What Is Command-Line Interface (CLI)?

Command-Line Interface (CLI) is a computer user interface (UI) that utilizes a set of pre-programmed commands in a text-based environment to manipulate files, applications and operating system configuration.

While most of the commercial operating systems today ship with a GUI (Graphical User Interface) by default, a majority of the server OSs are still operated using CLI. Command-line interface is also accessible in GUI environments using terminal emulator programs.