# Linux : Basic Commands

## Linux :

Linux, an open-source operating system, is a powerful and versatile platform that has become the backbone of modern computing. Its flexibility, security, and a wide array of commands make it an essential tool for developers, sysadmins, and enthusiasts alike. Linux provides a command-line interface that enables users to interact with the system efficiently and perform various tasks, from simple file management to complex network configurations.

## Basic Commands:

* **pwd:** It gives the present working directory.
    

```bash
$ pwd
/home/user/projects/my_project
```

* **echo:** `echo` command is used to display text or messages in the terminal or command-line interface
    

```bash
$ echo "Hello, World!"
Hello, World!

//Using Escape Sequences
$ echo "First Line\nSecond Line\nThird Line"
First Line
Second Line
Third Line
```

* **ls:** command in Linux is used to list files and directories in the current working directory. It provides valuable information about the contents of a directory, such as file names, permissions, ownership, size, and modification timestamps.
    

```bash
// Listing files and directories

$ ls
file1.txt  file2.txt  directory1  directory2

//Displays information like file permissions,hard links,owner, group, 
file size, timestamp, and the name of each file/directory.

$ ls -l
-rw-r--r-- 1 user user 1024 Aug 1 10:00 file1.txt
-rw-r--r-- 1 user user 2048 Aug 1 11:00 file2.txt
drwxr-xr-x 2 user user 4096 Aug 1 12:00 directory1

//Hidden Files

$ls -a

//Files size human readable like "K" for kilobytes

$ ls -lh
-rw-r--r-- 1 user user 1.0K Aug 1 10:00 file1.txt
-rw-r--r-- 1 user user 2.0K Aug 1 11:00 file2.txt
```

* **whoami:** Command in Linux is used to display the current user's username.
    
* **cd:** Change Directory, It allows you to navigate to different directories within the file system.
    

```bash
// To a particular directory
$ cd Documents

//Home Directory
$ cd ~

//Parent Directory (One Level Up)
$ cd ..
```

* **mkdir:** Command in Linux is used to create directories or folders. It allows you to create single directories, multiple directories, and nested directories.
    

```bash
//Single directory
$ mkdir new_folder

//Multiple directory
$ mkdir folder1 folder2 folder3

//Nested directory
$ mkdir -p A/B/C/D/E
```

* **touch & cat:** Commands in Linux are used for creating and viewing files, respectively. The `touch` command is used to create empty files or update the timestamp of existing files.
    

```bash
//Empty file
$ touch file.txt

//View Contents of a file
$cat file.txt

//Creating a new file with content 
$cat > newfile.txt
This is my first file
(Press CTRL+D to save and exit)

//Combine multiple files into one
$ cat file1.txt file2.txt > combined_file.txt

//Appending content to existing file
$ cat new_content.txt >> existing_file.txt

//Display content with line numbers
$ cat -n file.txt
   1  Line 1
   2  Line 2
   3  Line 3
```

* **Basic editors:**
    
    * **Vi/Vim:** A classic and powerful modal text editor.
        
    * **Nano:** It is a user-friendly and straightforward editor for beginners.
        
    * **Sublime Text:** Fast, simple, and extensible editor with a free evaluation version.
        

### Creating a fruits.txt and fruits1.txt with Vi editor:

1. ```bash
    $vi fruits.txt
    (Editor will open , Press 'i' for insert mode
     and enter the data. To save and exit  press 'ESC+ :wq')
    
    $vi fruit1.txt
    (Repeat the same process as above)
    ```
    
    ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690836747253/ab4d4c75-3770-4886-8f29-4f81fa682b37.png align="center")
    
2. **head, tail, and diff commands:** Commands in Linux are used to display the top and bottom lines of a file, respectively.
    
    1. `diff` command in Linux, the notation "1c1" represents a change that has occurred between two files being compared.
        
    2. **General Format of the diff**
        
        ```bash
        line_number_1cchange_type line_number_2
        ```
        
        * `line_number_1`The line number in the first file where the change occurred
            
        * `change_type`The type of change that occurred. The most common change types are:
            
            * `c`indicates that a change (modification) has occurred in the line.
                
            * `a`indicates that a new line has been added in the second file.
                
            * `d`indicates that a line has been deleted from the first file.
                
        * `line_number_2`The line number in the second file where the corresponding change occurred
            
        
        ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690836983982/402d0275-fe6d-489d-99aa-2d52fa85886e.png align="center")
        
    
    *In conclusion, Linux commands offer a powerful and efficient way to interact with the operating system through the command-line interface*.
    

*Thank you for taking out valuable time and effort to read till the very end; feedback is always welcomed and appreciated.*