A command-line interpreter (also called a command line shell, command language interpreter, or abbreviated as CLI) is a computer program that reads lines of text entered by a user and interprets them in the context of a given operating system or programming language.
Command-line interpreters as user interfaces
Command-line interpreters allow users to issue various commands in a very efficient (and often terse) way. This requires the user to know the names of the commands and their parameters, and the syntax of the language that is interpreted.
From the 1960s onwards, user interaction with computers was primarily by means of command-line interfaces, initially on machines like the ASR-33 Teletype, but then on early CRT-based computer terminals such as the VT52.
All of these devices were purely text based, with no ability to display graphic or pictures. For business application programs, text-based menus were used, but for more general interaction the command line was the interface.
From the early 1970s the Unix operating system on minicomputers pioneered the concept of a powerful command-line environment, which Unix called the "shell", with the ability to "pipe" the output of one command in as input to another, and to save and re-run strings of commands as "shell scripts" which acted like custom commands.
The command-line was also the main interface for the early home computers such as the Commodore PET, Apple II and BBC Micro - almost always in the form of a BASIC interpreter. When more powerful business orientated microcomputers arrived with CP/M and later MSDOS computers such as the IBM PC, the command-line began to borrow some of the syntax and features of the Unix shells such as globbing and piping of output.
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