Introduction to GNU/Linux and Bash Shell

GNU/Linux Operating System Architecture

• Operating System (OS) Definition:

  • An Operating System is a collection of software that enables effective utilization and management of computer hardware.

• Core Components of an Operating System:

  • Kernel:
  • Manages core activities of the operating system.
  • Linux: A free and open-source kernel, developed mostly using the C programming language.
  • GNU Foundation Software:
  • A collection of utility programs developed by the GNU foundation that interact with the kernel to perform various tasks for the user.
  • GNU software is far more important than the Linux kernel itself.
  • Even the Linux kernel is compiled using the GCC compiler provided by the GNU foundation.

• GNU vs. Linux Terminology:

  • Stating "I am using Linux" is technically incorrect for most desktop and server systems.
  • Users are primarily using GNU tools running on top of the Linux kernel.

• Operating System Support Capabilities:

  • Multi-user: Allows multiple users to access and use the same computer simultaneously and/or at different times.
  • Multiprocessing: Supports and utilizes more than one computer processor (CPU).
  • Multitasking: Allows multiple software processes to run concurrently at the same time.

• Graphical Desktop & Distributions:

  • Provides a highly customizable graphical desktop environment similar to Windows or macOS.
  • Different Linux distributions (such as Ubuntu, Fedora, Mint, etc.) provide different Graphical User Interfaces (GUIs).

Bash Shell & Terminal Operations

• Server Environment Standards:

  • Most server systems run GNU/Linux and typically do not use a graphical desktop interface.
  • Access and control are accomplished via the GNU bash shell.

• Shell Definition & Functions:

  • A shell is a program that helps start up (or launch) other programs.
  • Operates inside a terminal window.
  • Bash (Bourne Again Shell) is a popular shell for GNU/Linux, providing a textual or command-line interface (CLI).

• Terminal Interface Mechanics:

  • Commands are entered at the shell prompt, which is usually represented by the $ symbol.
  • Example prompt representation: cse278@vbox:~$
  • Output generated by executed programs is displayed directly inside the terminal.
  • The Bash shell can also be executed in integrated terminal environments, such as the VS-Code Terminal.

• Fedora Virtual Machine (VM) Navigation:

  • In CSE-278, coursework utilizes a Fedora VM.
  • Launching a terminal in Fedora: Click the Activities button located at the top-left corner of the desktop screen.

Shell Command Structure & Syntax

• Procedure to Execute Shell Commands:

  1. Type Command Name: Selected based on the specific operation to perform.
  2. Specify Options:
  • Modifies or tunes the behavior of the command.
  • Each command has distinct options, typically starting with a single dash - or double dashes --.
  • Option descriptions and effects can be researched via manual (man) pages.
  1. Supply Arguments:
  • Additional parameters such as file names, directory names, or path strings.
  1. Execute: Press the Enter key to run the command.

• Annotated Command Syntax Example:

  • Full command string: $ g++ -g -Wall -std=c++17 hello.cpp
  • Detailed functional breakdown:
  • Command: g++ (GNU C++ compiler)
  • Options: -g (include debug symbols), -Wall (enable all compiler warnings), -std=c++17 (use C++17 standard)
  • Arguments: hello.cpp (source code file argument)

Fundamental Shell Commands Reference

• Directory Technical Terminology:

  • "Directory" (dir) is the technical computer term for a graphical "folder".

• Core Command Set:

  • pwd: Print Current Working Directory (CWD) / Show Present Working Directory (PWD).
  • ls <dir>: List files in the current working directory, or in directory <dir> if specified.
  • cd <dir>: Change current working directory to specified directory <dir>.
  • cp <file1> <file2>: Copy file or path <file1> to destination <file2>.
  • mv <file1> <file2>: Move (or rename) file or path <file1> to <file2>.
  • rm <file1>: Remove (delete) file <file1>.
  • clear: Clear all content from the active terminal screen.
  • mkdir <dir>: Create a new directory named <dir>.

Directory Structure, Files, and Path Navigation

• Command Prompt Workflow Requirements:

  • Maintain continuous awareness of the Current Working Directory (CWD).
  • Construct an precise mental model of the overall directory hierarchy.
  • Formulate file path strings mentally prior to executing commands.

• Sample Directory Tree Layout:

  • Base path: /home/harveysd
  • Structural layout:
  • /home/harveysd/
    • cse278/
    • exercise1/
    • homework1/
    • public_html/
    • hw2/

• Directory Operations Example:

  • Context: CWD is set to cse278 (/home/harveysd/cse278).
  • Goal: Copy data.txt from exercise1 into the homework1 directory.
  • Equivalent Command Options:
  • Option 1: $ cp exercise1/data.txt homework1
  • Option 2: $ cp exercise1/data.txt homework1/data.txt

• Relative Path Meta-Names:

  • ./ (dot-slash): Refers directly to the Current Working Directory (CWD).
  • ../ (dot-dot-slash): Refers to the parent directory of the current location.
  • ../../: Refers to the grandparent directory (no upper limit on chaining ../ sequences).
  • ~/ (tilde-slash): Refers to the user's home directory (operates as an absolute path representation).

• Practical Relative Path Navigation Examples:

  • Initial state assumption: CWD is /home/harveysd/cse278.
  • Task 1: Copy file data.txt from exercise1 to public_html:
  • Command: $ cp exercise1/data.txt ../public_html
  • Task 2: Change CWD to hw2:
  • Command: $ cd ../public_html/hw2
  • Verification: Executing $ pwd returns /home/harveysd/public_html/hw2.

Terminal Productivity & Execution Control

• Tab Completion:

  • Use the Tab key to automatically complete directory or file names.
  • Prevents spelling mistakes and avoids typing long directory or file paths manually.

• Command History Navigation:

  • Press the Up and Down arrow keys to navigate and re-run previous commands in the shell history.

• Interrupting Execution:

  • Press Control+C (Ctrl+C) simultaneously to interrupt or stop a process if a command is hanging or running indefinitely.

• Mastery Practices:

  • Gaining fluency in Bash requires constructing an accurate mental model through regular practice.
  • Practice method: Create sample directories, write copy/move/delete command challenges, execute them in the terminal, and verify the resulting directory state.