The terminal & the shell

## 0. The terminal & the shell
      Overview of the terminal and shell - what are they and why is it still worth it to learn to use them today
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      ## What is the terminal?

The terminal is a program that provides a window where you can interact with the command line.

It's essentially the "container" that displays text and accepts keyboard input.

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Popular modern terminal emulators include:

- Alacritty
- Ghostty
- Kitty
- Windows Terminal (windows only)
- iTerm2 (macOS only)
- and many more

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Each terminal emulator might have a variety of advanced and unique features.

> _For example_, Kitty was the first terminal to use GPU-based rendering and is able to display images.

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## The Shell

The shell is the actual command interpreter that processes the commands you type.

It's the program running inside the terminal that understands and executes your commands.

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Popular shells include:

- sh
- bash
- zsh
- PowerShell
- fish
- nushell
- and more

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## sh

sh is the original Unix shell

It is designed to be simple and portable across different Unix-like operating systems.

It is a specification defined by the POSIX standard.

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## Bash

Bash is a shell interpreter first released in 1989, with the latest version (5.3) released in July 2025.

It is popular and powerful with more advanced features and quality-of-life improvements.

Bash is a **superset** of sh.

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## POSIX

The **Portable Operating System Interface** is a standard specified by the IEEE to ensure compatibility between different operating system. It has been evolving since 1988.

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It encompasses a large number of tools, programs and operating systems behaviours such as:

- Process creation and control
- File system operations
- Signals
- Pipes
- Utility programs
- and more

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## GNU coreutils

GNU coreutils is a implementation of common Unix utilities

It aims to be POSIX-compliant, but extends tools with multiple additional features.

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There are also multiple other implementations of the common Unix toolset such as:

- Plan9
- BSD
- BusyBox
- uutils
- and more

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Each of these implementations comes with its owns specifics, features and quirks that are too numerous and finicky to cover in detail.

> This course does NOT aim to teach you how to write the _most_ portable shell scripts, so we are NOT limiting ourselves to the POSIX standard.

Bash basics