Line interface (CLI or) is a text-based interface used for entering commands. In the early days of computing, before the mouse, it has been the standard method for interacting with a computer. While the graphical user interface (GUI) has largely replaced CLI, they are still included with many operating systems such as Windows and OS X.
There are many different types of command line interfaces, but the two most popular are DOS (Windows) and bash (for Linux and Mac OS X). Each uses its own CLI command syntax, but they all work the same way. For example, each has a CLI command prompt is displayed when the interface is ready to accept a command. When you type a command, it appears next to the command prompt and press Enter when the command is executed.
Examples of prompts for various command-line interfaces with the root folder as the current directory.
Windows (DOS): C: \>
OS X (bash): My iMac: / me $
Linux (bash): [root @ myserver /] #
The standard way to change directories in most CLI is using the cd command followed by the directory path. If you use Windows, you can type cd C: \ Users to access the Users folder. If you are using OS X, you can type cd / Volumes / SSD / users (assuming that the drive name is "SSD"). Some other commands are identical between DOS and bash, but each CLI supports many different commands as well. For example, to list the contents of the current directory, type dir and ls DOS in the bash shell.
Most people prefer a standard graphical user to a single command line interface. However, some operations may actually be performed more quickly by using a keyboard instead of a mouse. Therefore, CLI are often used by network administrators and webmasters for common tasks such as file transfer and check the server status.
NOTE: A command line interface is sometimes called a console or terminal window. OS X includes a utility called "Terminal" which functions as the CLI for OS X