03. Basic Shell Commands in Linux

What we will learn in this post?

• 👉 Essential Linux Shell Commands
• 👉 File and Directory Management Commands
• 👉 Process Management Commands
• 👉 File Permissions and Ownership
• 👉 Redirection and Piping in Linux
• 👉 Conclusion!

Essential Linux Shell Commands ✨

These commands are the building blocks of navigating and managing files in Linux.

Navigation & Listing 🗺️

• pwd (Print Working Directory): Shows your current location. pwd
• cd (Change Directory): Moves you to a different directory. cd /home/user changes to the /home/user directory.
• ls (List): Shows files and directories in the current location. ls -l (long listing) shows detailed information.

File Manipulation 🗂️

• cp (Copy): Copies files or directories. cp file1.txt file2.txt copies file1.txt to file2.txt.
• mv (Move/Rename): Moves or renames files/directories. mv file1.txt newfile.txt renames file1.txt.
• rm (Remove): Deletes files or directories. Use with caution! rm file.txt deletes file.txt. rm -r directory recursively deletes a directory (and its contents).
• mkdir (Make Directory): Creates a new directory. mkdir new_directory creates the new_directory.

Example: File Management Workflow

graph TD
    A["📂 Create Directory"] --> B{"📋 Copy File?"};
    B --> C["✏️ Rename File"];
    C --> D{"📄 List Files?"};
    D --> E["🗑 Remove File"];

    %% Custom Styles
    classDef actionStyle fill:#1E90FF,stroke:#00008B,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef decisionStyle fill:#FFD700,stroke:#B8860B,color:#000000,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef dangerStyle fill:#FF6347,stroke:#B22222,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;

    %% Apply Classes
    class A actionStyle;
    class C actionStyle;
    class E dangerStyle;
    class B decisionStyle;
    class D decisionStyle;

For more in-depth information, explore these resources:

• Linux Documentation Project
• The Linux Command Line

Remember to always be careful when using rm, especially with the -r flag, as deleted data is typically unrecoverable. Practice these commands in a safe environment (like a virtual machine) to avoid accidental data loss.

File & Directory Management in Linux 📁

Creating and Deleting

• Creating Files: touch my_file.txt creates an empty file named my_file.txt. touch is like giving a file a name.
• Creating Directories: mkdir my_directory creates a new folder named my_directory. mkdir -p dir1/dir2 creates nested directories.
• Deleting Files: rm my_file.txt deletes my_file.txt. Use rm -r my_directory to remove a directory and its contents (be careful!).

Finding and Viewing

• find: Locates files based on criteria. find . -name "*.txt" finds all .txt files in the current directory and below.
• locate: A faster, but less accurate, way to find files based on name (uses a database). locate my_file.txt.
• tree: Displays the directory structure in a tree-like format. tree . shows the current directory’s structure.

Other Useful Commands

• cp source destination: Copies files or directories. cp my_file.txt backup.txt
• mv source destination: Moves or renames files/directories. mv my_file.txt new_file.txt
• rm -rf my_directory: Recursively deletes a directory and its contents (use with extreme caution!).

Example: File Operations

graph TD
    A["📄 Create file: `touch file.txt`"] --> B{"🔍 File exists?"};
    B -- "✅ Yes" --> C["✏️ Modify file"];
    B -- "❌ No" --> C;
    C --> D["🗑 Delete file: `rm file.txt`"];

    %% Custom Styles
    classDef createStyle fill:#1E90FF,stroke:#00008B,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef decisionStyle fill:#FFD700,stroke:#B8860B,color:#000000,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef actionStyle fill:#32CD32,stroke:#006400,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef dangerStyle fill:#FF6347,stroke:#B22222,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;

    %% Apply Classes
    class A createStyle;
    class B decisionStyle;
    class C actionStyle;
    class D dangerStyle;

For more information, check out the Linux Documentation Project. Remember to always back up your data before performing potentially destructive actions like using rm -rf!

Linux Process Management: Your Handy Toolkit 🛠️

Monitoring Processes 👀

• ps: Shows running processes. ps aux displays a detailed list.
• top: Displays dynamic, real-time process information, constantly updated. Use top to see CPU and memory usage.
• htop: An interactive, improved version of top with a user-friendly interface.

Managing Processes 🕹️

• kill: Terminates processes. kill <PID> sends a termination signal; kill -9 <PID> forces termination (use cautiously!).
• jobs: Lists background jobs. Useful for managing processes started with &.

Examples ✨

• List all processes: ps aux
• Kill process with ID 1234: kill 1234
• Forcefully kill process with ID 5678: kill -9 5678 (Use with care!)
• List background jobs: jobs

Further Exploration 🚀

For more in-depth information, explore the man pages (e.g., man ps, man kill). Many online resources also offer comprehensive guides.

Note: Always be careful when using kill -9, as it can lead to data loss if not used appropriately. Try a gentler kill first.

File Permissions & Ownership 🧑‍💻

Every file has an owner, a group, and permissions controlling who can access it (read, write, execute).

Understanding Permissions 🔑

Permissions are represented by three sets of three characters (e.g., rwxr-xr-x). Each set applies to the owner, group, and others respectively. r=read, w=write, x=execute. - means no permission.

Example: rwxr-xr-x

• Owner: Read, write, and execute.
• Group: Read and execute.
• Others: Read and execute.

Modifying Permissions with chmod ⚙️

chmod changes permissions. You can use octal (e.g., chmod 755 file.txt) or symbolic (e.g., chmod u+x file.txt adds execute permission for the user) modes.

• u = user, g = group, o = others, a = all
• + = add, - = remove, = = set

Modifying Ownership with chown & chgrp 👤👥

chown changes the owner, and chgrp changes the group. For example:

• chown john:users file.txt changes the owner to “john” and the group to “users”.
• chgrp developers file.txt changes the group to “developers”.

For more info: chmod man page, chown man page

Mastering Command-Line Power: Redirection & Pipes ⚡️

Input/Output Redirection: Changing the Flow 🔄

Imagine your commands as tiny workers. Redirection lets you control where they get their input from and send their output to.

Redirection Symbols:

• >: Sends output to a new file. ls -l > file_list.txt creates file_list.txt containing the ls -l output.
• >>: Appends output to an existing file. date >> file_list.txt adds the current date to the file.
• <: Takes input from a file. wc -w < my_document.txt counts words in my_document.txt.

Pipes: Connecting Commands 🔗

Pipes let you chain commands together, passing a command’s output as the input to the next. Think of it as an assembly line!

Example: ls -l | grep "txt" first lists files (ls -l), then filters for only those containing “txt” (grep "txt").

Pipe Symbol:

• |: The pipe symbol connects commands.

graph LR
    A["📂 List files: `ls -l`"] --> B{"🔗 Pipe `|`"};
    B --> C["🔍 Filter: `grep 'txt'`"];

    %% Custom Styles
    classDef commandStyle fill:#1E90FF,stroke:#00008B,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef pipeStyle fill:#FFD700,stroke:#B8860B,color:#000000,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;
    classDef filterStyle fill:#32CD32,stroke:#006400,color:#FFFFFF,font-size:14px,stroke-width:3px,rx:15px,shadow:5px;

    %% Apply Classes
    class A commandStyle;
    class B pipeStyle;
    class C filterStyle;

This shows ls -l’s output feeding into grep "txt".

For more information:

• Linux Command Line Tutorial (General Linux commands and redirection/piping)

By mastering redirection and pipes, you can streamline your workflow and boost your command-line efficiency! 🎉

Conclusion

And that’s a wrap! We hope you enjoyed this post. 😊 We’d love to hear your thoughts – what did you think? Any questions or suggestions? Let us know in the comments below! 👇