A command-line interface (CLI) is a text-based way to control software from a terminal instead of clicking through windows and menus. Users type commands, flags, and paths, and the program responds directly in the shell.
In cyber security, CLIs matter because they are central to developer, admin, and incident-response work. Attackers also target that trust. Malicious installers, phishing pages, and fake documentation often mimic legitimate terminal workflows so a user will copy and run a command without checking its source. That makes the CLI a common delivery point for malware, credential theft, and system changes. Defenders rely on the same interface to inspect logs, hunt processes, verify package provenance, and automate hardening. Good practice is to prefer documented repository commands, review scripts before execution, and restrict privileged shell access where possible.