For the next step, we are going to simulate collaborating. You can think of this either as collaborating with another person, or as what you might do if you were using a git repo on two different computers (say, your work computer and your laptop at home).

We can simulate working with a collaborator using another copy of the repository on our local machine. To do this, cd to the directory /tmp. (Note the absolute path: don’t make tmp a subdirectory of the existing repository). Instead of creating a new repository here with git init, we will git clone the existing repository from GitHub:

$ cd /tmp
$ git clone https://github.com/vlad/planets.git

git clone creates a fresh local copy of a remote repository. (We did it in /tmp or some other directory so that we don’t overwrite our existing planets directory.) Our computer now has two copies of the repository:

After Creating Clone of Repository

Let’s make a change in the copy in /tmp/planets:

$ cd /tmp/planets
$ nano pluto.txt
$ cat pluto.txt

It is so a planet!

$ git add pluto.txt
$ git commit -m "Some notes about Pluto"

 1 file changed, 1 insertion(+)
 create mode 100644 pluto.txt

then push the change to GitHub:

$ git push origin master

Counting objects: 4, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (3/3), 306 bytes, done.
Total 3 (delta 0), reused 0 (delta 0)
To https://github.com/vlad/planets.git
   9272da5..29aba7c  master -> master

Note that we didn’t have to create a remote called origin: Git does this automatically, using that name, when we clone a repository. (This is why origin was a sensible choice earlier when we were setting up remotes by hand.)

Our three repositories now look like this:

After Pushing Change from Duplicate Repository

We can now download changes into the original repository on our machine:

$ cd ~/planets
$ git pull origin master

remote: Counting objects: 4, done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 3 (delta 0), reused 3 (delta 0)
Unpacking objects: 100% (3/3), done.
From https://github.com/vlad/planets
 * branch            master     -> FETCH_HEAD
Updating 9272da5..29aba7c
Fast-forward
 pluto.txt | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 pluto.txt

which gives us this:

After Pulling Change to Local Repository

In practice, we would probably never have two copies of the same remote repository on our laptop at once. Instead, one of those copies would be on our laptop, and the other on a lab machine, or on someone else’s computer. Pushing and pulling changes gives us a reliable way to share work between different people and machines.