Git is a distributed version control system 1
Some house-cleaning here. We assume of course you have Git installed, (hopefully >= 1.7.0).
First thing to do is to setup your identity. This identifies you to other people who download the project.
$ git config --global user.name "Your Name" $ git config --global user.email [email protected]
As a helpful step, you may want to set Git to use your favourite editor
$ git config --global core.editor emacs
First, clone this repository:
$ git clone https://github.com/kuahyeow/git-workshop.git
Once you have cloned your repository, you should now see a directory called git-workshop. This is your working directory
$ cd git-workshop $ ls
For the curious, you should also see the .git subdirectory. This is where all your repository’s data and history is kept.
$ ls -a .git
You will see :
branches config description HEAD hooks info objects refs
Now, let’s try adding some files into the project. Create a couple of files.
Let’s create two files named bob.txt and alice.txt.
$ touch alice.txt bob.txt
Let’s use a mail analogy.
In Git, you first add content to the staging area by using git add. This is like putting the stuff you want to send into a cardboard box. You finalize the process and record it into the git index by using git commit. This is like sealing the box – it’s now ready to send.
Let’s add the files to the staging area
$ git add alice.txt bob.txt
You are now ready to commit. The -m flag allows you to enter a message to go with the commit at the same time.
$ git commit -m "I am adding two new files"
We should now have a new commit. To see all the commits so far, use git log
$ git log
The log should show all commits listed from most recent first to least recent. You would see various information like the name of the author, the date it was commited, a commit SHA number, and the message for the commit.
You should also see your most recent commit, where you added the two new files in the previous section. However git log does not show the files involved in each commit. To view more information about a commit, use git show.
$ git show
You should see something similar to:
commit 5a1fad96c8584b2c194c229de7e112e4c84e5089 Author: kuahyeow <[email protected]> Date: Sun Jul 17 19:13:42 2011 +1200 I am adding two new files diff --git a/alice.txt b/alice.txt new file mode 100644 index 0000000..e69de29 diff --git a/bob.txt b/bob.txt new file mode 100644 index 0000000..e69de29
In this section, we are going to add more changes, and try to recover from mistakes.
Be forewarned, this next step is going to be hard. We will need to add some content to alice.txt.
Open alice.txt and type in your favourite line from a song, or:
e.g. Lorem ipsum Sed ut perspiciatis, unde omnis iste natus error sit voluptatem accusantium doloremque laudantium
Then save the file
What did we change? A very useful command is git diff. This is very useful to see exactly what changes you have done.
$ git diff
You should see something like the following:
diff --git a/alice.txt b/alice.txt
index e69de29..2aedcab 100644
--- a/alice.txt
+++ b/alice.txt
@@ -0,0 +1 @@
+Lorem ipsum Sed ut perspiciatis, unde omnis iste natus error sit voluptatem accusantium doloremque laudantium
Now let’s add our modified file, alice.txt to the staging area. Do you remember how ?
Next, check the status of alice.txt. Is it in the staging area now?
Let’s say we did not like putting Lorem ipsum into alice.txt. One advantage of a staging area is to enable us to back out before we commit – which is a bit harder to back out of. Remembering the mail analogy – it’s easier to take mail out of the cardboard box before you seal it than after.
Here’s how to back out of the staging area :
$ git reset HEAD alice.txt
Unstaged changes after reset: M alice.txt
Compare the git status now to the git status from the previous section. How does it differ?
Your staging area should now be empty. What’s happened to the Lorem Ipsum changes? It’s still there. We are now back to the state just before we added this file to staging area. Going back to the mail analogy, we just took our letter out of the box.
Sometimes we did not like what we have done and we wish to go back to the last recorded state. In this case, we wish to go back to the state just before we added the Lorrem ipsum text to alice.txt.
To accomplish this, we use git checkout, like so:
$ git checkout alice.txt
You have now un-done your changes. Your file is now empty.
Most large code bases have at least two branches – a ‘live’ branch and a ‘development’ branch. The live branch is code which is OK to be deployed on to a website, or downloaded by customers. The development branch allows developers to work on features which might not be bug free. Only once everyone is happy with the development branch would it be merged with the live branch.
Creating a branch in Git is easy. The git branch command, when used by itself, will list the branches you currently have
$ git branch
The * should indicate the current branch you are on, which is master.
If you wish to start another branch, use git checkout -b (new-branch-name) :
$ git checkout -b exp1
Try git branch again to check which branch you are currently on:
$ git branch exp1 * master
The new branch is now created. Now let’s work in that branch. To switch to the new branch:
$ git checkout exp1
git checkout (branch-name) is used to switch branches.
Let’s perform some commits now,
$ echo 'some content' > test.txt $ git add test.txt $ git commit -m "Added experimental txt"
Now, let’s compare them to the master branch. Use git diff
$ git diff master
Basically what the above output says is that test.txt is present on the exp1 branch, but is absent on the master branch.
Git is good enough to handle your files when you switch between branches. Switch back to the master branch
Try switching back to the master branch (Hint: It’s the same command we used to switch to the exp1 branch above)
Now, where’s our test.txt file ?
$ ls README.textile alice.txt bob.txt gamow.txt
As you can see the new file you created in the other branch has disappeared. Not to worry, it is safely tucked away, and will re-appear when you switch back to that branch.
Now, switch back to the exp1 branch, and check that the test.txt is now present.
We now try out merging. Eventually you will want to merge two branches together after the conclusion of work.
git merge allows you to do that.
Git merging works by first switching the branch you want to into, and then running the command to merge the other branch in.
We now want to merge our exp1 branch into master. First, switch to the master branch.
git checkout master
Next, we merge the exp1 branch into master :
$ git merge exp1
Do you see the following output ?
Merge made by recursive. test.txt | 1 + 1 files changed, 1 insertions(+), 0 deletions(-) create mode 100644 test.txt
You have to be in the branch you want merge into and then you always specify the branch you want to merge.
At this point, you can also try out gitk to visualize the changes and how the two branches have merged
Git is pretty good at merging automagically, even when the same file is edited. There are however, some situations where the same line of code is edited there is no way a computer can figure out how to merge.
This will trigger a conflict which you will have to fix.
We now practise fixing merge conflicts. Recall that conflicts are caused by merges which affect the same block of code.
Here’s a branch I prepared earlier. The branch is called alpher. Run the code below to set it up (don’t worry if you can’t understand it)
$ git checkout alpher
You should now have a new branch called alpher. Try merging that branch into master now and fix the ensuing conflict.
You should see a conflict with the gamow.txt file. This means that the same line of text was edited and committed on both the master branch and the alpher branch. The output below basically tells you the current situation :
Auto-merging gamow.txt CONFLICT (content): Merge conflict in gamow.txt Automatic merge failed; fix conflicts and then commit the result.
If you open the gamow.txt file, you will see something similar as below:
$ cat gamow.txt <<<<<<< HEAD It was eventually recognized that most of the heavy elements observed in the present universe are the result of stellar nucleosynthesis (http://en.wikipedia.org/wiki/Stellar_nucleosynthesis) in stars, a theory largely developed by Bethe. ======= http://en.wikipedia.org/wiki/Stellar_nucleosynthesis Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances. For the creation of elements during the explosion of a star, the term supernova nucleosynthesis is used. >>>>>>> alpher
Git uses pretty much standard conflict resolution markers. The top part of the block, which is everything between <<<<<< HEAD and ====== is what was in your current branch.
The bottom half is the version that is present from the alpher branch. To resolve the conflict, you either choose one side or merge them as you see fit.
For example, I might decide to choose the version from the alpher branch.
Now, try to fix the merge conflict. Pick the text that you think is better (Ask for help if stumped)
Once I have done that, I can then mark the conflict as fixed by using git add and git commit.
$ git add gamow.txt $ git commit -m "Fixed conflict"
Congratulations. You have fixed the conflict. All is good in the world.
You have learnt :
- Clone a repository
- Commit files
- Check status
- Check diff
- Undoing changes
- Branching and merging
- Fixing conflicts
But, wait. There’s more. What about this distributed sharing thing with Git ?
To be able to share, we’ll need a server to host our git repositiories. GitHub (github.com) is probably the easiest place to begin with.
Go sign up for an account at GitHub; Or login into your GitHub account if you had previously signed up.
Hint: You may need to setup git cache your GitHub password – see https://help.github.com/articles/set-up-git
Then come back here, we’ll wait.
A repository (repo) is a place where you would store your code. You were practising on your very own repo just now in Part 1!
The following tutorial will show you how to create a GitHub repo – which you can then share with others
Then come back here, we’ll wait.
Go to this tutorial
Then come back here, we’ll wait.
In which you will be collaborating with your team-mates using GitHub…
You have learnt:
- Forking a repo at GitHub
- Git push
- Git pull
I throughly recommend these resources to continue your Git practice:
- http://try.github.com Another beginners tutorial for git
- http://git-scm.com Official website, with very useful help, book and videos
- http://gitref.org
- http://www.kernel.org/pub/software/scm/git/docs/everyday.html
This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License
http://creativecommons.org/licenses/by-nc-sa/3.0/
Original Author: Thong Kuah
Contributors: Nick Malcolm