CLI

A command-line interface (CLI) is a text-based user interface for interacting with computer programs. In a CLI, users type commands into a console or terminal, and the program returns text output. CLIs are typically driven by a command interpreter or shell that parses input, performs operations, and launches other programs.

Historically, CLIs emerged from early computing with teletype terminals and batch processing. They became the standard interface on Unix-like systems through shells such as sh, Bash, and later Zsh, while Microsoft Windows provided Command Prompt and, more recently, PowerShell. Modern environments also offer cross-platform shells and scripting engines.

Core concepts include commands, options or flags, and arguments that modify behavior. Users can combine commands with pipelines to pass output from one program to another, and with redirection to save or feed data from files. Scripting languages and shell environments enable automation through loops, conditionals, and variables.

Advantages of CLIs include speed, lower resource usage, scriptability, and powerful remote administration. They are well suited for automating repetitive tasks, managing servers, and performing batch operations. Drawbacks include a steeper learning curve, less discoverability for new users, and the possibility of syntax errors with complex commands.

Examples of widely used CLIs are Bash, Zsh, and Fish on Unix-like systems; Command Prompt and PowerShell on Windows. PowerShell Core (pwsh) provides cross-platform capabilities and object-oriented output.

In practice, CLIs remain central to software development, system administration, and automation, often via terminal sessions, scripts, and continuous integration workflows. They enable precise control and reproducibility, complementing graphical interfaces rather than replacing them in many tasks.