Instead of an introductionHello! Today we're going to talk about a version control system, namely Git.You have nothing to do with programming if you don't know/understand Git. But the beauty is that you don't have to keep all the Git commands and features in your head in order to be continuously employed. You need to know a set of commands that will help you understand everything that is happening.
Git basicsGit is a distributed version control system for our code. Why do we need it? Distributed teams need some kind of system for managing their work. It is needed to track changes that occur over time. That is, we need to be able to see step-by-step which files have changed and how. This is especially important when you are investigating what changed in the context of a single task, making it possible to revert the changes.
Installing GitLet's install Java on your computer.
Installing on WindowsAs usual, you need to download and run an exe file. Everything is simple here: click on the first Google link, perform the install, and that's it. To do this, we will use the bash console provided by Windows. On Windows, you need to run Git Bash. Here's how it looks in the Start Menu: Now this is a command prompt you can work with. To avoid having to go to the folder with the project every time in order to open Git there, you can open the command prompt in the project folder with the right mouse button with the path we need:
Installing on LinuxUsually Git is part of Linux distributions and is already installed, since it is a tool that was originally written for Linux kernel development. But there are situations when it is not. To check, you need to open a terminal and write: git --version. If you get an intelligible answer, then nothing needs to be installed. Open a terminal and install Git on Ubuntu. I'm working on Ubuntu, so I can tell you what to write for it: sudo apt-get install git.
Installing on macOSHere, too, you first need to check whether Git is already there. If you don't have it, then the easiest way to get it is to download the latest version here. If Xcode is installed, then Git will definitely be automatically installed.
Git settingsGit has user settings for the user who will submit work. This makes sense and is necessary, because Git takes this information for the Author field when a commit is created. Set up a username and password for all your projects by running the following commands:
If you need to change the author for a specific project, you can remove "--global". This will give us the following:
git config --global user.name "Ivan Ivanov" git config --global user.email firstname.lastname@example.org
git config user.name "Ivan Ivanov" git config user.email email@example.com
A bit of theory...To dive into the topic, we should introduce you to a few new words and actions...
- git repository
- how to ignore some files (.gitignore)
Statuses in GitGit has several statues that need to be understood and remembered:
How should you understand this?These are statuses that apply to the files containing our code:
- A file that is created but not yet added to the repository has the "untracked" status.
- When we make changes to files that have already been added to the Git repository, then their status is "modified".
- Among the files that we have changed, we select the ones that we need, and these classes are changed to the "staged" status.
- A commit is created from prepared files in the staged state and goes into the Git repository. After that, there are no files with the "staged" status. But there may still be files whose status is "modified".
What is a commit?A commit is the main event when it comes to version control. It contains all the changes made since the commit began. Commits are linked together like a singly linked list. More specifically: There is a first commit. When the second commit is created, it knows what comes after the first. And in this manner, information can be tracked. A commit also has its own information, so-called metadata:
- the commit's unique identifier, which can be used to find it
- the name of the commit's author, who created it
- the date the commit was created
- a comment that describes what was done during the commit
What is a branch?A branch is a pointer to some commit. Because a commit knows which commit precedes it, when a branch points to a commit, all those previous commits also apply to it. Accordingly, we could say that you can have as many branches as you want pointing to the same commit. Work happens in branches, so when a new commit is created, the branch moves its pointer to the more recent commit.
Getting started with GitYou can work with a local repository alone as well as with a remote one. To practice the required commands, you can limit yourself to the local repository. It only stores all the project's information locally in the .git folder. If we're talking about the remote repository, then all the information is stored somewhere on the remote server: only a copy of the project is stored locally. Changes made to your local copy can be pushed (git push) to the remote repository. In our discussion here and below, we are talking about working with Git in the console. Of course, you can use some sort of GUI-based solution (for example, IntelliJ IDEA), but first you should figure out what commands are being executed and what they mean.
Working with Git in a local repositoryNext, I suggest that you follow along and perform all the steps that I did as you read the article. This will improve your understanding and mastery of the material. Well, bon appetit! :) To create a local repository, you need to write:
This will create a .git folder in the console's current directory. The .git folder stores all information about the Git repository. Don't delete it ;) Next, files are added to the project, and they are assigned the "Untracked" status. To check the current status of your work, write this:
We are in the master branch, and here we will remain until we switch to another branch. This shows which files have changed but have not yet been added to the "staged" status. To add them to the "staged" status, you need to write "git add". We have a few options here, for example:
- git add -A — add all files to the "staged" status
- git add . — add all files from this folder and all subfolders. Essentially, this is the same as the previous one
- git add <file name> — adds a specific file. Here you can use regular expressions to add files according to some pattern. For example, git add *.java: This means that you only want to add files with the java extension.
To check the status, we use the command already known to us:
git add *.txt
Here you can see that the regular expression has worked correctly: test_resource.txt is now has the "staged" status. And finally, the last stage for working with a local repository (there is one more when working with the remote repository ;)) — creating a new commit:
Next up is a great command for looking at the commit history on a branch. Let's make use of it:
git commit -m "all txt files were added to the project"
Here you can see that we have created our first commit and it includes the text that we provided on the command line. It is very important to understand that this text should explain as accurately as possible what was done during this commit. This will help us many times in the future. An inquisitive reader who has not yet fallen asleep may be wondering what happened to the GitTest.java file. Let's find out right now. To do this, we use:
As you can see, it is still "untracked" and is waiting in the wings. But what if we don't want to add it to the project at all? Sometimes that happens. To make things more interesting, let's now try to change our test_resource.txt file. Let's add some text there and check the status:
Here you can clearly see the difference between the "untracked" and "modified" statuses. GitTest.java is "untracked", while test_resource.txt is "modified". Now that we have files in the modified state, we can examine the changes made to them. This can be done using the following command:
That is, you can clearly see here what I added to our text file: hello world! Let's add our changes to the text file and create a commit:
To look at all commits, write:
git add test_resource.txt git commit -m "added hello word! to test_resource.txt"
As you can see, we now have two commits. We'll add GitTest.java in the same way. No comments here, just commands:
git add GitTest.java git commit -m "added GitTest.java" git status
Working with .gitignoreClearly, we only want to keep source code alone, and nothing else, in the repository. So what else could there be? At a minimum, compiled classes and/or files generated by development environments. To tell Git to ignore them, we need to create a special file. Do this: create a file called .gitignore in the root of the project. Each line in this file represents a pattern to ignore. In this example, the .gitignore file will look like this:
Let's take a look:
``` *.class target/ *.iml .idea/ ```
- The first line is to ignore all files with the .class extension
- The second line is to ignore the "target" folder and everything it contains
- The third line is to ignore all files with the .iml extension
- The fourth line is to ignore the .idea folder
Clearly, we do not want to somehow accidentally add the compiled class to the project (using git add -A). To do this, create a .gitignore file and add everything that was described earlier: Now let's use a commit to add the .gitignore file to the project:
And now the moment of truth: we have a compiled class GitTest.class that is "untracked", which we did not want to add to the Git repository. Now we should see the effects of the .gitignore file:
git add .gitignore git commit -m "added .gitignore file"
Perfect! .gitignore +1 :)
Working with branches and suchNaturally, working in just one branch is inconvenient for solitary developers, and it is impossible when there is more than one person on a team. This is why we have branches. As I said earlier, a branch is just a movable pointer to commits. In this part, we'll explore working in different branches: how to merge changes from one branch into another, what conflicts may arise, and much more. To see a list of all branches in the repository and understand which one you are in, you need to write:
You can see that we only have one master branch. The asterisk in front of it indicates that we are in it. By the way, you can also use the "git status" command to find out which branch we are in. Then there are several options for creating branches (there may be more — these are the ones that I use):
git branch -a
- create a new branch based on the one we are in (99% of cases)
- create a branch based on a specific commit (1% of cases)
Let's create a branch based on a specific commitWe will rely on the commit's unique identifier. To find it, we write:
I have highlighted the commit with the comment "added hello world..." Its unique identifier is 6c44e53d06228f888f2f454d3cb8c1c976dd73f8. I want to create a "development" branch that starts from this commit. To do this, I write:
A branch is created with only the first two commits from the master branch. To verify this, we first make sure to switch to a different branch and look at the number of commits there:
git checkout -b development 6c44e53d06228f888f2f454d3cb8c1c976dd73f8
And as expected, we have two commits. By the way, here's an interesting point: there is no .gitignore file in this branch yet, so our compiled file (GitTest.class) is now highlighted with "untracked" status. Now we can review our branches again by writing this:
git status git log
You can see that there are two branches: "master" and "development". We are currently in development.
git branch -a
Let's create a branch based on the current oneThe second way to create a branch is to create it from another. I want to create a branch based on the master branch. First, I need to switch to it, and the next step is to create a new one. Let's take a look:
- git checkout master — switch to the master branch
- git status — verify that we are actually in the master branch
If you are unsure whether this branch is the same as "master", you can easily check by executing "git log" and looking at all the commits. There should be four of them.
git checkout -b feature/update-txt-files
Conflict resolutionBefore we explore what a conflict is, we need to talk about merging one branch into another. This picture depicts the process of merging one branch into another: Here, we have a main branch. At some point, a secondary branch is created off of the main branch and then modified. Once the work is done, we need to merge one branch into the other. I will not describe the various features: In this article, I only want to convey a general understanding. If you need the details, you can look them up yourself. In our example, we created the feature/update-txt-files branch. As indicated by the name of the branch, we're updating text. Now we need to create a new commit for this work:
Now, if we want to merge the feature/update-txt-files branch into master, we need to go to master and write "git merge feature/update-txt-files":
git add *.txt git commit -m "updated txt files" git log
As a result, the master branch now also includes the commit that was added to feature/update-txt-files. This functionality was added, so you can delete a feature branch. To do this, we write:
git checkout master git merge feature/update-txt-files git log
Everything is clear so far, yes? Let's complicate the situation: now let's say that you need to change the txt file again. But now this file will be changed in the master branch as well. In other words, it will change in parallel. Git will not be able to figure out what to do when we want to merge our new code into the master branch. Let's go! We'll create a new branch based on master, make changes to text_resource.txt, and create a commit for this work:
git branch -D feature/update-txt-files
git checkout -b feature/add-header ... we make changes to the file
Go to the master branch and also update this text file on the same line as in the feature branch:
git add *.txt git commit -m "added header to txt"
git checkout master … we updated test_resource.txt
And now the most interesting point: we need to merge changes from the feature/add-header branch to master. We are in the master branch, so we only need to write:
git add test_resource.txt git commit -m "added master header to txt"
But the result will be a conflict in the test_resource.txt file: Here we can see that Git could not decide on its own how to merge this code. It tells us that we need to resolve the conflict first, and only then perform the commit. OK. We open the file with the conflict in a text editor and see: To understand what Git did here, we need to remember which changes we made and where, and then compare:
git merge feature/add-header
- The changes that were on this line in the master branch are found between "<<<<<<< HEAD" and "=======".
- The changes that were in the feature/add-header branch are found between "=======" and ">>>>>>> feature/add-header".
We can convince ourselves that this is a special, unusual case. Let's continue:
You may notice that the description suggest writing only "git commit". Let's try writing that:
git add *.txt
And just like that, we did it — we resolved the conflict in the console. Of course, this can be done a little easier in integrated development environments. For example, in IntelliJ IDEA, everything is set up so well that you can perform all the necessary actions right within it. But IDEs do a lot of things "under the hood", and we often don't understand what exactly is happening there. And when there is no understanding, problems can arise.
Working with remote repositoriesThe last step is to figure out a few more commands that are needed to work with the remote repository. As I said, a remote repository is some place where the repository is stored and from which you can clone it. What kind of remote repositories are there? Examples:
GitHub is the largest storage platform for repositories and collaborative development. I have already described it in previous articles.
Follow me on GitHub. I often show off my work there in those areas that I am studying for work.
GitLab is a web-based tool for the DevOps lifecycle with open source. It is a Git-based system for managing code repositories with its own wiki, bug tracking system, CI/CD pipeline, and other functions.
After the news that Microsoft bought GitHub, some developers duplicated their projects in GitLab.
BitBucket is a web service for project hosting and collaborative development based on the Mercurial and Git version control systems. At one time it had a big advantage over GitHub in that it offered free private repositories. Last year, GitHub also introduced this capability to everyone for free.
And so on…
There is now a complete local copy of the project. To be sure that the local copy of the project is the latest, you need to pull the project by writing:
git clone https://github.com/romankh3/git-demo
In our case, nothing in the remote repository has changed at present, so the response is: Already up to date. But if I make any changes to the remote repository, the local one is updated after we pull them. And finally, the last command is to push the data to the remote repository. When we have done something locally and want to send it to the remote repository, we must first create a new commit locally. To demonstrate this, let's add something else to our text file: Now something quite common for us — we create a commit for this work:
The command to push this to the remote repository is:
git add test_resource.txt git commit -m "prepared txt for pushing"
Well, that's all I wanted to say. Thanks for your attention. Follow me on GitHub, where I post various cool example projects related to my personal study and work.
- Official Git documentation. I recommend it as a reference.
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