Git branches

Questions

• How to not ruin working code when adding new features?
• How to work on parallel tracks (many developers, versions)?
• How to fix mistakes?

Learning outcomes of 'Branches'

• learners can

  • explain and evaluate the usefulness of branches
  • create, switch and delete a git branch locally

Instructor notes

Prerequisites are:

• git basics

Lesson Plan:

• Total 50 min
• Theory 15
• Exercise 25
• Discussions 10 min

Changes

• practical examples than just explain the concept.
• Git branch couple to SDLC??
• exercises
  • advanced exercises

Branching and merging

Software development is often not linear:

• We typically need at least one version of the code to "work" (to compile, to give expected results, ...).
  • This is the main branch (former master)
• At the same time we work on new features, often several features concurrently. Often they are unfinished.
• We need to be able to separate different lines of work really well.

Isolated tracks of work

The strength of version control is that it permits the researcher to isolate different tracks of work, which can later be merged to create a composite version that contains all changes.

• We see branching points and merging points.
• Main line development is often called master or main.

• Other than this convention there is nothing special about master or main, it is just a branch.

• A group of commits that create a single narrative are called a branch.

• There are different branching strategies, but it is useful to think that a branch tells the story of a feature, e.g. "fast sequence extraction" or "Python interface" or "fixing bug in matrix inversion algorithm".

Three ways to name a branch

• Issues: #45: Concrete examples
• Features: GUI module
• Personal: Björn

Typical workflows

One typical workflow:

• create branch
• switch to it
• work, work, work, ..., and test
• add and commit
• once feature is ready, switch back to main
• make clear which branch you are in
• merge new-feature to present branch
• remove branch

In VS Code

• Here is where you handle branches

• Click and you have the possibility to

  • create a new branch

  

  • and switch between existing branches

  

In command line

git branch new-feature  # create branch, switch to it
git add/commit                   # work, work, work, ..., and test
git switch master          # once feature is ready, switch back to master
(git checkout <branch>)     # Old commead for switching branch, but also going back in history to earlier commit
git branch                   # make clear which branch you are in
git merge new-feature        # merge work to present branch
git branch -d new-feature    # remove branch

git push doesn't work with new branch

• you always have to pull before a push:

git pull #

• You may need to be more detailed:

git push --set-upstream origin new-branch

Git graph

• We can get an overview of graphs

• GitHub

  • 

  • Link to last year

  • Link to this year

• VS Code

  • 

Graph alias in command line

An important alias

• We can define an alias in Git, to be able to nicely visualize branch structure in the terminal without having to remember a long Git command.

git config --global alias.graph "log --all --graph --decorate --oneline"

This will enable you to use git graph for short

Example

$ git graph
* 000b440 (HEAD -> main) rm print
| * 4d4acaf (modularity) 4 modular files
|/
| * 2d4e252 (jupiter) add jupiter
|/
* b9465e4 (origin/main) planet.py documentation
* 6a416b5 add folders and planet code

gitGraph

commit id: "add folders and planet code"
commit id: "add planet.py documentation"
branch jupiter
checkout jupiter
commit id: "add jupiter"
checkout main
branch modular
checkout modular
commit id: "4 modular files"
checkout main
commit id: "rm print"

Show unstaged/uncommitted modifications

• When you are done editing the files, try "git diff"
• When you select a file in the Source Control view, the editor shows a diff view that highlights the file changes, compared to the previously committed file.

• Press "M"

In console

git diff

• You can use arrows or enter to scroll the output and quit with q.
• You will see some things like this.

Output from 'diff'

diff --git a/ingredients.txt b/ingredients.txt
index 4422a31..ba8854f 100644
--- a/ingredients.txt
+++ b/ingredients.txt
@@ -2,3 +2,4 @@
 * 1 chili
 * 1 lime
 * 2 tsp salt
+* 1/2 onion
diff --git a/instructions.txt b/instructions.txt
index 7811273..2b11074 100644
--- a/instructions.txt
+++ b/instructions.txt
@@ -4,3 +4,4 @@
 * squeeze lime
 * add salt
 * and mix well
+* enjoy!

Test

• What is a branch?
• What is the problem that branches alleviate?
• What is the name/names of the most important branch?
• What is our git branching setup?
• What is the goal of that setup?
• Why do we use that setup instead of a different one?
• What is the purpose of each of those branches?
• Does creating a branch create a new version? Why?
• Does changing a branch change the content of your local computer? Why?
• Does deleting a branch create a new version? Why?

Exercises

Have VS code side-by-side with GitHub window

Exercise 1: create, switch and delete a git branch

Learning outcomes

• Create, switch and delete a git branch
• Build up experience using git without troubleshooting

gitGraph
    commit id: "Before start"
    commit id: "Branching version"
    branch sven
    checkout sven
    commit id: "Modify my file"

• For our shared GitHub repository, create a branch with your first name that is unique, e.g. sven, sven_svensson or sven_svensson_314. You may branch off from main or develop (if it exists). You may use the web interface (easiest!) or use VS Code

• On your local computer:

  • update the repository (pull)
  • switch to the new branch
  • change the content of the repository, for example, by creating a file in learners/[your_name]/[your_name]_is_on_[your_branch_name]
  • push your changes online.
• On GitHub, verify that your changes on your branch can be found online
• On your local computer, switch to the main branch, as we'll delete the branch you are on now
• Delete your branch (i.e. the one with the unique name). You may use the web interface (easiest!) or use the VS Code
• On your local computer, update your code (pull)

Answers

• For our shared GitHub repository, create a branch with your first name that is unique, e.g. sven, sven_svensson or sven_svensson_314. You may branch of from main or develop (if it exists). You may use the web interface (easiest!) or use the command line

Click on 1, type your branch name at 2 (in this case, richel), then click 3. Done!

If you wish to use the command line

git pull

• On your local computer:
  • switch to the new branch

Switch to the new branch, for example, richel, by doing:

git switch richel

• On your local computer:
  • change the content of the repository, for example, by creating a file in learners/[your_name]/[your_name]_is_on_[your_branch_name]

This can be any change you'd like. To create a file under Linux (and maybe this works on other operating systems too), one can do:

touch learners/richel/richel_is_on_richel.txt

After the change, commit these:

git add .
git commit -m "Richel is on richel"

• On your local computer:
  • push your changes online.

Do:

git push

And your code may end up online.

If that does not work, do:

git pull

and try pushing again, maybe multiple times, as many people are pushing to the shared repo.

git push doesn't work with new branch

• you always have to pull before a push:

git pull #

• You may need to be more detailed:

git push --set-upstream origin new-branch

• On GitHub, verify that your changes on your branch can be found online

Make sure you look at the correct branch, as displayed at 1. Then your commit message shows up at 2.

• On your local computer, switch to the main branch, as we'll delete the branch you are on now

Switch to the main branch, for example, main, by doing:

git switch main

• Delete your branch (i.e. the one with the unique name). You may use the web interface (easiest!) or use the command line

Click on 'Branches', as shown in the image above.

Click on garbage bin, as shown in the image above.

The branch will now be deleted, as shown in the image above.

• On your local computer, update your code

Do:

git pull

This is for VS Code

• On your local computer:
  • update the repository

On your local computer, navigate to the folder of the shared project and update: pull/sync

• On your local computer:
  • switch to the new branch

Switch to the new branch, for example, richel, by doing:

• On your local computer:
  • change the content of the repository, for example, by creating a file in learners/[your_name]/[your_name]_is_on_[your_branch_name]

This can be any change you'd like.

After the change, commit these ("+" and "commit")

• On your local computer:
  • push your changes online.

Push "Sync"

And your code may end up online.

If that does not work, try pushing again, maybe multiple times, as many people are pushing to the shared repo.

• On GitHub, verify that your changes on your branch can be found online

• Make sure you look at the correct branch, as displayed by the "drop-down button".
• Then your commit message shows up in the yellow section
  • ”Ignore if a pull request shows up”

• On your local computer, switch to the main branch, as we'll delete the branch you are on now

Switch to the main branch.

• Delete your branch (i.e. the one with the unique name).
• You may use the web interface (easiest!) or use VS Cde

In VS Code

GitHub

Click on 'Branches', as shown in the image above.

Click on garbage bin, as shown in the image above.

The branch will now be deleted, as shown in the image above.

• On your local computer, update your code

Sync or Pull again!

Need a video for command line?

See a video here

Summary

git switch -b wild-idea    # create branch, switch to it, work, work, work ...
git switch main          # realize it was a bad idea, back to main/master

Parts to be covered!

• ☑ Source/version control
  • Git
  • We have a starting point!
  • GitHub as remote backup
  • branches
• ☑ Planning
  • ☑ Analysis
  • ☑Design
• ☑ Testing
  • Different levels
• ☐ Collaboration
  • GitHub
  • pull requests
• ☐ Sharing
  • ☑ open science
  • ☐ citation
  • ☑ licensing
• ☐ Documentation
  • ☑ in-code documentation

Keypoints

• A branch is a division unit of work, to be merged with main sometime
• Both git locally and GitHub can be used
• You can delete a branch safely after merging

See also

More about branches

Reference Git

• Main git book
• Pro Git
• Tsitoara, Mariot, and Mariot Tsitoara. "Git best practices." Beginning Git and GitHub: A Comprehensive Guide to Version Control, Project Management, and Teamwork for the New Developer (2020): 79-86.