- 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
.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
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'll have to 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.
For the following steps, make sure you are not ssh'd into your instructional
account. If you are ssh'd, you can log out by typing the command
Type the following command on your terminal on your personal computer, where
***is your three-letter login:
scp firstname.lastname@example.org:.ssh/id_rsa ~/.ssh/cs61b_id_rsa
This command will copy the private ssh key of your instructional account into a new file called
.sshdirectory in the root directory of your personal computer. If you cannot see your
~/.sshdirectory on your personal computer, 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!).
Next, run the following command:
echo "IdentityFile ~/.ssh/cs61b_id_rsa" >> ~/.ssh/config
This command will append the line
IdentityFile ~/.ssh/cs61b_id_rsato the
configfile in the
Then, run the following command:
This command will output the contents of the
~/.ssh/configfile. Make sure it contains the line
Finally, you must correctly set your
cs61b_id_rsafile permissions by using the command:
chmod 600 ~/.ssh/cs61b_id_rsa
Otherwise you will get the "WARNING! UNPROTECTED PRIVATE KEY FILE!" message later.
Now, continue below under the sub-section that matches your operating system.
Mac or Linux
We've packaged the rest of the setup described here in a Python3 script called
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
All of the setup has been abstracted away by using this script, but you should read 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. In general, however, be careful with the remove command (be sure not to misspell ~/repo), as 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.
We will now configure Git as if we are a student named Fred with login
cs61b-***. When you are setting up your computer, use the same commands but
replace Fred's information with your information and
*** with your
Having installed Git, Fred will first perform 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 "email@example.com" 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
git push command
Fred now will establish 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 firstname.lastname@example.org: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 email@example.com:shared
We'll see how to use this remote reference later.
D. Using Your Repository
For this course, you must 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). The
combines the contents of this branch with the contents of your working
directory, which in our case will add a directory called
hw3. 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 files
test1.out, you would use the command
git add test1.inp test1.out
(from inside the directory
~/repo/hw3). 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
testing directory. Once you add any new files,
you can create a new commit (snapshot) for
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 to
git add before committing; otherwise, the changes will not be committed. The
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 them with
git add them.
Periodically, you will want to transmit your work to your central repository on
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 the
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
push command with some
regularity, since it provides an extra backup copy of your work on your central
If you work on hw3 from two different local repositories (say from home and on
the instructional machines), then (if you have used
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
git pull --rebase
after first committing anything you've done to this local repository. (This
command will work without the
--rebase, but we suggest using it for this
course, because it keeps the history of versions (the "log") simple. Without
--rebase option, you get what are called merge commits, having multiple
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
git commit, we do
not see these changes, since your central repository under
cs61b-taa is 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.
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
hw3-1. 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 <firstname.lastname@example.org> Date: Tue Jan 27 16:32:17 2015 -0800 Experimentally refactor my solution to problem 3. commit 4f7d9e65744c8b528289746bf911cb81ded7c5e2 Author: Fred Student <email@example.com> Date: Wed Jan 26 15:36:28 2015 -0800 Add tests. No errors detected so far. commit 2aea9782d7000bb07277617b9f81bea485374d27 Author: Fred Student <firstname.lastname@example.org> Date: Wed Jan 22 15:34:55 2015 -0800 Begin work on 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 "email@example.com" 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 firstname.lastname@example.org:students/cs61b-*** repo cd repo git remote add shared email@example.com: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):
git pull --rebase
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):