A command line interface (CLI) is a text-based way to control a computer by typing commands instead of clicking buttons or menus. It is often used through a terminal or shell, and it gives direct access to system tools, files, and administrative functions.
In cyber security, CLIs matter because they are powerful and precise. Defenders use them for automation, incident response, log review, and system hardening. Attackers also rely on them because many malware families, post-exploitation tools, and remote access workflows are easiest to run from text prompts. That makes command syntax, path selection, and environment awareness important: a single wrong command can damage data, while a carefully used CLI can quickly reveal suspicious processes, network connections, or misconfigurations. The interface is simple, but the results can be highly consequential.