Git Fundamentals¶

Prerequisites¶

Before using Git, check that it is installed and learn about commands available for troubleshooting. This section covers verifying the installation and accessing Git’s built-in help.

Checking Git Version¶

To verify that Git is installed and to see which version is on your system, use the following command:

git --version

Example Output: git version 2.34.1 This command outputs the currently installed Git version, such as 2.34.1. If Git is not installed, it will prompt you to install it.

Git Config¶

Before starting to work with repositories, it’s important to configure your Git settings. The git config command customizes Git’s behaviour, such as setting your username and email, which are used to identify the author of each commit.

Setting up Git Configurations¶

Below are the most common options for configuring Git. Run these commands from any directory.

Global or Local Configuration

Git configurations can be set globally (for all repositories) or locally (for the current repository only).
- Global: Use the --global flag to set a configuration that applies to all repositories on your machine.
- Local: Omitting the --global flag sets the configuration for the current repository only.
```
git config --global <option> <value>
git config <option> <value>   # Sets for the current repository only
```
Setting Username and Email

To identify yourself in commits, set your username and email:
```
git config --global user.name "Your Name"
git config --global user.email "yourname@domain.com"
```
user.name

Specifies your name, which will appear in the commit history.

user.email

Sets your email address, which is attached to each commit.
Viewing Configuration Settings

To check your current Git configuration, use:
```
git config --list
```
This command lists all settings, including username, email, and other configurations.
Core Editor

Git uses a default text editor for writing commit messages. By default, this is often vim on Linux, but you can change it with the core.editor option. For example, to set vim as the editor:
```
git config --global core.editor "vim"
```

core.editor: Sets your preferred text editor for commit messages and other Git operations.

Essential Git Commands¶

Git Command	Explanation
`git init`	Initializes a new Git Repository in the current directory
`git status`	Shows the current status of the repository, including staged, unstaged, and untracked files.
`git clone <respository_url>`	Clones a repository from a remote source to your local machine.
`git add <file_or_directory>`	Adds specified files or directories to the staging area, preparing them for a commit. Use `.` to add all changes in the directory.
`git commit -m "commit message"`	Commits staged changes to the repository with a descriptive message.
`git push <remote> <branch>`	Pushes local changes to a remote repository. Typically, the remote is `origin`, and the branch is `main` or `master`.
`git pull <remote> <branch>`	Fetches changes from a remote repository and merges them into the current branch.

Creating a new repository¶

Start by creating a new folder called git-example.

mkdir git-repo
cd git-repo

Create a file here called README.md with just a header for Git Example

echo "# Git Repo " > README.md

The first thing you need to start tracking any project in git is initialize it. This can be done at anytime and changes will be tracked from that point on.

git init

Now that the folder is tracked with git you can look at the status

git status

On branch master

No commits yet

Untracked files:
 (use "git add <file>..." to include in what will be committed)
        README.md

nothing added to commit but untracked files present (use "git add" to track)

So you can see that there's a file that isn't yet tracked by git, because it's new.

You can add that file to our commit

git add README.md

Running status again will show that it is now staged and will be included in our next commit

git status

On branch master

No commits yet

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)
        new file:   README.md

So we can now commit this has our first commit

git commit -m "inital commit"

-m is for the commit message. If you don't specify it at the command line it will launch your default editor (nano in this case) for you to write a commit message.

Running status again will show that there is no untracked changes

git status

On branch master
nothing to commit, working tree clean

Modify README.md to add some text to it

README.md

# Git Example 2
Something

Again, look at the status to see the current state

git status

You see the file tagged as being modified. We can see exactly what has been modified by running a diff

git diff

diff --git a/README.md b/README.md
index 0b86574..f5b70f7 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,2 @@
-# Git Example
+# Git Example 2
+Something

Add the file and commit the changes

git add .
git commit -m "modified the text"

Now we can look at the history of changes

git log

commit 4f77676cc0d52de6bebb17a6e39d4194886b59c3 (HEAD -> master)
Author: Your Name <you@domain.com>
Date:   Thu Jun 19 18:08:18 2025 +0000

    modified the text

commit 8f9e6608b62d47e0c0d96b134473869895a3523a
Author: Your Name <you@doamin.com>
Date:   Thu Jun 19 17:43:02 2025 +0000

    initial commit

The changes are in decending order of time, with the latest commit at the top.

So now let's say you want to undo the change you just did because it broke something. Take the commit number of the latest change and revert it

git revert 4f77676cc0d52de6bebb17a6e39d4194886b59c3

Running log again you'll see it created a third commit saying it was reverting the second one. It doesn't actually delete the second one from the history

Cloning a Repository¶

To start, on server1, clone this repository

git clone https://github.com/PureLogicIT/101-linux-certificates-git

It will create a directory called 101-linux-certificates-git. Change to that directory

cd 101-linux-certificates-git

Checkout the branch called, git-branch

git checkout git-branch

There should be two mew files, index.html and default.conf.

In index.html Set a welcome message to use for your website later

<!doctype html>
<html>
<head>
  <meta charset="utf-8">
  <title>Tutorial</title>
</head>
<body>
<h1>WELCOME MESSAGE HERE</h1>
<p>We have just configured our Nginx web server on Ubuntu Server!</p>
</body>
</html>

After making that edit, you can use git to see changes that happened.

git status

On branch master
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
    (use "git add <file>..." to update what will be committed)
    (use "git restore <file>..." to discard changes in working directory)
        modified:   index.html

no changes added to commit (use "git add" and/or "git commit -a")

You can inspect the specific changes of that file.

git diff index.html

Next we'll include that file in our commit

git add index.html

You can see the staged file.

git status

On branch master
Your branch is behind 'origin/master' by 1 commit, and can be fast-forwarded.
  (use "git pull" to update your local branch)

Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        modified:   index.html

We'll need to set a description message to this commit. You should add a useful message detailing the changes of the commit.

git commit -m "Set a welcome message"

Again you can check status of the change.

git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
    (use "git push" to publish your local commits)

nothing to commit, working tree clean

Then simply push your local changes which have been commited to the remote repo.

git push
Username for remoterepo: <username>
Password for remoterepo:
Enumerating objects: 7, done.
Counting objects: 100% (7/7), done.
Delta compression using up to 8 threads
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 923 bytes | 923.00 KiB/s, done.
Total 4 (delta 3), reused 0 (delta 0), pack-reused 0
remote: . Processing 1 references
remote: Processed 1 references in total
To remoterepo/ILTrainingCourses/101-linux-certificates-git.git
   c2f983d..801fee5  master -> master

Branching and Merging¶

Git Command	Explanation
`git branch`	Lists all the branches in the repository.
`git branch <new-feature>`	Add a branch name to create a new branch.
`git checkout <new-feature>`	Switches to the specified branch. Added a `-b` creates and switches to the new branch.
`git merge <branch>`	Merges the specified branch into the current branch.
`git branch -d <branch>`	Deletes the specified branch. Will fail if there are unmerged changes. Use `-D` to force deletion.

Undoing Changes¶

Git Command	Explanation
`git reset <file>`	Unstages a file withou discarding the changes.
`git checkout --`	Discards changes in a file by restoring it to the last committed version.
`git revert a1b2c3d4`	Creates a new commit that undoes the changes from a specified commit.
`git reset --hard a1b2c3d4`	Resets the current branch to a specified commit and discards all changes since that commit.

Viewing History and Logs¶

Git Command	Explanation
`git log`	Shows the commit history for the repository. Use `--oneline` for a simplfied view.
`git diff`	Shows differences between files in the working directory and the staging area. Add a file name to see changes for a specific file.
`git show <commit>`	Displays information and changes for a specified commit.

Working with Remote Repositories¶

Git Command	Explanation
`git remote -v`	Lists all remote connections for the repository. Each remote connection has a name and a URL.
`git remote add <name> <url>`	Adds a new remote repository with a specified name.
`git fetch <remote>`	Retrieves changes from a remote repository without merging them.

Additional Resources¶

For more on git config and other Git commands, consult the Git documentation or use git --help for further assistance.