Algorithms and OOD (CSC 207 2014S) : Labs

Laboratory: Getting Started with Git on the Command Line


Summary: In this laboratory, you will be practicing using Git. You will use the command line to manage your git repositories. (Eclipse has a plugin, EGit, that makes it easier to interact directly with GitHub. However, many programmers find it much easier to use Git from the command line, and so we will do so.)

In case you've forgotten what you learned in the reading, there is a list of useful commands at the end of this lab.

Preparation

a. Make sure you’ve read the Introduction to Git reading.

b. Make sure that you've done the Introduction to Eclipse lab

c. Log in and open a terminal window.

d. Create a directory to use for this lab. I'd suggest something like ~/CSC207/Git.

e. Open Eclipse.

Exercises

Exercise 1: Make an Account

If you haven't already done so, create a GitHub account at https://github.com/

Exercise 2: Configure Your Linux Account

As you may recall, your life is easier if you do a bit of configuration before working with Git. If you haven't already done so, configure your account (name, email, editor).

First, open a new terminal window.

Next, type these commands.

$ git config --global user.name "YourName"
$ git config --global user.email username@
grinnell.edu

Finally, set your editor.

$ git config --global core.editor editor

You can use emacs, vi (or vim, or vim.basic), or even gedit.

Exercise 3: Create a New Repository

a. Log in to your GitHub account.

b. Somewhere on the page (along the right hand column, at the time of this writing, but it changes), there should be a button labeled New Repository (although that name changes, too). Click that button. A dialog should appear.

c. Name your repository (e.g., git-exercise). Click the buttons to make it public and to initialize the repository with a README file. Choose the Java .gitignore file. Choose a license you like. Finally, click Create Repository.

Exercise 4: Cloning Your Repository

The easiest way to clone a repository is by using the HTTPS address of your repository. Get that address from the GitHub page (either from the address bar or from HTTPS Clone URL widget).

Open a terminal window and cd to the directory you created in the preliminaries. For example,

$ cd ~/CSC207/Git 

Once you are in that directory, use git clone to copy the repository you created.

Verify that the repository contains the files that you expected.

Exercise 5: Importing Into Eclipse

In Eclipse, start the New Java Project Wizard with File > New > Java Project.

Pick a name for your project.

Uncheck Use Default Location

Enter the directory for your Git repository. It should be something like /home/username/CSC207/Git/git-exercise.

Click Finish.

You should now see an Eclipse project that matches your Git repository. You may want to open one of the files (e.g., the LICENSE or README.md) and check.

Warning! Eclipse behaves strangely if you put the Git repository inside the Eclipse directory. I'd suggest setting up two directories for this class, one for things created in Eclipse, and one for things under Git.

Exercise 6: Identifying Changes

Return to your terminal window and cd to your Git repository.

$ cd ~/CSC207/Git/git-exercise 

Issue a git status command to see what files Eclipse created. Git should list them as “Untracked files”. You may also see some modified files.

Use git add to add the files and other changes to the repository.

Use git commit to commit those additions and updates.

Use git push to send them back to the GitHub repository.

Exercise 7: Add Some Java

In the Eclipse lab, you created a simple “Hello World” Java program. Create a similar program in your new repository. That is,

a. Create a new package, such as edu.grinnell.csc207.username.hello.

b. Create a new class, such as HelloWorld.

c. Add a main method to the class that has the following form.

  public static void 
    main (String[] args) 
  {
    System.out.println ("Hello, GitHub!");
  } // main(String[])

d. Run your program to make sure that it works as you'd expect.

e. Save your program.

Exercise 8: Commit and Push Your Code

You've updated the repository and so should commit the code to the repository. You should also push it back to the main repository. So do so now. (That is, use the sequence of status, add, commit, and push to get the Java files into the GitHub repository.) (Note that we usually don't push immediately immediately after each commit, but it's handy to do so now. Normally, we do a series of small commits and only push once we've reached a larger goal.)

Go to GitHub and see if the changes you have made are visible. You may need to navigate a few layers deep, since Eclipse makes a directory for each portion of the package.

Exercise 09: Making Updates on GitHub

Although we normally update code in our local copy of the repository, it is also possible to update code directly on GitHub. Navigate to the Java code you just wrote and click the Edit button.

Change the output. Then scroll to the bottom of the page, enter a commit message, and click Commit.

Exercise 10: Pulling Updates from GitHub

Our primary repository is now updated. How about our local repository? Let's see. Switch back to the terminal window. Look at the file in the finder using less.

It is unlikely that the Java code changed. Why? Because you haven't told Git to pull the updated version. Do so now.

Once you've issued the git pull command, verify that the file has indeed been updated in your local copy of the repository.

Finally, use git log to see a list of changes that have been made.

Exercise 11: Viewing Changes in Eclipse

Switch back to Eclipse. Open the Java code you created and edited. Has it changed?

Your are likely to see a message from Eclipse that your code is now out of synch, along with instructions for synching. Follow them.

Exercise 12: Making Changes in Eclipse

In Eclipse, change the output of your program slightly (i.e., change one of the strings). Save the file.

In the terminal, type git status to determine whether or not Git saw the change. (It should note that your file has been changed.)

Next, type git diff to see what the change was. You should see your new code prefixed by plus signs, old code by minus signs, and a bit of context.

Commit your change, but don't push it.

Exercise 13: Conficting Changes

You have a local change that has not been pushed. Let's see what happens if someone else also makes a change.

On GitHub, update the Java file by adding another print statement.

Determine what happens when you try to pull the updated version.

If all goes as expected, you should get a message like the following:

Auto-merging FILE
CONFLICT (content): Merge conflict in FILE
Automatic merge failed; fix conflicts and then commit the result.

Open the file in Eclipse. You are likely to see lines that look something like this

<<<<<<< HEAD
        CODE
=======
        OTHER CODE
>>>>>>> 68f7b764bb0e83971245e8db7e58c330c9d9d25c

These lines show the conflict. Fix the conflict and save the file.

Back in the terminal, add and commit the changed file. Then try pulling again. Git should now be happy.

For Those With Extra Time

Extra 1: SSH Connections

You did this lab using HTTPS connections to GitHub. HTTPS connections are easy and straightforward. However, they also require you to type a password each time you push code back to GitHub.

GitHub also permits you to create a pair of private and public RSA keys and to use SSH connections with those keys. In that case, you may have to type the passphrase you associated with your keys, but you won't have to enter your GitHub account info.

Figure out how to set up an SSH connection with GitHub.

Extra 2: Shared Repositories

You'll need to do this exercise with a partner.

First, figure out how to give someone else administrative access to your repository.

Next, verify that they have administrative access by having them make a change and upload it to the repository.

Finally, figure out what happens if the two of you make changes.

Some Useful Git Commands

git config --global user.name "Your Name"
git config --global user.email your_email@example.com
git config --global core.editor editor

git help
git clone
git add
git commit
git pull
git push

Copyright (c) 2013-14 Samuel A. Rebelsky.

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