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GIT is a great technology, please take time to learn it. DON’T procrastinate because you cannot avoid it. You will be using it every day, several times a day. So you’d better learn and be comfortable with it.
GIT is more than just a "set of commands" that you have to learn. Throughout the years, we have learned that the best way to teach GIT is by understanding the concepts and meaning of the technology first rather than just giving you a list of commands to use.
Being the only developer in a project is an utopia. Normally, you collaborate with other developers, and, without GIT, that becomes a big problem. That’s why we need a repository of information to centralize and manage changes. With a repository we are addressing the following:
The purpose of GIT is to interact with the repository of a project (a set of files) as they change over time.
A GIT repository is comprised of the following:
The GIT repository is stored in the same directory as the project itself in a -hidden- subdirectory called .git:
A commit object contains three things:
The parent commit objects are those commits that came first. Generally a commit object will have one parent commit. One generally takes a project in a given state (commit), makes a few changes, and saves the new state (commit) of the project.
At the beginning, a project always has one commit object with no parents. This is the first commit that is made to the project repository.
The heads of the repository are like the "revision history of the project." A revision history is a list of commit objects that altogether contain all the changes that you and your other team members have made to the project files.
Every time you make a new commit, the head will move to that new commit. This way you are able to have access to the entire project history of commits.
You can move the head if you want. It does not necessarily have to always be the last commit, but you must remember that you can only review commits that came before the commit to which the head is pointing at. Commits made after the commit to which the head is pointing at are not possible to be reviewed.
Heads mark the beginning of a revision history. In GIT, we call the "revision history" a "branch," and it is possible to have several revision histories.
By default, every repository has one branch called Master, with its corresponding HEAD that points to the last commit of that branch.
Example: Let’s say that you are starting to develop the "Login" feature/functionality of a website. You can create a new "branch" of the repository called "login" so that your commits are not part of the main revision history of the project. Once you are comfortable with your code, you can then merge your branch and delete your head. This will reset the main HEAD of the master branch to the last commit you made and add your new code to the main branch (master) of the repository.
☝Note on Terminology: The terms "branch" and "head" are nearly synonymous in GIT. Every branch is represented by one head, and every head represents one branch. Sometimes, "branch" will be used to refer to a head and the entire history of commits preceding that head, whereas "head" will be used to refer exclusively to a single commit object (the most recent commit in the branch).
You can create a new repository whenever you want during the project – it does not have to be at the beginning! The only essential thing to do this is that the project has no other repository that has already been created.
To create a repository, navigate in your command line to the root directory of the project and run the command
git init. Remember that the directory does not need to be empty.
This will create a .git directory in the [project] directory. Make sure that the folder was successfully created (you can run the command
ls -l to read the directory content in the command line).
After you have made some changes to the files of the project, you may want to save/submit those changes into the repository. This is called a "commit."
To create a commit, you will need to do two things:
git add. If a file has not changed since the previous commit (the "parent" commit), GIT will automatically include it in the commit you are about to perform. You will only need to add files that you have newly created or modified. Note that it adds directories recursively, so
git add. will add everything that has changed.
git committo create the commit object. The new commit object will have the current HEAD as its parent (after the commit is completed, HEAD will point to the new commit object).
Say you create three commits this way…your repository will look like this:
Other commands that are useful at this point:
git logshows a log of all commits starting from HEAD back to the initial commit. It can do more than that, of course.
git statusshows which files have changed between the current project state and HEAD. Files are put in one of three categories: (1) New files that haven’t been added (with git add), (2) Modified files that haven’t been added, and (3) Files that have been added.
git diffshows the difference between HEAD and the current project state. With the --cached option, it compares added files against HEAD; otherwise it compares files not yet added.*
git rmmark files to be moved (renamed) and removed, respectively, much like
My personal workflow usually looks this: I first do some programming, and, afterwards, I end up updating some files, then I run the following commands:
git status //to see what files I changed. git diff [file] //to see exactly what I modified. git commit -a -m [message] //to commit.
Now that you’ve created commits, how do you refer to a specific commit? GIT provides many ways to do so. Here are a few:
HEADrefers to the commit object referenced by HEAD. You can also use the name (such as master).
To create a branch, let’s say your repository looks like this:
Lets jump back to commit (2) and start new work from there. You will first need to know how to reference the commit. You can use
git log to get the SHA1 name of (2)
git log commit df73f34fac344778e1f5a836fb88a897e0b8d491 Author: Alejandro Sanchez <firstname.lastname@example.org> Date: Wed Mar 8 13:18:37 2017 -0500
In my case, the hash SHA1 name of the branch was: df73f34fac344778e1f5a836fb88a897e0b8d491
Now, we can use the
git branch command to start a new branch from that particular commit on:
git branch [new-head-name] df73f34fac344778e1f5a836fb88a897e0b8d491
This command will create a new head with the given name, and point that head at the requested commit object. If the commit object is left out, it will point to HEAD.
Now our commit tree looks like this:
In order to start working on that new branch, you need to set the current head to the head we just created. This is done with git checkout:
git checkout [head-name]
This command does the following:
☝Important note: If there are any uncommitted changes when you run git checkout, GIT will behave very strangely. The strangeness is predictable and sometimes useful, but it is best to avoid it. All you need to do, of course, is commit all the new changes before checking out the new head.
After checking out the [new-head] head, you will fix the headers. Now you can add and commit the changes as above. The resulting repository looks like this:
After you have finished implementing a new feature in a branch, you will want to bring that new feature into the main branch, so that everyone can use it. You can do so with the
git merge or
git pull command.
The syntax for the command is as follows:
git merge [head] git pull . [head]
These commands perform the following operations. Let the current head be called current, and the head to be merged called merge
☝GIT can get very confused if there are uncommitted changes in the files when you ask it to perform a merge. So, make sure to commit whatever changes you have made so far before you merge.
A conflict arises if the commit to be merged into has a change in one specific place, and the current commit has a change in the exact same specific place. GIT has no way of telling which change should take precedence.
To resolve the commit, edit the files to fix the conflicting changes. Then run
git add to add the resolved files. Next, run
git commit to commit the repaired merge. GIT remembers that you were in the middle of a merge, so it sets the parents of the commit correctly.
GIT can function without needing to connect to an external server because all the git files are located inside of the .git folder.
However, this means that, in order to manipulate the repository, you need to also have access to the working files. This means that two GIT developers cannot, by default, share a repository.
To share work among developers, GIT uses a distributed model of version control. It assumes no central repository. It is possible, of course, to use one repository as the "central" one, but it is important to understand the distributed model first.
Say you and your friend want to work on the same project. Your friend already has done some work on it. There are three tasks you need to perform to figure out how to do so:
GIT provides a number of transport protocols for sharing repository information, such as SSH and HTTP. We will be using SSH.
To start working in collaboration with remote projects, we will need to know the remote URL of the project. When using SSH, the remote will look like this:
For example, when using a repository from github.com, you can find the remote in the repository home page:
If you are working on a local repository and you want to connect it to a remote repository, you can add a remote. First, look for the remote URL in the remote repository.
Once you know the remote URL, you can add it to your project. You have to pick an alias for the remote – by default we normally use "origin." Add the remote by executing the following command:
git remote add origin [remote-url] //to make sure the remote has been properly set we can get the url value git remote get-url origin
Lets say you have a branch in your local repository called "new-branch." That branch can be uploaded doing the following:
git push origin [new-branch]
If someone else has ALSO pushed some changes to that branch, GIT will reject the push and will tell you to first download those changes to your local repository before continuing.
You will have to (1) download the files, (2) merge them into your code and (3) resolve any conflicts that may have appeared.
After you solve any and all conflicts, you can go ahead and try to git push again.
Let’s say that there is a branch in the remote repository called "development." You can download this branch into your own repository by performing the following command:
git pull origin new-branch
git pull command will try to merge all the incoming files into your local branch. If it finds any conflicting code, it will give you an error and ask you to resolve those conflicts.
After you fix the conflicts, you can
git add the files and
git commit everything to keep a clean error-free copy of your code in the repository.
To make a copy of a remote repository for your own use, run git clone [remote-specification].
For example, if the remote repository is located in
email@example.com:alesanchezr/myfirstrepo.git, you would run:
git clone firstname.lastname@example.org:alesanchezr/myfirstrepo.git
This would do the following:
myfirstrepoand initialize a repository in it.
originto the new repository, and associate origin with
email@example.com:alesanchezr/myfirstrepo.gitas described below. (Like master, origin is a default name used by Git.)
origin/\[head-name\]that correspond to the heads in the remote repository.
origin/\[current-head-name\]head, namely the one that was currently active in the repository being cloned.
A remote repository reference is an alias GIT uses to refer to the remote repository. Generally it will be origin. Among other things, GIT internally associates the remote-specification with the remote repository reference, so you will never need to refer to the original repository again.
From now one, you will be able to say
origin instead of
A branch that tracks a remote branch retains an internal reference to the remote branch. This is a convenience that allows you to avoid typing the name of the remote branch in many situations, as will be described below.
The important thing to note is that you now have a complete copy of your friend’s entire repository. When you branch, commit, merge, or otherwise operate on the repository, you operate only on your own repository. GIT only interacts with your friend’s repository when you specifically ask it to do so.
🔗 Say your friend’s repository looks like this:
Here is a list of other great resources to learn GIT: http://sixrevisions.com/resources/git-tutorials-beginners/
You should especially try these two: