Branches

Overview

Teaching: 20 min
Exercises: 0 min

Questions

• What are branches?

• How can I work in parallel using branches?

Objectives

• Understand why branches are useful for:

• working on separate tasks in the same repository concurrently

• trying multiple solutions to a problem

• check-pointing versions of code

• Merge branches back into the main branch

So far we’ve always been working in a straight timeline. However, there are times when we might want to keep our main work safe from experimental changes we are working on. To do this we can use branches to work on separate tasks in parallel without changing our current branch, main.

We didn’t see it before but the first branch made is called main. This is the default branch created when initializing a repository and is often considered to be the “clean” or “working” version of a repository’s code.

We can see what branches exist in a repository by typing

$ git branch

* main

The ‘*’ indicates which branch we are currently on.

In this lesson, Alfredo wants to create two new categories of recipes, one for starters and one for desserts. However, he does not want to work on the main branch because it is stable and he wants to keep it safe

First let’s make the starter branch. We use the same git branch command but now add the name we want to give our new branch

$ git branch starters

We can now check our work with the git branch command.

$ git branch

* main
  starters

We can see that we created the starters branch but we are still in the main branch.

We can also see this in the output of the git status command.

$ git status

On branch main
nothing to commit, working directory clean

To switch to our new branch we can use the checkout command we learned earlier and check our work with git branch.

$ git checkout starters
$ git branch

  main
* starters

Before we used the checkout command to checkout a file from a specific commit using commit hashes or HEAD and the filename (git checkout HEAD <file>). The checkout command can also be used to checkout an entire previous version of the repository, updating all files in the repository to match the state of a desired commit.

Branches allow us to do this using a human-readable name rather than memorizing a commit hash. This name also typically gives purpose to the set of changes in that branch. When we use the command git checkout <branch_name>, we are using a nickname to checkout a version of the repository that matches the most recent commit in that branch (a.k.a. the HEAD of that branch).

Here you can use git log and ls to see that the history and files are the same as our main branch. This will be true until some changes are committed to our new branch.

Now lets create a starter recipe called ClassicBruschetta.md.
For simplicity sake, we will touch ClassicBruschetta.md to create an empty file but imagine we spent hours working on this recipe.

$ touch ClassicBruschetta.py

Now we can add and commit the file to our branch.

$ git add analysis.py
$ git commit -m "Wrote classic bruschetta recipe"

[starters x792csa1] Wrote classic bruschetta recipe
 1 file changed, 1 insertion(+)
 create mode 100644 ClassicBruschetta.py

Lets check our work!

$ ls
$ git log --oneline

As expected, we see our commit in the log.

Now let’s switch back to the main branch.

$ git checkout main
$ git branch

* main
  starters

Let’s explore the repository a bit.

Now that we’ve confirmed we are on the main branch again. Let’s confirm that analysis.py and our last commit aren’t in main.

$ ls
$ git log --oneline

We no longer see the file ClassicBruschetta.md and our latest commit doesn’t appear in this branch’s history. But do not fear! All of our hard work remains in the starters branch. We can confirm this by moving back to that branch.

$ git checkout starters
$ git branch

  main
* starters

$ ls
$ git log --oneline

And we see that our ClassicBruschetta.md file and respective commit have been preserved in the starters branch.

Now we can repeat the process for our bash script in a branch called desserts.

First we must checkout the main branch again. New branches will include the entire history up to the current commit, and we’d like to keep these two tasks separate.

$ git checkout main
$ git branch

* main
  starters

This time let’s create and switch two the desserts branch in one command.

We can do so by adding the -b flag to checkout.

$ git checkout -b desserts
$ git branch

* desserts
  main
  starters

We can use ls and git log to see that this branch is the same as our current main branch.

Now we can make ClassicTiramisu.md and add and commit it. Again imagine instead of touching the file we worked on it for many hours.

$ touch ClassicTiramisu.md
$ git add ClassicTiramisu.md
$ git commit –m “Wrote recipe for classic tiramisu”

[bashdev 2n779ds] Wrote recipe for classic tiramisu
 1 file changed, 1 insertion(+)
 create mode 100644 ClassicTiramisu.md

Lets check our work again before we switch back to the main branch.

$ ls
$ git log --oneline

Alfredo decides his classic bruschetta recipe needs more work before it is ready. But, he is happy with the classic tiramisu recipe.

Let’s merge this version into our main branch so we can use it for our work going forward.

Merging brings the changes from a different branch into the current branch.

First we must switch to the branch we’re merging changes into, main.

$ git checkout main
$ git branch

  desserts
* main
  starters

Now we can merge the desserts branch into our current branch (main). In english, this command could be stated as “git, please merge the changes in the desserts branch into the current branch I’m in”.

$ git merge desserts

Updating 12687f6..x792csa1
Fast-forward
 ClassicTiramisu.md | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 ClassicTiramisu.md

Now that we’ve merged the desserts into main, these changes exist in both branches. This could be confusing in the future if we stumble upon the pythondev branch again.

We can delete our old branches so as to avoid this confusion later. We can do so by adding the -d flag to the git branch command.

git branch -d desserts

Deleted branch desserts (was x792csa1).

Alfredo decides he doesn’t want to keep the starters branch either. So he wants delete it.

$ git branch -d bashdev

error: The branch 'starters' is not fully merged.
If you are sure you want to delete it, run 'git branch -D starters'.

Since we’ve never merged the changes from the starters branch, git warns us about deleting them and tells us to use the -D flag instead.

Since we really want to delete this branch we will go ahead and do so.

git branch -D starters

Deleted branch starters (was 2n779ds).

Key Points

• Branches can be useful for developing while keeping the main line static.