More git

Grzegorz Kowzan

1. More git

1.1. Rewriting history – simple cases

Clone rotsim2d repository: 

git clone git@github.com:gkowzan/rotsim2d.git

You want to fix the last commit, change the commit message or completely change the commit: 

git commit --amend

You want to change the messages of many commits (use reword and edit): 

git rebase --interactive 5409de0

You want to modify some previous commit (modify typo in raw_amp_to_amp): 

git rebase --interactive 5409de0

1.2. Rewriting history

You added several new features in quick succession but your work was a bit haphazard:

  • commit 1 - feature A
  • commit 2 - feature B
  • commit 3 - continue feature B
  • commit 4 - tweak feature A

You want to clean up the history before pushing these changes to remote repository:

  • commit 1 - feature A
  • commit 4 - tweak feature A
  • commit 2 - feature B
  • commit 3 - continue feature B

or even:

  • combine commit 1 and 4 - feature A, tweak feature A
  • commit 2 - feature B
  • commit 3 - continue feature B

enter git rebase.

1.3. Example - reordering commits

Combine windows scripts commits (reorder and then squash): 

git rebase -i 14dbd52

1.4. Example - splitting commits

Split commit 142c2db into two: 

git rebase -i 3d3691b
git reset HEAD^
git add --patch rotsim2d/symbolic/results.py
git commit -m 'add theta_labels'
git add rotsim2d/symbolic/results.py
git commit -m 'add polarization conditions'
git rebase --continue

1.5. Rebasing - exercises

Download rpi_stepper_motors repository from

http://fizyka.umk.pl/~gkowzan/teaching/python3/class2/rpi_stepper_motors.zip

Exercise 1: Change the commit message of the last commit from "working" to "fixed limit checking in Move"

Exercise 2: Combine the last two commits (bc4926a, 7c4af8b) into one.

Exercise 3: Split commit 1034483 into two commits: removed looper function, removed old functions.

1.6. Sharing your work

You commonly want to put your code on some server to access it from another computer or share it with others.

Most common services that allow it are: Github, Gitlab, Bitbucket.

We will use Github.

  1. Create github account if you don't have one yet.
  2. Generate ssh keys and add them to the account.
  3. Follow along as I create a remote private repository on GitHub.
  4. Associate remote repository with your local one.
  5. Push your work to the server.

1.7. Working with remotes

Add remote for your repository: 

git remote add github <url>

Try pushing and pulling. Set upstream.

Clone repository to a different directory.

Rename main branch, change main branch on github, remove old remote branch.

1.8. Dealing with remote conflicts

Introduce conflicting changes in remote repo and local copy.

Use git pull with rebase strategy to resolve the problem.

1.9. Sharing your work – exercises

Exercise 1: Make a new private repository on github. Clone the repository. Rename the remote from origin to github. Add a file README.md and push it to github.

1.10. Searching history

We can use git log to see only the changes we want to see. 

git log --oneline -S pws_autospan

shows only commits that changed the number of occurrences of pws_autospan, so it will show when the function definition and its uses were introduced. It won't show changes to the function body.

To track evolution of a function we can use: 

git log --oneline -L :pws_autospan:rotsim2d/propagate.py

1.11. Seaching history – exercise

Exercise 1: Find all commits that changes pws_autospan. Split each commit to contain only changes to the pws_autospan function. Combine the pws_autospan commits into a single commit.