The primary characteristic of a command-line interface (CLI) is its text-based interaction model, where users communicate with the operating system or software through typed commands rather than graphical elements. This interface allows for efficient execution of tasks, as users can quickly input specific commands to navigate systems, manage files, or run applications. While CLIs require a steeper learning curve compared to graphical user interfaces (GUIs), they offer greater control and flexibility, particularly for advanced users or in scripting scenarios. CLIs are widely utilized by programmers, system administrators, and power users for automation and productivity.