Command line interface (CLI)
In the beginning there was the command line (textual) interface (CLI), which enabled you to give Linux commands from the command line. There was no mouse or icons to drag and drop. Some programs, such as emacs, implemented rudimentary windows using the very minimal graphics available in the ASCII character set. Reverse video helped separate areas of the screen. Linux was born and raised in this environment.
Naturally all of the original Linux tools were invoked from the command line. The real power of Linux still lies in this environment, which explains why many Linux professionals work exclusively from the command line.