Command basics

Although Unix is a complex system, most users get along well using only a small fraction of the commands available. Unix also has many shortcuts available to make things easier to remember and type.

Case sensitivity

One of the most important things to remember about Unix commands is that they are case sensitive, which means the system distinguishes between uppercase and lowercase letters. Most Unix commands are all lowercase, but you need to remember that Unix "p" and "P," for example, are not the same. This means that you could have four files named "FILE", "file", "fiLE", and "File." UNIX sees all four as different.

Command line

The command line is one way to interact with the computer. It shows the name of the machine you are logged in to and usually the directory that you are in, followed by a greater than sign (>). Enter the commands described here at the command line.

The Unity command line you see upon logging in should look something like the following

unity%

If you log in to Unity by telnet or modem, the command line is your only interface to Unity. If you log in from a Unix-based workstation running an X Window System, you can access Unity with numerous windows from which to run applications.

The Eos command line you see upon logging in should look something like the following

eos%

There is no name or machine name unless you alter the way the system displays the prompt.

Entering commands

To enter a command, just type the command and press the button on your keyboard marked "return" or "enter."

When you enter a command, the machine processes it, displays any output and returns you to the command line:

[/ncsu/dewindha]...>date
Tue Jun 18 10:16:06 EDT 1996
[/ncsu/dewindha]...>

Command syntax

Unix commands use the syntax

command -options arguments

Command is a one-word name for a command (for example, ls is the command to use to get a listing of files and directories).

Options are used to modify or qualify the command. You should precede any options you enter with a dash (minus sign -). You may at times specify just one option, such as -v, or multiple options, such as -ir or -laF.

Argument is usually the file or directory upon which the command operates. You can also think of arguments as the "input" that the command uses to produce its output.

The command name is always the first thing you type at the command line. Options follow the command, and arguments follow the options.

Not all commands allow or require you to specify options or arguments, and not all commands are available to all users.

Last modified July 20, 2004 by cawalker