by Clarence Castillo for NTU Open Source Society
This workshop features a hands-on approach to learning the basics of Git. Familiarity with how to use your computer's terminal or command prompt would be useful but not required to complete this workshop.
Disclaimer: This document is only meant to serve as a reference for the attendees of the workshop. For a full, comprehensive documentation of Git, please check the official reference manual.
Artwork by @hyde-brendan
When: Friday, 19 October 2018. 6:30 PM - 8:30 PM.
Where: LT1 Nanyang Technological University
Who: NTU Open Source Society
Please raise your hand any time during the workshop or email your questions to me later.
For errors, typos or suggestions, please do not hesitate to post an issue! Pull requests are very welcome, thank you!
This workshop is primarily about getting yourselves started with Git. We will begin by covering some background on version control systems, then move on to how to get it running on your system and then finally cover some of the basic commands you'll be using almost 80% of the time when working with Git.
Unlike most of our workshops, we'll actually walk you through the installation and setup phase since it's pretty much integral to the rest of the workshop's content.
Version control is a system that keeps track of changes to a set of files over time such that you are able traverse and access certain versions of it later. It's often used to maintain versions of software source code but in reality it can be used with any type of file on a computer as well.
There are many things that can describe what Git is but one thing I need to point out is that Git != GitHub. Git is a Version Control System while GitHub is a hosting service for Git repositories. Essentially, Git is the tool and GitHub is one of the services available out there to host projects that use Git.
Essentially, Git is a distributed version control system aimed at speed, data integrity and support for distributed, non-linear workflows. It is a mature, actively maintained open source project developed in 2005 by Linus Torvalds, the famous creator of the Linux OS kernel.
To fully understand and appreciate Git, we have to first remember what developers were using before it and get an insight as to why it was replaced. Git superseded Subversion by rethinking one of its core designs - centralised revision control. This resulted in a system where branching was highly discouraged because of how difficult it was to do merging and how forking was more or less nonexistent due to its centrality.
Thanks to Git's distributed architecture, branching became trivial, merging manageable and forking a feature. Rather than have only a single place for the full version history, every working copy is now a repository that can contain the full history of all changes.
Now that we've discussed what Git is and why we should be using it, let's dive into the actual usage of Git.
For Mac OS X, you may already have it if you've installed XCode before (verify your installation as shown below). If not, the easiest way to install it would be using the Git for Mac Installer.
For Windows, use the latest stand-alone Git for Windows Installer and follow the default configuration as shown in the wizard screen.
To verify your installation, open a terminal or command prompt and execute:
$ git --version
git version 2.19.1For accountability, Git needs your identity to associate with any commits that you create. To configure this, execute the following commands replacing the placeholders with your actual information:
$ git config --global user.name "Firstname Lastname"
$ git config --global user.email "useremail@email.com"For the purposes of this workshop, we'll rewrite the iconic song I'll Make a Man Out of You utilising Git to illustrate how easily it can be used to improve your workflow.
For now, let's start fresh by initialising a local directory. To do that, you'll need to use the git init <directory> command. This command is a one-time directive you use only during the initial setup of a new repo. Initialise a git repository named be-a-man and cd into that automatically created folder.
$ cd /path/to/workspaces
$ git init be-a-man
Initialized empty Git repository in /path/to/workspaces/be-a-man/.git/
$ cd be-a-manFor now, take note of the path which you created this repository. We'll come back to it once we've covered some required fundamentals about Git.
A Git repository is a virtual storage of your project. Kinda like a directory accompanied by a ledger that keeps track of all changes done to its contents.
These repositories are usually obtained in one of the two ways. We can either
- Initialise a local directory as a Git repository, or
- Clone an existing repository hosted elsewhere.
What we just did earlier was to initialise a local directory as a Git repository using git init. Notice that Git automatically creates the directory if you supply it the name of the folder as an argument, otherwise it will initialise the exact directory where the command was executed.
There are three main sections which Git maintains to keep track of the repository's internal state: the Working Directory, the Staging Area and the Git Directory.
Working Directory
Holds the actual files. Reflected as is by the local OS's file system. Represents the immediate changes made to content inside the repository. Files are further classified as either tracked or untracked (more on this in awhile).
Staging Area
Think of this area as the buffer between the Working Directory and the Git Directory. Changes to the Working Directory are promoted to the Staging Area to be bundled together for the next commit.
Git Directory (Repository)
Being the most important section, this is where Git stores the history of committed changes done to your project. This is also the only section of your repository that gets propagated to other remote repositories.
The basic git workflow goes something like this:
- Add/modify files inside the working directory. This is usually done outside using an IDE.
- Selectively stage changes that are to be part of the next commit. These can be in the form of entire files or simply chunked lines of code changed within a file.
- Commit the staged stuff to the git directory. This stores a permanent snapshot of the tracked files into the commit history.
To determine which files are in which state, use the git status command. Running this command immediately after git init should give the following output.
$ git status
On branch master
No commits yet
nothing to commit (create/copy files and use "git add" to track)The output above tells us that none of the tracked files are modified. This is expected because we initialised this repo from an empty directory, hence there shouldn't be any tracked or untracked files to begin with.
The command also tells us which branch we're currently on. By default, this branch is always master but we can easily change this to a different branch. More on branching at the later part of the workshop.
Open your favourite text editor and create a new text file named lyrics.txt. Let's begin by writing the song's first stanza. This represents a segment of your source code you've written which you'd like to be comitted to the repository.
Let's get down to business
To defeat the Huns
Did they send me daughters
When I asked for sons?
To see our change, run git status again with the new file. You'll see that it is untracked because Git sees a file you didn’t have before.
$ git status
On branch master
No commits yet
Untracked files:
(use "git add <file>..." to include in what will be committed)
lyrics.txt
nothing added to commit but untracked files present (use "git add" to track)To track the new file, use the git add command. Running git status again right after it should indicate that lyrics.txt is now tracked and ready for a commit.
$ git add lyrics.txt
$ git status
On branch master
No commits yet
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: lyrics.txt
To illustrate how staging really works, let's take it up a notch by modifying our file even after staging it. Open lyrics.txt and add the song's next stanza right below the first one. Your file should now look like this:
Let's get down to business
To defeat the Huns
Did they send me daughters
When I asked for sons?
You're the saddest bunch I ever met
But you can bet before we're through
Mister, I'll make a man
Out of you
Note that the above modification does not in anyway affect what's already staged because Git stages a file exactly as it is when the git add command was executed. If you commit now, lyrics.txt will be as it was when we staged it and this is how it will go into the commit, not the version of the file as it looks in your working directory which includes the second stanza.
To verify, check your repository's status again and you'll notice that it detected a modification to our file. You'll see that lyrics.txt is now written as both staged and not staged. The staged entry refers to the version of the file when we tracked it for the first time using git add and the unstaged version refers to the tracked version of the file including our modification.
$ git status
On branch master
No commits yet
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: lyrics.txt
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)
modified: lyrics.txt
If you think git status is too vague for you and if you want to see the per-line diffrence between what's in your working directory and what's in your staging area, use git diff. This command will show you which lines you've changed but not yet staged.
$ git diff
diff --git a/lyrics.txt b/lyrics.txt
index 1783c2d..cc65c09 100644
--- a/lyrics.txt
+++ b/lyrics.txt
@@ -1,4 +1,9 @@
Let's get down to business
To defeat the Huns
Did they send me daughters
-When I asked for sons?
\ No newline at end of file
+When I asked for sons?
+
+You're the saddest bunch I ever met
+But you can bet before we're through
+Mister, I'll make a man
+Out of you
\ No newline at end of file
Suppose we need both stanzas to be included in our first commit. We need to run git add again to stage the latest version of the file. Notice that Git squashes your modifications together such that there is no distinction between the two changes. It would appear as if you wrote both stanzas together which is expected because the file hasn't been committed yet.
$ git add lyrics.txt
$ git status
On branch master
No commits yet
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: lyrics.txtNow that we're at the final stage of the workflow, commit the changes using git commit. For traceability, Git requires every commit to be accompanied by a message which summarises the change done. The easiest way to provide this is to utilise the -m flag like this:
$ git commit -m "Implement first and second stanzas"
[master (root-commit) d6c19b1] Implement first and second stanzas
1 file changed, 9 insertions(+)
create mode 100644 lyrics.txtExecuting git status again tells us that there is nothing in our staging area and that our working directory is clean. Clean just means that our working directory is at par with the latest snapshot (commit) of our git directory.
$ git status
On branch master
nothing to commit, working tree clean
For this section, we'll be discussing how to view the stuff that's already inside your staging area. This comes really handy especially because it tells you what's going to be part of your next commit.
Edit and stage lyrics.txt one more time to implement the chrous. Our file should now look something like this after this step.
Let's get down to business
To defeat the Huns
Did they send me daughters
When I asked for sons?
You're the saddest bunch I ever met
But you can bet before we're through
Mister, I'll make a man
Out of you
Be a man
We must be swift as the coursing river
Be a man
With all the force of a great typhoon
Be a man
With all the strength of a raging fire
Mysterious as the dark side of the moon
To review the content of our staging area, use git diff again but with the --staged flag. This command compares your staging area to the last commit.
$ git diff --staged
diff --git a/lyrics.txt b/lyrics.txt
index cc65c09..e2b5721 100644
--- a/lyrics.txt
+++ b/lyrics.txt
@@ -6,4 +6,12 @@ When I asked for sons?
You're the saddest bunch I ever met
But you can bet before we're through
Mister, I'll make a man
-Out of you
\ No newline at end of file
+Out of you
+
+Be a man
+We must be swift as the coursing river
+Be a man
+With all the force of a great typhoon
+Be a man
+With all the strength of a raging fire
+Mysterious as the dark side of the moon
\ No newline at end of file
You may be surprised that the output aboves tells us that we've also modified the line Out of you although all we did was just insert the new chorus after it. It's not be obvious at first but the reason why Out of you is detected as modified is because we've added an invisible newline character \n after it so that we can insert the next stanza.
Commit the staged entries using git commit and make sure to provide a commit message using the -m flag.
$ git commit -m "Implement chorus"
[master acc59ac] Implement chorus
1 file changed, 9 insertions(+), 1 deletion(-)
After having created several commits, you’ll probably want to look back to see what has happened. To do this, Git provides the git log command which shows the commit logs.
$ git log
commit acc59acfcddddd645049f28e746d2bba3e55f69b (HEAD -> master)
Author: Clarence Castillo <clarencecastillo@outlook.com>
Date: Sun Oct 14 14:30:34 2018 +0800
Implement chorus
commit d6c19b133c0cac1a366fb88603b1790b8369e405
Author: Clarence Castillo <clarencecastillo@outlook.com>
Date: Sun Oct 14 14:27:51 2018 +0800
Implement first and second stanzasBy default, Git lists the commits made in a repository in reverse chronological order, with the most recent ones up on the top. Each commit is accompanied with its SHA-1 checksum, the name and email of the author, the date written and the commit message.
There isn't a strict do-or-die rule out there that tells you how exactly you should be writing your commit messages but there are some agreed upon guidelines which attempt to standardise this practice.
For starters, here's a list of tips you may want to keep in mind when writing commit messages:
- Limit your commit message to 50 characters
- Capitalise the message
- Do not end the message with a punctuation
- Use the imperative stance
- Avoid uninformative, look-elsewhere messages
One trick that I always use when writing a commit message is to try come up with a statement which completes the phrase If applied, this commit will .... This method forces you to write in the imperative stance and encourages you to give a descriptive phrase about the commit.
In addition, the commit message is conventionally split into the message title and message body using a blank line. Though used in practice, this is actually not required especially if the subject title is more than sufficient to describe the change.
Different teams practice different strategies but what's important is that having a good guideline for creating commits and sticking to it makes working with Git and collaborating with other developers a lot easier.
Branching is a mechanism where you diverge from the main line of development (commit history) and do work on it independent of the main line. Most VCS tools do have this feature but it is somewhat an expensive process, often requiring the entire source code to be copied physically which can take a long time for not-so-small projects.
Essentially, commits in Git are just objects that contain a pointer to the snapshot, some metadata, and pointers to the commit which came before it.
Git makes branching incredibly lightweight because branches in Git are simply small movable pointers that point to one of the commits. As you make more commits in a branch, the branch pointer moves forward automatically.
When you initialise a new repository and create your first commit, a new branch called master is created by default. This branch is just like any other branch and the only reason why you'll see most repositories have it is because it's the default name and most developers just can't be bothered to change it.
To create a new branch, use the command git branch <name>. By default, this creates a new pointer to the same commit you're currently on, but you can easily change this by providing the SHA-1 checksum of the commit you'd like to branch out of.
Git uses a special pointer called HEAD to determine which branch you're currently on. When you create a new branch, Git does not automatically move HEAD into that new branch. To switch to different one, run the command git checkout <branch>.
To illustrate how branches work, let's write a different version of the song on a different branch so we can easily switch back to the original version later. Name the branch as business and don't forget to checkout.
$ git branch business
$ git checkout business
Switched to branch 'business'
Open your text editor again and modify only the first stanza as follows. Be sure to leave the other stanza and the chorus untouched.
Let's get down to business
To outbid the Huns
Here I have some figures
And some facts and sums!
Changing the song lyrics correctly as instructed above should give you the following results when running git diff.
$ git diff
diff --git a/lyrics.txt b/lyrics.txt
index e2b5721..1529e97 100644
--- a/lyrics.txt
+++ b/lyrics.txt
@@ -1,7 +1,7 @@
Let's get down to business
-To defeat the Huns
-Did they send me daughters
-When I asked for sons?
+To outbid the Huns
+Here I have some figures
+And some facts and sums!
You're the saddest bunch I ever met
But you can bet before we're through
Now that we're happy with the change, let's stage and commit it. Since we're on a different branch, we can safely do this without worrying about the original version of the song.
$ git add *
$ git commit -m "Edit first stanza"
[business d6a9526] Edit first stanza
1 file changed, 3 insertions(+), 3 deletions(-)
$ git log
commit d6a9526373b1fd0476f13dd176b05d878877e199 (HEAD -> business)
Author: Clarence Castillo <clarencecastillo@outlook.com>
Date: Sun Oct 14 14:49:14 2018 +0800
Edit first stanza
commit acc59acfcddddd645049f28e746d2bba3e55f69b (master)
Author: Clarence Castillo <clarencecastillo@outlook.com>
Date: Sun Oct 14 14:30:34 2018 +0800
Implement chorus
commit d6c19b133c0cac1a366fb88603b1790b8369e405
Author: Clarence Castillo <clarencecastillo@outlook.com>
Date: Sun Oct 14 14:27:51 2018 +0800
Implement first and second stanzasNotice that git log output also tells us where the branches are currently pointing to. Since HEAD is pointing to business when we created the commit, it automatically forwarded the branch along with it while keeping the other branch master untouched.
Let's add one more commit to this branch by modifying the second stanza and the chorus together. The file should look like this now.
Let's get down to business
To outbid the Huns
Here I have some figures
And some facts and sums!
It's the saddest lot you've ever bought
But if you bet on this one too
Mister, I'll make you a buck
Or two
Business man
We must be swift as the stock exchanges
Business man
With all the force of a great tycoon
Business man
With all the strength of a thriving market
Mysterious as my company's revenues
Like before, stage and commit the changes done to the song.
$ git add *
$ git commit -m "Edit second stanza and chorus"
[business 30e6abb] Edit second stanza and chorus
1 file changed, 11 insertions(+), 11 deletions(-)
Suppose we've decided that our work with the modification of the song is complete and that we're ready for it to be merged back into the main branch. There are a few ways we can go about merging these two branches together. We can either fast-forward master into business, or squash everything we've done in business as one big chunk and commit it to master.
Since master is pointing to a commit which business branched out of, and that there's no new commits to master, we can easily do a fast-forward merge because all we have to do is make the pointer traverse along the commit path all the way to where business is currently located.
$ git checkout master
Switched to branch 'master'
$ git merge business
Updating acc59ac..30e6abb
Fast-forward
lyrics.txt | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)As for the latter type of merge, it can be viewed as squashing all the changes in the business branch as one big change and applying that to the master branch, creating a new commit in the process. We can do this with the same merge command but with the --no-ff flag.
$ git checkout master
Switched to branch 'master'
$ git merge business --no-ff -m "Merge business into master"
Merge made by the 'recursive' strategy.
lyrics.txt | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)In every merge, there's a source branch and a target branch. The distinction between the two determines which moves forward in the tree. Notice that for both methods above we had to checkout the target branch master first before running the merge.
In our case, we can only merge business into master because everything in master is already in business. Trying to merge master into business will tell you that the branch is already up to date and that there's no need for a merge.
There's no one right way of doing this but what's important is that you know the difference between the two. Personally, I prefer the second approach because it explicitly writes to the commit history that we've merged business into master, unlike the first approach which silently moves the pointer into another commit.
Using Git via the terminal can be really fast and it makes sense to learn it first because the terminal is Git's native environment. That's where the latest features are always available and only in the command line do we see the full suite of tools Git has to offer.
Although some developers still prefer the text-based interface, it may not always be the best choice for all tasks especially when a visual representation is needed or when its users are much more comfortable with a point-and-click interface.
For this workshop, we'll be using GitKraken to illustrate how GUIs can be used to manage your Git workflow. As for this section, the walkthrough will be done live so there's no need to refer to this document until the next section.
To be able to collaborate with other developers on any Git project, you need to know how to manage your remote repositories. For this section, we'll be discussing remote management basics such as adding remotes, cloning, forking, synchronising and pushing. At the end of it, we'll also cover how to open pull requests to let other repository maintainers synchronise their version of the code with your copy.
In particular, we'll be using GitHub Flow as an example of how developers can easily work together using Git. It is designed around a particular workflow centered on what we call a Pull Request.
- Fork the project
- Create a topic branch from main branch
- Make commits to that branch
- Push branch to GitHub
- Open a Pull Request
- Discuss, review, modify branch
- Project owner merges or closes the Pull Request
For the rest of the workshop, we'll use the GUI client and GitHub to visually walk you through how to learn these remote management skills. I'll walk you through how to create a repository on GitHub, how to add that remote to the repository we just made, and how to push our changes to the remote repository.
Remote repositories are copies of your project that are hosted somewhere else. The term remote could mean a public Git hosting service like GitHub, or a self-hosted server running Git, or even the very same machine you're working on but on a different directory.
Cloning is the process of using Git to receive a full copy of a remote repository into your local machine. Essentailly, this process involves initialising a local repository and then synchronising it to the latest commit.
- Create a new directory
- Initialise as Git repository
- Add remote
- Syncrhonise with remote repository
- Checkout default branch
Forking a repo involves creating an entire copy of one repository into a new repository. This is often done via the Git hosting service to either propose changes to someone else's project or to create a new independent version of the project.
When changes are available in branch master of remote origin that is not present in our local copy, it is often denoted that branch origin/master is ahead of master (local). Conversely speaking, we can also say that master (local) is behind origin/master. To synchronise our local copy with the remote, we can either fetch and then manually do a fast forward or do a pull.
We use the term fetch to get the changes done available in our remote repository. After doing that, you should now have references to all the branches from that remote which you can merge in or inspect from your local copy.
The other term pull is used when you want to fetch and then fast-forward right after it. They're pretty much the same except that it automatically merges the changes done in the remote repository branch into your local branch.
When changes are done in our local branch master which aren't reflected in branch master of remote origin, then we can say that origin/master is behind master (local). We use the term push to synchronise our local changes to the remote repository.
Issuing pull requests is the formal way of telling others about changes you've done to a repository. Once it's created, interested parties (usually project maintainers, reviewers, owners, etc) can review the set of changes, discuss potential modifications and even push follow-up commits if needed.