Unix & Linux

• UNIX is an operating system known for its multitasking and multi-user capabilities, developed in the 1970s at AT&T Bell Labs.
• Linux is an open-source, UNIX-like operating system kernel created by Linus Torvalds in 1991.
• Linux and UNIX share similarities in commands and utilities, as well as filesystem hierarchy, but differ in licensing and development.

Terminal

Definition: The terminal (or console) is a command-line interface used to interact with UNIX/Linux systems. You enter commands, and the system responds back with output. It's a way to communicate directly with the operating system.

Important Concepts:

• Prompt: This indicates that the terminal is waiting for input. It often provides context, such as the current user and host.
• Shell: As mentioned, the shell interprets the commands entered into the terminal. There are different shells available, with bash being one of the most popular.
• Commands: These are instructions that you can type into the terminal. Examples include ls (list files), cd (change directory), and pwd (print working directory).
• Arguments: Many commands take additional inputs, called arguments. For instance, with the cd command, the directory you want to navigate to is the argument.
• Flags/Options: These modify the behavior of commands. They usually start with a or -. For example, ls -l lists files in "long format."

Basic Commands:

1. ls

List files and directories.

• ls -l: List in long format, showing file permissions, number of links, owner, group, size, and time of last modification.

  bash
  
  

• drwxr-xr-x 5 user staff 160B Sep 9 09:50 Documents/

• ls -a: List all entries, including hidden ones (those starting with a dot).

• ls -lh: List in long format with human-readable sizes (e.g., 1K, 234M, 2G).

2. cd