Remote repositories

Overview

Teaching: 15 min
Exercises: 20 min

Questions

• Is my local repository the same as the remote one?

• How can I send my local changes to the remote one?

• How can I get the changes others have made?

Objectives

• Explain the differences between a local and a remote repository.

• Explain what tracking and upstream mean.

• Use the push command to send changes on the local branch to the remote one.

• Use the pull command to update your local branch with the remote one.

Remote and local repositories

• The example repository you just created is a remote repository: it is hosted by a third party hosting system - GitHub in this case.
• The recipe repository you created earlier was a local repository: it was just a directory on your hard drive using git for version control.
• Local and remote repositories can be synchronized, so changes are accessible by other contributors.
• This synchronisation is not automatic: it has to be done explicitly for each branch you want to keep up to date (see pull and push below ).
• The default name for a remote repository synchronised with a local one is origin.

Tracking and upstream

• A local branch synchronised with a remote one is said to be tracking that remote branch.
• The remote branch being tracked is called the upstream branch.
• As mentioned, we will be working in this course with the main branch only, but the concepts are applicable to all branches.

Configuring repositories

Depending on whether you are starting from a remote repository and want to get a local one out of it or the other way around, the steps are different.

Configuring a remote repository from a local one

In this case, you have a local repository and you want to synchronise it with a new, remote one. Let’s create a remote for the recipe repository you worked on earlier.

• Create a new repository in GitHub, as in the last episode. Give it a name, description and choose if it should be public or private, but do not add any other file (no README or licence).
• You will be offered a few options to populate the remote repository. We are interested in the third one. You will need to make sure HTTPS is selected (not SSH) for your personal access token to work.
• Launch a new command line interface and run cd recipe to navigate to the directory where you have your local repository - then execute:

git remote add origin ADDRESS_OF_YOUR_REMOTE_REPO
git push --set-upstream origin main

For example, for this course’s repository, the address would be: https://github.com/ImperialCollegeLondon/introductory_grad_school_git_course.git In general, it is something like: https://github.com/USERNAME/REPO_NAME.git

macOS and Linux users: You will be asked to provide your GitHub username and password. Enter your personal access token (PAT) as your password. Windows users: You will be presented with a CredentialHelperSelector dialog box. Ensure “manager-core” is selected and check the box for “Always use this from now on”. Press Select. From the next dialog select “Token” then paste the PAT you saved earlier and press “Sign in”. On subsequent interactions with GitHub your credentials will be remembered and you will not be prompted.

• The first line above will set the GitHub repository as the remote for your local one, calling it origin.
• The second line will push your main branch to a remote one called origin/main, setting it as its upstream branch.
• You can check if things went well by going to GitHub: the repository there should contain all the files of your local repository.

Configuring a local repository from a remote

This involves the git command clone. Let’s create a local copy of the example repository you created remotely in the last episode.

• On GitHub, press the down arrow in the far top right, next to your picture, and choose “Your repositories” from the drop-down menu.
• Choose the example repository from the list.
• In the main screen of your repository, click on the green button on the right, Code, and copy the address that appears in the Clone section. This should look similar to https://github.com/YOUR_USERNAME/example.git.
• Open a new command line interface and execute the commands:

cd $HOME
git clone ADDRESS_OF_YOUR_REMOTE_REPO
cd example

• This will download the remote repository to a new example directory, in full, with all the information on the branches available in origin, if any, and all the git history.
• By default, a local main branch will be created tracking the origin/main branch.
• You can find some information on the repository using the commands already discussed, like git log.

Pushing

• Its basic use is to synchronize any committed changes in your current branch to its upstream branch: git push.
• Changes in the staging area will not be synchronized.
• If the upstream branch has changes that you do not have in the local branch, the command will fail, requesting you to pull those changes first (see below).

Pushing an updated README

You want to update the README file of the example repository with more detailed information of what the repository is about and then push the changes to the remote.

Modify the README file of your local copy of example with your preferred editor (any change is good enough, but better if they are useful - or at least, funny!) and synchronise the changes with the remote. Check on GitHub that you can view the changes you made.

Solution

git add README.md
git commit -m COMMIT_MESSAGE
git push

Pulling

• Opposite to git push, git pull brings changes in the upstream branch to the local branch.
• You can check if there are any changes to synchronize in the upstream branch by running git fetch, which only checks if there are changes, and then git status to see how your local and remote branches compare in terms of commit history.
• It’s best to make sure your repository is in a clean state with no staged or unstaged changes - so, all changes committed.

Conflicts

If the local and upstream branches have diverged - for example if you edited something directly in the repository and also locally - the command will attempt to merge both. This merging might be a smooth, transparent process - Git is pretty smart when it comes to merging branches - but might also result in conflicts that need to be resolved before proceeding.

This is part of the scope of the intermediate Git and GitHub course that you can find in https://imperialcollegelondon.github.io/intermediate_grad_school_git_course/

Pulling an updated README

When reviewing your new README file online, you have discovered a typo and decided to correct it directly in GitHub. Modify the README file online and then synchronise the changes with your local repository (tip: you can edit any text file directly in GitHub by clicking in the little pencil button in the upper right corner).

Solution

git fetch
git status

This will indicate that the remote branch is ahead of your local branch by 1 commit. Since there are no diverging commits, it is safe to pull.

git pull

Key Points

• origin is typically the name of the remote repository used by GitHub.

• Local and remote repositories are not identical, in general.

• Local and remote repositories are not synchronized automatically.

• push and pull commands only affect the branch currently checked out.