Command Line Interface: Commands, Parameters & Options

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  • 0:08 Computer User Interface
  • 0:43 Command Line Interface
  • 1:23 Mainframes
  • 2:12 Modern Command Line
  • 3:12 Commands, Parameters & Options
  • 5:47 Lesson Summary
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Lesson Transcript
Instructor: Paul Zandbergen

Paul has a PhD from the University of British Columbia and has taught Geographic Information Systems, statistics and computer programming for 15 years.

Despite the popularity of graphical user interfaces, command line is still widely used. In a command-line interface, a user interacts with a computer by typing in lines of text. Learn about the use of commands, parameters and options.

Computer User Interface

Computer software needs a user interface so a user and a computer can interact. A user interface controls how you enter instruction and how information displays on screen. A modern computer desktop has an easy-to-use graphical user interface, or GUI (pronounced as gooey). If you have not used computers for very long, that may be the only type of interface that you have ever seen.

In the early days of computing, things looked very different. A typical interface consisted of a black display with letters in white, yellow or green. There was no pointing device, such as a mouse. The user interface consisted of a command-line interface.

Command-Line Interface

To use a computer back in the early 1980s, you had to type in commands. Every menu option in a typical software application was a different command. This is referred to as a command-line interface. In this type of interface, a user interacts with a computer by typing in lines of text. Output is typically displayed only as characters and numbers.

Command line was the most widely used interface until the introduction of Windows and Apple OS in the mid-1980s. Despite the popularity of graphical user interfaces, command line is still widely used. This includes mainframe applications, but many other types of applications use command line, as well.


A mainframe computer is a centralized computer system used by large organizations. Mainframe computing was in widespread use before the emergence of personal computers. Some organizations still use these systems, in part because moving an entire system to a new platform can be costly. In mainframe systems, all the processing is done by a central computer, and individual users access the system using a terminal.

Such terminals are no longer in widespread use, but sometimes the applications on the mainframes still need to be used. This requires the use of terminal emulator software. Terminal emulator software creates a video terminal interface to a mainframe system that runs within the regular operating system of a desktop computer. The user interface for many mainframe systems is a command-line interface.

Modern-Day Command Line

Command line has not disappeared with the decline of mainframe systems - on the contrary. Let's look at some examples of modern-day use of command line:

• The UNIX operating system was developed in the 1960s and was a command-line interface. Many variants of the UNIX operating system have been developed over the years, and some of these are still in use. Many of the components of the popular Linux operating system are based on UNIX. Linux uses both a graphical user interface and a command-line interface.

• Many software applications on different operating systems continue to use command line because it is often very efficient. Command line is very much like a programming language. So, for many computer programmers, using command line is a natural way to interact with computer systems. Command line is often used to automate repetitive tasks that would be cumbersome to carry out using a graphical user interface.

• Many system administrators use special tools and utility software to manage computer networks and systems. These software applications often use a command-line interface, even if they are not UNIX-based.

Commands, Parameters & Options

Let's look at some simple examples of what command line looks like. The examples below are taken from UNIX, but other uses of command line employ a similar logic.

When you start a command-line interface, you are typically staring at a black screen with a blinking cursor. Sometimes the first line is preceded by a $ or > symbol. Now you can start typing in your commands. Once you have typed one line with the command and any additional details, you simply hit the Enter key to execute the command.

For example, the 'cd' command brings you to your home directory, where 'cd' stands for 'change directory.' In other operating systems, a directory is also called a system folder or just a folder - basically where on the computer are you working.

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