CertiGuide to A+ (A+ 4 Real)  9  Chapter 5: The Linux Operating System       9  Linux System Interface: The Command line

Linux System Interface: The Command line 1 The User Model

Basic Linux commands take the form of:

Command [options] [argument1 argument2 ...]

All items within [ ] are not always needed for the command to function properly. Options are optional items that modify the way the command operates. Commands take input from what is called the standard input, usually the keyboard, process or filter that information and send it to the standard output, usually the display. Arguments may change the standard input to a file or some other device.

An example will help illustrate. The command ls will list the files and directories within a directory and without options; it gives a simple listing of files and directories with the directory requested. For example:

ls -l /home/newuser

Will show a long listing (-l option - long listing) of all the files and directories within the directory/home/newuser in long format. Notice that the space after the command ls is essential to separate the command from the option -l, also there is a space that separates the option from the argument. The command line uses spaces as delimiters so it can know when the command the ends and when the the option begins, likewise the space between the option and the argument provides a similar function. All commands take this same general form.

Linux System Interface: The Command line 1 The User Model