# Linux Basics

In 1991 Linus Torvald started developing Linus Kernel.

The Kernel is the most importand piece in the OS which allows hardware to taslk to the software.

## Popolar Linux Distributions.

* **Debian** \- Very stable core
    
* **Red hat Enterprise(RHEL)** - Greate for enterprise applications in corporate
    
* **Ubuntu** \- Debian based OS
    
* **Fedora** \- Uses Red Hat in the backend
    
* **Linux Mint** \- It’s Ubuntu based
    
* **Gentoo** \- This is for advanced users
    
* **Arch Linux** - Lightweight and community driven
    
* **openSUSE** - Great for new Linux user with easy to use graphical installer.
    

## **Basic Commands**

**echo**: This command just print out the text command and display.

```bash
echo Hello World
```

**pwd(Print Working Directory)**: As the name suggest, it will print the directory path

* **pwd -L** : Logical path
    
* **pwd -P** : Physical Path
    

```bash
labex:project/ $ pwd
/home/labex/project
labex:project/ $ cd symlink_dir 
labex:symlink_dir/ $ pwd -L
/home/labex/project/symlink_dir
labex:symlink_dir/ $ pwd -P
/home/labex/project/real_dir
```

**cd(Change Directory)**:

Absolute path: This is the path from the root directory. The root is the head honcho. The root directory is commonly shown as a slash (`/`). Every time your path starts with `/`, it means you are starting from the root directory. For example, `/home/asit/Desktop`.

Relative path: This is the path from where you are currently in the filesystem. If I was in location `/home/asit/Documents` and wanted to get to a directory inside `Documents` called `learnings`, I don’t have to specify the whole path from root like `/home/asit/Documents/learnings;` I can just go to `learnings/` instead.

```bash
labex:~/ $ cd /home     
labex:/home/ $ cd labex/asit/Documents/
labex:Documents/ $ learnings
```

1. **cd .** : (current directory): This is the directory you are currently in.
    
2. **cd ..** : Takes you to the directory above your current one.
    
3. **cd ~** : This directory defaults to your “home directory,” such as ~/.
    
4. **cd -** : This will take you to the previous directory you were just at. Ex - It takes from home directory(`~/` to the previously accessed directory which is → `~/asit/Documents`)
    

**cd /etc**: This is absolute path. **/etc** contains the **configuration files**.

```bash
labex:~/ $ cd /etc 
labex:/etc/ $ pwd
/etc
```

```bash
labex:~/ $ /home 
labex:/home/ $ cd labex/asit/Documents/London 
labex:London/ $ cd .
labex:London/ $ cd ..
labex:Documents/ $ cd ~
labex:~/ $ cd -
~/asit/Documents
labex:Documents/ $
```

**ls(List Directories)**: This is to list the directories and files. In the below example when we put the command `ls` for our `Document/` folder, the 2 folders inside were listed. i.e → **learnings** and **London**

```bash
labex:Documents/ $ ls
learnings  London
```

**Note**: We can give specific path for ls and it will show the content such as folders and files inside that path. See the below example.

```bash
labex:asit/ $ ls Documents 
learnings  London
```

* **ls -a** : a stands for **all**. This will list out all files and folders including the **hidden ones**.
    
* **ls -l** : l stands for **long**. This shows the detail list in **long format**.
    
* **ls - la/ ls - al** : This will show all in long format depends upon the in the order in which the the command is written.
    

```bash
labex:project/ $ ls -a
.  ..  data_file.txt  test  test_file.txt
labex:project/ $ ls -l
total 8
-rw-rw-r-- 1 labex labex 12 Sep 24 02:27 data_file.txt
drwxrwxr-x 2 labex labex  6 Sep 24 02:27 test
-rw-rw-r-- 1 labex labex 27 Sep 24 02:27 test_file.txt
```

1. File Permissions: The first column (e.g., `-rw-rw-r--`) shows the file permissions.
    
    * The first character indicates the file type (`-` for regular file, `d` for directory).
        
    * The next three characters show owner permissions.
        
    * The next three show group permissions.
        
    * The last three show permissions for others.
        
    * `r` means read, `w` means write, and `x` means execute.
        
2. Number of Links: The number right after the permissions (1 for files, 2 for the directory in this example).
    
3. Owner Name: The username of the file owner (labex in this case).
    
4. Group Name: The group that has access to the file (also labex here).
    
5. File Size: Size in bytes (12 for data\_file.txt, 6 for the test directory, and 27 for test\_file.txt).
    
6. Last Modification Date and Time: When the file was last changed (Aug 7 11:23 for all files here).
    
7. File or Directory Name: The name of the file or directory.
    

**ls -lh** : -h stands for human readable.

```bash
labex:project/ $ ls -lh
total 8.0K
-rw-rw-r-- 1 labex labex 12 Sep 24 02:27 data_file.txt
drwxrwxr-x 2 labex labex  6 Sep 24 02:27 test
-rw-rw-r-- 1 labex labex 27 Sep 24 02:27 test_file.txt
```

**ls - lt/ ls -ltr: -t** is for sorting and **\-tr** is for reverse sorting. It is sorted by modification time.

```bash
labex:project/ $ ls -lt
total 8
-rw-rw-r-- 1 labex labex 12 Sep 24 02:27 data_file.txt
drwxrwxr-x 2 labex labex  6 Sep 24 02:27 test
-rw-rw-r-- 1 labex labex 27 Sep 24 02:27 test_file.txt
labex:project/ $ ls -ltr
total 8
-rw-rw-r-- 1 labex labex 27 Sep 24 02:27 test_file.txt
drwxrwxr-x 2 labex labex  6 Sep 24 02:27 test
-rw-rw-r-- 1 labex labex 12 Sep 24 02:27 data_file.txt
```

**ls -l test:** It lists the content. if the file is empty then it is show like the below

```bash
labex:project/ $ ls -l test
total 0
```

**ls | cowsay:** Show output in a fun way :)

```bash
labex:project/ $ ls | cowsay
 __________________________________
< data_file.txt test test_file.txt >
 ----------------------------------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||
```

**Note:** There are many more `ls` options to explore. Here are a few more you might find useful:

* `-R`: List subdirectories recursively (shows contents of all subdirectories)
    
* `-S`: Sort by file size (largest first)
    
* `-X`: Sort alphabetically by entry extension
    
* `-1`: List one file per line (useful for scripts)
    

Installing and starting **wsl - Windows Subsystem** **For Linux** in Windows.

```bash
wsl --install

wsl ~
```

**touch** : This is to use create new empty file

```bash
touch mysuperduperfile
touch banana.jpg
```

**file :** This is to find out what kind of file the file is

```bash
labex:Code/ $ file banana.jpg
banana.jpg: empty
```

**cat** : This is for viewing the **content of the file**. This is also for **concatenate multilple** files. This is only helpful for small files. It combines multiple files and show their output.

```bash
cat dogfile birdfile
```

### **<mark>Note: Linux is Case Sensitive</mark>**

**mkdir**: This means **make directory**

```bash
labex:~/ $ cd ~
labex:~/ $ mkdir -p maze/twisty/little/passages
labex:~/ $ cd maze/twisty/little/passages
labex:passages/ $ pwd
/home/labex/maze/twisty/little/passages
```

```bash
labex:project/ $ mkdir ~/project/digital_garden/notes
labex:project/ $ mkdir ~/project/digital_garden/projects
mkdir ~/project/digital_garden/resources
labex:digital_garden/ $ ls ~/project/digital_garden 
notes  projects  resources
```

**mkdir -p:** It allows you to make a parent directory

```bash
labex:digital_garden/ $ mkdir -p ~/project/digital_garden/projects/web_app/src/components
```

This command does a lot at once:

* It creates a `web_app` folder inside `projects`
    
* Inside `web_app`, it creates an `src` folder
    
* Finally, inside `src`, it creates a `components` folder
    

la -R: This is to display the content recursively

```bash
labex:digital_garden/ $ ls -R ~/project/digital_garden/projects/web_app
/home/labex/project/digital_garden/projects/web_app:
src

/home/labex/project/digital_garden/projects/web_app/src:
components

/home/labex/project/digital_garden/projects/web_app/src/components:
```