Most home and business computer users are familiar with the Graphical User Interface (GUI) elements of Windows. Clicking icons and menu items is an easy, intuitive way to launch programs, configure applications and hardware, and navigate around a computer.

However, there is another way to launch programs and interact with the computer. The Command Line Interface (CLI) is a text-based system of entering commands where the user types the commands and options at the keyboard. While often harder to learn, the CLI does offer some advantages. For example, many web or database servers do not utilize a GUI, since drawing the graphical interface uses up valuable memory and processor time. Administering these important machines requires knowledge of the CLI. Also, there are many applications that only have a text-based interface and cannot be run using a GUI. If a computer cannot boot normally, the command line may be the only way to run data recovery software to rescue the system.

The Windows command line.

Before the more familiar Windows XP or Vista interfaces, there was only MS-DOS (Microsoft Disk Operating System.) All file editing, hardware configuration, networking, memory allocation was done by typing commands into a shell, which is simply a user interface to the operating system.

Windows still has a powerful command line tool called cmd. It is accessed by clicking the Start button, selecting Run, and typing cmd into the textbox. Once at this shell, there are many commands the user can enter. The most basic are the navigation commands – commands that let you move around the folders on the computer. The commands dir and cd list the contents of the current directory, and allow you to change directory, respectively. Other useful commands include:

• copy – copy a file

• move – move a file

• edit – opens a text editor

• cls – clears the shell's screen

A complete list of commands can be found at these site:

• Computerhope.com

• ss64.com

• sophos.com

• techiwarehouse.com

Some good, general Windows CLI tutorials are:

• commandwindows.com

• A site from the University of Colorado

• Another from the James Madison University

• And one from Princeton

In addition to the basic commands, there are many utilities available at the command line. Ipconfig lets the user configure network settings, and nslookup is useful for finding a website's IP address.

The Linux command line.

The command line is more important on Linux systems. Linux computers are often set up with no graphical interface, leaving the command line the only way of interacting with the machine. In Linux, there is no 'cmd' program, but there are many terminals to choose from. All Linux distributions come with a default terminal program, usually accessed by clicking an icon or menu item. Xterm, aterm, and gnome-terminal are popular terminals.

Some Linux commands are the same as Windows commands. 'cd' changes directories, and nslookup performs the same. Most Linux commands are different, and there are many more of them to learn. These are some good tutorials on the Linux command line:

• tuxfiles.org – contains links to many CLI topics

• linuxcommand.org – a more in-depth tutorial

• linfo.org – a beginner-level tutorial

Knowledgeable users can use the command line to write scripts – small programs that perform some task. Windows calls these scripts batch files, while in Linux they are generally called bash scripts. System administrators can write intricate scripts that perform complicated tasks quickly and easily. For Linux especially, many scripts are freely available that perform tasks like data recovery and file recovery.

Both Windows and Linux makes use of environment variables . These are values that affect the way programs behave. To view the environment variables on a Linux computer, type 'env' (without the quotes) at the command line. On Windows, type 'set'.

Detailed knowledge of the command line is a mandatory skill for system administrators and advanced computer users. But even for the average home user, familiarity with the CLI will allow them to do more with their computers.