Linux

• An OS shell is a program that exposes an operating system's services to a human user or other programs.
• An OS shell is a special application that uses the kernel API in just the same way as it is used by other application programs.
• The shell operates like an REPL by offering a user interface that allows users to interact with the OS: it prompts the user for input, interpreting their input, and then handling output from the underlying operating system.
• Depending on a computer's role and particular operation, shells use either a command-line interface (CLI) or a graphical user interface (GUI).
• Since the OS shell is actually an application, it may easily be replaced with another similar application, for most operating systems.
• In 1979, there was no access.
• In 1978, there was no access.
• In 1989, there was no access.
• In the 90s, in 1990, there was no access.
• In the 70s, in 1971, there was no access.
• Command-line shells require the user to be familiar with commands and their calling syntax, and to understand concepts about the shell-specific scripting language (for example, bash).
• The term "shell" is often used to refer specifically to command-line interfaces (CLIs).
• Graphical shells provide graphical interfaces, examples include the Windows desktop interface, macOS Finder, and GNOME or KDE for Linux.
• Graphical shells place a low burden on beginning computer users and are characterized as being easy to use, yet most GUI-enabled operating systems also provide CLI shells, normally for performing advanced tasks.
• Operating systems provide various services to their users, including file management, process management (running and terminating applications), batch processing, and OS monitoring and OS configuration.
• Most operating system shells are not direct interfaces to the underlying kernel, even if a shell communicates with the user via peripheral devices attached to the computer directly.
• Components of a shell include prompt, commands, arguments, and built-in commands.
• Command-line shells provide a command-line interface (CLI) to the operating system, while graphical shells provide a graphical user interface (GUI).
• Command-line shells are incredibly flexible.
• Other possibilities, although not so common, include a voice user interface and various implementations of a text-based user interface (TUI) that are not CLI, such as text-based menu systems.
• Most operating system shells fall into one of two categories – command-line and graphical.
• Many computer users use both depending on the task to be performed.
• Key functions of a shell include command execution, scripting, file & directory manipulation, and I/O redirection.
• On Unix-like systems, Secure Shell protocol is usually used for text-based shells, while SSH tunneling can be used for X Window System–based graphical user interfaces (GUIs).
• On Microsoft Windows, Remote Desktop Protocol can be used to provide GUI remote access, and since Windows Vista, PowerShell Remote can be used for text-based remote access via WMI, RPC, and WS-Management.
• Initially available on multi-user mainframes, which provided text-based UIs for each active user simultaneously by means of a text terminal connected to the mainframe via serial line or modem, remote access has extended to Unix-like systems and Microsoft Windows.
• A shell works by initializing, waiting for a command, parsing a command, executing a command, and waiting again.
• The relative merits of CLI- and GUI-based shells are often debated.
• Shells are actually special applications that use the kernel API in just the same way as it is used by other application programs.
• A shell manages the user– system interaction by prompting users for input, interpreting their input, and then handling output from the underlying operating system (much like a read–eval–print loop, REPL).
• Since the operating system shell is actually an application, it may easily be replaced with another similar application, for most operating systems.
• A shell refers to an interface that allows users (human users or other programs) to interact with a system (which doesn't have to be an OS).
• A shell can be either command-line based (where users type in commands) or graphical (where users interact with visual elements like icons and windows).
• A shell acts as a bridge between the user (human user or other program) and the system (which doesn't have to be an OS), interpreting user inputs and conveying them to the system in a manner it can understand them and then displaying the system's outputs back to the user.
• A shell is an interface layer that shields users from the complexities of the underlying system while providing a means of interaction.
• In the 40s and 50s, early interactive systems provided a simple command-line interpreter as part of the resident monitor.
• The primary interaction with macOS is through its graphical interface, known for its design aesthetics and user-friendly principles.
• MacOS is based on a Unix derivative called Darwin, inheriting many characteristics of Unix, including the use of shells.
• The Bourne Shell, also known as sh, is the original Unix shell, written by Stephen Bourne.
• Common commands in these early systems would log the user on and off the system, allocate, free, and manipulate devices and files, and query various pieces of information about the system or a user process.