# Linux Command Line Basics

The Linux Command Line Interface (CLI), also known as the shell or terminal, is a powerful tool for interacting with the operating system. Mastering basic commands is essential for developers, especially when working with servers, cloud environments, or containers.

## 1. Navigation

*   **`pwd` (Print Working Directory):** Shows the full path of the current directory.
*   **`ls` (List):** Lists files and directories in the current folder.
    *   `ls -l`: Detailed list (permissions, size, owner).
    *   `ls -a`: Show hidden files (starting with `.`).
*   **`cd` (Change Directory):** Moves to a different folder.
    *   `cd documents`: Go to 'documents'.
    *   `cd ..`: Go up one level.
    *   `cd ~`: Go to the home directory.

## 2. File Manipulation

*   **`touch filename`:** Creates an empty file or updates the timestamp of an existing one.
*   **`mkdir foldername`:** Creates a new directory.
*   **`cp source destination`:** Copies files or directories.
    *   `cp -r folder new_folder`: Recursively copy a directory.
*   **`mv source destination`:** Moves or renames files.
*   **`rm filename`:** Removes (deletes) a file. **Warning: There is no Recycle Bin.**
    *   `rm -r folder`: Removes a directory and its contents.

## 3. Viewing File Content

*   **`cat filename`:** Prints the entire content of a file to the screen.
*   **`less filename`:** View file content one page at a time (use arrows to scroll, `q` to quit).
*   **`head filename`:** Shows the first 10 lines of a file.
*   **`tail filename`:** Shows the last 10 lines of a file.
    *   `tail -f filename`: Follows the file in real-time (great for logs).

## 4. Permissions

Linux file permissions determine who can read, write, or execute a file.

*   **`chmod` (Change Mode):** Changes permissions.
    *   `chmod +x script.sh`: Make a file executable.
    *   `chmod 755 file`: Owner can read/write/execute; others can read/execute.
*   **`chown` (Change Owner):** Changes the file owner and group.
    *   `chown user:group file`

## 5. System & Processes

*   **`sudo` (SuperUser DO):** Runs a command with administrative (root) privileges.
*   **`top` / `htop`:** Displays running processes and resource usage (CPU, RAM).
*   **`ps`:** Lists current processes.
*   **`kill pid`:** Terminates a process by its Process ID (PID).
*   **`grep`:** Searches for text patterns within files or output.
    *   `cat file.txt | grep "error"`: Find lines containing "error".

[[programming/docker-and-containers]]
[[programming/cloud-computing-basics]]