bash_scripts

Initial Script:

!ls -l /content/Basics/
!chmod +x /content/Basics/*
!sed -i 's/\r$//' /content/Basics/*

!chmod 777 "/content/Basics"
!ls -ld "/content/Basics"

---

!bash /content/Basics/01_if.sh

---

!bash /content/Basics/02_loop.sh

---

!bash /content/Basics/03_file.sh

---

!bash /content/Basics/04_input_output.sh

!cat /content/Basics/04_op.log
!cat /content/Basics/04_combined.log
!cat /content/Basics/04_error.log

---

!bash /content/Basics/05_string.sh

---

!bash /content/Basics/06_disk_usage_report.sh

---

!bash /content/Basics/07_case.sh

---

!bash /content/Basics/08_exit_status.sh

---

!bash /content/Basics/09_posix_vs_bash.sh

---

!bash /content/Basics/10_disk_monitor.sh

---

!bash /content/Basics/11_colab_test.sh

---

!bash /content/Basics/12_functions.sh

---

!bash /content/Basics/13_arrays.sh

---

!bash /content/Basics/14_arithmetic.sh

---

!bash /content/Basics/15_parameters.sh one two three four

---

!bash /content/Basics/16_heredoc.sh

---

!bash /content/Basics/17_traps.sh

---

!bash /content/Basics/18_cron_demo.sh

---

!bash /content/Basics/19_save_to_file.sh

---

!bash /content/Basics/20_save_with_flock.sh

---

!bash /content/Basics/20_save_with_flock.sh

---

!bash /content/Basics/21_redirection.sh

---

!bash /content/Basics/22_variables.sh

---

!bash /content/Basics/23_posargs.sh dog cat horse

---

!bash /content/Basics/24_array.sh

---

!bash /content/Basics/25_readpipe.sh

---

!cat /etc/passwd |bash /content/Basics/25_readpipe.sh

---

!bash /content/Basics/26_getopts.sh -a testarg dog cat horse

---

!bash /content/Basics/26_getopts.sh -b

---

!bash /content/Basics/26_getopts.sh -a hello

---

!bash /content/Basics/26_getopts.sh -a -c test # triggers ":)"

---

!bash /content/Basics/26_getopts.sh            # triggers \?

---

!bash /content/Basics/99_best_practices.sh

---

🐚 What is Bash?

Bash (short for Bourne Again SHell) is a command-line shell and scripting language used in Linux and Unix-based systems. Think of it as the tool you use to "talk" to your computer using typed commands instead of clicking.

• It's used to run commands, automate tasks, and write scripts (mini programs).

• Commonly used for:

  • Automating software installs
  • Moving and editing files
  • Monitoring system performance
  • Writing startup scripts or cron jobs

📁 Example command:

echo "Hello, world!"

---

💻 What is an Operating System (OS)?

An Operating System (OS) is the core software that manages your computer’s hardware and runs applications.

• It acts like a bridge between you and the machine.

• Examples:

  • Windows (by Microsoft)
  • macOS (by Apple)
  • Linux (used in servers, and comes in versions like Ubuntu, CentOS, Fedora)

🧠 The OS manages:

• Memory
• Files and storage
• Programs
• Network connections
• User interfaces

---

🔗 In Context:

• Bash runs inside the OS (usually Linux or Unix).
• Bash is the tool you use within the OS to control and automate things.

🧱 What is a Unix-Based System?

A Unix-based system is any operating system that is either derived from, inspired by, or compatible with the original UNIX OS created in the 1970s at AT&T's Bell Labs.

🔑 Key Idea:

Unix introduced the idea of small, powerful tools that can be combined together, a multi-user, multitasking system with a command-line interface (shell). This philosophy still powers most modern systems.

---

🧑‍💻 Common Unix-Based Systems

System	Description
Linux	Open-source Unix-like OS (e.g., Ubuntu, CentOS, Fedora)
macOS	Apple’s OS, built on a Unix-certified base (Darwin)
BSD	True Unix descendant (e.g., FreeBSD, OpenBSD)
Solaris	Formerly from Sun Microsystems, Unix-certified
AIX / HP-UX	Proprietary Unix systems used in enterprise servers

---

⚙️ Features of Unix-Based Systems

• Multi-user: Multiple people can use the same system at the same time
• Multitasking: Can run multiple programs/processes at once
• Shell access: Command-line interface like Bash, Zsh, or sh
• File-based everything: Devices, settings, and data are represented as files
• Security & permissions: Strong user-level access control

---

🧩 Unix vs. Unix-Like vs. Unix-Based

Term	What it Means	Example
Unix	Original, certified Unix OS	Solaris
Unix-based	Derived from certified Unix code	macOS
Unix-like	Not certified, but behaves like Unix	Linux, Android

---

✅ Summary

A Unix-based system is a powerful, stable, and secure OS built on Unix principles. If you're using Linux or macOS, you're already using one!

---

🧠 The Key Difference

🔹 Linux Commands

These are standalone programs installed on a Unix/Linux system. Examples:

• ls, cat, cp, mv, grep, awk, sed, find, top, chmod, mkdir These live in directories like /bin, /usr/bin, etc.

🔹 Bash (Bourne Again Shell)

Bash is a command-line shell and scripting language — it's a program that lets you run those Linux commands, write scripts, and automate workflows.

Think of Bash as your interpreter — it:

• Interprets your commands (like ls)
• Supports scripting features: loops (for, while), variables, conditionals (if, case), arrays, and functions

---

🧩 How They Work Together

• You enter Linux commands into a Bash shell.
• Bash then finds and executes those commands.
• When writing Bash scripts, you’re combining logic (if, while, functions) with those Linux commands.

For example:

#!/bin/bash

for file in *.txt; do
  echo "Processing $file"
  cat "$file"
done

• for, do, echo → Bash features
• cat → a Linux command

---

🧪 Analogy

Think of Bash as your programming language, and Linux commands as the built-in tools you can call from that language.

---

✅ Summary

Concept	Description
Linux command	A system utility like ls, grep, etc.
Bash	A shell that lets you run and script with those commands

---