Command Line Definition

A command line is the space to the right of the command prompt on an all-text display mode on a computer monitor (usually a CRT or LCD panel) in which a user enters commands and data. It provides a means of communication between a user and a computer that is based solely on textual input and output.

An all-text display mode, also referred to as a command line interface (CLI), can be provided by both a console and a terminal window. A console is a display mode for which the entire monitor screen shows only text and no images (including icons, pull-down menus and frames around the text). A terminal window is a text-only window that emulates a console and that can be opened in a GUI (graphical user interface) display mode.

A command is an instruction given by a human to tell a computer to do something. Commands are generally issued by typing them in at the command line and then pressing the ENTER key, which passes them to the shell. A shell, also referred to as a command interpreter, is a program that reads commands that are typed on a keyboard and then executes (i.e., runs) them.

A command prompt, also referred to as a prompt or a shell prompt, is a short, automatically generated text message at the beginning of the command line that serves to (1) inform a user that the system is ready for the next command, data element or other input and (2) help the user plan and execute subsequent operations. When using the bash shell, which is the default shell on Linux, the command prompt by default contains the name of the user, the name of the computer and the name of the current directory (i.e., the directory in which the user is currently working). For example, the command prompt for a user named andrew who is currently working in a directory named work on a computer named localhost would look like [andrew@localhost work]$.

The terms command line, command prompt and shell prompt are often used synonymously, particularly when instructions regarding commands are being provided. For example, part of an instruction for performing some task might say: "Enter the following at the command line," "Enter the following at the command prompt," or "Enter the following at a shell prompt."

When using a GUI on a Unix-like operating system, there are two ways to obtain a command line or a CLI. One is to open a terminal window, which can be accomplished by clicking on the appropriate icon or menu item with the mouse cursor. The other is to switch out of the GUI to a console, which can be accomplished without closing any currently open programs on Linux by pressing the CTRL, ALT and F1 keys simultaneously. After completing any desired command line operations, the GUI can be restored by pressing the ALT and F7 keys simultaneously.

Created June 9, 2005.
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