Linux Command Line Interface (CLI) – Linux Terminal Tutorial

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In a Linux system, the CLI is typically accessed using a terminal emulator, which is a program that provides a terminal window where users can enter commands. The terminal window is usually connected to a shell, which is a command-line interpreter that executes the commands that the user enters.

The CLI is a powerful tool for performing a wide range of tasks on a Linux system. It allows users to do things that are not possible using a GUI, such as automating tasks using scripts, running multiple commands at once, and accessing system resources that are not exposed through the GUI.

History of Linux Command Line Interface (CLI)

The Command Line Interface (CLI) has a long history that dates back to the early days of computing. The first computers were large and expensive, and only accessible to a select group of researchers and engineers. These early computers were operated using a command line interface, where users would enter commands through a keyboard and receive output on a display screen.

One of the earliest examples of a command line interface was the Dartmouth Time-Sharing System (DTSS), which was developed at Dartmouth College in the early 1960s. DTSS was one of the first computer systems to allow multiple users to access the same computer simultaneously, and it was operated using a command line interface.

As technology progressed, computer systems became more powerful and more accessible to a wider range of users. In the 1970s, the Unix operating system was developed, which featured a powerful command line interface and set the standard for future operating systems.

The Unix CLI was copied and modified by many other operating systems, including Linux and Microsoft Windows. These operating systems expanded on the Unix CLI, adding new commands and features to make it more user-friendly.

In the 1980s, the first graphical user interfaces (GUIs) were introduced, which allowed users to interact with computers using a mouse and a visual interface rather than a command line. The GUI became the standard for most personal computers, and the command line interface was largely seen as a relic of the past.

However, the command line interface has remained popular among developers and system administrators, who find it to be a more efficient and powerful way to interact with a computer. Today, the command line interface is still widely used in many operating systems, including Linux, Unix, and Windows.

Working Principle of Linux Command Line Interface (CLI)

In a Linux operating system, the Command Line Interface (CLI) works by allowing users to enter commands through the terminal, which is a text-based interface that allows users to interact with the operating system. The terminal receives the command and sends it to the shell, which is the program that interprets and executes the command.

The shell is responsible for interpreting the command and determining what actions should be taken. It does this by analyzing the command and any arguments or options that are included with it. Once the shell has determined what actions need to be taken, it will execute the command by running the appropriate program or script.

The shell also provides a number of built-in commands and features that can be used to perform a wide range of tasks. For example, the “ls” command can be used to list the files and directories in a directory, while the “cd” command can be used to change the current working directory.

The shell also provides a number of features that can be used to customize the command line interface, such as command completion, command history, and tab completion. These features make it easier for users to enter commands and navigate the file system.

Additionally, the shell provides a number of environment variables, which are variables that can be used to store information about the environment in which the shell is running. These variables can be used to configure the behavior of the shell and the programs that it runs.

In summary, the CLI in Linux OS works by allowing users to enter commands through the terminal, which are then interpreted and executed by the shell. The shell provides a number of built-in commands and features, as well as environment variables, that can be used to customize the command line interface and perform a wide range of tasks.

The CLI is also useful for troubleshooting and debugging problems on a Linux system, as it allows users to access low-level system details and diagnostic information that is not available through the GUI.

In Conclusion, the CLI is an important part of the Linux operating system, and it is used by many developers and system administrators to perform a wide range of tasks on Linux systems.

The command-line shells provide a command-line interface, while the graphical line shells provide a graphical user interface. Though both shells perform operations, the graphical user interface shells perform slower than the command line interface shells.

Types of Linux Command Line Interface (CLI)

There are several types of Command Line Interface (CLI) in Linux, each with its own set of features and capabilities. Some of the most commonly used types of CLI in Linux include:

1. Bourne Shell (sh): This is the original Unix shell, and it is still widely used in Linux today. It is a simple and lightweight shell that provides a basic set of features and commands.
2. POSIX Shell (sh): The POSIX shell is a standard shell defined by the IEEE POSIX specification. It is a strict subset of the Bourne shell and it is intended to be a portable and compatible shell across different operating systems. It is widely used in Linux and Unix as a default shell for many scripts and applications that need to be portable.
3. Bourne Again Shell (bash): This is an improved version of the Bourne shell that includes many additional features, such as command completion and command history. It is the most widely used shell in Linux today and is the default shell on most Linux distributions.
4. C Shell (csh): This shell was developed to be more similar to the C programming language, and it includes a number of features that are designed to make it easier to use for programmers.
5. Korn Shell (ksh): This shell was developed to be compatible with both the Bourne shell and the C shell, and it includes many additional features, such as command line editing and job control.
6. Z Shell (zsh): This is a highly customizable shell that includes a wide range of features, such as command completion, command history, and tab completion. It also includes many additional features such as spelling correction, and it’s often used by advanced Linux users.
7. Fish Shell (fish): This is a modern, user-friendly shell that is designed to be easy to use. It includes features such as syntax highlighting, auto-suggestions, and command completion.

List of Linux CLI Terminology Definitions

1. Linux Command Line: The command line interface in Linux allows users to interact with the operating system using text-based commands, as opposed to a graphical user interface.
2. CLI Linux: CLI, or command line interface, is a type of interface in Linux that allows users to interact with the operating system using text-based commands.
3. Linux Terminal Commands: Terminal commands are specific instructions that can be entered into the terminal, or command line interface, in Linux to perform various tasks and operations.
4. Linux shell Commands: Shell commands are a set of commands that can be used in the Linux command line interface, or terminal, to perform various tasks and operations.
5. Linux Command Prompt: The command prompt is the symbol or text that indicates that the terminal is ready to accept commands in Linux.
6. Linux Command Line Interface: The command line interface, or CLI, is a type of interface in Linux that allows users to interact with the operating system using text-based commands.
7. Linux Command Line Tools: The set of tools that can be used in the Linux command line interface to perform various tasks and operations.
8. Linux Shell Scripting: Shell scripting is a method of automating tasks in Linux using a shell, or command line interface.