Getting by with Git

Date: 2015-11-07

Update: 2023-11-26

This tutorial introduces just enough Git commands to make a project. Be aware that it uses trunk as the main branch instead of master.

Global Settings

It is important for people to know who you are when committing changes. Create a file ~/.gitconfig (by typing git config --global -e in a terminal) to contain some minimal information about yourself like:

  name = Alex Klinkhamer
  email =
  default = matching

If sharing your real email address on every commit feels weird, note that it can be fake. However, if going down this route, consider using a noreply address from GitHub to associate your commits with you (or at least to your GitHub account).

Making a Remote Repository

Code shouldn’t just be stored on one machine because the hard drive may crash or we may have multiple work machines. Therefore, we should make a repository on a server that all of our machines can access. Let’s assume you want to make a project named $proj and store a copy of it on a remote server at $remote_url like:


In this case, the $remote_url is hosted on an SSH-accessible server, but it could be a path on your local machine like $HOME/repo/$proj.git. If it’s a GitHub URL like, then just use GitHub to create the repository and skip this section.

Let’s create $remote_url repository used in this example. First SSH in:

mkdir -p ~/repo/$proj.git
cd ~/repo/$proj.git

Private. If this is a project just for you, then all we need to do is initialize the repository.

git init --bare

Public. If this is a project should be shared with everyone on the remote machine, we must allow people to get to the repository and make it readable and writable by everyone.

chmod a+x ~/ ~/repo
git init --bare --shared=0666

Shared with Group. Usually a public repository isn’t the greatest idea because anyone on the machine can mess with your code. If you have the luxury of having a group containing all members, we can restrict access to the group. Let it be defined as group=my_group.

chmod a+x ~/ ~/repo
chgrp $group .
chmod g+rwxs .
git --bare init --shared=group

Basic Commands

This section describes the minimal amount of knowledge you need to use git. Note that some commands (git pull and git push) assume some default values which were set by git clone.

Check out Code

Back on your own machine, get a copy of the repository using git clone.

mkdir -p ~/code
cd ~/code
git clone $remote_url
cd $proj

After this initial clone, it is simple to pull changes other people have made.

git pull

Check in Code

To add a new file to version control:

echo "# $proj has begun!" >
git add

To see what files have been added, modified, or are not tracked by git, use the status command.

git status

To commit all of your changes:

git commit -a

This will open an editor so you can explain your changes in a commit message. The editor is determined by the $EDITOR environment variable, which is probably nano by default… pretty easy to use. If you only have a short message and don’t want to work in an editor, the message may be specified directly.

git commit -a -m 'Add README'

One can also change the most recent commit or its message (ONLY DO THIS IF THE COMMIT HAS NOT BEEN PUSHED).

git commit -a --amend

Finally, push your changes to the repository, otherwise nobody will see them! When it’s the first commit, you generally need to specify a push location and branch like git push origin master. I tend to prefer a trunk branch instead of the default master one since it matches Subversion terminology. Setting that up is a couple of extra commands but is pretty hassle free afterwards:

git branch -M trunk
git push -u origin trunk
git push origin trunk

For all pushes after the first one, origin and trunk are implied.

git push

If you still need the origin and trunk arguments, you can set the defaults in an editor with git config -e or directly like:

git config branch.trunk.merge refs/heads/trunk
git config branch.trunk.remote origin

To see other options:

git config -l

Misc File Operations

Add file, remove file, move file, or discard changes.

git add new-file.c
git rm unwanted-file.c
git mv old-file.c new-file.c
git checkout HEAD file-with-changes.c

If you previously added a file and want to remove it, you must be rather forceful.

git rm -f --cached unwanted-file.c

See previous commit messages.

git log
git log --follow file-that-has-moved.c

Working with Others

The above instructions are fine for working by yourself, but what about when others are making changes concurrently? In short, make sure trunk has a linear history by working on branches and only squash merging to it.

git pull upstream trunk
git checkout stage
git merge trunk
# Note your commit message and redo it.
git reset --soft trunk
git commit -a -S
# We rewrote history. Time to force push.
git push -f origin stage

A Note on Commit Messages

Most commits do warrant some description. Imagine if your changes broke something, and someone else (or “future you”) is tasked with fixing it. Without a meaningful commit message to read, that person doesn’t know your intent in making those original changes, and their change may break something else! (Side note: Use tests to protect your code from others.)

A commit message should be formatted with the first line being a short description (cut off at 50 characters), followed by an empty line, and then more detailed explanation. I tend to prefer small code changes these days, with most documentation in examples and tests, leaving the commit messages to explain why code is being changed how it is.

My old style noted what changed where. It served me well for a long time, so here’s an example:

Add normal mapping to raytracer

1. In the raytraced version, one can now specify a normal map in
   object coordinates to give the illusion of a more complex surface.
  a. material.c/h  map_normal_texture()
  a. wavefront-file.c  readin_wavefront()
  a. raytrace.c  fill_pixel()
     - This function is getting too complicated...

2. When determining the normal of the track's surface, be sure the damn
   thing is normalized! This only affects tracks without vertex normals.
  b. motion.c  apply_track_gravity()

3. Clean up some parse code with the addition of a new macro.
  a. util.h  AccepTok()
  c. wavefront-file.c
    + readin_wavefront()
    + readin_materials()
  c. dynamic-setup.c  readin_Track()

Changes are described in order of priority and hierarchically by: intent (number prefix), file (letter prefix), function or class (+' prefix, or on same line if there's room), and extra description (-‘ prefix). The letter prefixes signify the type of change: c means change code, b means bug fix, a means add code (new functionality), r means remove code, and d means comment/documentation changes (if the file also contains code). The letters may be a bit pedantic (former colleagues used a `*’ prefix instead).