Slides

Git Branching Work-flows

  • When working in Git you will find using branches helpful
  • Branches are a core part of Git and can make working with others easier
  • There are several general strategies for using branches

Branch Basics

  • Branches are a lightweight tool for managing change in Git
  • master is the name of the default branch
  • a branch always points to a commit
    • which could point to other commits recursively
    • eventually all branches point back to some spot on master
    • other branches contain all the changes since they diverged from master

Example: Branch Basics Diagram

Branch Basics Diagram

Branching Commands

command description
git checkout -b x create a new branch named x based off the current commit
git checkout x switch to the branch named x
git branch list all known branches
git merge x merge branch x into the current branch

LAB: branch

We will now pretend to be planning a party. We want to think about the party favors for a while before merging them into the main shopping list.

  1. enter your Shopping List repo

    cd shopping
    
  2. create a new branch called party

    git checkout -b party
    
  3. in this branch, add a few party items (like cake or booze) to the list using your text editor

  4. make a commit on this branch containing the party items

    git add .
    git commit -m "party stuff"
    
  5. switch back to master. Notice that the party items are now gone.

    git checkout master
    
  6. switch back and forth a few times and see the party items reappear and disappear

Git Merge

  • git merge takes a branch and connects it to another

    • usually you merge to and from master into a feature branch
  • to merge is to create a new commit on the current branch

    • that "merge commit" has two parents, and represents all changes from both branches

Merge Conflicts

If there are merge conflicts, resolve them. This is a manual process and can be frustrating and confusing. The basic rule is that if there is a conflict, you need to look for lines like this:

<<<<<<<<<<<<<<<<
foo
----------------
bar
>>>>>>>>>>>>>>>>

and then manually edit the files until all the chevrons and dashes are gone, and what's left is correct. In this example, you might choose foo or bar, or foobar, or bar + foo, or something altogether different. Then git add the corrected file and follow the instructions on the console to finish the merge.

Merge Conflicts (cont.)

As a more realistic example of a conflict:

<<<<<<<<<<<<<<<<
Hours: M-F open at 9, closed weekends
----------------
Hours: 9:00 am to 5:00 pm
>>>>>>>>>>>>>>>>

This example shows why git cannot automatically resolve intra-line conflicts. As a human, you are the only one capable of making this sort of semantic choice. You must decide whether this file would be better off with one or the other or a creative combination of both changes, and you should communicate with other humans about this decision, in the GitHub discussion thread or face-to-face.

LAB: merge

  • on master, add some other non-party-related items to the list, and make a new commit with these items
  • merge your party branch into master
  • there will probably be conflicts. Don't panic!
  • in a text editor, resolve the conflicts
  • when you're satisfied, finish the merge with git add and git commit

with merges, it's usually best to run git commit without a message since git fills in a good message for merges already. This will open the message in a console text editor, usually vi. If it looks good, exit vi by typing :q!

  • finally, run git log --graph to see your commit history with a little ASCII art diagram of the branches diverging and converging

Links