Conventions (UNIX in a Nutshell: System V Edition)

0.3. Conventions

This book follows certain typographic conventions, outlined below:

Constant width: is used for directory names, filenames, commands, program names, functions, and options. All terms shown in constant width are typed literally. It is also used to show the contents of files or the output from commands.
Constant width italic: is used in syntax and command summaries to show generic text; these should be replaced with user-supplied values.
Constant width bold: is used in examples to show text that should be typed literally by the user.
Italic: is used to show generic arguments and options; these should be replaced with user-supplied values. Italic is also used to indicate URLs, macro package names, comments in examples, and the first mention of terms.
%, $, #: are used in some examples as the C shell prompt (%) and as the Bourne shell or Korn shell prompt ($). # is the prompt for the root user.
?, >: are used in some examples as the C shell secondary prompt (?) and as the Bourne shell or Korn shell secondary prompt (>).
program(N): indicates the “manpage” for program in section N of the online manual. For example, echo(1) means the entry for the echo command.
[ ]: surround optional elements in a description of syntax. (The brackets themselves should never be typed.) Note that many commands show the argument [files]. If a filename is omitted, standard input (usually the keyboard) is assumed. End keyboard input with an end-of-file character.
EOF: indicates the end-of-file character (normally CTRL-D).
^x, CTRL-x: indicates a “control character,” typed by holding down the Control key and the x key for any key x.
|: is used in syntax descriptions to separate items for which only one alternative may be chosen at a time.
: is used at the bottom of a right-hand page to show that the current entry continues on the next page. The continuation is marked by a .

A final word about syntax. In many cases, the space between an option and its argument can be omitted. In other cases, the spacing (or lack of spacing) must be followed strictly. For example, -wn (no intervening space) might be interpreted differently from -w n. It's important to notice the spacing used in option syntax.