Training: Git

Welcome to this repository of training materials for using Git to version-control your code.

The training materials will be written in Git Bash so we will mostly be interfacing via the command terminal.

Who are these training materials for?

In no ways is this training material meant to be a comprehensive nor exhuastive guide. Instead, it is designed with the enterprise/business user in mind.

In particular, it is created from this perspective to enable users to become familiarised with and get-started with using Git.

References

For a highly-recommended intro to Git, there is a Software Carpentry course.

Chapter 1

Moving Folders across Repos

Consider the following use-case scenario:

You add a folder, folder_x, to a repo, repo_a, and do a bunch of work on it, so subsequently have 15 commits associated to this folder.

Perhaps you want to split the massive repo, repo_a, into smaller repos, repo_b, repo_c, ..., so that it is clearer what each repo is doing and managing the dependencies better. You thus want folder_x in repo repo_b.

You want to move folder_x and its git commit history into repo_b with minimal of effort.

Phrased in this way, the problem statement is thus:

  • Goal:
    • Move folder x from repo_a to repo_b.
  • Constraints:
    • repo_a contains other files and folders that you don't want moved.
    • You want to preserve the git commit history for the file you are moving.

Note, the instructions below also work with a file you want to move to a new repo.

The high-level steps to follow are:

  1. Get folder ready for the move
  2. Merge folder into new repository

Get folder ready for the move

Copy from GitHub the URL of the repository that you want to take folder_x away from, repo_a. We label this as <repo_a url>.

Then enter the following in your terminal/shell.

# take copy of repo_a onto your local file system
git clone <repo_a url>
# move into `repo_a`
cd <repo_a>
# remove link to the repo on GitHub so you avoid doing anything stupid
git remote rm origin
# remove anything not related to `folder_x`
git filter-branch --subdirectory-filter <folder_x path> -- --all
# create folder to store `folder_x` in
mkdir <folder_x>
# move `folder_x` into newly-created folder
mv * <folder_x>
# get git to recognise and then record the change
git add .
git commit -m "<commit_message>"

Merge folder into new repo

Copy from GitHub the URL of the repository that you want to move folder_x to, repo_b. We label this as <repo_b url>.

Then enter the following in your terminal/shell:

# take copy of repo_b onto your local file system
git clone <repo_b url>
# move into `repo_b`
cd <repo_b>
# link to `repo_a` directory path which now only has `folder_x`' commit history
git remote add branch-repo-a <repo_a directory>
# bring `repo_a` commit history to `repo_b`
git pull branch-repo-a master --allow-unrelated-histories
# remove link to repo_a directory as no longer needed
git remote rm branch-repo-a

References

This section was inspired by the following: