- Setting up a Local Repository
- Using Your Repository
- Submitting Your Work
- Quick Summary
Git is a distributed version-control system that has become the norm in the open-source software community. Developers within a team (or in our case, a class) each work on separate repositories, and may from time to time synchronize all or part of the contents of their repositories with one or more other repositories. There need be no central repository, in fact.
This document describes a minimal set of commands for using Git in this course to submit assignments and acquire skeleton files. It is not any kind of tutorial or introduction to Git. Consult this brief introduction and this Git documentation for an overview of Git and details of its various commands.
If you are working from your own machine, be sure to install Git, if it is not already installed. If you followed the lab1b setup, you should have Git already installed.
Git terminology uses the term repository to mean an organized
collection of versions (called commits) of a directory structure,
a checked-out copy of the one of those commits (a working directory)
possibly in the process of modification, and a staging area
(called the index) used to track what goes into the next commit.
Usually, the set of commits and the index are stored in a directory named
.git at the top level of the working directory. The term bare repository
refers to a directory containing only the set of commits (what would be a
.git directory in an ordinary repository, but with no index). Typically,
we use bare repositories as central copies of versions that will be
shared by several repositories.
Each student has a bare central repository that we maintain for you on
the instructional servers under the account
cs61b-taa. You, the staff,
and the autograding software all have access to this repository.
In addition, we've set up for you one local repository
under your cs61b instructional account in a directory called
repo. It is a
clone of your central repository, together with a checked-out
working directory from one of its commits (generally your latest).
You are free to set up other such local clones (say on your personal laptop
or home computer). The central repository will serve to keep them all in sync
with each other (at least if you follow the instructions here), so that you
can work on any of several machines.
C. Setting up a Local Repository
Regardless of if you plan on using your local computer or a lab computer, you must do this section. This part sets up a local repository on your instructional account. Open up the terminal on the lab computer (or ssh in from your personal computer) and type:
This invokes a script that will create a clone of a central repository for your work (one that we and the autograder share).
Don't worry if you get this error, it's perfectly fine and you can continue:
error: pathspec 'master' did not match any file(s) known to git. Error: Could not checkout master branch. Trying to create it.
If you are only planning to use a lab computer, you may skip this part. However, if you plan to be using a non-lab computer, then you must first install the appropriate ssh private key for access to your central repository. Don't worry about what it is for now.
We highly recommend that you read section D of the instructional accounts guide if you are confused with the commands.
First, get on your instructional account by ssh-ing into the account via your local computer. Once you are in your instructional account, type:
Then, do the command:
and you should see two files
id_rsa.pub, which contain, respectively,
the private and public ssh keys used by our repositories.
You can view the contents of this file from the terminal by using the command:
Highlight the contents of
id_rsa (be sure to highlight the
-----BEGIN RSA PRIVATE KEY----- and
-----END RSA PRIVATE KEY----- lines as well), and copy them.
Next, go to your personal computer's ~/.ssh directory (NOT the instructional account), and create a new file called
cs61b_id_rsa (do not override your own
id_rsa file). You can do this all on the command line of your personal computer by running:
touch cs61b_id_rsa vim cs61b_id_rsa (Type i to insert) (Right-click and paste) (Press Esc) (Type :wq and Enter to save and quit)
If you cannot see your ~/.ssh directory, you might have hidden files active. To fix this issue, you should Google how to show hidden files (this will be an exercise on how to solve problems on your own!).
To use the key when ssh-ing, open on your local computer the file
~/.ssh/config (or create a file with that name if it does not already exist) and add the line:
Finally, you must correctly set your
cs61b_id_rsa file permissions by using the command:
chmod 400 ~/.ssh/cs61b_id_rsa
Otherwise you will get the WARNING! UNPROTECTED PRIVATE KEY FILE! later.
Now, continue below under the sub-section that matches your operating system.
Mac or Linux
If you plan to be using a non-lab computer that is either a Mac or Linux machine, then you should set up a local repository on it according to the following section.
If you haven't already, first install the appropriate ssh private key for access to your central repository according to the "Non-Lab Computers" sub-section above.
We've packaged the rest of the setup described here in a Python3
remote-init-git-repo. You can access the script here.
Create a new file called
remote-init-git-repo on your personal computer, then copy and paste the contents
of the script into your file. Then, run:
(where DIR is where the file lives on your personal computer).
Alternatively, this script also resides on the instructional servers at
You should read the corresponding section of the Windows setup below to understand what this script is doing.
If you encounter the error when running the script:
Repo already exists
then type the command:
rm -rf ~/repo
Then you can rerun the script and it should work.
But be careful with this remove command in general (be sure not to misspell ~/repo). It will permanently delete your files.
If you plan to be using a non-lab computer that is Windows machine, then you should set up a local repository on it according to the following section.
If you haven't already, first install the appropriate ssh private key for access to your central repository according to the "Non-Lab Computers" sub-section above.
Next, we will configure Git as if we are a student named Fred with login
cs61b-***. Having installed Git, Fred first performs some general configuration that
will apply to all repositories used from his account (for this course or elsewhere):
git config --global user.name "Fred Student" git config --global user.email "firstname.lastname@example.org" git config --global push.default simple
The first two lines set the name and email that Git will record in commits
and logs. The last line is a safety measure that affects the
command described later.
Fred initially establishes a working directory containing a local clone of his
central repository in a directory
~/repo (actually, any name works;
the name we use in your instructional account):
cd git clone email@example.com:students/cs61b-*** repo
This will copy the contents of Fred's personal bare repository on
into the new local working directory
repo/.git, and will then check
out its head version into
repo as well. Initially, this head version is the
master and is empty.
There will be various resources that we provide, including skeleton (starter) files for projects and assignments. Fred can add a reference to these resources to his repository with the commands
cd repo git remote add shared firstname.lastname@example.org:shared
We'll see how to use this remote reference later.
D. Using Your Repository
Keep each assignment or project, ASSGN, in a subdirectory of that name in your working directory. Typically, we provide an initial set of files for each assignment. You can initialize an assignment directory, say for hw3, like this:
cd repo # If not already there git fetch shared # Fetch current copy of skeleton files git merge -m "Start hw3" shared/hw3 # Add or update your master directory from # our remote version of hw3. git push # Save your local updated master directory # to your central repository.
shared/hw3 is a remote branch containing a copy of the
subdirectory from the staff repository (which we maintain).
merge command combines the contents of this branch with the contents of
your working directory, which in our case will add a directory called
Later, if the staff makes changes to the skeleton
after you have done this initial merge, you can use essentially
the same sequence:
git fetch shared # Fetch current copy of skeleton files git merge -m "Get updates to hw3 skeleton" shared/hw3 git push
to add these changes to your files.
Work on hw3 now proceeds as a sequence of edits and commits. After editing,
adding, and deleting files, you first inform Git of any new files that it
should start tracking. For example, if when working on hw3, you create
test1.out, you would use the
git add test1.inp test1.out
(from inside the directory
Or, if these files are stored in a new subdirectory called
hw3/testing, you can use the command
git add testing
to add all the files in the
Once you add any new files, you can create a new commit (snapshot)
git commit -m "ADD YOUR COMMIT MESSAGE HERE"
You should replace the text inside the quotation marks with a commit message
for the new commit. Descriptive commit messages are generally a good idea,
since they help you identify commits when using the
git log command to list
the commits you have made. In later courses (and real life), they are especially
useful for complex team projects where one is trying to keep other team members
informed of what changes you've made and why.
Before doing either of the
git merge commands above (either to start or
update an assignment), be sure that you use
git commit, since you won't
otherwise be able to commit.
Before performing a
git commit, it's a good idea to make sure
that all your files are accounted for. The command
will indicate any files that are untracked, meaning that
git commit will
pay no attention to them and will not save or update them. Generally, we
suggest that you use
git add on these files (or get rid of them entirely
if they are unneeded) before committing. This way you avoid the
annoying (and, alas, rather common) problem of thinking that you have submitted
a file when you have not.
Files that are being tracked and have been changed must also be subjected
git add before committing; otherwise, the changes will not be committed.
git status command will tell which files have "changes not staged for
commit", and that therefore should be added. Generally, however, I find it
more convenient to use the command
git commit -a -m ...
which will first add all these unstaged commits and then commit them.
This does nothing with untracked files, so you will still need to check for
git status and
git add them.
Periodically, you will want to transmit your work to your central
cs61b-taa (from which your local repository was cloned).
This is especially true when you intend to hand it in
or do further work on it from a different local
repository. Also, pushing to the central repository provides you an
additional backup of your work—one that you cannot accidentally erase.
The command to push to your central repository is just
which (assuming you've used the procedures described in this document for configuration and for creating assignments) will by default push your master branch and everything committed to it to the central repository. Don't try to push, however, without first committing any outstanding changes.
Git's distributed nature means that you can create an arbitrarily long
sequence of commits before pushing them. It's not necessary to be connected to
cs61b-taa repositories (or indeed, the Internet) to use
Git's version-control features. We've been suggesting that you execute
after merges, but in fact you can delay this until you wish to
submit your assignment or until you think you might need to transfer your work
to another of your local repositories. Still, it is wise to use the
command with some regularity, since it provides an extra backup copy of your
work on your central repository.
If you work on hw3 from two different local
repositories (say from home and on the instructional machines), then (if you
git push to push your work from one local repository
to your central repository) you can bring the other local repository
up to date with any changes you made with the command
(after first committing anything you've done to this local repository).
One last thing. Periodically, you will run into merge conflicts. For more information on merge conflicts themselves and how to resolve them, please read this documentation.
E. Submitting Your Work
The staff does not immediately see changes to your local repositories.
That is, when you modify, add, or delete a file or when you execute
we do not see these changes, since your central repository under
not changed. To be seen by us (or our testing software), your commits must be pushed
as described in the preceding section.
Furthermore, we don't treat all your commits, even when pushed, as submissions until you mark them as such. To submit one of your committed versions, create (and subsequently push) an appropriately named tag. For example, when you first want to submit hw3, first commit any changes in your hw3 directory, and then do this:
git tag hw3-1
A tag is a named reference to a particular commit. After using
git tag on a commit, you can later check out that commit by
name check what you committed. For example,
git checkout hw3-1
(after examining the commit at this tag, do be sure to
git checkout master in
order to get back to your development branch. Otherwise, you will create
great confusion for yourself.)
Submission is not complete until you push the work to us:
git push # To push the hw3 branch (if not yet done) git push --tags # To push hw3-1 (and any other tags)
Subsequent submissions should be named
hw3-3, etc. We take the
highest-numbered tag as your final submission. You can submit at any time,
even when you have many intervening commits. For example, if you have submitted
hw3-2 and decide that the last submission is bogus, and the first
one was better, you can execute
git tag hw3-3 hw3-1
hw3-3, the latest submission, as a synonym for
In fact, if the commit you want to submit was not previously tagged, you can
find its unique id using
git log and then tag that. For example,
you might see
git log commit ff39e11f5e292a0c81f3cb65c2a39c7b301a595a Author: Fred Student <email@example.com> Date: Tue Jan 27 16:32:17 2015 -0800 Experimentally refactor my solution to problem 3. commit 4f7d9e65744c8b528289746bf911cb81ded7c5e2 Author: Fred Student <firstname.lastname@example.org> Date: Wed Jan 26 15:36:28 2015 -0800 Add tests. No errors detected so far. commit 2aea9782d7000bb07277617b9f81bea485374d27 Author: Fred Student <email@example.com> Date: Wed Jan 22 15:34:55 2015 -0800 Begin work one hw3.
Now to submit the second commit back (from 1/26) as your first submission, execute
git tag hw3-1 4f7d9e
(The unique ids in Git are hexadecimal SHA-1 hashcodes of the contents of the commits. You only need to specify a sufficiently long prefix of the hashcode to uniquely identify which commit you mean.)
Again, after adding any new tags, you must use
git push --tags
to push them to the repository that the staff (and autograder) see.
Submission dates and times will be taken from the time of the commit tagged by
hw3-n, and not from the time you created the tag.
While it is possible to delete tags, it shouldn't be necessary, since the autograder will ignore tags that don't refer to known assignments and you can always supersede a tag with a higher-numbered one.
F. Quick Summary
These commands assume you have account
To initialize Git on a particular system: This is already done on the instructional machines.
git config --global user.name "Fred Student" git config --global user.email "firstname.lastname@example.org" git config --global push.default simple # Suggested
To create a local copy of your personal repository in directory
repoand connect it up our shared repository:
git clone email@example.com:students/cs61b-*** repo cd repo git remote add shared firstname.lastname@example.org:shared
To start an assignment named ASSGN (e.g.,
hw3), from our skeleton, first make sure all your local work is committed, and then use
cd repo # If not already there git fetch shared # Fetch current copy of skeleton files git merge -m "Start assignment ASSGN" shared/ASSGN git push
To see the current status of a repository, including files that have been added, removed, or modified; files that are in the working directory, but not in the current commit ("untracked"); and discrepancies between the current branch and the remote branch it is tracking (gets pushed to or pulled from):
The message will tell you how to undo changes from the last commit, should you want to.
To start tracking a file (or directory) Foo.java, so that it will be added to the repository on the next commit:
git add Foo.java
To commit modifications to all tracked files in the local repository:
git commit -a
This does nothing with untracked files.
To transmit commits on the current branch to the remote (
To fetch new commits from the
cs61b-taarepository that have been pushed from another local directory (commit current work first):
To submit assignment ASSGN, make sure everything you want is committed and then execute
git tag ASSGN-n git push git push --tags
where n is a sequence number larger than those of existing tags.
To see tags that you have created (not necessarily pushed):