Help Topic: Getting Started with Git

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Getting Started with Git

Git is a version control software that allows users to develop source code in a distributed manner, keeping track of changes, conflicts and versions. You will be highly encouraged to use Git or a similarly capable version control tool during the course. But for now, we focus just on installing Git and knowing just enough to check out software from the web to be used in the course.

How to tell if Git is already installed    [top]

Your machine may already have a version of git installed. It is typically preinstalled on macOS, and may be preinstalled in some Linux distros as well. To check, try: 

  $ which git
  /usr/bin/git

If you get a response like the one above, you're all set. If git is not installed you will get a response like the one below: 

  $ which git
  git: command not found

If the which command is telling you it cannot find the git command, you probably just don't have git installed. However it may be that you simply don't have the directory containing the git executable in your shell path. To rule this out, try the following (if using macOS, or GNU/Linux): 

  $ cd /usr/bin
  $ which ./git
  ./git

To check if git is already installed via another method (i.e. MacPorts), try: 

  $ cd /opt/local/bin
  $ which ./git
  ./git

If you see the above, it is simply a matter of adding directory to your shell path. Do this now, or see the help topic on augmenting your shell path:

http://oceanai.mit.edu/ivpman/help/help-add-shellpath

Getting Git in GNU/Linux    [top]

If you're running GNU/Linux you probably have access to a package manager such as apt and already know how to use it to some degree. To install packages like Git, you need root privileges. Assuming your user accont has root privileges, do the following, and enter your normal login password if prompted: 

  $ sudo apt install git

See the discussion above on how to confirm whether git has been successfully installed, and adjust your shell path if need be.

Getting Git in macOS    [top]

If you're running on a Mac (macOS) you can use MacPorts or Homebrew to install Git. If you haven't installed either of these package managers, see the separate help topic on this. To install packages like Git, you may need root (admin) privileges. Assuming your user account has the necessary privileges, do the following, and enter your normal login password when or if prompted: 

  $ sudo port install git

See the discussion above on how to confirm whether git has been successfully installed, and adjust your shell path if need be.

Using Git to clone a repository    [top]

The Git executable is git and takes a number of arguments on the command line for interacting with a software repository. The most essential is the command to clone, i.e., download, a repository from a server. 

  $ git clone <url> [<destination>]

Below is the git command for checking out the MOOS-IvP software repository: 

  $ git clone https://github.com/moos-ivp/svn-mirror.git moos-ivp

A checkout essentially results in the download of a directory from a server. The name of this directory in the server is the final component of the URL, which may include the \*.git suffix. The name assigned to the directory in the local system typically defaults to the base name of the repository, but can be defined using the optional destination argument – the last component in the example command above, given after the repository's URL. In the above example, the base name of the repository would be svn-mirror, and the last (optional) argument in the above example command line ensures the local copy will be listed under moos-ivp upon download.

0.1   Configuring your Git environment    [top]

When committing changes to a repository, Git creates an attribution record so the author can be identified. You can tell Git what name and email address you want associated with your commits by setting the global defaults: 

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

    Alternatively, you can remove the --global argument to set repo-specific defaults; the default behavior is equivalent to setting the --local argument explicitly. This is useful when you mange both personal and work repositories, and you want to ensure the system employs the correct email address for each case.

    To check the local and global configurations, you can use the following commands: 

  $ git config --local --list     #(invoked within a checked out tree)
  $ git config --global --list    #(can be invoked anywhere; reads ~/.gitconfig)

More can be learned about Git online. There are numerous help pages, cheat sheets, and the official Git book is even free online. On this course website we do have a few help pages of our own you can check out:

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