Branches

Overview

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

BASH

$ git branch

OUTPUT

* main

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

In this lesson, Dracula is trying to run an analysis and doesn’t know if it will be faster in bash or python. To keep his main branch safe he will use separate branches for both bash and python analysis. Then he will merge the branch with the faster script into his main branch.

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

BASH

$ git branch pythondev

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

BASH

$ git branch

OUTPUT

* main
  pythondev

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

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

BASH

$ git status

OUTPUT

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.

BASH

$ git checkout pythondev
$ git branch

OUTPUT

  main
* pythondev

Callout

We can use 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.

BASH

$ git log --oneline

OUTPUT

e98a594 (HEAD -> pythondev, main) Discuss concerns about Mars' climate for Mummy
33d27e2 Add concerns about effects of Mars' moons on Wolfman
7e1e559 Start notes on Mars as a base

Now lets make our python script.
For simplicity sake, we will create an empty file but imagine we spent hours working on this python script for our analysis.

Use the “New file” button to create a new file called analysis.py.

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

BASH

$ git add analysis.py
$ git commit -m "Wrote and tested python analysis script"

OUTPUT

[pythondev x792csa1] Wrote and tested python analysis script
 1 file changed, 1 insertion(+)
 create mode 100644 analysis.py

Lets check our work!

BASH

$ git log --oneline

OUTPUT

d5f2565 (HEAD -> pythondev) Wrote and tested python analysis script
e98a594 (main) Discuss concerns about Mars' climate for Mummy
33d27e2 Add concerns about effects of Mars' moons on Wolfman
7e1e559 Start notes on Mars as a base

As expected, we see our commit in the log.

Now let’s switch back to the main branch.

BASH

$ git checkout main
$ git branch

OUTPUT

* main
  pythondev

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.

BASH

$ git log --oneline

OUTPUT

e98a594 (HEAD -> main) Discuss concerns about Mars' climate for Mummy
33d27e2 Add concerns about effects of Mars' moons on Wolfman
7e1e559 Start notes on Mars as a base

Callout

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

BASH

$ git checkout pythondev
$ git branch

OUTPUT

  main
* pythondev

BASH

$ git log --oneline

And we see that our analysis.py file and respective commit have been preserved in the pythondev branch.

Checkout the main branch again to prepare for creating another new branch based on the version history in main. New branches will include the entire history up to the current commit, and we’d like to keep these two tasks separate.

BASH

$ git checkout main
$ git branch

OUTPUT

* main
  pythondev

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

This time let’s create and switch to the bashdev branch in one command.

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

BASH

$ git checkout -b bashdev
$ git branch

OUTPUT

* bashdev
  main
  pythonndev

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

BASH

$ git log --oneline

OUTPUT

e98a594 (HEAD -> bashdev, main) Discuss concerns about Mars' climate for Mummy
33d27e2 Add concerns about effects of Mars' moons on Wolfman
7e1e559 Start notes on Mars as a base

Now we can make analysis.sh and add and commit it. Again imagine instead of creating an empty file we worked on it for many hours.

Use the “New File” button to create a new file called analysis.sh

BASH

$ git add analysis.sh
$ git commit -m "Wrote and tested bash analysis script"

OUTPUT

[bashdev 2n779ds] Wrote and tested bash analysis script
 1 file changed, 1 insertion(+)
 create mode 100644 analysis.sh

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

BASH

$ git log --oneline

OUTPUT

dff27fa (HEAD -> bashdev) Wrote and tested bash analysis script
e98a594 (main) Discuss concerns about Mars' climate for Mummy
33d27e2 Add concerns about effects of Mars' moons on Wolfman
7e1e559 Start notes on Mars as a base

So it turns out the python analysis.py is much faster than analysis.sh.

We will merge the pythondev branch into our main branch via a Pull Request so we can use it for our work going forward.

Before we can create a Pull Request on GitHub, we need to push this branch to the remote repo

Let’s checkout & push the pythondev branch:

BASH

$ git checkout pythondev
$ git push

Whoops, we got an error:

OUTPUT

fatal: The current branch pythondev has no upstream branch.
To push the current branch and set the remote as upstream, use

    git push --set-upstream origin pythondev

To have this happen automatically for branches without a tracking
upstream, see 'push.autoSetupRemote' in 'git help config'.

While our main branch was already on both our local and remote repositories, our pythondev branch is only on our local computer. You can check this by going to GitHub and searching for the pythondev branch - you won’t find it!

We need to use the -u flag in our command and specify the destination branch.

BASH

$ git push -u origin pythondev

OUTPUT

Enumerating objects: 12, done.
Counting objects: 100% (12/12), done.
Delta compression using up to 8 threads
Compressing objects: 100% (8/8), done.
Writing objects: 100% (12/12), 1.07 KiB | 1.07 MiB/s, done.
Total 12 (delta 2), reused 0 (delta 0), pack-reused 0 (from 0)
remote: Resolving deltas: 100% (2/2), done.
To https://github.com/vlad/planets.git
 * [new branch]      pythondev -> pythondev
branch 'pythondev' set up to track 'origin/pythondev'.

The ‘-u’ Flag

You may see a -u option used with git push in some documentation. This option is synonymous with the --set-upstream-to option for the git branch command, and is used to associate the current branch with a remote branch so that the git pull command can be used without any arguments. To do this, simply use git push -u origin <branch-name>.

Now, we can go back to GitHub and verify that we have a new branch named pythondev.

Key Points

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