The Command Line and Man Pages

We've already discussed the command line - that is, commands you type
after the shell prompt. This section describes the structure of more
complicated command lines.

A minimal command line contains just a command name, such as whoami. But
other things are possible. For example, you might type: man whoami. This
command requests the online manual for the whoami program (you may have to
press the space bar to scroll through the documentation or press q to
quit). A more complicated example is man -k PostScript. This command line
has three parts. It begins with the command name, man. Then it has an
option or switch, -k, followed by an argument, PostScript. Some people
refer to everything except the command name as the parameters of the
command. So, options and arguments are both parameters.

Options change the behavior of a command, switching on particular features
or functionality. They usually have a - before them. The GNU utilities
also have ``long forms'' for the options; the long form of -k is -apropos.
You can enter man -h or man -help to get a full list of options for the
man command. Every command will have its own set of options, though most
have -help and -version options. Some commands, such as tar, do not
require the ``-'' before their options for historical reasons.

Anything that isn't an option and isn't the command name is an argument
(in this case, PostScript). Arguments can serve many purposes; most
commonly, they are filenames that the command should operate on. In this
case, PostScript is the word you want man to search for. In the case of
man whoami, the argument was the command you wanted information about.